Digitized by the Internet Archive in 2015 https://archive.org/details/b2130046x_0003 THE CYCLOPAEDIA OF ANATOMY and PHYSIOLOGY. VOL. III. LONDON : MERCHANT SINGER AND CO., PRINTERS, IN GRAM-COURT, FENCIIURCH-STREET. THE CYCLOPAEDIA OF ANATOMY and PHYSIOLOGY. EDITED BY ROBERT B. TODD, M.D. F.R.S. FELLOW OP THE ROYAL COLLEGE OF PHYSICIANS; PHYSICIAN TO KING'S COLLEGE HOSPITAL; AND PROFESSOR OF PHYSIOLOGY AND OF GENERAL AND MORBID ANATOMY IN KING'S COLLEGE, LONDON, ETC. ETC. VOL. III. INS PL A. LONDON: SHERWOOD, GILBERT, AND PIP EE, PATERNOSTER- ROW. 1847. 6 6-761 CONTRIBUTORS. ROBERT ADAMS, Esq. Surgeon to the Richmond Hospital, and Lecturer on Anatomy and Surgery, Dublin. B. ALCOCK, M.B. Dublin. W. P. ALISON, M.D. F.R.S.E. Prof, of the Pract. of Med. in the Univ. of Edin. &c. JOHN ANDERSON, Esq. M.E.S. Richmond. J. APJOHN, M.D. M.R.I.A. Prof, of C hem. to the Royal Coll. of Surgeons, Ireland. VICTOR AUDOUIN, M.D. Paris. Professeur-Administrateurau Museed'HistoireNaturelle. B. G. BABINGTON, M.D. F.R.S. Physician to Guy's Hospital. THOMAS BELL, F.R.S. Professor of Zoology in King's College, London. CHARLES BENSON, M.D. M.R.I.A. Prof, of Med. to the Royal Col. of Surgeons, Ireland. J. BISHOP, F.R.S. London. JOHN BOSTOCK, M.D. V.P.R.S. London. W. BOWMAN, F.R.S. Assistant-Surgeon to the King's College Hospital and the Royal Ophthalmic Hospital, Moorfields, and De- monstrator of Anatomy, King's College, London. J. E. BOWMAN, Esq. Demonstrator of Chemistry in King's College, London. W. T. BRANDE, F.R.S. Professor of Chemistry to the Royal Institution, &e. J. E. BRENAN, M.D. G.BRESCHET, M.D. Surgeon to the Hotel-Dieu, Paris. W. BRINTON, Esq. Demonstrator of Anatomy in King's College, London. W. B. CARPENTER, M.D. F.R.S. Lect.on Physiology at the London Hospital, &c. JOHN COLDSTREAM, M.D. Leith. Memb.of theWernerian Nat. Hist. Soc. of Edinb. &c. DAVID CRAIGIE, M.D. F.R.S.E. Fellow of the RoyalCollege of Physicians, Edinburgh, &c . T. BLIZARD CURLING, Esq. Lect. on Surg, and Assist. Surg, to the Lond. Hospital. G. P. DESHAYES, M.D. Paris. A.T. S. DODD, Esq. H. DUTROCHET, M.D. W.F.EDWARDS, M.D. F.R.S. II. MILNE EDWARDS, M.D. Prof.of Nat. History to the College of Henry IV., and tothe Central School of Arts and Manufactures, Paris. ARTHUR FARRE, M.D. F.R.S. Professor of Midwifery in King's College and Physician Accoucheur to King's College Hospital. R. D. GRAINGER, F.R.S. Lect. on Anat. and Phys. at St. Thomas's Hospital. R. E. GRANT, M.D. F.R.S. L. & E. Fell, of the Roy. Coll. of Physicians, Edinb. and Prof.of Comp. Anatomy and Zoology in Univ. College, &c. &c. W. A. GUY, M.D. Prof. For. Med. King's College, London, and Physician to King's College Hospital. M. HALL, M.D. F.R.S. L. & E. London. HENRY HANCOCK, Esq. Lect. on Anat. and Physiology at, and Surgeon to the Charing-Cross Hospital. ROBERT HARRISON, M.D. M.R.I.A. Prof, of Anat. and Surg, in the Univ. of Dublin. JOHN HART, M.D. M.R.I.A. Pror. of Anat. in the Royal Coll. of Surf . Dublin. A. IIIGGINSON, Esq'. Liverpool." ARTHUR JACOB, M.D. M.R.I.A. Professor of Anatomy and Physiology to the Royal College of Surgeons in Ireland. GEORGE JOHNSON, M.D. Assistant Physician to King's College Hospital, and resident Medical Tutor in King's College, London. T. RYMER JONES, F.R.S. Prof.of Comp. Anat., in King's College, London. T. WHARTON JONES, F.R.S. London. T. WILKINSON KING, Esq. SAMUEL LANE, Esq. Lecturer on Anatomy, St. George's Hospital, London . F. T. MACDOUGALL, Esq. JOHN MALYN, Esq. C. MATTEUCCI. Professor of Physics in the University of Pisa. ROBERT MAYNE, M.D. Lect. on Anat. & Phys. Richmond Hospital, Dublin. W. A. MILLER, M.D. F.R.S. Profcssorof Chemistry in King's College, London. W. F. MONTGOMERY, M.D. M.R.I.A. Fellow of and Professor of Midwifery to the King and Queen's College of Physicians in Ireland. GEORGE NEWPORT, F.R.S. Vice-Pros, of the Entomological Society of London. R. OWEN, F.R.S. F.G.S. Hunterian Professor of Comparative Anatomy and Physiology to the Royal College of Surgeons in London. JAMES PAGET, Esq. Lect. on Anat. & Phys. St. Bartholomew's Hospital. RICHARD PARTRIDGE, F.R.S. Prof.of Descrip. and Surg. Anat. in King's Coll. Lond. BENJAMIN PHILLIPS, F.R.S. London. Surgeon to the Westminster Hospital. SIMON ROOD PITTARD, Esq. London. W. H. PORTER, Esq. Prof, of Surgery to the Royal Coll. of Surg, in Ireland. J. C. PRICIIARD, M.D. F.R.S. Corresponding Member of the Institute of France, Member of the Royal Academy of Medicine of Pal is. G. O. REES, M.D. F.R.S. Assistant Physician to Guy's Hospital. J. REID, M.D. Prof, of Medicine in the University of St. Andrews. EDWARD RIGBY, M.D. F.L.S. Lect. on Midwifery at St. Bartholomew's Hospital. J. FORBES ROYLE, M.D. F.R.S. F.G.S. Professor of Materia Medicain King's College, London. HENRY SEARLE, Esq. London. W. SHARPEY, M.D. F.R.S. Prof, of Anat. and Physiol, in Univ. Coll. London. JOHN SIMON, F.R.S. Lecturer on Pathology, St. Thomas's Hospital. J. Y. SIMPSON/.M.D. Fellow of the Royal College of Physicians, and Pro- fessor of Midwifery in the University of Edinhurgh. SAMUEL SOLLY, F.R.S. Assistant Surgeon to St. Thomas's Hospital. GABRIEL STOKES, M.D. J. A. SYMONDS, M.D. Physician tothe Bristol General Hospital, and Lectu- rer on the Theory and Practice of Medicine at the Bristol Medical School. ALLEN THOMSON, M.D. Fellow of the Royal College of Surgeons, and Professor of the Institutes of Medicine in the University of Edinburgh. JOHN TOMES, Esq. Surgeon- Dentist to the Middlesex Hospital. WM. TREW, Esq. W. VROLIK, Prof. Anat. and Phys. at the Athenaeum of Amsterdam. RUDOLPH WAGNER, M.D. Prof.of Med. & of Comp. An at. in theRoy.U ni.EiUtngen. W. H. WALSHE, M.D. Physician to University College Hospital. R. WILLIS, M.D. W. J. ERASMUS WILSON, F.R.S. Consulting Surgeon to the St. Pancras Infirmary. CONTENTS OF THE THIRD VOLUME \ R. Adams, Esq. ■ ■ T. W. Jones, Esq. Bishop, Esq. .. W.H.Porter, Esq. 114 A.T.S.Dodd, Esq. A.T.S.Dodd, Esq. Instinct Dr. Alison Irritability Dr. Marshall Hall Knee-joint, Normal ) , TT. r ' l A. Higginson, Esq. Anatomy J Knee-Joint, Abnormal Anatomy of the . . Lacrymal Organs . . • Larynx, Normal Ana tomy Larynx, Abnormal Anatomy Leg, Regions of Leg, Muscles of ... Life Dr. Carpenter.. . . Liver E. Wilson, Esq... Luminousness, Animal Dr. Coldstream . . Lymphatic & Lacteal ) „ Esq System 5 Lymphatic System, } Dr TlM Abnormal Anatomy 5 Mammalia Professor Owen . . Mammary Glands .... S. Solly, Esq Marsupialia Professor Owen . . Membrane Dr. Todd Meninges Dr. Todd Microscope Dr. Carpenter. . . . Milk Dr.G.O. Rees . . Mollusca Professor Owen . . Monotremata Professor Owen .. Motion, Animal, in- ) r D. , „ \ J. Bishop, Esq. . . eluding Locomotion * Mucus Dr. G. O. Rees .. Mucous Membrane . . W. Bowman, Esq. Muscle W. Bowman, Esq. Muscular Motion .... W. Bowman, Esq. Page 1 29 44 48 78 100 12G 137 141 160 197 205 232 234 245 257 331 331 331 358 363 366 407 481 484 506 519 Muscular System, ) Comp. Anatomy ' Myriapoda Neck, Muscles and ) Regions of the. . ) Nervous System . . Nerve Nervous System, Comp. Anatomy Nervous Centres, } Normal Anatomy S Nervous Centres, ) Abnormal Anat. i Nervous System, } Physiology of the J Ninth Pair of Nerves Nose Nutrition (Esophagus Optic Nerves Orbit Organic Analysis .. Osseous System, } Comp. Anatomy S Osseous Tissue .... Pachydermata .... Pacinian liodies . . Par Vagum. Parotid Region .... Parturition Penis Perineum Peritoneum Pharynx Pisces Page Professor R. Jones.. 530 Professor R. Jones. . 545 J. Simon, Esq 561 Dr. Todd 585 Dr. Todd 591 J. Anderson, Esq. . . 601 Dr. Todd 626 Dr. Todd 712 Dr. Todd 720c G. Stokes, Esq 721 J. Paget, Esq 723 Dr. Carpenter 741 Dr. G. Johnson .... 758 Dr. Mayne 762 Dr. G. Johnson 782 Dr. Miller 792 Professor R. Jones . . 820 J. Tomes, Esq 847 Professor R. Juiits.. 858 W. Bowman, Esq... 876 Dr. J. Reid 881 Dr. G. Johnson .... 9(»2 Dr. Rigby 904 E. Wilson, Esq 909 Dr. Mayne 919 S. R. Pitlard, Esq . . 935 W. Trew. Esq 915 Professor R. Jones.. 955 ERRATA IN VOLUME THE THIRD. Page 684, col. 2, line 44, after "medulla oblongata," insert "and the cerebrum." 700, col. 2, line 19,. fur" testes," read "nates." line 20, for " nates," read "testes." line 36, for "thalami," read "thalamus." 708, col. 1, line 10, for" distend," read "exist." 711, col. 1, line 59, for " optic thalami," read " hemispheres." 712, col. 2, line 40, for " Seinruch," read " Steinruch." line 41, for " Hermann, Nasse," read "Hermann Nasse." At page 902, see a list of Errata in the article Pak Vagum. ADDITIONAL ERRATA IN VOLUME THE THIRD. Page 71, col. 1, line 1 and 2, for " six times," read " six lines." 287, col. 1, line 1, for " Peophagous," read " Poephagous." 351, col. 1, line 7, for " made be made," read " may be made." 361, col. 2, line 28 from bottom, for " analysis," read " analyses." 409, col. 1, fig 207, insert " B " at the angle which is not lettered. 409, col. 2, last line, for " g," read " G." 417, col. 2, lines 2 and 3, for " quadratus femoris," read " quadriceps extensor femoris." 418, col. 1, line 26 from bottom, for " separated," read "adapted." 433, col. 1, line 5, for " or ad — cd, in the second movement; the tail being," read " or ad — cd ; in the second movement, the tail being." line 10, for " ab," read " ad." 441, col. 1, line 7, dele " Sect. IV." 610, col. 1, line 5, for " molar," read " motor." 667, col. 1, line 19, for " foramen," read " fore-arm." 715, col. 1, line 39, for " in membranous," read " in a membranous." 716, col. 1, line 33 from bottom, for " his," read " this." 720x, col. 2, line 2 from bottom, for " posterior and posterior," read " anterior and pos- terior." 722s, col. l,line 8 from bottom, for " cerebri," read " cerebelli." 751, col. 1, line 19, for " had," read " have." 830, col. 1, line 10 from bottom, for " resemble," read " resembling." col. 2, line 6, for " it," read " them." 849, col. 2, in description of cut, for " animal," read " earthy." THE CYCLOPAEDIA ANATOMY AND PHYSIOLOGY. INSTINCT. — This word is often applied to the mental acts of the lower animals, as if it were truly applicable to the whole of these acts ; but a little consideration will shew, first, that this word, in its more approved and correct acceptation, is applicable only to a part of the mental operations, which may be inferred from the observation of the actions and habits of animals; and secondly, that in this restricted sense, the term is applicable to a part of the operations of the human mind itself; and that the subject of instinct cannot be tho- roughly understood, unless information regard- ing it is sought in the consciousness of our own minds, as well as in the observation of other living beings. The study of this subject is therefore equally important as a part of natural history, of mental philosophy, and of human physiology ; and is a good dlustration of the necessity of this latter science being based on the observation and generalization of the laws and conditions of vital action through- out the whole extent of the animal creation. It is obvious, indeed, that various mental acts, of which we are conscious in ourselves, may be inferred, with perfect confidence, to take place throughout the whole range of the animal kingdom, and even that some of them must be performed with greater energy and precision in some of the lower tribes than in man. The different external senses attain their highest perfection in different animals ; that of smell, for example, probably in the predaceous mammalia, that of touch in the antenna of insects, and that of sight in the predaceous birds ; it is not likely that any one is enjoyed in its highest perfection by man ; and what ■'have been accurately distinguished from mere VOL. III. sensations as the perceptions of external things, i. e. the notions as to the qualities of these, which naturally present themselves to our minds in consequence of sensations being felt, would seem in various instances to follow the sensa- tions more quickly and more surely in other animals than in us ; for it is generally allowed that what appear to be acquired perceptions of the eye to us, i. e. the notions of the distance, size, and form of visible objects, are instanta- neously made known to many of the lower animals the very first time that those objects make impressions on their retinae; the faculty of Intuition, which we must admit as part of the source of our own knowledge, appears to exist in greater perfection in other animals, and the notions of external things which they thus acquire are amply sufficient to regulate their muscular motions. It is equally plain that many of the strictly mental acts, of which our complex trains of thought are composed, are habitually performed by animals ; that they have a perfect recollec- tion of past sensations, implying the exercise of the powers of memory and of conception ; that the emotions of fear, of joy, of affection, of anger, even of jealousy, are as distinctly indi- cated by their actions as by those of man ; that under the influence of these emotions their mental operations are excited or depressed, and their attention fixed or distracted, and their volition excited, as in our own case; and that their actions are habitually guided by a clear perception, or rather, we should say, by conti- nual correct applications, of a first principle of belief, which is generally admitted to be an ultimate fact in the constitution of the human mind, and on which much stress has been 2 INSTINCT. laid by our ablest metaphysicians, " the belief of the permanence of the order of nature," or the conviction, " that what has been as an an- tecedent, will be followed by what has been as a consequent ;" otherwise the lessons of expe- rience would be lost upon them, and no change could be effected in their habits by education. Under the influence of this mental law, it is certain that their recollections of past sensations excite in them various desires, and afford mo- tives to action, which prompt many of their movements exactly on the same principle by which the greater number of what are strictly called voluntary human actions are determined ; the object in view, in both cases, being simply to procure known pleasure or to avoid known pain, and the same metaphysical question pre- senting itself to the speculative inquirer as to both, viz. the question whether the voluntary power is really to will what we please, or is only to do what we will. Further, the various muscular movements required for any such actions, and the sensations and emotions which excite them, are gradually linked together by the mental principle of the association of ideas, so as to become obedient to the law of Habit in animals equally as in man. It has been generally admitted, since the time of Locke, that the essential inferiority of the intellect of animals, as compared with that of man, lies in their very limited enjoyment of the faculty of abstraction, by which the mind is enabled to single out the different qualities or relations of the individual objects of sense, and make them the subject of abstract thought, and thereby form general notions, which are at once perceived to be equally applicable to many individual cases; and by help of which it continually elevates itself above the contem- plation of individuals, and classifies and me- thodizes its knowledge, and fits it for useful application, — for the deduction of inferences in reasoning, for the formation of fancied scenes in works of imagination, and for the adapta- tion of means to ends in practice. It is obvious, also, that none of those still more general or abstract notions which conti- nually suggest themselves to the human mind in the course of the operations that are excited by the senses, such, for example, as space, time, number, power, &c. are indicated by any mani- festations that we see of the mental acts of the lower animals ; and it may be stated, in general, that the limitation of their minds to particulars, and the want of the power of raising the thoughts to general ideas, and dwelling on the contemplation of these, is the grand obstacle to their adapting means to ends, drawing infe- rences from premises, or enjoying the use of language. The objections that have been started to this doctrine do not appear of much weight. Darwin, while he set aside the statement of Locke, endeavoured to distinguish instincts as " actions excited by sensations," employed about the possession of pleasurable objects, or the avoiding of painful ones, already in our power, while voluntary (i.e. rational) actions are employed " about the means to acquire such objects." But this distinction appears, on reflection, to be substantially the same. The two noblest and most characteristic of the facul- ties of the human mind, as defined by logi- cians, those of Reasoning and of Imagination, (the latter of which is truly applicable to every kind of contrivance or adaptation of means to ends, of which we are capable,) evidently im- ply the existence of a mental power of forming and dwelling on general ideas, which are equally applicable to many individual cases; and if animals possessed this latter power, we might confidently expect to see them exhibit indica- tions of the two former. Why is it, for example, that the monkeys, who have been observed to assemble about the fires which savages have made in the forests, and been gratified by the warmth, have never been seen to gather sticks, and rekindle them when expiring ? Not, certainly, because they are incapable of understanding that the fire which warmed them formerly will do so again, but because they are incapable of abstracting and reflecting on that quality of wood, and that relation of wood to fires already existing, which must be comprehended, in order that the action of renewing the fire may be suggested by what is properly called an effort of Reason. Or why is it, that the different classes of predaceous animals, although surrounded by the materials out of which the human race has manufactured so many implements of warfare, have never been able to avail themselves of any of them in aid of the instruments of destruction with which nature has furnished them ? Apparently, because they are incapable of forming such general notions of the qualities and relations of external things, as aie essential to the processes of imagination and reasoning, by which men are led to the contrivance, and guided in the use, of artificial weapons. Again, although many of them are suscepti- ble of the emotions of joy, and to a certain degree of gratitude and attachment, founded on the sense and recollection of benefits, none of them seem capable of forming the slightest notion of that Divine Power, which has sug- gested itself to the human intellect in all ages, and even in the rudest conditions of human existence ; we should regard any act of praise or prayer as an infallible indication of a mental capacity of the same rank as our own. Exceptions to this principle, to a certain ex- tent, must be admitted, as will afterwards ap- pear, and the explanation of some of them is certainly obscure ; but the general fact un- doubtedly is, that those operations of the human intellect which imply the formation of general or abstract notions, or in the language of Dr. Brown, the suggestion of relations, are beyond the power of the lower animals. In- deed reflection on the nature of language, on the small number of words (only substantive nouns, and only part of these) which apply to individual objects, and on the necessity of the power of forming some kind of abstract or general notion, as indispensable to the use of every other kind of word, is sufficient to esta- blish, and is perhaps the simplest way of dis- tinctly conceiving, the essential difference be- INSTINCT. 3 tween the constitution of the mind of man and of that of the dumb animals. But it has nevertheless been long observed, that while animals are thus incapable of com- prehending the importance or devising means for the attainment of objects which we perceive to be within their reach, and clearly and imme- diately important to them, they habitually per- form many actions which are admirably adapted to the attainment of certain ends, and these often remote and obscure, and known to us only by means of repeated observation and re- flection, and strictly inductive reasoning. No animals, for example, are capable of such ob- servation and comprehension of the laws of nature, as to procure for themselves at pleasure artificial heat or regular and uniform supplies of food ; but many are seen to form nests or burrows, and lay up magazines of provisions, early in the autumn, which are to protect them against cold and famine during the winter ; while others, even while the temperature is still mild, undertake long and painful aerial voy- ages, whereby they escape from the rigours of a northern climate, and enjoy the warmth and abundance of the tropical regions. Such pro- visions for future contingencies are within the power of man, but in him they are clearly de- pendent on the power of forming and applying general notions ; and if the lower animals pos- sessed that power, we can see nothing to hinder their enjoying the use of language, and might confidently expect to see many indications of varied contrivance for their own immediate convenience, which never present themselves to any observer of their habits. The utter ab- sence of intelligence in the other actions of animals, corresponding to that which ap- pears manifestly to regulate certain actions which accomplish certain definite purposes, is our first reason for believing that, while nature has vouchsafed to man alone the enjoyment of what we call Reason, — the power of compre- hending her laws, and so adapting means to ends as to turn these laws to his own advan- tage,— she has provided for the maintenance of other animals, not only by the circumstances in which she has placed them in the world, but also by imparting to them, on certain occasions, a peculiar mental impulse, urging them to the performance of certain actions which are useful to themselves or to their kind, but the use of which they do not themselves perceive, and their performance of which is a necessary con- sequence of their being placed in certain cir- cumstances, and often, more particularly, of their feeling certain sensations. And this is the general notion which we attach to the term Instinct. The term, it must be remembered, stands in opposition, not to the will, but to the reason of man. The most correct expression of the difference between an action prompted by in- stinct and one prompted by reason is, that in the first case the will acts in obedience to an impulse which is directly consequent on certain sensations or emotions, felt or re- membered; in the last it acts in obedience to au impulse which results from acts of reasoning and imagination. It is incorrect to say, that all the actions of animals differ from those of man in being performed without anticipation of their effects. Many of the most familiar actions of animals are guided by a perfectly correct anticipation of their conse- quences, (otherwise they would not be suscep- tible of training); but it is such an anticipation as implies the exercise only of the faculty of memory. The term Reason is properly applied to the anticipation of those consequences of actions, of which we can be informed only by processes of reasoning and imagination, im- plying the exercise of the faculty of abstraction, and the formation of general notions or ideas. In some instances, the instinctive impulse, consequent on a particular sensation or suc- cession of sensations being felt, acts im- mediately on certain nerves and muscles ; and no experience is necessary, in order that the action required, although a complex and dif- ficult one, may be performed with perfect pre- cision, as in the case of the winking of the eye, or shrinking of the arm from injury, or of suction and deglutition following certain im- pressions on the mouth and throat. These actions seem to be very nearly if not precisely on the same footing as those which have been described by Whytt and others as the natural effects of sensation, and by Dr. Marshall Hall as indications of what he terms the reflex func- tion of the spinal cord, — such as the actions of breathing, coughing, sneezing, vomiting, &c. ; and in which the intervention of sensation, al- though strongly indicated, is not universally admitted. But in the greater number of cases, the in- stinctive determination appears to act not di- rectly on the nerves and muscles, but on the train of mental changes which serves as the motive to the exertion of the will ; it extends to a long succession of actions, performed by individuals or by societies, each of which takes place under the influence of a mental deter- mination of a permanent character, and is often effected by a succession of voluntary efforts, which may require some habit and experience in order that they may be performed with pre- cision. Thus many animals require some length of experience before they acquire the use of their limbs or of their wings; but having acquired that power, they are taught by instinct to use them for the purpose of flight immediately on feeling certain sensations and emotions. In all such cases the actions are strictly voluntary, although the will acts, as we believe, in obedience to instinct, not to reason ; and this seems to be the proper view to be taken of such long-continued and ad- mirably combined actions as we see in the for- mation of the nests of birds, or of the houses of beavers, or in other instances to be afterwards mentioned. The sensations of these animals, at particular seasons, excite a variety of mental operations, but these operations are all con- trolled and directed by the desire or propensity to the performance of certain definite actions, whether by the individual alone or in concert with others. In the performance of these ac- B 2 4 INSTINCT. tions, the sensations, the voluntary powers, the memory and instinct of the animals are all brought into play ; but we have no reason to believe that the animals performing them are capable of anticipating their ultimate result. In all cases, those actions which are en- titled to the appellation of Instinctive are ge- nerally understood to be characterized by two marks, quite sufficient to distinguish them from the effects of voluntary power guided by rea- son : 1. That, although in many cases expe- rience is required to give the will command over the muscles concerned in them, yet the will, when under the influence of the instinc- tive determination, acts equally well the first time as the last ; no experience or education is required, in order that the different voluntary efforts requisite for these actions may follow one another with unerring precision; and 2. That they are always performed by the same species of animal nearly, if not exactly, in the same manner ; presenting no such variation of the means applied to the object in view, and admitting of no such improvements in the pro- gress of life or in the succession of ages, as we observe in the habits of individual men, or in the manners and customs of nations, adapted to the attainment of any particular ends by those voluntary efforts which are guided by Reason. " The manufactures of animals," says Dr. Reid, " differ from those of men in many striking particulars. No animal of the species can claim the invention. No animal ever in- troduced any new improvement, or variation from the former practice. Every one has equal skill from the beginning, without teaching, without experience or habits. Every one has its art by a kind of inspiration, i. e. the ability and inclination of working in it without any knowledge of its principles." A third distinc- tive mark, naturally resulting from the last, is at least equally characteristic, although much less generally observable, — that these instinc- tive actions are seen to be performed in cir- cumstances which reason informs us to be such as to render them nugatory for the ends which are usually accomplished by them, and for which they are obviously designed. The efforts made by migratory birds, even when confined, at their usual period of migration, — the mistake of the flesh-fly who deposits her eggs on the carrion-plant instead of a piece of meat,* or of the hen who sits on a pebble in- stead of an egg, or of the mule which remains immoveably fixed by terror instead of escaping from the flood which threatens to overwhelm it, (as exemplified in the inundation of the valley of Luisnes in Savoy in 1818,) or of the bee which gathers and stores up honey even in a climate where there is no winter, f are so many proofs, that an instinctive action is prompted by an impulse, which results merely from a particular sensation or emotion being felt, not by anticipation of the effect which the action will produce. * Kirby. + See Kirby and Spnnce, Introduction to Ento- mology, vol. ii. p. 469. But, in order to have demonstrative proof of the essential difference between instinct and reason, and of the correctness of the view which we take of the nature of that mental impulse which prompts what we call the in- stinctive actions of animals, it is only neces- sary to reflect on what passes within ourselves on occasion of certain actions of the very same class being performed by us. It is dif- ficult, indeed, in adult age, to distinguish those actions which we perform instinctively from those which we have learnt by repeated efforts to perform habitually ; but in the case of infants we see complex actions, useful or necessary to the system, performed with per- fect precision at a time when we are certain that the human intellect is quite incompetent to comprehend their importance or anticipate their effects ; yet we cannot doubt that it is by a mental impulse that they are excited, because we perform the same actions in the same cir- cumstances in adult age, and are then con- scious of the impulse which prompts them. " It is an instinct," says Bichat, " which I do not understand, and of which I cannot give the smallest account, which makes the infant, at the moment of birth, draw together its lips to commence the action of sucking," to be fol- lowed by the still more complex act of deglu- tition. " This cannot be ascribed to the mere novelty of the sensations which it experiences from external objects, for the general effect of such sensations is to determine various agita- tions or irregular movements indeed, but not an uniform movement, directed to a deter- minate end. If we examine different animals at the moment of birth, we shall see that the special instinct of each directs the execution of peculiar movements. Young quadrupeds seek the mamma of their mothers, birds of the order Gallinaceee seize immediately the grain which is their appropriate nourishment, while the young of the Carnivorous birds merely open their mouths to receive the food which their parents bring to their nests. In general, it is very important to distinguish the irregular or varied movements which, at the moment of birth, are produced simply by the new sensations and excitements which the body receives, from those definite actions which are the effect of instinct, a cause of which we can give no further explanation." In fact, when we attend to the simple action of deglutition,* as performed in our mature years, we may be conscious that it results from the same instinctive impulse which guided it with unerring precision in the new-born infant, long before the voluntary power of simply raising the hand to the mouth had been ac- quired. If we were to consult only the grati- fication of our sensations, we should keep any grateful food in the mouth; for when it is swal- lowed the gratification immediately resulting from it is at an end, and there is no peculiar pleasure attached, in other circumstances, to the mere act of deglutition ; but all we can * [I. e. that part of the act which is dependent on the voluntary movement of the tongue to pass on the food to the isthmus faucium. — Ed.] INSTINCT. 5 observe by attention to our own feelings on such occasions is, that while we feel the sen- sations of hunger and thirst, we feel also a pro- pensity, all but irresistible, to swallow what- ever grateful food or drink is in the mouth. This propensity is not only prior to reason, but stronger than reason, and prompts us to action more surely and more energetically than the mere recollection of the effects previously resulting from food or drink taken into the sto- mach could have done. If we reflect further, we shall find that there are various other sensations, with which we can feel, in our own persons, that an instinctive impulse is naturally linked. The term Appe- tite does not express the whole of these, although it is only by referring to the action which it uniformly prompts that an appetite can be distinguished from another sensation. Sympathetic movements, such as breathing, coughing, sneezing, vomiting, &c. are ascribed by Whytt and others to sensations ; and laugh- ter, weeping, the expression of feeling in the countenance and features, &c. are strictly refer- able to emotions of mind, and in the perform- ance of all these actions, a propensity which may be called strictly instinctive, because prior to experience, and independent of reason- ing, may be frequently and distinctly felt, and is from the first equally effectual in exciting very complex muscular movements, as the impulse to swallow food in the mouth. We may specify several other kinds or modes of action, which we are all conscious of frequently per- forming, and which we perform on many oc- casions in obedience, not to any effort of reason, but to a truly instinctive impulse, natu- rally consequent on certain sensations or emotions, and felt even in adult age to be inde- pendent of, as they are in the infant prior to, any anticipation of remote consequences, — viz. 1. those which are prompted by the instinct of self-preservation, (as the winking of the eye- lids when the eyes are threatened with injury, the shrinking of any limb or part of the body which is struck, the projection of the arms when we are about to tall forwards on the face,* the act of crying from pain or from fear); 2. those which are prompted by the instinct of shame, as when the saliva escapes from the mouth, when the sphincters fail in their office, or the sense of modesty is out- raged ; 3. those which are prompted by the instinct of imitation, existing more or less in the early stage of all human existence, and whereby we are all led to fashion our language, manners, and habits, on the model of those around us, and particularly of those persons with whom we have either the most frequent inter- course, or the intercourse which is most fitted to make an impression on our minds; 4. those which are prompted by the emotions of affec- * Let any one try the experiment of attempting to fall forward on liis face, with his arms extended at his sides, and he will he immediately conscious of the instinctive impulse which urges liiin to throw forward his arms ; and which he feels dis- tinctly and resists with difficulty, even when he knows that he is about to fall only on soft matter which cannot injure him. tion and pity, or still more decidedly by the impulse of maternal love, on witnessing the helpless condition of young infants.* We do not enter into details on these subjects at pre- sent, but merely mention them as examples, in which we may safely and legitimately avail ourselves of the evidence of consciousness to assure ourselves of the essential peculiarity, and of the paramount authority, of the in- stinctive impulse, as distinguished from the voluntary effort, which results from a train of reasoning. It has been often said that the nature of instinct is absolutely mysterious and inscru- table ; but if what has now been stated he correct, this can be said of instinct only in the same sense in which it may be said of all mental acts without exception ; the essence of mind, like that of matter, being wholly in- scrutable. The churucters of the instinctive impulse may be distinguished as clearly as those of any other mental act, in the only way in which any such act can be distin- guished, viz. by attention to our own conscious- ness ; although we never could have antici- pated a priori that this kind of mental impulse could have extended to so long continued and complex actions, and to the concerted ope- rations of so many individuals, as the operations of some animals indicate. Having satisfied ourselves of the existence of certain instinctive impulses, both in the lower animals and in ourselves, essentially dis- tinct from those voluntary efforts which are guided by reason, we need not be perplexed at finding that there is much difficulty in some individual instances, in determining to which class of mental acts particular actions ought to be referred. However difficult it may be in any in- dividual instance, to decide whether an action, of man or of animals, is the effect of a blind in- stinct, or of reason, anticipating and desiring its consequences, there can be no doubt or difficulty as to the fact, that these two distinct kinds of mental determination to the perform- ance of actions exist. Neither do we consider it of any import- ance to enter on the metaphysical speculations which ingenious men have hazarded at different times as to the nature of the agent, by which the instinctive actions may be supposed to be immediately excited. Some philosophers have been so strongly impressed with the admirable adaptation of means to ends which these phe- nomena present, in animals manifestly devoid of reason, that they have believed them to be in all cases the immediate offspring of the divine intelligence, and have expressed their theory in the form of an axiom, " Deus anima brutqrum," which, it is humbly conceived, is admissible only in the same sense in which we assent to the more general assertion, " Deus anima mundi." Mr. Kirby, in his very learned and elaborate Bridgewater Treatise on the History, Habits, and Instincts of Animals, seems to favour the [* The greater number of the'actions enumerated may, however, be accounted for on the principle of reflux nervous action, now so generally admitted by physiologists. — Ed.] 6 INSTINCT. idea which other philosophers have maintained, of intermediate agents between the Divine will and the living beings on earth, by which the actions of the latter are guided ;* but in pro- secuting this idea he is disposed to regard the proximate cause of instinct, as he expresses it, not as metaphysical, but merely as physical, and to suppose that " light, heat, and air, or any modification of them " may be the inter- mediate agents " employed by the Deity to excite and direct animals, when their intellect cannot, in their instinctive operations ;" and that " the organization of the brain and nervous system may be so varied and formed by the Creator as to respond in the way that he wills, to pulses upon them from the physical powers of nature. "f On this it may be observed that this last sentence expresses no more than the truth, whatever opinion we may form as to the mode, in which tlie response of the nervous system of an animal to the impressions made on it by physical agents takes place; but if it be meant by the expression, that the proximate cause of instinct is probably not metaphysical but physical, to exclude all mental operation, and all consciousness of effort, from the instinctive actions of animals, we can regard the theory only as a denial of all mental acts or affections in any of the lower animals, and as easily con- tradicted by the whole analogies of their struc- ture, by observation of their habits, and by the evidence of our own consciousness in the performance of those precisely similar instinc- tive actions which have been noticed above. It seems quite unreasonable to doubt that the immediate cause of all the actions that we call instinctive, is a strictly mental effort, but the occurrence of that effort in every case when it is required must in all probability be always held as an ultimate fact in the animal ceconomy ; and all speculations as to its inti- mate nature or proximate cause may be re- garded as mere conjectures, on a subject which is beyond the reach of the human faculties. Nor would any thing be gained, in the infer- ence as to final causes, from establishing any one of these conjectures ; for the mental constitution of man himself, and of the whole lower ani- mals, is equally a part of the contrivance of the Divine Artificer of the world, as the laws of motion or the properties of light. He who could make man after his own image could assuredly impart such mental propensities to other beings, as well as to man, as were ne- cessary for the ends for which the creation was designed. And when we attempt, in all hu- mility, but at the same time in confident re- liance on the mental powers which He has vouchsafed to us, to draw inferences as to His existence and attributes from the study of created things, we do so, not by vainly attempt- ing to comprehend the nature of the energy by which any of the changes (physical or mental) occurring around us are effected, but simply by observing the adaptation of means to ends in those regular and uniform laws which we are * See vol. ii. p. 243-4. t Vol. ii. p. 255-6. enabled to infer from the observation of such changes, — which we ascribe to His authority, and beyond which we feel that it is not yet given us, by any exercise of our minds, to ascend. In enabling us to draw those in- ferences, the instincts of animals, as we shall afterwards state, are of peculiar importance ; but the inferences are the same, whatever opi- nion we may adopt as to the mode in which the Divine Intelligence so indicated rules the wills of the animal creation. Having said so much of the characteristics of this class of phenomena, and endeavoured to set them in the proper point of view, we shall next offer a very rapid sketch of the varied instincts exhibited in the different tribes of animals, arranging them simply according to the purposes which they seem destined to serve, and shall conclude with a few general reflections. It may be premised that it certainly seems reasonable a priori to suppose, that the struc- ture of the nervous system, and especially of the brain, of different animals, will bear some relation to the kind of instinctive propensities which they exhibit. In the size of the sen- sitive and motor nerves, and portions of the cerebro-spinal axis whence these originate, par- ticularly the spinal cord, medulla oblongata, and optic lobes (or corpora quadrigemina),in the higher animals, this relation may be distinctly perceived; and it has been further confidently stated by some phrenologists, that strong evi- dence of certain of their peculiar doctrines may be deduced from observation of the size and form of the brains of animals, as compared with their instincts ; but this last speculation certainly cannot be carried further than the vertebrated animals, which form but a small part of the living beings that are continually guided and ruled by the laws of instinct; and even in them no such relation of the size and form of the brain, or of any part of the brain, to the general intelligence of an animal, or to any par- ticular instinct, has been fully ascertained. In- deed, until some such essential difference shall be observed between the habits and instincts of the dolphin, or other cetaceous animals, and the predaceous fishes, as may correspond to the extraordinary difference of the size and struc- ture of their brains, (that of the former being much larger in proportion to the spinal cord than the human brain, and of complex struc- ture, while that of the latter is not larger than the optic lobes or corpora quadrigemina of the same animal, and of very simple structure,) such speculations may be safely distrusted.* Mr. Kirby has stated that the principal in- stincts of animals may be referred to three heads; those relating to their food, those re- lating to their propagation and the care of their offspring, and those relating to their hybernation . But this enumeration is certainly defective, and indeed will hardly include several which * We cannot suppose this difference to be con- nected with the difference in the mode of respi- ration of these animals, because we know that the only part of the central masses of the nervous system of either, concerned in that function, is the medulla oblongata. INSTINCT. 7 he has himself accurately described. The fol- lowing appears a more comprehensive enume- ration. Three great classes of instinctive ac- tions may be distinguished ; the first designed for the preservation of individuals; the second for the propagation and support of their off- spring ; and the third for various purposes im- portant either to the race of animals exhibiting them, or to other animals, but not distinctly referable to either of the formei heads. Each of these classes admits of obvious sub- divisions. I. Of instincts designed for- the preservation of the individuals exhibiting them, we may enumerate the following : — 1. All animals are endowed with instincts prompting them to some means of escaping or repelling injury or violence, but these are ex- ceedingly various, both as to the kind and as to the degree of complexity of the actions which they excite ; from the simple retraction of the tentacula of the infusory Y'orticella, or of the Medusa, Polype, or Actinia, up to the active and formidable resistance of the ele- phant or the tiger. The most common instinct of self-preservation excited by the emotion of fear, is that which prompts to flight, an in- stinct so obviously existing in the human species, that the effort by which it is resisted has in all ages been regarded with respect; and another very common propensity in animals is that which prompts to concealment. This is often combined with flight, as in most of the Carnivorous Mammalia, the Kodentia, the Ce- tacea, the diving birds, reptiles, insects, &c. ; but some of the higher animals, and many of the Mollusca and insects, and others of the lower tribes, remain quite motionless and counterfeit death when under the influence of fear ;* and it is remarkable that when the cir- cumstances of the animals render this mode of defence the most effectual, it is that adopted, in preference to flight, even by single species of families, the other members of which shew no such instinct, as in the case of the ptarmi- gan, which so frequently cowers among the grey lichen, or the snow on the mountain- tops, instead of taking wing like the moor fowl, or in that of the hedge-hog, which on occasion of any imminent danger makes no effort but that of coiling itself into a ball. In many instances the instinct either of flight or concealment is aided by very various special contrivances, equally instinctive, fitted either to deceive, or to alarm, or injure an assailant. Some even of the Mollusca, and some of the reptiles, as the toad, squirt water on him ; many reptiles and some lower animals, as the scorpion, bee, wasp, &c, even some of the gelatinous radiata,f have the power of emit- * " In this situation, spiders will suffer them- selves to be pierced with pins and torn to pieces, without discovering the smallest sign of pain. This simulation of death has been ascribed to a strong convulsion or stupor occasioned by terror ; but this solution of the phenomenon is erroneous. If the object of terror is removed, in a few se- conds the animal runs off with great rapidity." — Duncan On Instinct. t Kirhy, vol. i. p. 198. ting irritating matter of greater or less inten- sity ; the electrical animals, as the gymnotus and torpedo, use their appointed weapons ; the hedge-hog and porcupine oppose their sharp thorns to any one who attempts to molest them ; many insects and some reptiles protect them- selves by emitting peculiarly fetid effluvia; the cuttle-fish tribe have the remarkable power of emitting an inky fluid which darkens the wa- ter and hides them ; and on the other hand there is reason to believe that the phosphores- cent light which so many marine animals ex- hibit, may be suddenly augmented on occa- sion of any threatening of injury, and serve as a means of defence.* (See Luminousness.) The means of defence, and the instincts guid- ing them, in the case, not only of the higher Carnivorous animals, but many of the stronger of the Herbivorous classes, the elephant, the hog, the horse, the buffalo, the deer, &c. re- quire no illustration. The instinct which prompts many animals to utter cries when injured or threatened, (as well as on other occasions and for other purposes,) deserves notice as a means of protection, parti- cularly on this account, that as it is one of the instincts which most clearly extends to the human race, so we may perceive in man, as well as in some of the lower animals, that its use is not merely to frighten assailants, but especially to procure assistance and protection for the young animal from its parents. 2. The most conspicuous and most remark- ably varied of the instincts under this head are those by which the food of different ani- mals is procured. With the exception of the sponges, and some others of the lowest Zoo- phyta, in which the nourishment is supplied by currents, all animals have organs corresponding to a mouth and stomach, into which aliments are taken by a process of deglutition, imply- ing sensations and instinctive efforts conse- quent on these; and in the Articulata and Mollusca, the most important central organ of the nervous system seems to be the nervous collar surrounding the oesophagus, which in the vertebrated animals seems to be developed and subdivided into the first, fifth, and part of the eighth pairs of nerves, with the corres- ponding portions of the cerebro-spinal axis, by which the sensation of hunger is felt, the suitable nourishment discriminated, and the instinctive effort, whether of deglutition only, or of mastication more or less powerful ac- cording to the food, is excited. In some instances subsidiary instincts are also implanted in certain animals, which are essential to their digestion and nutrition. The art of cookery, as universally practised by the human race, may be said to be the result of experience; but this cannot be said of the pro- pensity of many animals to swallow salt, still less of the swallowing of gravel or pebbles by the graminivorous birds, or of the copious draughts of water, sufficient to store the nu- merous and peculiar cells of their first and second stomachs, which are taken by the camel * Ibid, vol. i. p. 178. 8 INSTINCT. or llama before they enter on the deserts, and which enable them subsequently to subsist without water for many days. But the instincts by which animals are en- abled to search for and obtain food may be easily supposed to be much more numerous and varied than those by which they merely seize and swallow it, and in fact furnish the conditions by which the varieties of the whole structure of animals are chiefly determined. Probably the greatest number of animals are nourished by the vegetable world in the living or dead state, and are continually guided by sensations, to which instinctive efforts are at- tached,— i. e. by appetites, — in the selection of food, which may in general be found and seized without much difficulty. But through- out the whole animal kingdom, from the mi- croscopic animalcules up to the largest of the Mammalia, a very great number of carni- vorous animals are found, who subsist on, and continually repress the numbers of, the herbi- vorous tribes ; and it may easily be supposed that the instincts implanted in these animals, which oppose and counteract the varying efforts at self-preservation already mentioned, will be more varied, and bear more marks of contri- vance and ingenuity. Accordingly, from the numerous Vorticella:, or other animalcules, of the order Rotatoria, which excite currents in the water around them, and so attract into their stomachs many of the smaller ani- malcules, up to the lion, the whale, or the eagle, we find an infinite number of con- trivances and instinctive propensities, served by organs, by which the predaceous animals, of all the orders, are enabled to prey on the others. The Polype, Echinus, and Actinia, for example, among the Zoophyta, seize their prey, as it is brought to them by the waves, with their numerous tentacula ; the Entozoa, and the leech and other of the Annelides, have the faculty and the necessary instinct of attach- ing themselves to the larger animals in the situations which suit them, as the (Jirrhipedes or barnacles do to vegetable substances. The cuttle-fish and other predaceous MoMusca have legs furnished with admirably constructed suckers and powerful jaws, and most of the Crustacea have claws and mandibles, suf- ficient to enable them to seize and destroy ma- rine animals of very considerable size ; and it is unnecessary to enlarge on the powerful means of destruction, or on the instincts guid- ing their use, which are seen in many genera of each of the classes of vertebrated animals. There is often a peculiar instinct guiding each of the Carnivorous Mammalia to the part of the body of its victim where it can most easily inflict a mortal wound, to the throat in the case of a large animal, to the head in that of a small one, of which the cranium may be pierced. In the greater number of them, however, the instinctive actions by which their prey is obtained are distinguished only by power and violence ; and although much con- trivance is employed for adapting the different parts of the structure to the habits and des- tination of the animals, there is little apparent ingenuity in the modes in which the animals perform their office in creation. The attitude and gesture of the cat, the pointer, or the tiger, " slow stealing with crouched shoulders on his prey," is an example of instinctive con- trivance preliminary to the act of violence. The aspect and expression of many carnivo- rous animals, — not only of the Mammalia and birds, but of the shark, the cuttle-fish, the scorpion, the tiger-beetle, &c, are so adapted to the feelings and instincts of the animals on which they feed, as often to deprive them of the power of flight or resistance ; and it is maintained by many, that some of the predace- ous animals have the power of fascinating their prey by merely fixing their eyes on them. Many have ascribed this power to the serpent ; and Mr. Kirby asserts it with confidence of the fox * A few only of the predaceous ani- mals, as the dog and wolf, have the instinct of associating together for procuring their prey. It has been stated that the pelican and tiie dog-fish have a similar instinct. f But the more striking indications of con- trivance in the actions prompted by this in- stinct are to be found in some of the less pow- erful of the carnivorous tribes. The Lophius Piscatorius or fishing-frog, although a large fish, having no strength or speed, obtains its prey by stratagem, plunging itself in mud, or covering itself with sea-weed: " it lets no part of it be perceived except the extremity of the filaments that fringe its body, which it agitates in different directions, so as to make them ap- pear like worms. The fishes, attracted by this apparent prey, approach and are seized by a single movement of the fishing-frog, and swal- lowed by his enormous throat, and retained by the innumerable teeth by which it is armed." J A still more singular art is practised by the Choetodon rostratus, which feeds on flies, and, as Sir Charles Bell states, actually takes aim at them, and shoots them with a drop of water.§ The instinct of the myrmecophaga or ant-eater, which protrudes the tongue to allure flies to settle on it, and then suddenly retracts it to devour them, also deserves notice. A more complex art is practised by the ant-lion, which digs a pitfall in the track usually followed by ants, and conceals itself in the bottom of it, waiting for its prey. But of all contrivances in the animal creation for procuring food, the most complex and artificial are those of the different genera of spiders, equally curious on account of the peculiar organs by which they spin their webs, as of the peculiar and varied instincts by which they are guided in using them. || For example, " any common black and white spider (Salticus Scenicus), which may always be seen in summer on sunny rails, &c, when it spies a fly at a distance, ap- proaches softly, step by step, and seems to measure his distance from it by the eye; then if he judges that he is within reach, first fixing * Vol. ii. p. 2(19. t See Darwin's Zoon. vol. i. p 229, 249. X See Kirby, vol. ii. p. 406, and pi. xiii. $ Bridgwater Treatise, p. 200. || See Kirby, vol. ii. p. 184 and 286. INSTINCT. a thread to the spot on which lie is stationed, by means of his fore feet, which are much larger and longer than the others, he darts on his victim with such rapidity, and so true an aim, that he seldom misses it. He is pre- vented from falling by the thread just men- tioned, which acts as a kind of anchor, and enables him to recover his station."* Again, the kmd of spider that has received the name of Geometric, " having laid the foundation of her net, and drawn the skeleton of it, by spinning a number of rays, converging to a centre, next proceeds, setting out from that point, to spin a spiral line of unadhesive web, like that of the rays, which it intersects, and after numerous circumvolutions finishes this at the circumference. This line, in conjunction with the rays, serves as a scaffolding for her to walk over, and also keeps the rays properly stretched. Her next labour is to spin a spiral or labyrinthiform line from the circumference towards the centre, but which stops somewhat short of it; this line is the most important part of the snare. It consists of a fine thread, stud- ded with minute viscid globules, like dew,which by their viscid quality retain the insects which fly into the net. The snare being thus finished, the little geometrician selects a concealed spot in the vicinity, where she constructs a cell, in which she may hide herself and watch for game; of the capture of which she is informed by the vibrations of a line of communication, drawn between her cell and the centre of her snare. "f 3. Many animals are guided by instinct to form habitations for themselves, of very various kinds, for protection against injury and against cold, from the simple contrivance of the earth- worm, which closes the orifice of its hole with leaves or straw, up to the elaborate structures of the bee, the ant, or the beaver. Here we observe a singular but easily understood diffe- rence between the inhabitants of water and air. The greater number of the more delicate animals that inhabit the sea, chiefly of the Mollusca and Crustacea, are provided by nature with shells, or very firm integuments, evidently for protec- tion against the violence of the waves, in the formation of which instinct has little or no share; but there are some of the Annelides inhabiting water, as the Sabella and Terebella, and the larvae of some moths, which have a sin- gular instinct enabling them to form habitations sufficient for their own protection, "by collect- ing grains of sand and fragments of decayed shells, &c. which they agglutinate together by means of a viscid exudation, so as to form a firm defensive covering, like a coat of mail." This may be stated as the intermediate link be- tween the habitations given to the Mollusca and Crustacea by nature, and those which many land animals have organs and instincts enabling them to form for themselves. " The manoeuvres of the terebella are best observed by taking it out of its tube and placing * Kirby. vol. ii. p. 298. t Ibid. p. 295. See also Darwin's Zuon. vol. i. p. 253. it under water upon sand. It is then seen to unfold all the coils of its body, to extend its tentacula in every direction, often to a length exceeding an inch and a half, and to catch, by their means, small fragments of shells and the larger particles of sand. These it drags to- wards its head, carrying them behind the scales which project from the anterior and lower part of the head, where they are immediately ce- mented by the glutinous matter which exudes from that part of the surface. Bending the head alternately from side to side, while it con- tinues to apply the materials of its tube, the terebella has very soon formed a complete collar, which it sedulously employs itself to lengthen at every part of the circumference with an activity and perseverance highly inte- resting. For the purpose of fixing the different fragments compactly, it presses them into their places with the erected scales, at the same time retracting the body. Hence the fragments, being raised by the scales, are generally fixed by their posterior edges, and thus, overlaying each other, often give the tube an imbricated appearance. " Having formed a tube of half an inch or an inch in length, the terebella proceeds to burrow ; for which purpose it directs its head against the sand, and contracting some of the posterior rings, effects a slight extension of the head, which thus slowly makes its way through the mass before it, availing itself of the materials which it meets with in its course, and so con- tinues to advance til! the whole tube is com- pleted. After this has been accomplished, the animal turns itself within the tube, so that its head is next the surface, ready to receive the water which brings it food, and is instrumental in its respiration. In summer the whole task is completed in four or five hours ; but in cold weather, when the worm is more sluggish, and the gluten is secreted more scantily, its progress is considerably slower."* The habitation formed by the water-spider, which is not exposed to the violence of the sea, shews much greater delicacy of workmanship, as well as greater variety of instinct. " The insects that frequent the waters," says Kirby, " require, as well as those that inhabit the earth, predaceous animals to keep them within due limits, and the water-spider is one of the most remarkable on whom that office is imposed by the Creator. To this end her in- stinct instructs her to fabricate a kind of diving- bell, for which purpose she usually selects still waters. Her house is an oval cocoon filled with air, and lined with silk, from which threads issue in every direction, and are fast- ened to the surrounding plants ; in this cocoon, which is open below, she watches for her prey, and even appears to pass the winter, when she closes the opening. It is most commonly en- tirely under water, but its inhabitant has filled it with air for respiration, by which she is ena- bled to live in it. She conveys the air in the following manner : she usually swims upon her back, when her abdomen is enveloped in a * Roget's Briclgewater Treatise, vol. i. p. 279. 10 INSTINCT. bubble of air, and appears like a globe of quick- silver ; with this she enters her cocoon, and displacing an equal mass of water, again ascends for a second lading, till she has suffi- ciently filled her house with it, so as to expel all the water. The males construct similar habitations by the same manoeuvres. How these little animals can envelope their abdomen with an air-bubble, and retain it till they enter their cells, is still one of Nature's mysteries that have not been explained." We need say nothing of the habitations formed by solitary animals of the higher tribes, chiefly by burrowing under ground, for their own protection and comfort ; but the most curi- ous of such solitary habitations on the earth's surface are also furnished by the tribe of spiders. " Some species of spiders, M. Audouin re- marks, are gifted with a particular talent for building: they hollow out dens; they bore galleries ; they elevate vaults ; they build, as it were, subterranean bridges; they construct also entrances to their habitations, and adapt doors to them, which want nothing but bolts, for without any exaggeration, they work upon a hinge and are fitted to a frame. The interior of these habitations is not less remarkable for the extreme neatness which reigns there; whatever be the humidity of the soil in which they are constructed, water never penetrates them ; the walls are nicely covered with a tapestry of silk, having usually the lustre of satin, and almost always of a dazzling white- ness. " The habitations of the species in question are found in an argillaceous kind of red earth, in which they bore tubes about three inches in depth and ten lines in width. The walls of these tubes are not left just as they are bored, but are covered with a kind of mortar, suffi- ciently solid to be easily separated from the mass that surrounds it.'' " The door that closes the apartment is still more remarkable in its structure. If the well were always open, the spider would sometimes be subject to the intru- sion of dangerous guests. Providence has there- fore instructed her to fabricate a very secure trap-door which closes the mouth of it. To judge of this door by its outward appearance, it appears to be formed of a mass of earth coarsely worked, and covered internally by a solid web, which would be sufficiently wonder- ful for an animal that seems to have no special organ for constructing it ; but when divided vertically, it is found to be a much more com- plicated fabric than its outward appearance in- dicates, it being formed of more than thirty alternate layers of earth and web emboxed, as it were, in each other, like a set of weights for small scales. " If these layers of web are examined, it will be seen that they all terminate in the hinge, so that the greattr the volume of the door the more powerful is the hinge. The frame in which the tube terminates above, and to which the door is adapted, is thick, arising from the number of layers of which it consists, and which seem to correspond with those of the door; hence the formation of the door, the hinge, and the frame, seem to be a simultaneous operation ; except that in fabricating the first, the animal has to knead the earth as well as to spin the layers of web. By this admirable arrangement these parts always correspond with each other, and the strength of the hinge and the thickness of the frame will always be proportioned to the weight of the door. " The interior surface of the cover to the tube is not rough and uneven like its exterior, but perfectly smooth and even like the walls of the tube, being covered with a coating of white silk, but more firm, and resembling parchment, and remarkable for a series of minute orifices placed in the side opposite the hinge, and ar- ranged in a semicircle ; there are about thirty of these orifices, the object of which, M. Au- douin conjectures, is to enable the animal to hold her door down in any case of emergency against external force, by the insertion of her claws into some of them." * But the most extraordinary habitations formed by the instincts of animals are those which are the joint result of the labours of communities; and here we observe the same difference as has been already noticed, between the inhabitants of the air and of the ocean. Many of the ani- mals that inhabit the latter are formed by na- ture, as Mr. Kirby expresses it, (and evidently with a view to the rude shocks to which they are exposed,) " into a body politic, consisting of many individuals, separate and distinct as inhabiting different cells, but still possessing a body in common, and many of them receiving benefit from the systole and diastole of a com- mon organ ; thus by a natural union is symbo- lized what in terrestrial animal communities re- sults from numerous wills uniting to effect a common object. The land, as far as I recol- lect, exhibits no instance of an aggregate animal, nor the ocean of one which, like the beaver, lemming, bee, wasp, &c. forms associations to build and inhabit a common house. "f And there is a curious family, named Salpa, in which the individuals are attached to each other almost like bees in their cells at birth, and are afterwards separated when they have acquired strength; thus forming the link be- tween the aggregated sea animals (such as Co- rals, Madrepores, Sertularia, Flustra, &c.) and the associated land animals. The habitations that are formed by animals of the latter description, although in very diffe- rent parts of the scale of beings, afford equally curious evidence of skill and contrivance, and of the wills of numerous individuals, bound together by a common instinct, as surely as the materials of which the aggregate animals are composed. Take, for example, the houses of beavers. " Beavers set about building some time in the month of August: those that erect their habitations in small rivers or creeks in which the water is liable to be drained off, with won- derful sagacity provide against that evil by * Kirby, vol. ii. p. 287, ct seq. t Kirbj, vol. i. p. 222. INSTINCT. 11 forming a dike across the stream, almost straight where the current is weak, but where it is more rapid, curving more or less, with the convex side opposed to the stream. They construct these dikes or dams of the same materials as they do their lodges, viz. of pieces of wood of any kind, of stones, mud, and sand. These causeways oppose a sufficient barrier to the force both of water and ice ; and as the willows, poplars, fkc.&c. employed in constructing them often strike root in it, it becomes in time a green hedge in which the birds build their nests. " By means of these erections the water is kept at a sufficient height, for it is absolutely necessary that there should be at least three feet of water above the extremity of the entry into their lodges, without which, in the hard frosts, it would be entirely closed. This entry is not on the land side, because such an open- ing might let in wild animals, but towards the water. " They begin to excavate under water at the base of the bank, which they enlarge upwards gradually, and so as to form a declivity, till they reach the surface ; and of the earth which comes out of this cavity they form a hillock, with which they mix small pieces of wood and even stones ; they give this hillock the form of a dome from four to seven feet high, from ten to twelve long, and from eight to nine wide. As they proceed in heightening, they hollow it out below, so as to form the lodge which is to receive the family. At the anterior part of this dwelling, they form a gentle declivity termina- ting at the water, so that they enter and go out under water. " The interior forms only a single chamber resembling an oven. At a Little distance is the magazine for provisions. Here they keep in store the roots of the yellow water-lily, and the branches of the black spruce, the aspin, and the birch, which they are careful to plant in the mud. These form their subsistence. Their magazines sometimes contain a cart-load of these articles, and the beavers are so industrious that they are always adding to their store." * The nests so admirably constructed by what have been called the perfect societies of insects, the white ants or termites, the ants or formica?, the bees, wasps, and humble bees, are well known, and have been often described. The materials used by the two first genera are chiefly clay, with bits of straw or wood, cemented by animal secretions ; the bees manufacture wax for the purpose. " The wasps and hornets are remarkable for the well-known curious papier-mache edifices, in the construction of which they employ fila- ments of wood, scraped from posts and rails with their own jaws, mixed with saliva, of which the hexagonal cells in which they rear their young are formed, and often their combs are separated and supported by pillars of the same material ; and the external walls of their nests are formed by foliaceous layers of their ligneous paper." f * Ki.hy, vol. ii. p. 510. t Kirby, loc. tit. p. 335. " The tree-ants, again, are remarkable for forming their nests on the boughs of trees of different kinds; and their construction is sin- gular, both for the material and the architec- ture, and is indicative of admirable foresight and contrivance ; in shape they vary from glo- bular to oblong, the longest diameter being about ten inches, and the shortest eight. The nests consist of a multitude of thin leaves of cow-dung, imbricated like tiles upon a house, the upper leaf formed of one unbroken sheet covering the summit like a skull-cap. The leaves are placed one upon another in a wavy or scalloped manner, so that numerous little arched entrances are left, and yet the interior is perfectly secured from rain. They are usually attached near the extremity of a branch, and some of the twigs pass through the nest. A vertical section presents a number of irregular cells, formed by the same process as the exte- rior. Towards the interior the cells are more capacious than those removed from the centre, and an occasional dried leaf is taken advantage of to assist in their formation. The nurseries for the young broods in different stages of developement are in different parts of the nest."* What is most peculiar in the habitations of all these " perfect societies of insects," is the formation, by the same working members of these societies, of cells of different size and form, suited for the different classes or ranks of indi- viduals which, as we shall afterwards state, each of these associations comprises ; and the occasional alteration of the size and form of the cells, when circumstances occur, which will be afterwards mentioned, to make an alteration of their destination advisable. There are other examples among insects, of imperfect societies or associations, found tempo- rarily and during the larva state only, which unite in forming tents under which they feed, and which shelter them from sun and rain. This is done by the larvae of several species of butterfly and moth.f 4. The next instincts which may be noticed under this head are those connected with the hybernation of animals ; for in almost every case in which this faculty (which is found so gene- rally in the lower tribes, particularly reptiles and insects, as well as in the order Cheiroptera and several others of the higher animals,) exists, there is attached to it some instinctive propensity, prompting the animal, even although it be not one of those which form houses for themselves, at least to search for some suitable residence in which it may be sheltered during the winter, whether under ground, under stones or timber, under the bark of trees, &c; and it is very re- markable that their hiding places are often found, or formed, long before the weather has become very cold. " I am led to believe from my own observation," says Mr. Spence, " that the days which the majority of coleopterous insects select for retiring to their hybernaculaare some of the warmest days of autumn, when * IbiH. p. 340. t Spence and Kirby, vol. ii. p. 21. 12 INSTINCT. they may be seen in great numbers alighting on walls, rails, path-ways, &c."* Some insects, and many larvae (as the silk-worm) approaching to the state of pupae, form a covering for them- selves by exudations from their own bodies, likewise at some distance of time before the frosts set in. Many hybernating animals ex- hibit so little of any vital action as to require little or no nourishment during the winter, ex- cepting the product of absorption of their own fat ; but it is also well known that many of different orders (as the beaver, the hedgehog, the squirrel, the dormouse, the bee, which are seldom or never quite torpid,) are guided by instinct to lay up stores of provisions, on which they subsist during the winter. Some of these, as the lemming, have been observed to spread out their stores to dry in fine weather. Some of the most curious of the provisions of this kind are the following : — " There is an animal, the rat-hare, which is gifted by its Creator with a very singular in- stinct, on account of which it ought rather to be called the liuy-maker, since man may or might have learned that part of the business of the agriculturist, which consists in providing a store of winter provender for his cattle, from this industrious animal. Professor Pallas was the first who described the quadruped exercising this remarkable function, and gave an account of it. The Tungusians, who inhabit the country beyond the lake of Baikal, call it Pika, which has been adopted as its trivial name. " About the middle of the month of August these little animals collect their winter's pro- vender, formed of select herbs, which they bring near their habitations and spread out to dry like hay. In September they form heaps or stacks of the fodder they have collected under places sheltered from rain or snow. Where many of them have laboured together, their stacks are sometimes as high as a man, and more than eight feet in diameter. A subterranean gallery leads from the burrow below the mass of hay, so that neither frost nor snow can intercept their communication with it. Pallas had the pa- tience to examine their provision of hay piece by piece, and found it to consist chiefly of the choicest grasses and the sweetest herbs, all cut when most vigorous, and dried so slowly as to form a green and succulent fodder ; he found in it scarcely any ears or blossoms, or hard and woody stems, but some mixture of bitter herbs, probably useful to render the rest more whole- some. "-\ " Although," says Kirby, " ants during the cold winters in this country remain in a state of torpidity, and have no need of food, yet in warmer regions during the rainy seasons, when they are probably confined to their nests, a store of provisions may be necessary for them. Now although the rainy season, at least in America, is a season in which insects are full of life, yet the observation that ants may store up provi- sions in warm countries is confirmed by an account sent me by Colonel Sykes, with respect * Introduction to Entomology, vol. ii. p. 438. t lb. p. 507. to another species which appears to belong to the same genus as the celebrated ants of visi- tation, by which the houses of the inhabitants of Surinam were said to be cleared periodically of their cock-roaches, mice, and even rats. The present species has been named by Mr. Hope the provident ant. These ants, after long-con- tinued rains during the monsoon, were found to bring up and lay upon the earth on a fine day, their stores of grass seeds and grains of Guinea corn, for the purpose of drying them. Many scores of these hoards were frequently observable on the extensive parade at Poona."* The great and important instinct of migration is another means by which the lives of many animals are preserved during winter. The number of species of birds, which pass the summer to bring forth their young in this country, but disappear from it in autumn, and are known to spend the winter in the south of Europe or Africa, has been stated at not less than five-sixths of the whole number resident here during the summer, and these are replaced by many other species, chiefly aquatic birds and waders, but likewise the fieldfares, redwings, starlings, &c. which have brought forth their young in the colder climates, and return here for the winter. There are others, as the crane and stork, which perform similar migrations, but are rarely seen in this country. The migra- tions of the larger birds from the northern regions are chiefly performed in large bodies, forming angular lines, very high in the air; those of the smaller birds of passage, swallows, singing birds, &c. that go southwards from hence, seem to take place less regularly, and have been less accurately observed. There are also many annual migrations from one part of this country to another, in spring and autumn, as of the plovers and lapwings, curlews, ring ouzels, &c. It is still doubtful with what sensations the propensity to perform these peri- odical migrations is chiefly connected, whether with changes of temperature, or deficiency of food, or with the changes of the sexual desire, (as maintained by Jenner.f) But it is certain that the migrations take place while the tem- perature is still such as is well borne by the animals ; indeed of most of the species of birds of passage some individuals are frequently observed not to migrate; \ and it is equally certain that most of the birds of passage do not gradually withdraw, as if following the gradual changes of the food on which they live, but go off suddenly, and perform their voyages, par- ticularly in autumn, so rapidly, as to be much exhausted and emaciated at the end of them ; so that it is certainly not under the influence of sensations gradually changing and tending to partial and successive changes of place, but under that of a strong determination, overcom- ing the motives to action which are usually predominant, and commanding strenuous and painful exertion at a time when no great incon- venience is felt, that these voyages are per- * Vol. ii. p. 344. \ Phil. Trans. 1824. X See Darwin, Zuonomia, sect. xvi. 12. INSTINCT. 13 formed. And if, with Darwin and some others, we doubt of the existence of a blind instinctive propensity as the cause of these movements, we have no resource but to ascribe them to a very high degree of intelligence, combined with much mental resolution, and extending to all or almost all the individuals of the species, enabling them to foresee evils that are still remote, and determining them to undergo labour, fatigue, and danger in order to avoid them. It has also been repeatedly ascertained that the same indi- viduals return after their six months of absence and long voyages, to the very spots where they had been brought forth, implying a power of discernment and recollection which appear to us quite inconceivable. Of such high qua- lities of mind we see no indications in the other actions of these birds, excepting only in their preparations for the nurture of their young ; and if they really possessed these qualities, we might expect with perfect confidence to see them devise many contrivances for their comfort and convenience, and to witness variations and im- provements in habits, which we know from the writings of the ancient naturalists to have been perfectly uniform and stationary at least since the time of Aristotle. There are some of the Mammalia, chiefly of the order Ruminantia, which likewise perform periodical migrations in the natural state, as has been particularly noticed in America, of the bison, the musk-ox, and rein-deer. A similar instinct has been observed in the quaggas in Africa ; and a singular observation, as shewing a variation of instinct according to varying cir- cumstances, was made by Dr. Richardson, that the American black bear, when lean, and from that cause unfitted for hybernation, migrates in severe winters from the northward into the United States. The periodical migrations of fishes appear to be designed for the benefit of their offspring, not for their own preservation ; and there are other migrations, in immense numbers, of various kinds of animals which are not periodical, and of which the object is still obscure, but which do not fall under the present head. II. Of instincts for the propagation and support of offspring. — Of the very curiously varied instincts of animals connected with the propagation and support of their off- spring, we need not dwell on those which must necessarily attend the very various kinds of organs (so well arranged and de- scribed by Cuvier), by which the impreg- nation of the ova in the different tribes of animals is effected — the instincts, e.g. which prompt most male fishes to impregnate eggs already laid, and many reptiles to impregnate them at the moment of their emission from the body of the female, or which guide the different warm-blooded animals in the different modes of their sexual intercourse. The in- stincts which enable animals to anticipate and provide for the wants of their young are still more varied, and imply mental processes of greater complexity. The most important of these may be referred to the following heads. 1- This is probably one object of the migra- tions of birds above-mentioned, and certainly the main object of the migrations of great swarms of fishes, both in the sea, and of those which ascend the rivers ; to which the same observations, as to the return to the same spot whence they had formerly departed, and as to the labours and hazard which the instinct im- pels them to incur, are in many instances appli- cable. " The cod-fish makes for the coast at spawn- ing time, going northward ; this takes place towards the end of winter, or the beginning of spring. " The mackarel hybernates in the Arctic, Antarctic, and Mediterranean Seas, where it is stated to select certain depths of the sea called by the natives Barachouas, which are so land- locked, that the water is as calm at all times as in the most sheltered pools. " It is in these that the mackarel, directed by instinct, pass the winter. In the spring they emerge in infinite shoals from their hiding places, and proceed southward for the purposes of depositing their eggs in more genial seas. " What the mackarel is to the north of Europe, the thunny is to the south. It de- posits its eiigs in May and June, when it enters the Mediterranean, seeking the shores in shoals arranged in the form of a parallelogram, or as some say, a triangle, and making a great noise and stir. " The herring may be said to inhabit the arctic seas of Europe, Asia, and America, from whence they annually migrate at different times in search of food, and to deposit their spawn. Their shoals consist of millions of myriads, and are many leagues in width, many fathoms in thickness, and so dense that the fishes touch each other." " The largest and strongest are said to lead the shoals, which seem to move in a certain order, and to divide into bands as they proceed, visiting the shores of various islands and countries, and enriching their in- habitants." " They seek places for spawning where stones and marine plants abound, against which they rub themselves alternately on each side, all the while moving their fins with great rapidity." " In temperate climates the salmon quits the sea early in the spring, when the waves are driven by a strong wind against the river currents." " They leave the sea in numerous bands formed with great regularity. The largest individual, which is usually a female, takes the lead, and is followed by others of the same sex, two and two, each pair being at the distance of from three to six feet from the preceding one ; next come the old, and after them the young males in the same order." " They employ only three months in ascending to the sources of the Maraguon, the current of which is remarkably rapid, which is at the rate of nearly forty miles a day ; in a smooth stream or lake their progress would increase in a four-fold ratio. Their tail is a very powerful organ, and its muscles have wonderful energy ; by placing it in their mouth, they make of it a very elastic spring, for, letting it go with violence, they raise themselves in the air to the 14 INSTINCT. height of from twelve to fifteen feet, and so clear the cataract that impedes their course ; if they fail in their first attempt, they continue their efforts till they have accomplished it. The female is stated to hollow out a long and deep excavation m the gravelly bed of the liver to receive her spawn."* A similar periodical emigration has been ob- served in other animals, particularly in some of the Crustacea. " Several of the crabs forsake the waters for a time, and return to them to cast their spawn ; but the most celebrated of all is that known by the name of land-crab, and alluded to by Dr. Paley as the violet-crab, and which is called by the French the tourlourou. They are natives of the West Indies and South Ame- rica. In the rainy season, in May and June, their instinct impels them to seek the sea, that they may fulfil the great law of their Creator, and cast their spawn. They descend the moun- tains, which are their usual abode, in such numbers that the roads and woods are covered with tliem." " They are said to halt twice every day, and to travel chiefly in the Dight. Arrived at the sea-shore, they are there reported to bathe three or four times, when retiring to the neighbouring plains or woods, they repose for some time, and then the females return to the water, and commit their eggs to the waves. This business dispatched, they endeavour to regain, in the same order, the country they had left, and by the same route, but only the most vigorous can reach the mountains." f The object of all these migrations is, that the female animals may have an opportunity of de- positing their eggs where they will be in circum- stances suited to their development, particularly as to the essential requisites, exposure to heat and to air. 2. The same object, the choice of a suitable place for depositing their eggs, is accomplished in other instances by very different instincts im- planted in female animals. " Reptiles," says Kirby, " and Fishes do not feel the instinctive love for their young, after birth, which is ex- hibited by quadrupeds and birds, but are in- variably instructed by the Creator to select a place in which their eggs can be hatched either by artificial or solar heat." Many of them likewise, as the salmon, dig holes before depositing them, for their protection. Those of the serpents which are not ovo-viviparous, bury their eggs in sand, or in heaps of fer- menting matter. The Saurians also select a proper place for their eggs, the crocodile, e.g. the sands beside rivers ; " one species of sala- mander commits a single egg to a leaf of Persicaria, protects it by carefully doubling the leaf, and then proceeding to another, repeats the manoeuvre till her oviposition is finished. Toads and frogs lay their eggs in water, sur- rounded by a gelatinous envelope which forms the first nourishment of the embryo," corres- ponding to the albumen of the bird's egg. In like manner every insect is directed by nature to place its eggs in situations where its * Kirby, vol. i. t Ibid. young, when disclosed, will find its appro- priate nourishment ; some burrowing in the earth for this purpose ; many flies in dead animal matter about to putrefy ; many in dif- ferent parts of living vegetables;* bees and ants in the cells where they are to be fed by the working members of their hives, &c. A spe- cies of the ichneumon fly and some of the wasps have been observed to bury caterpillars along with their eggs, on which their larvae are to feed, and another fly to deposit its eggs on the back of a caterpillar, when the larvae feed on the secretion by which the covering of the pupa is to be formed. f 3. The instincts called into action in the nidification, particularly of birds, are so nume- rous, varied, and admirably adapted to their purpose, as to have called forth admiration in all ages. The pairing of the parent birds at the beginning of spring, when the labour is to begin ; the choice of a place suited to the habits of the species, on the ground, under ground, in rocks, on the edge of lakes or of the sea, in marshes, in bushes, on trees, on buildings of all descriptions ; the choice of the materials, and the labour exerted for com- pleting the work ; some using clay, some sand, some moss, some leaves, some straw or twigs, some moss or lichen ; many forming a rough outside of materials hardly to be distinguished from the surrounding objects, while the inside is warm and smooth ; some building in very pe- culiar forms to impede the access to their young; the tailor-bird sewing leaves together with distinct stitches, and the Java swallows forming their gelatinous nests, as the bees manufacture their waxen cells, from the contents and secre- tions of their own stomachs ; — all furnish proofs of contrivance too obvious and too nearly ad- justed to varying circumstances, to have es- caped the attention even of careless observers. Many of the Mammalia make some kind of provision, although less artificial, for the re- ception of their progeny. " Cats search about inquisitively for a concealed situation ; bur- rowing animals retire to the bottom of their burrows, and several of the Rodentia make beds of their own hair to receive their young ; " all beasts of prey, whose progeny come into the world blind and helpless, have some kind of retreat in which they supply them at once with warmth and nourishment. Many insects, also, besides those which associate in hives, use various precautions for the covering and pro- tection of their eggs. 4. The instinct of incubation, which forms the next part of the provisions for the repro- duction of birds, the extraordinary change then effected in the habits of the female bird, par- ticularly when attended and cheered, as hap- pens in so many cases, by the equally temporary instinct of song of the male bird, — is another natural phenomenon too striking and interesting to have escaped observation; and the object of * In this choice insects seem to be guided by the sense of smell, at least in the case where the food of the larvae to be brought forth is different from that of the parent. f Darwin. , INSTINCT. 15 this provision of nature has been fully elucidated by the observations of Reaumur and many others as to the efficacy of artificial heat in procuring the development of the chick. 5. The instincts of many parent animals are likewise the means adopted by nature for pro- curing nourishment for the young. This is observed as to those of the lower orders whose young are brought forth in circumstances ren- dering it impossible for them to procure their own food (as the bee and wasp), and also as to the carnivorous tribes, both of birds and quad- rupeds ; the exertion requisite for procuring their prey being beyond the power of the young animal, the instinct of the parent supplies the defect. In most cases fresh supplies of food are daily or even hourly brought to the young animals, but in some instances stores of nou- rishment are provided for the young of the higher animals, equally as for those of the bee or ant; the pelican brings a large supply in his pouch from a single fishing; and according to the observations of an author in the Magazine of Natural History, some of the carnivorous animals have the curious instinct of storing up with this view animals not dead, but stupified by injury of the brain. " I dug out," says he, " five young pole-cats, comfortably imbedded in dry withered grass ; and in a side hole, of proper dimensions for such a larder, I poked out forty large frogs and two toads, all alive, but merely capable of sprawling a little. On examination 1 found that the whole number, toads and all, had been purposely and dex- trously bitten through the brain."* Lastly, the young of all warm-blooded animals being unable for some time after they come into the world to maintain their own temperature, would soon perish of cold, even if capable of procuring their own food, but for the protection they receive from their parents. This seems to be the most general final cause of the o-Togyri or maternal affection so strongly implanted in all these animals, and to which so much of the first period of the existence of their offspring is intrusted, but of which there is little trace in the lower tribes. As, however, the dangers to which these young animals are exposed are numerous and varied, so nature has provided against them, not by a propensity to the performance of one kind of action only, bat by a vigilant and permanent feeling which controls all the habits of the parent animal, and prompts many actions, some of which are strictly instinctive, while others ought rather to be called voluntary, but are quite at variance with the ordinary habits of the animals. Eveiy one must be aware of the increased ferocity given to the female carnivo- rous animals during the time that they are occupied with the care of their young, and of the resolution with which birds, at other seasons pacific and even timid, will resent any intrusion on their nests or young broods ; of the provi- dent care of the cat or the lioness, which carries her young in her mouth, and of almost all fe- male warm-blooded animals, which gather them * Magazine, &c. vol. vi. p. 20ti. close to their bodies for protection from cold ; of the anxiety of the hen which has sat on duck's eggs, when the ducklings take to the water; of the resolution and ingenuity with which the lapwing fixes on herself the attention of passengers who may come near her nest, &c. But what most distinctly indicates that all this care and anxiety are unconnected with any such anticipation of the results as would be acquired by a process of reasoning, is the absolute indif- ference which succeeds, when the parent animal at length sees her offspring independent of her assistance — " And once rejoicing, never knows them more." III. Various instinctive propensities may be observed in animals, the object of which is the advantage of the race or of the animal creation generally, rather than of the individual or his progeny, and some the object of which is still obscure. Some of these are, like the maternal affection last mentioned, obviously partaken by the human race, or even chiefly perceptible in those animals which have much con- nexion with man. The instinctive attachments not only of dogs but various domestic animals to their masters or attendants, of cats to houses, of sheep to particular hills or pastures, might be illustrated by many curious anecdotes, and seem to be very similar to the feelings which, after being fully developed in the human race, and strengthened and extended by the reflective powers of the human mind, obtain the names of family affection, of local attachment, of patriotism, ike. If the instinct of modesty exists in hardly any animals, the desire of clean- liness may be observed in many. The instinct of imitation, formerly noticed, and which is of so essential importance to all human enterprises in which the cooperation of numbers is re- quired, is perhaps more distinctly observable in individual monkeys than in any other ani- mals, although it is probable that a similar feeling may be part of the bond of association by which many animals are congregated toge- ther in the mode to be presently noticed. The intuitive perception of the signs of emotion or passion in the countenance and gestures which precedes and excites the tendency to imitation in man, is obviously common to us with many other animals. In fact, although we rigidly maintain the essential superiority of the intellect of man over that of all other animals, we have already stated that the greater number of the active powers of the human mind which furnish the chief motives to action are on the same fooling with those which operate on the lower animals. Not only are our appetites similar to theirs, but the greater number of the desires of which we are conscious are either shared with us by them, or at least would seem to belong to the same class as their instincts. Thus the desire of approbation is quite obvious at least in some of the domestic animals, and the desire of society, as observed by Stewart, seems to act very generally, although variously, in the ani- mal creation. The desire of power may be thought to be more peculiar to man, and we 1(3 INSTINCT. have every reason to believe that no other ani- mal can reflect on the possession of power in the abstract, or indulge in the imagination of scenes in which it is to be exerted, or rejoice in the acquisition of wealth of any kind, as the means of exercising power and procuring pleasure, independently of the actual enjoy- ment of them; but many of the practical exemplifications of this desire come into direct comparison with, and probably involve feelings very similar to, the instincts of animals. Thus the pleasure which men feel in exerting power over the elements around them may be seen, in the case of children, to be prior to the expe- rience of any practical advantage from the arts of architecture, of mechanics, or of navigation ; and it may be confidently asserted, that but for this pleasure attending the exercise of those arts (and which may be supposed to be very similar to that which animates the beaver, the bird, or the ant in their respective labours,) they could never have been prosecuted with success. So also the pleasure which man in all ages has felt both in hunting and destroying animals, and also in acquiring dominion over them and sub- jecting them to his power, is clearly quite different from the anticipation of the useful purposes to which, whether dead or living, they may be applied, and appears precisely similar, both in its nature and in its object or final cause, to some of the instincts of animals. Indeed, in conformity to what has been already said of the essential peculiarities of the human intellect, it is only those motives to action which imply the previous formation of general notions or abstract ideas, that we can regard as peculiar to man ; and we may accord- ingly state that the desire of knowledge (we may even say more specifically,- of scientific knowledge, ' rerum cognoscere causas') and the sense of obligation religious and moral, are the motives to action which we believe to be truly peculiar to the human race. The most important instinct of animals refer- able to this head, clearly and strongly felt like- wise by man, (although combined in his case with many other feelings,) is the instinct of congregation. More or less of the desire of society is seen in a great majority of animals ; but we may refer to this head many actions of animals, wherein many individuals of the same species cooperate, of which the object is in many instances still obscure, but to which the animals are impelled with an energy, and fre quently a self-devotion, attesting the strength of the mental feeling, and completely super- seding their usual habits. Messrs. Spence and Kirby enumerate not less than five kinds of association of insects to form what they term imperfect societies. " The first of these associations (for the sake of company only) consists chiefly of insects in their perfect state. The little beetles called whirlwigs, — which may be seen clustering in groups under warm banks in every river and every pool, wheeling round and round with great velocity, at your approach dispersing and diving under water, but as soon as you retire resuming their accustomed movements, — seem to be under the influence of the social principle, and to form their assemblies for no other purpose than to enjoy together in the sun- beam the mazy dance. Impelled by the same feeling, in the very depth of winter, even when the earth is covered with snow, the tribes of Tipulida (usually but improperly called gnats) assemble in sheltered situations at mid-day where the sun shines, and form themselves into choirs that alternately rise and fall with rapid evolutions. " Another association is that of males during the season of pairing. Of this nature seems to be that of the cockchafer and fernchafer, which, at certain periods of the year and hours of the day, hover over the summits of the trees and hedges like swarms of bees. '• The males of another root-devouring beetle ( Hoplia argentea, F.) assemble by myriads before noon in the meadows, when in these infinite hosts you will not find a single female. " The next description of insect associations is of those that congregate for the purpose of travelling or emigrating together. De Geer has given an account of the larvae of certain gnats (Tipula, L.) which assemble in considerable numbers for this purpose, so as to form a band of a finger's breadth, and of one or two yards in length. And what is remarkable, while upon their march, which is very slow, they adhere to each other by a kind of glutinous secretion. " Kuhn mentions another of the Tipulide, the larvae of which live in society and emigrate in files. " But of insect emigrants none are more celebrated than the locusts, which, when arrived at their perfect state, assemble in such numbers as in their flight to intercept the sun-beams and to darken whole countries, passing from one region to another, and laying waste kingdom after kingdom. " The same tendency to shift their quarters has been observed in our little indigenous devourers, the Aphides. " It is the general opinion in Norfolk, Mr. Marshall informs us, that the saw-fly ( Tenthre.do ) comes from over sea. A farmer declared he saw them arrive in clouds so as to darken the air; the fishermen asserted that they had repeatedly seen flights of them pass over their heads when they were at a distance from land, and on the beach and cliffs they were in such quantities that they might have been taken up by shovels full. Three miles in- land they were described as resembling swarms of bees. " It is remarkable that of the emigrating insects here enumerated, the majority, for in- stance the Libellu'.ae, the Coccinellae, Carabi, Cicadae, &c. are not usually social insects, but seem to congregate, like swallows, merely for the purpose of emigration. " The next order of imperfect associations is that of those insects which feed together. " Two populous tribes, the great devastators of the vegetable world, the one in warm and the other in cold climates, to which I have already alluded under the head of emigrations INSTINCT. 17 — I mean Aphides and Locusts, — are the best examples of this order. " So much as the world has suffered from these animals, it is extraordinary that so few observations have been made upon their history, economy, and mode of proceeding. " The eggs of the locusts were no sooner hatched in June," says Dr. Shaw, " than each of the broods collected itself into a compact body, of a furlong or more in square, and then marching directly forwards towards the sea, they let nothing escape them ; they kept their ranks like men of war, climbing over as they advanced every tree or wall that was in their way ; nay, they entered into our very houses and bed- chambers like so many thieves. A day or two after one of these hoides was in motion, others were already hatched to march and glean after them. Having lived near a month in this manner they arrived at their full growth, and threw off their nympha state by casting their outward skin." " The transformation was per- formed in seven or eight minutes, after which they lay for a short time in a torpid and seem- ingly languishing condition ; but as soon as the sun and the air had hardened their wings by dry- ing up the moisture that remained on them after casting their sloughs, they re-assumed their former voracity with an addition of strength and agility." " According to Jackson they have a govern- ment amongst themselves similar to that of the bees and ants; and when the king of the locusts rises, the whole body follow him, not one soli- tary straggler being left behind. But that locusts have leaders like the bees or ants, dis- tinguished from the rest by the size and splen- dour of their wings, is a circumstance that has not yet been established by any satisfactory evidence; indeed, very strong reasons maybe urged against it." " The last order of imperfect associations approaches nearer to perfect societies, and is that of those insects which the social principle urges to unite in some common work for the benefit of the community. " Many larva of Lepidoptera associate with this view, some of which are social only during part of their existence, and others during the whole of it. " A still more singular and pleasing spectacle when their regiments march out to forage, is exhibited by the P recessionary Bombyx. This moth, which is a native of Fiance and has not yet been found in this country, inhabits the oak. Each family consists of from 600 to 800 individuals. When young, they have no fixed habitation, but encamp sometimes in one place and sometimes in another under the shelter of their web ; but when they have attained two- thirds of their growth, they weave for themselves a common tent. About sun-set the regiment leaves its quarters ; or, to make the metaphor harmonize with the trivial name of the animal, the monks their ccenobium. At their head is a chief, by whose movements their procession is regulated. When he stops all stop, and pro- ceed when he proceeds ; three or four of his immediate followers succeed in the same line, vol. nr. the head of the second touching the tail of the first ; then comes an equal series of pairs, next of threes, and so on as far as fifteen or twenty. The whole procession moves regularly on with an even pace, each file treading on the steps of those that precede it. If the leader, arriving at a particular point, pursues a different direc- tion, all march to that point before they turn."* Examples of occasional associations, more or less resembling all these, and of which the object is in many instances still obscure, may be found in all the classes of the higher ani- mals, as is obvious, when we consider to how many tribes of animals the term gregarious is usually applied, e. g. to almost all the Rumi- nantia, some of the Pachydermata, and a few of the Rodentia. Some of the genus Muridas (rats and mice) have been long known to migrate, occasionally, in a manner resembling the locusts. " The general residence of the lem- ming," says Pallas, " is in the mountainous parts of Lapland and Norway, from which tracts at uncertain periods it descends in im- mense troops, and by its incredible numbers becomes a temporary scourge to the country, devouring the grain and herbage, and com- mitting devastations equal to those of an army of locusts." " It is observable that their chief emigrations are made in the autumns of such years as are followed by severe winters." " The ground over which they have passed appears at a distance as if it had been ploughed, the grass being devoured to the roots in numerous stripes or parallel paths, of one or two spans broad, and at the distance of some yards from each other." " The army moves chiefly at night, or early in the morning. No obstacles that they meet in their way have any effect in altering their route, neither fires, nor deep ravines, nor torrents, nor marshes, nor lakes ; they proceed obstinately in a straight line, and hence many thousands perish in the waters." " If disturbed, in swimming over a lake, by oars or poles, they will not recede, but keep swim- ming directly on, and soon get into regular order again." " In their passage over land, if attacked by men, they will raise themselves up, uttering a kind of barking sound, and fly at the legs of their invaders, and will fasten so fiercely on the end of a stick, as to suffer them- selves to be swung about without quitting their hold, and are with great difficulty put to flight." " The major part of these hosts is destroyed by various enemies, as owls, hawks, weasels, ex- clusively of the number that perish in the waters, so that but a small part survive to return, as they are sometimes observed to do, to their native mountains." The campagnol, or short-tailed rat, has been known to com- mit similar ravages in France. It is obvious here, that under the influence of this instinct, and of the excitement of numbers (in which, as in our own race, the principle of imitation is probably much concerned) the usual motives to action of these animals are superseded, and their usual habits changed. We are still uncertain as to the use, or final * Introduction to Entomology, letter xvi. c 18 INSTINCT. cause, of the various congregations of birds that we daily witness, and of the varying habits which they then exhibit — crows, e. g. herons, and many water birds, roosting and bringing forth their young in large irregular societies ; the crows, besides, assembling at particular hours of the day, at all seasons ; some of the genus Parus, particularly the great and long-tailed titmouse, feeding in small flocks at all seasons ; — plovers and lapwings keeping separate during the season of hatching and rearing their offspring, but assembling in flocks after their young have attained matu- rity;— most of the birds of this country in the depth of winter associating in flocks much greater than can be necessary for the sake of warmth ; — the hen chaffinches, and perhaps the females of other birds, congregating separately; — many of these flocks consisting of multi- tudes moving quite irregularly, but all of them having apparently some means of intercom- munication or agreement; — some of them, as the starlings, performing very singular evo- lutions in concert; and many, as wild geese and other water-birds, always showing the dis- position to fly in regular lines. The greatest of all the congregations of birds are those of the migrating pigeons in America, described by Audubon, as forming clouds which pass over the whole extent of a town for several hours together, and as settling on ex- tensive districts of the woods in such multi- tudes as to cause much devastation among the branches. But the most extraordinary of all the asso- ciations of animals are those which have re- ceived the title of the perfect societies of in- sects,— the bees, wasps, hornets and ants in the order of Hymenoptera, and the white ants or termites, in that of Neuroptera. The most important facts as to them seem to have been ascertained, partly by numerous former ob- servers, but chiefly by the Hubers, Latreille, and others in the present age. The essential peculiarity of these associations of insects appears to be the complete sepa- ration of the males and females, on whom the propagation of the species depends, from the working members of the communities, by whom the habitations are constructed, and who pro- cure food both for the young and for the more perfect insects. In the case of the bees, the only prolific female is the queen-bee; the males are the drones; the working bees, constituting the mass of the community, are sterile females, and the larva? and pupa are confined to the cells and helpless ; the ants appear to differ from these only in the perfect females being much more numerous (only a few, however, being retained in each ant-hill); but the termites differ, in the larvae and even the pupae being working members, the males and females, when brought to perfection, always wandering abroad, and one of each sex in the perfect state only existing in each nest, being in fact forcibly detained there. Among these animals there is also a separate class, believed to be analogous to the working bees, i. e. to be sterile females, larger than the labourers, and which are thought to act exclu- sively as the soldiers of the community, — the smaller working ants (larvae) always disap- pearing, and these larger and fiercer animals shewing themselves, when any of the works are attacked.* These associations differ from all others existing among animals, in the extraordinary instinct of respect and devotion shewn by the working members to the impregnated female, — single in each swarm of bees, and in each nest of termites, and few in number in each nest of ants, — and with this instinct most of their other peculiarities seem to be connected. But it is justly observed by Mr. Spence, that if we suppose all the labours of the bees and the ants to be guided by instincts, we must ne- cessarily attribute to these animals a much greater number and variety of instinctive pro- pensities, and more extraordinary modifications of them to suit varying circumstances of their condition, than to any of what are usually called the higher animals. " In the common duck, one instinct leads it at its birth from the egg to rush to the water ; another to seek its proper food ; a third to pair witli its mate; a fourth to form a nest; a fifth to sit upon its eggs till hatched ; a sixth to assist the young ducklings in extricating them- selves from the shell ; and a seventh to defend them when in danger until able to provide for themselves : and it would not be easy as far as my knowledge extends, to add many more instinctive actions to the enumeration, or to adduce many specimens of the superior classes of animals endowed with a greater number. " But how vastly more manifold are the instincts of the majority of insects ! " As the most striking example of the whole, I shall select the hive-bee, — begging you to bear in mind that I do not mean to include those exhibited by the queen, the drones, or even those of the workers, termed by Huber cirieres (wax-makers) ; but only to enumerate those presented by that portion of the workers, termed by Huber nourrices or petites abeilles, upon whom, with the exception of making wax, laying the foundation of the cells, and col- lecting honey for being stored, the principal labours of the hive devolve. " By one instinct bees are directed to send out scouts previously to their swarming in search of a suitable abode; and by another to rush out of the hive after the queen that leads forth the swarm, and follow wherever she bends her course. Having taken possession of their new abode, whether of their own selection or prepared for them by the hand of man, a third instinct teaches them to cleanse it from all im- purities ; a fourth to collect propolis, and with it to stop up every crevice except the entrance : a fifth to ventilate the hive for preserving the purity of the air ; and a sixth to keep a con- stant guard at the door. " In constructing the houses and streets of their new city, or the cells and combs, there are probably several distinct instincts exercised ; * See Spence and Kirby, vol. ii. p. 39. INSTINCT. 19 but not to leave room for objection, 1 shall regard them as the result of one only : yet the operations of polishing the interior of the cells, and soldering their angles and orifices with propolis, which are sometimes not under- taken for weeks after the cells are built; and the obscure but still more curious one of var- nishing them with the yellow tinge observable in old combs, seem clearly referable to at least two distinct instincts. " In their out-of-door operations several dis- tinct instincts are concerned. By one they are led to extract honey from the nectaries of flowers ; by another to collect pollen after a process involving very complicated manipu- lations, and requiring a singular apparatus of brushes and baskets ; and that must surely be considered a third which so remarkably and beneficially restricts each gathering to the same plant. It is clearly a distinct instinct which inspires bees with such dread of rain, that even if a cloud pass before the sun, they return to the hive in the greatest haste. " Several distinct instincts, again, are called into action in the important business of feeding the young brood. One teaches them to swal- low pollen, not to satisfy the calls of hunger, but that it may undergo in their stomach an elaboration fitting it for the food of the grubs ; and another to regurgitate it when duly con- cocted, and to administer it to their charge, proportioning the supply to the age and con- dition of the recipients. A third informs them when the young grubs have attained their full growth, and directs them to cover their cells with a waxen lid, convex in the male cells, but nearly flat in those of workers, and by a fourth, as soon as the young bees have burst into day, they are impelled to clean out the deserted tenements and make them ready for new oc- cupants. " Numerous as are the instincts already mentioned, the list must yet include those connected with that mysterious principle which binds the working bees of a hive to their queen : — the singular imprisonment in which they retain the young queens that are to lead off a swarm, until their wings be sufficiently expanded to enable them to fly the moment they are at liberty, gradually paring away the waxen wall that confines them to an extreme thinness, and only suffering it to be broken down at the precise moment required ; — the attention with which in these circumstances they feed the imprisoned queen by frequently putting honey on her proboscis, protruded from a small orifice in the lid of her cell ; — the watchfulness with which, when at the period of swarming more queens than one are re- quired, they place a guard over the cells of those undisclosed, to preserve them from the jealous fury of their excluded rivals ;— the exquisite calculation with which they inva- riably release the oldest queens the first from their confinement ; — the singular love of mo- narchical dominion, by which, when two queens in other circumstances are produced, they are led to impel them to combat until one is de- stroyed ;— the ardent devotion which binds them to the fate and fortune of the survivor; — the distraction which they manifest at her loss, and their resolute determination not to accept of any stranger until an interval has elapsed sufficiently long to allow of no chance of the return of their rightful sovereign ; — and (to omit a further enumeration) the obedience which in the utmost noise and confusion they shew to her well-known hum. " I have now instanced at least thirty dis- tinct instincts with which every individual of the nurses amongst the working-bees is en- dowed; and if to the account be added their care to carry from the hive the dead bodies of any of the community ; their pertinacity in their battles, in directing their sting at those parts only of the bodies of their adversaries which are penetrable by it; their annual autum- nal murder of the drones, &c. &c. — it is cer- tain that this number might be very consider- ably increased, perhaps doubled."* To these instincts, in the case of some species of ants we shall certainly have to add those by which they are guided in carrying on a regular system of warfare, either with other hives of the same species or with other species, in subjuga- ting and bringing up as workers or slaves those that they have subdued, and likewise in sub- jecting to their dominion tribes of Aphides.f But all this becomes still more surprising, because more at variance with the usual in- stincts of animals, when we consider the power of adapting their operations to changes in their circumstances, which such associations of in- sects possess. " It is," says Mr. Spence, " in the deviations of the instincts of insects and their accommoda- tion to circumstances, that the exquisiteness of these faculties is most decidedly manifested. The instincts of the larger animals seem capable of but slight modification. They are either ex- ercised in their full extent or not at all. A bird, when its nest is pulled out of a bush, though it should be laid uninjured close by, never attempts to replace it in its situation ; it contents itself with building another. But in- sects in similar contingencies often exhibit the most ingenious resources, their instincts surpri- singly accommodating themselves to the new circumstances in which they are placed, in a manner more wonderful and incomprehensible than the existence of the faculties themselves." This observation we support by various in- stances taken from the history of different in- sects ; but the most extraordinary are from the societies of insects of which we now speak ; and of these the following are only a specimen. " The combs of bees are always at an uniform distance from each other, namely, about one- third of an inch, which is just wide enough to allow them to pass easily, and have access to the young brood. On the approach of winter, when their honey-cells are not sufficient in number to contain all the stock, they elongate them considerably, and thus increase their capa- * Introduction to Entomology, vol. ii. p. 498 et seq. t Introd. to Entomology, letter xvii. c 2 20 INSTINCT. city. By this extension the intervals between the combs are unavoidably contracted ; but in winter well-stored magazines are essential, while from their state or comparative inactivity spa- cious communications are less necessary. On the return of spring, however, when the cells are wanted for the reception of eggs, the bees contract the elongated cells to their former dimensions, and thus re-establish the just dis- tances between the combs which the care of their brood requires. But this is not all. Not only do they elongate the cells of the old combs when there is an extraordinary harvest of honey, but they actually give to the new cells which they construct on this emergency, a much greater diameter as well as a greater depth. " The queen-bee, in ordinary circumstances, places each egg in the centre of the pyramidal bottom of the cell, where it remains fixed by its natural gluten : but in an experiment of Huber, one whose fecundation had been re- tarded, had the first segments of her abdomen so swelled that she was unable to reach the bottom of the cells. She therefore attached her eggs (which were those of males) to their lower side, two lines from the mouth. As the larvae always pass that state in the place where they are deposited, those hatched from the eggs in question remained in the situation assigned them. But the working bees, as if aware that in these circumstances the cells would be too short to contain the larvae when fully grown, extended their length, even before the eggs were hatched. " The working bees, in closing up the cells containing larvae, invariably give a convex lid to the large cells of drones, and one nearly flat to the smaller cells of workers ; but in an ex- periment instituted by Huber to ascertain the influence of the size of the cells on that of the included larva;, he transferred the larvae of workers to the cells of drones. What was the result ? Did the bees still continue blindly to exercise their ordinary instinct? On the con- trary, they now placed a nearly flat lid upon these large cells, as if well aware of their being occupied by a different race of inhabitants." But the most extraordinary of all these varia- tions of the operations of bees are seen in two cases which have been often produced for the sake of experiment, and of which the result appears to have been repeatedly and carefully observed. " If a hive be in possession of a queen duly fertilized, and consequently sure, the next sea- son, of a succession of males, all the drones, towards the approach of winter, are massacred by the workers with the most unrelenting fero- city. This would seem to be an impulse as naturally connected with the organization and very existence of the workers, as that which leads them to build cells or store up honey. But however certain the doom of the drones if the hive be furnished with a duly fertilized queen, their undisturbed existence through the winter is equally certain if the hive has lost its sovereign, or if her impregnation has been so retarded as to make a succession of males in the spring doubtful ; in such a hive the workers do not destroy a single drone, though the hot- test persecution rages in all the hives around them." Again, " in a hive which no untoward event has deprived of its queen, the workers take no other active steps in the education of her suc- cessors,— those of which one is to occupy her place when she has flown off at the head of a new swarm in spring, — than to prepare a certain number of cells of extraordinary capacity for their reception while in the egg, and to feed them when become grubs with a peculiar food until they have attained maturity. This, there- fore, is their ordinary instinct ; and it may hap- pen that the workers of a hive may have no neces- sity, for a long series of successive generations, to exercise any other. But suppose them to lose their queen. Far from sinking into that inac- tive despair which was formerly attributed to them, after the commotion which the rapidly- circulated news of their calamity gave birth to has subsided, they betake themselves with an alacrity from which man, when under misfor- tune, might deign to take a lesson, to the repa- ration of their loss. Several ordinary cells are without delay pulled down and converted into a variable number of royal cells, capacious enough for the education of one or more queen- grubs selected out of the unhoused working grubs — which in this pressing emergency are mercilessly sacrificed — and fed with the appro- priate royal food to maturity. Thus sure of once more acquiring a head, the hive return to their ordinary labours, and in about sixteen days one or more queens are produced, one of which steps into day and assumes the reins of state." There can be no doubt that the perfect order and regularity seen in all the operations of these societies of insects could not be main- tained without some mode of communication among the different individuals concerned in these operations; and it appears distinctly that such means of communication exist, and that it is in consequence of their being exercised, for example, that a swarm of bees, when it leaves a hive, takes the direction to a spot pre- viously fixed on, and carefully examined, by a small number of scouts, as observed by Mr. Knight* When such facts are duly considered, we cannot be surprised to find so intelligent a na- turalist as Mr. Spence acknowledging that he had at one time arranged them as indications of reason in these animals. But on further consideration, we shall probably see cause to acquiesce in his later and more matured judg- ment, which ascribes them to strictly instinc- tive, although singularly varying propensities; chiefly on two grounds, which exactly corre- spond to what was stated in the beginning of this paper as the most distinctive characters of instinct: 1. that although various contrivances are fallen on by all bees to enable them to con- tinue their usual operations under varying ex- ternal circumstances, yet there is no such variety observed either in the conduct of individuals * Phil. Trans. 1807. INSTINCT. 21 of the species or in the conduct of different communities, as we cannot doubt must occur if the inhabitants of every hive were guided, on such unusual occasions, by processes of reason- ing, by observation of the laws of nature, by experience, and anticipation of the effects of their actions. If such mental processes were their guide, we should certainly observe a diffe- rence in the conduct of experienced workers, and of those just emerged from their pupae ; and we should observe some variety in the ex- pedients adopted in different hives for meeting such accidents or difficulties. 2. While the varying operations of these animals for one particular end, the preservation of their own lives and the perpetuation of their species, are planned and combined in such a manner as to indicate consummate intelligence as to what is essential for that purpose, all these indications of instinct are limited to that object, and we see no evidence of the exercise of their senses suggesting to them any other trains of thought, or exciting them to the prosecution of other objects, such as a number of human intellects capable of planning and executing such works would certainly, sooner or later, attempt to accomplish. The degree of uniformity seen in their operations, and the limitation of the ob- jects on which their faculties are exerted, are therefore our reason for thinking (although we do not wish to express ourselves with absolute confidence on the subject) that the mental pro- cesses concerned, even in those the most elabo- rate and artificial of the works of animals, be- long to the same class as those notions of man which are prompted by his instinctive propen- sities as distinguished from his reason. At the same time it ought to be stated, that there are many acts of individual animals, or of particular communities, in which we must admit that, although instinct is concerned, it must be guided by mental operations, in which short processes of reasoning, involving certain general ideas, must have been concerned. Several instances, quoted by Mr. Spence, seem hardly to admit of any other interpretation, e. g. the following from Iluber. The bees of some of his neighbours protected themselves against the attacks of the death's-head moth, (Sphinx atropos,) by so closing the entrance of the hive with walls, arcades, &c. built of a mixture of wax and propolis, that these ma- rauders could no longer intrude themselves. Pure instinct would have taught " the bees to fortify themselves on the first attack ; if the occupants of a hive had been taken unawares by these gigantic aggressors one night, on the second at least the entrance should have been barricadoed. But it appears clear, from the statement of Huber, that it was not until the hives had been repeatedly attacked, and robbed of nearly their whole slock of honey, that the bees betook themselves to the plan so success- fully adopted for the security of their remaining treasures; so that reason, taught by experience, seems to have called into action their dormant instinct.'' Again, " a German artist, a man of strict vera- city, states that in his journey through Italy he was an eye-witness to the following occurrence. He observed a species of Scarabseus busily en- gaged in making, for the reception of its egg, a pellet of dung, which when finished it rolled to the summit of a small hillock, and repeatedly suffered to tumble down its side, apparently for the sake of consolidating it by the earth which each time adhered to it. During this process the pellet unluckily fell into an adjoin- ing hole, out of which all the efforts of the beetle to extricate it were in vain. After several ineffectual trials, the insect repaired to an ad- joining heap of dung, and soon returned with three of his companions. All four now applied their united strength to the pellet, and at length succeeded in pushing it out; which being done, the three assistant beetles left the spot and returned to their own quarters."* A number of other instances have been col- lected by Mr. Duncan. " Professor Fischer has published an account of a hen, which hen made use of the artificial heat of a hotbed to hatch her eggs." " A fact is stated by Reaumur of some ants, which, finding they could derive heat from a bee-hive, contrived to avail themselves of it by placing their larva? between the hive and an exterior covering." " Dr. Darwin observed a wasp with a large fly nearly as big as itself ; finding it too heavy, it cut off the head and the abdomen, and then carried off the remainder, with the wings at- tached to it, into the air : but again finding the breeze act on the wings, and impede its pro- gress, it descended, and deliberately cut off the wings. Instinct might have taught it to cut off the wings of all insects previous to flying away with them ; but here it attempted to fly with the wings on, was impeded by a certain cause, discovered what that cause was, and alighted to remove it. Is not this a comparison of ideas, and deducing, consequences from pre- mises ?" " M. de la Loubiere, in his relation of Siam, says, that in a part of that kingdom which lies open to great inundations, all the ants make their settlements on trees ; no ants' nests are to be seen any where else. Whereas in our country the ground is their only habitation." " We sometimes kill a cockroach," says Ligon in his history of Barbadoes, quoted by Spence, " and throw him on the ground, and mark what the ants will do with him ; his body is bigger than a hundred of them, and yet they will find the means to lay hold of him and lift him up; and having him above ground, away they carry him ; and some go by as ready assistants if any be weary, and some are officers that lead and shew the way ; and if the van-couriers perceive that the body of the cockroach lies across, and will not pass through the hole or arch through which they mean to cany him, order is given, and the body turned endways, and this is done a foot before they come to the hole, and without stop or stay."f * Introd. to Entomology, vol. ii. p. 525. t History of Barbadoes, p. 63. 22 INSTINCT. Colonel Sykes communicated to Mr. Kirby a singular anecdote of some of the black ants in India, which had been prevented, for some time, from getting to some sweatmeats, by having the legs of the table on which they stood immersed in basins filled with water, and besides painted with turpentine. After a time, however, the ants again reached the sweatmeats ; and it was found that they did so by letting themselves drop from the wall, above the table, on the cloth which covered it.* " In Senegal, where the heat is great, the ostrich neglects her eggs during the day, but sits on them at night. At the Cape of Good Hope, however, where the degree of heat is less, the ostrich, like other birds, sits upon her eggs both day and night." " Rabbits dig holes in the ground for warmth and protection ; but after continuing long in a domestic state, that resource being unnecessary, they seldom burrow." "A dog in a monastery, perceiving that the monks received their meals by rapping at a buttery-door, contrived to do so likewise, and when the allowance was pushed through, and the door shut, ran off with it. This was re- peated till the theft was detected." " A dog belonging to Mr. Taylor, a clergy- man, who lived at Colton, near Wolseley Bridge, was accused of killing many sheep. Complaints were made to his master, who as- serted that the thing was impossible, because he was muzzled every night. The neighbours persisting in the charge, the dog one night was watched, and he was seen to draw his neck out of the muzzle, then to go into a field, and eat as much of a sheep as satisfied his appetite. He next went into the river to wash his mouth, and returned afterwards to his kennel, put his head into the muzzle again, and lay very qui- etly dow n to sleep." " 1 observed," says the Rev. J. Hall in his Travels in Scotland, " two magpies hopping round a gooseberry bush, in a small garden near a poor-looking house, in a peculiar manner, and flying in and out of the bush. I stepped aside to see what they were doing, and found from the poor man and his wife, that as there are no trees all around, these magpies several succeeding years had built their nest, and brought up their young, in this bush ; and that foxes, cats, hawks, &c. might not interrupt them, they had barricadoed not only their nest, but had encircled the bush with briers and thorns in a formidable manner ; nay, so com- pletely, that it would have cost even a fox, cunning as he is, some days' labour to get into that nest. " The materials in the inside of the nest were soft, warm, and comfortable ; but all on the outside, so rough, so strong, and firmly en- twined with the bush, that without a hedge- knife, hatch-bill, or something of the kind, even a man could not, without much pain and trouble, get at their young ; as from the outside to the inside of the nest extended as long as my arm. * Bridgewater Treatise, vol. ii. p. 342. " These magpies had been faithful to one another for several summers, and drove off their young, as well as every one else who at- tempted to take possession of their nest. This they carefully repaired and fortified in the spring with strong rough prickly sticks, that they sometimes brought to it by uniting their force, one at each end, pulling it along, when they were not able to lift it from the ground."* Such examples leave no reasonable ground for doubt, that on certain subjects at least some animals are capable of short and simple processes of reasoning or of imagination, which appear to imply the perception of general truths, and the formation of certain general ideas, and that the difference, formerly stated between the operations of their minds and ours, in that respect, is one of degree only, not absolutely of kind. But this admission, it must be remembered, does by no means di- minish the force of the considerations formerly adduced to establish the essential distinction between the instinctive determinations prompt- ing the usual actions of animals, and some of those of men, and those volitions, whether in animals or men, which are consequent on the exercise of reason, and on such anticipation of their consequences as a process of reasoning only can afford. It is worth while to mention that in some instances animals have been thought to be pos- sessed of a faculty resembling reason, on ac- count of actions, very wonderful indeed, but which the possession of reason would not have enabled them to perform. Thus there are many instances of animals finding their way to their usual place of residence, after being re- moved from it in such a way as to prevent the mere act of recollection guiding them back. Mr. Duncanf mentions having seen a pigeon, which had been brought from London, let loose on Magdalen Bridge, in Oxford. " It flew first towards the north, but after several gyrations in the air, it flew directly east, and reached London within the appointed time, which was, I believe, three hours." And Mr. Spence gives an anecdote, well authenticated, of an ass from Gibraltar, thrown overboard from a vessel at a distance of 200 miles, which swam ashore, and in a few days afterwards pre- sented himself for admission when the gate of the fortress was opened in the morning. Two instances, equally extraordinary, have been stated on unexceptionable authority to the pre- sent writer ; one of a pointer which had been sent from Durham to the neighbourhood of Edinburgh by sea, and made his way back in a few days by land, to his master's house in the former county ; — the other of a kitten, which had been brought in a carriage a distance of above forty miles, to Edinburgh, and made its way back in a few days to its place of nativity in Stirlingshire, in doing which it must have crossed several bridges. Similar facts have been ascertained in several instances as to sheep ; and the cases of the swallow and of the * Duncan's Lectures on Instinct, t Ibid. INSTINCT. 23 salmon, returning to the spots where they were bred after their long migrations, are clearly analogous. But in such cases it is obvious that the pos- session of reason could not have enabled these animals, alone and unassisted, to find their way ; neither was the result properly referable to instinct, this term being properly applicable only to the feeling of attachment which prompted the return home, not to the know- ledge which the animals somehow acquired where their home was to be found. The only term properly applicable to the acquisition of this knowledge is intuition, and they should be added to other facts, which shew that in va- rious instances animals acquire, by the exercise of their senses, information as to external things, more obviously distinct from the sensa- tions themselves, than those perceptions which Dr. Reid has so clearly shewn to be strictly intuitive inferences, drawn by the human in- tellect from the intimations of the senses. There is yet another fact well ascertained of late years regarding the instincts of animals, which we must not omit to state, because it is the only one which gives plausibility to the notion of Darwin, that sensations and experi- ence would explain the whole phenomena of instinct. This is the fact, which seems well ascertained as to certain animals at least, — which is very probably true of man, and sus- ceptible of important practical application in his case, — that the acquired habits of one gene- ration may become instinctive propensities in the next. Thus it has been often observed that the progeny of well-trained pointers learn to point with very little instruction. It is stated by Darwin that dogs in the wild state, both in Africa and America, have been observed not to bark, that they gradually acquire that note from European dogs ; and that the latter, when turned loose, retain it for three or four generations, and gradually lose it ; and it has been ascertained that in South America, when horses which had been taught to amble had been allowed to run wild, their progeny for two or three generations continued to practice that pace, and then lost it.* Of the existence of such acquired instincts, therefore, there can be no doubt; but it need hardly be said that it is quite incompetent to explain the perfect uni- formity and the skilful contrivance observed in the instincts of animals ; both because its ope- ration seems too limited, and because that sup- position would only remove the difficulty as to the continuance of the instinctive operations from the present to the early generations of animals. In reviewing the varied phenomena of which we have given this hasty sketch, it is impos- sible not to be struck with the very important share which they occupy in the provisions by which the earth's surface is made a scene of continual activity and change. It is interest- ing to reflect on the different powers, to the This principle has heen lately investigated and illustrated by Mr. Knight, in a paper read before the Royal Society of London. operation of which we can trace the unceasing changes continually taking place around us, and particularly on the gradation, and very gradual transition that may be observed, from those by which inanimate matter is continually moved and changed, up to those which ema- nate from the intellect of man. By the ori- ginal impulse given to the world, and by the laws of gravitation and of motion impressed on all matter, the greater and more striking movements of the inanimate world around us are continually determined ; and by the laws of chemistry, these movements are made sub- servient to constant changes in the composition of the inanimate world. Again, by the laws which were impressed on the lower class of living beings at the time of their introduction into the world, and by the consequently in- cessant reproduction of vital affinities, which it is in vain to attempt to resolve h>to the che- mistry of dead matter, a constant succession of living vegetable structures is determined, merely by the agency of air and water, heat and light, on those already existing. By the peculiar chemical operation of these living structures, the air, the water, and all the ma- terials of the earth's surface are subjected to peculiar and continual changes, implying slow but incessant movements, which seem clearly to indicate attractions and repulsions, peculiar to the state of vitality. It is still perhaps doubtful whether in the case of vegetables a property of vital contraction is to be added to the active powers of nature. In immediate but still obscure connection with the lowest of the vegetable creation are the lowest of the animals, where we see the first and slightest indications of sensations, and the feeblest mo- tions consequent on sensations, which we judge to be similar to those that we ourselves ex- perience and excite ; and here also the vital power of contraction, on which the whole life and activity of animals essentially depends, first clearly manifests itself. Then tracing the animal creation upwards, we find that the world contains an infinite number and variety of sentient beings, the provisions for whose enjoyment we may well believe to have been the main object of Providence in all the ar- rangements on the surface of the earth; and to which are granted, in a pretty uniform grada- tion, more and more of the sensations and mental faculties by which nature is made known, and of the powers by which she may be controlled, until we arrive at the intellect and the capacity of Man. It appears farther that the maintenance, and reproduction, and the very existence of these animal structures are entrusted in part to the sensations of which they are made susceptible, and to the voluntary powers with which they are invested ; but that the introduction of these spontaneous powers into the regulation of their ceconomy is so very gradual, that it is hardly possible to say where the movements which result only from physical (although vital) causes terminate, and those which are excited by mental acts begin; — hardly possible, for example, to say, at least as to many animals, 24 INSTINCT. whether the reflex function of Dr. Mar- shall Hall, on which respiration, degluti- tion, the evacuation of the bowels and blad- der, &c. depend, is to be regarded as the re- sult of a merely physical impression on the nerves and spinal cord, like the impression of blood on the heart; or whether the sensations which naturally accompany these actions are, in the natural state, part of the cause which excites them. But that even when the volun- tary powers of animals are certainly the means employed for the ends of their creation, they are still very generally guided by the superior intelligence which has framed both their phy- sical and mental constitution, and which rules the mental but instinctive efforts consequent on the sensations that are felt, as surely as the laws of muscular contraction rule the move- ments of the heart ; and it is into the hands of man alone that the reins of voluntary power are absolutely resigned. And when we thus pass in review ihe sen- sorial and voluntary powers of animals, we are naturally led to the question, whether there is really in our own case so great an exception to those laws of nature which regulate all the other members of the animal creation ; whe- ther, admitting the essential superiority of the intellect or reason of man, the different desires and motives to action, which are implanted in him, are not equally subject to the control of the power that gives them, and whether their consequences are not as exactly ruled by laws and as fully anticipated, as those of the in- stincts of animals. Without entering fully on this abstruse ques- tion, we would take the liberty of remarking, in the view of placing it in its simplest form before our readers, that as the intimations of our own consciousness are the ultimate foun- dation of all the knowledge that we have or can have of our own minds, and as certain of the intuitive principles of belief which our minds naturally suggest to us must be trusted, if we are to inquire into the subject at all ; so the only question that can be reasonably proposed on this point is, whether there is any good reason for suspecting that the belief of our own free-will, which naturally attends cer- tain of the operations of our minds, is a de- ception; and that the analogy of other ani- mals is only applicable to the subject in so far as it can throw light on that question. Now, we find that the works of man, which we ascribe to his reason, and in the execution of which the consciousness of his free-will intervenes, are essentially different from those which we ascribe to the blind instincts of ani- mals, in the total absence (already noticed) of that uniformity which is so leading a charac- teristic of the effects of the latter; and we may reasonably assert that this is just the difference to be expected between the works of man and of other animals, on the supposition that the power concerned in the former is not subject to the direct influence and control of that higher intellect, by which the laws and limits of that concerned in the latter are irrevocably set; and therefore, that there exists no such analogy between the works of man and of other animals as need induce us to suspect, that the evidence of his consciousness on the point in question is not to be trusted. At the same time it ought to be observed, and perhaps has not been duly remarked, not only that the desires which are the principal motives to human action, are analogous to, sometimes identical with, the instincts of ani- mals, (many of them having been evidently given him with the same intention, and with a clear perception of their general result on his condition,) — but also that the constitution of the human mind appears from the intimations of our own consciousness to be such, as to allow of interposition of a superior power, controlling in a certain degree the will of man, without making itself obvious to his mind. For it is admitted by the soundest metaphy- sicians, that the only truly voluntary power which we are conscious of possessing over the train of thought in our minds, and therefore ultimately over many of our actions, operates only indirectly.* We have no power of de- termining the thoughts that succeed one ano- ther or regulating the order of their succes- sion ; and although various laws of association have been laid down, by which many of the component parts of the train appear to be con- nected, yet it will hardly appear to any one who reflects on the operations of his mind, that all the thoughts which succeed one ano- ther can be ascertained to have such bonds of connection with one another. At all events, the only strictly voluntary power which we are conscious that we possess, is that of singling out and detaining any particular portion of the train, whereby it may be made to predominate in the mind, and to produce practical results which might not otherwise have followed ; and even this kind of influence over the train of thought is not exercised exclusively by volition, but is produced in a great measure also by other causes, physical and moral. Now if this be so, how can we deny the possibility of a superior intelligence retaining a power of con-» trolling the acts of any individual human mind, or of any number of minds, either by suggest- ing particular thoughts, or by causing the mind to dwell upon particular thoughts in preference to others, without its sense of its own volun- tary power being interrupted or withdrawn, — nay, without the spontaneous voluntary power being really suspended, the only difference being in the degree of influence which it exerts over the train of thought and consequent vo- litions ? It has been said that the expression in Pope's Universal Prayer — * " So completely is the current of thoughts in the mind," says Stewart, " subjected to physical laws, that it has been justly observed by Lord Kames that we cannot, by an effort of our will, call up any one thought, and that the train of our ideas depends on causes which operate in a man- ner inexplicable by us. This observation, although it has been censured as paradoxical, is almost self- evident ; for to call up any particular thought sup- poses it to be already in the mind." — Elements, Sfe. ch. v. sect. 3. INSTINCT. 25 " And binding nature fast in fate, Left free the human will," is inconsistent with a striking passage in the Essay on Man : — *' Who knows but He whose hand the lightning forms, Who heaves old ocean, and who -wings the storms, Pours fierce ambition in a Cesar's mind, Or turns young Ammon loose to scourge man- kind ? " But if the foregoing statement of the mode of action of the only voluntary power which we are conscious of possessing over the train of our thoughts is correct, it does not appear possible to deny that ambition or any other passion may be infused into any human mind, without de- stroying the consciousness, or suspending the action of that voluntary power. And if we reflect on the characteristics of many nations that have appeared on the earth's surface — on the taste and genius of the Greeks, the mili- tary spirit of the Romans, the restless energy of the northern nations, the maritime adven- ture and commercial enterprise of Britain and America — and contrast these with the stationary civilization of China, or the languid, if not re- trograde condition of Italy, Spam, or Greece — is it unreasonable to suppose that the designs of Providence as to the progress of the human race are sometimes carried into effect by an oc- casional infusion into many individuals of our species, of feelings and desires, of the ultimate object of which they have as little perception as animals have of the purposes of their in- stincts ? But to prosecute this speculation farther would be foreign to the object of this paper. It is still to be remarked, in regard to in- stincts, that they have been long and justly regarded as among the most important pheno- mena in nature, in reference to the doctrine of final causes, or the inferences of design, and of the adaptation of means to ends in the arrange- ment of the universe ; and it is important to set in as clear a view as possible the proper use to be made of them in that enquiry. In fact, the whole plan of the construction of all the different classes of animals bears refe- rence to the instincts with which they are en- dowed, and would be useless without them. If the fangs and claws of the lion, the jaws and stomachs of the ox or the camel, or the bill and gizzard of the turkey, are admirably adapted for the prehension and subdivision of their respective aliments, as well as their organs of digestion for the assimilation of their food, all these provisions would have been useless, but for the instincts which nature has im- planted in these animals, by which their proper nourishment is sought, and the first part of the process of its assimilation is directed. The mutual adaptation of instincts to struc- ture, of structure to instincts, and of both to the ends of their creation throughout every part and function of an animal, and throughout every grade of the animal creation, has been illustrated by many authors, but perhaps most efficiently by Paley, as the most satisfactory of all the indications of the adaptation of means to ends which the study of the universe pre- sents. It is indeed so clearly the fact that all the arrangements of the structure of an animal are subordinate to the instincts with which it is endowed, that the whole study of Comparative Anatomy, and the whole classification of ani- mals in so far as it is founded on their varieties of structure, require to be regulated by this consideration. The general principle by which the details of these sciences are held together may be stated to be this : — that while nature has observed a certain unity of plan in the con- struction, certainly of all the vertebrated, per- haps to a certain degree of all, animals, she has likewise introduced in all parts of the scale just such modifications of that plan as the si- tuation in which each animal is placed, and the office it has to perform, or as the French ex- press it, as the conditions of its existence, demand ; and then has implanted in it pre- cisely such instincts as are required to enable it to maintain itself — to turn those provisions to account — to enjoy its allotted portion of sen- sitive pleasure, and to fulfil the other objects of its creation, under those conditions. The study of the instincts of animals may be said, therefore, to hold a necessary interme- diate place between the study of their struc- ture, and that of the ends or objects of their creation — the structure being subordinate to the instincts, as these are subordinate to the objects of existence ; and it is by attending to them that the immense extent and infinite va- riety of the adaptation of means to ends in the animal creation is perhaps most distinctly per- ceived. It is stated by Mr. Whewell, that although the study of Final Causes has been often re- jected from the science of Physiology, yet it has been found impossible to keep them se- parate. " The assumption of final causes in this branch of science is so far from being ste- rile, that it has had a large share in every disco- very which is included in the existing mass of knowledge. The doctrine of the circulation of the blood was clearly and professedly due to the persuasion of a purpose in the circulatory apparatus."* But there appears to be some ambiguity in this statement. The term physiology is properly applied to the in- vestigation of the physical causes of the phenomena of life — of the powers which are in operation, and the conditions under which they operate, in producing these phe- nomena. It is true that the different func- tions of life are dependent on one another in any individual animal ; and the science of phy- siology is most conveniently taught by arrang- ing their functions in the order of their de- pendence, and assigning, therefore, the final cause of each, after explaining the manner in which it is earned on. It is true, also, that the study of the uses to which the different func- tions are subservient, i. e. the study of final causes, has often led to the detection of phy- sical causes in this as in other sciences. But * Hist, of the Inductive Sciences, vol. iii. p. 467. 26 INSTINCT. the final cause cannot be substituted for the physical in physiology any more than in other sciences ; and this is what was meant by the assertion of Bacon, that the doctrine of final causes is sterile. The object of physiology is to explain, not why, but how, the various func- tions of life are carried on. But when the laws of life are even partially ascertained, and their application understood, i. e. when physiolo- gical facts are referred to their physical causes, they afford many proofs of design and con- trivance, and so furnish a most important ad- dition to the general science of final causes. The science, relative to living bodies, which may truly be said to have its foundations laid in the study of final causes, is the science of Com- parative Anatomy, or of animal morphology ; i. e. the exposition of the modifications which the general type of animal structure, and the plan of the functions carried on in that structure, undergo in the different classes of animals, and by means of which the objects of the animal cre- ation are accomplished by the laws of physio- logy throughout the whole extent of creation. These modifications are determined by the cir- cumstances in which animals are placed on the one hand, and by the purposes which they are to serve in the creation on the other. Every variation of structure has its use, in reference to one or other of these objects, and the branch of natural history which consists in the descrip- tion and arrangement of these varieties cannot be properly treated otherwise than by keeping their uses constantly in view. Thus, in regard to the function of digestion in the higher animals, its physiology, properly speaking, consists in reference to the laws of sensation, of instinct, of muscular motion, of secretion, as modified by changes in the condi- tion of the nervous system, of absorption, and of vital affinities and assimilation so far as they are known, by which the reception of aliment, and the changes on the aliment re- ceived into the body are effected ; in this en- quiry our object is explanation, and however useful the observation of the purpose served by the organs of digestion may be, in suggesting enquiries or experiments by which the laws of which we are in quest may be made out, it is an interruption, not an assistance, to refer to these purposes, or to the importance of the function in the animal ceconomy, as if we thus obtained an explanation of the phenomena : but when these different laws of vital action are explained, their adaptation to the object in view is properly stated as a branch of the doc- trine of final causes. And when we trace the modifications which the organs and function of digestion undergo in the different tribes of ani- mals, in the carnivorous, the herbivorous, and the graminivorous, — in the quadruped, the bird, the fish, the insect, the polype, &c, and compare these with the provisions for assimila- tion and nutrition in vegetables, our object is merely description, and the arrangement by which we must be guided in this department of natural history is clearly laid down by atten- tion to the purposes which these modifications are intended to serve, as adapted to the circum- stances and to the offices of animals, i. e. to their final causes. As, in this science of morphology, or in tracing the varieties of " metamorphosed sym- metry," we do not seek to assign the physical causes of any phenomena, it is no abuse of the doctrine of final causes to assume it as the basis of our arrangements ; and that the prin- ciple of the unity of plan in the animal crea- tion, without the study of the conditions of existence of the different tribes of animals, by which it is modified, and of the instincts ac- companying each modification, is truly sterile, was clearly shewn by Cuvier, and has been ably illustrated by Mr. Whewell.* This observation is strictly applicable to the instincts of animals, considered as an essential element in their physiology. We obtain no explanation of the phenomena of instinct by referring to their use, or final cause ; but the inferences drawn from the study of instincts, as to the existence and attributes of the Author of the universe, and the insight we thus acquire into the arrangements of the animal creation, are not, on that account, the less certain or the less important. In order to perceive the extent and import- ance of these inferences, it is necessary to con- sider, as has been stated above, not only the mutual adaptation of structure and instincts to each other, but also the adaptation of both, in the case of every animal, first, to the purposes of its own ceconomy, and secondly, to the purposes which it is fitted to serve in the general ceconomy of nature. Assuming, as we may safely do, that one great object, if not the most essential object, of all the arrangements of organized beings is to secure the greatest possible amount of sen- tient enjoyment throughout the world, the varying instincts and powers by which animals provide themselves with food will appear on consideration to be better adapted to the attain- ment of this end than they could have been on any other plan, consistently with the general laws, that animal enjoyment depends on the maintenance of organized animal structure, and this on the continual appropriation and assimi- lation of previously organized matter. The different races of animals are widely diffused over the globe by the powers which have been granted them of indefinite reproduction. Those of them which are immediately dependent on vegetables for subsistence are naturally limited by the extent of surface over which vegetation is spread ; and when this limit has been at- tained, the only expedient that can increase the number of animals (and it may be added, one which at the same time varies and multiplies the kinds of animal enjoyments) is to make animals prey on one another, either in the living or dead state. " Such is the command given," says Dr. Roger, " to countless hosts of living beings which people the vast expanse of ocean; to unnumbered tribes of insects which every spot of earth discloses ; to the greater number of the feathered race, and also to a * lb. p. 472, et seq. , INSTINCT. 27 more restricted order of terrestrial animals. To many has the commission been given to ravage and slaughter by open violence ; others are taught more insidious, though not less certain arts of destruction ; and some appear to be created chiefly for the purpose of quickly clearing the earth of all decomposing animal or vegetable materials (e. g. among the larger beasts of prey, the hyena, the jackall, the crow, and the vulture; among marine animals the Crustacea and nume- rous mollusca, and among the lower orders, innumerable tribes of insects.) " That a large portion of evil is the direct consequence of this system of extensive war- fare, it is in vain to deny. But although our sensibility may revolt at the wide scene of car- nage, our more sober judgment should place in the other scale the great preponderating amount of gratification which is the result. We must take into account the vast accession that accrues to the mass of animal enjoyment from the ex- ercise of those powers and faculties which are called forth by this state of constant activity ; and when this consideration is combined with that of the immense multiplication of life, which is admissible on this system alone, we shall find ample reason for acknowledging the wisdom and benevolent intentions of the Crea- tor, who, for the sake of a vastly superior good, has permitted the existence of a minor evil." * This consideration is forcibly stated by Mr. Kirby in relation to one very numerous class of animals. " The object of the creation of the Arachnidans seems to have been to assist in keeping within due bounds the insect popula- tion of the globe. The members of this great and interesting class are so given to multiply beyond all bounds, that were it not for the various animals that are directed by the law of their Creator to make them their food, the whole creation, at least the organized part of it, would suffer great injury, if not total destruc- tion, from the myriad forms that would invest the face of universal nature with a living veil of animal and plant devourers. To prevent this sad catastrophe, it was given in charge to the spiders, to set traps every where, and to weave their pensile toils from branch to branch and from tree to tree, and even to dive beneath the waters." " The Scorpions and other Pedipalps are found only in warm climates, where they are often very numerous. Insects multiply be- yond conception in such climates, and unless Providence had reinforced his army of insecti- vorous animals, it would have been impossible to exist in tropical regions. The animals we are speaking of not only destroy all kinds of beetles, grasshoppers, and other insects, but also their larvse and eggs."f Without going into further details as to the adaptation of the instincts and powers of animals to their office in the world, we may remark, that there are two peculiarities attend- ing many of the phenomena of Instinct, which make them perhaps more important than any others, as indications of Design in the universe. * Bridgewater Treatise, vol. i. p. 46. t Bridgewater Treatise, vol. ii. p. 302. 1. The evidence of design and of intellect which is drawn from the instinctive actions of animals, is precisely similar to, and comes into strict comparison with, that by which each of us is informed of the mental qualities, and even of the mental existence of every human being except himself. What evidence have we of the existence of reason in any of our fellow-men? Only this, that their actions and their words, which are a set of definite muscular actions, appear obviously to be directed to certain ends, and fitted for the attainment of these ends. Therefore, we say, they indicate design or con- trivance, i. e. reason or understanding, in the agents. The adaptation of means to ends is the indication of intellect, to which we yield practical assent every hour of our lives, and it would be a proof of deficiency of our own in- tellect if we failed to do so. Now, when we survey many of the instincts of animals, espe- cially many of those which are directed to the preservation of their lives or the reproduction of their species, — when we see birds of all kinds building nests for their future progeny, and afterwards vivifying their eggs by incuba- tion,— the salmon ascending rivers to deposit their eggs in contact with the atmosphere, — • beavers constructing their houses, — bees or ants piling together their cells and collecting their stores, — the migratory birds repairing to warm climates before winter, — the reptiles excavating their winter retreats, — the squirrel, the dor- mouse, or the pika, laying up their winter store of provisions, — the snail closing its shell and se- curing its magazine of air for the return of spring, — the spider spinning its web, and preparing its cell and trap-door, — the ant-lion digging his pit- fall,— the fishing-frog spreading his lines,- — the camel storing his stomach with water for con- sumption in the desert, — the pelican filling her pouch with food for her young, and an infinity of other contrivances which the organs of ani- mals enable them to execute, which they do execute day after day and year after year with perfect precision, and without which they could neither maintain their own existence nor perpe- tuate their species ; it is plain that we are con- templating a set of living muscular actions, equally adapted to certain definite ends, and equally efficient for the attainment of those ends, as the words or actions of any human being ; and we cannot, without obvious and gross inconsistency, decline to draw from them the same inference that we habitually deduce from the adaptation of means to ends by the muscular actions of human beings. And if we are satisfied by the considerations stated in the beginning of this paper, and, in the case of our own instinctive propensities, by the evidence of our own consciousness, that the reason and intelligence, and anticipation of consequences, which are concerned in, and may be inferred from, these instinctive actions of animals, are not the mental attributes of the animals them- selves, we have no resource but to attribute their mental qualities to a superior Being, who gave to the first individual of each species of animals, and perpetuated to each race, its organic structure, its sensations, its muscular 28 INSTINCT. powers, and its instinctive propensities. Ei- ther directly or indirectly a Mind, and that not the mind of any living animal, must rule, according to general laws, the instinctive ac- tions of all. It is true that there have been, in all ages, some resolute sceptics, who do not assent to the proposition that design can be traced from its effects, or that the observed adaptation of means to ends authorizes us to infer the exist- ence of an intelligent agent; but such a sceptic, if he be consistent, must also refuse his assent to the evidence of the existence of any sentient or intelligent being but himself. " How do I know," says Dr. Reid, " that any man of my acquaintance has understanding? I never saw his understanding. I see only certain effects, which my judgment leads me to conclude to be marks and tokens of it. But, says a sceptical philo- sopher, you can conclude nothing from these, unless past experience has informed you that such tokens are always joined with understand- ing. Alas, it is impossible I can have this ex- perience. The understanding of another man is no immediate object of sight, nor of any other faculty which God has given me ; and unless I can conclude its existence from tokens that are visible, I can have no evidence that there is understanding in any man." In fact, the sceptical reasoner who refuses his assent to the intuitive judgment by which we infer design from its effects, can only be truly and thoroughly consistent if he place no faith in any intuitive truth, or first principle of belief, and therefore disbelieves the suggestions of his own consciousness. " To such a scep- tic," says Dr. Reid, " I have nothing to say ; but of the semi-sceptics, I should beg to know, why they believe in the existence of their own impressions and ideas. The true reason I be- lieve to be, because they cannot help it ; and the same reason will make them believe many other things."* 2. The evidence of design, which we deduce from the instinctive actions of man himself, has this striking peculiarity, that we are actually conscious of the propensities which excite them, and at the same time know that the purpose or design of these actions is not of our own con- trivance. We may be said actually to feel the adaptation, designed by Nature, not by our- selves, of the constitution of our minds to the laws of external nature and to the wants of our bodily organization. The very same machinery, consisting of efforts of volition, of actions pro- pagated along nerves, and of contractions of muscles, which we put in motion to accom- plish any of those objects which our own intel- ligence and foresight enable us to understand, we here put in motion in obedience to propensi- ties implanted in us by nature, with as little knowledge of the purpose which it is to serve, and in the first instance with as little knowledge of the pleasure it is to procure, as the heart that beats within us has of the nature and uses of the circulation which it supports. In the performance of every one of these actions, we * Essays on Intellectual Powers, p. b'21 et seq. may truly say that the intelligent mind of man bows to the superior wisdom of the Author of Nature. The speculations of Darwin on this subject seem intended to weaken the evidence as to the divine existence and attributes drawn from the phenomena of instinct, first, by attempting to explain the instinctive movements of young animals on the principle of irregular move- ments being first produced by uneasy sensa- tions, and then those motions being selected, and voluntarily performed, which are found by experience to appease these sensations or pro- cure pleasure ; and secondly, by referring to the fact formerly stated, that most instinctive pro- pensities are linked to, and, as he expresses it, " under the conduct of sensations and desires." The first of these assertions is quite inconsistent with what has been observed by others (as already remarked) in regard to the commence- ment of the instinctive actions in young ani- mals.* As to the second, it is quite plain that the inference, which is drawn from the observed adaptation of means to ends in the phenomena of instinct, does not require that there shall be no mental antecedent exciting the instinctive pro- pensity, but only that the mental antecedent shall not be an anticipation, grounded on rea- soning, of the effect which the action will pro- duce. Even if the immediate antecedent of every instinctive effort were a pleasing sensa- tion, it would still be a fact, in the constitution of animals, that certain of their sensations, and not others, are naturally followed by certain definite muscular contractions, varying in the different tribes, and each adapted to a determi- nate end, known neither by experience nor by the reason of the animal exhibiting it; and this is the fact which justifies the conclusion in question. This has been already explained, and is so fully illustrated by Mr. Stewart in the answer, contained in his Life of Dr. Reid, to the criticisms of Darwin, that it is unnecessary to dwell upon it. But although it is clearly no objection to the evidence of design and benevolence in the Au- thor of Nature, drawn from the phenomena of instinct, that the instinctive propensities are often linked to and excited by certain pleasur- able sensations, yet it is a strong indication of the superior power by which they are implanted in the different orders of animals, that when they are in full force, and the object to be accomplished by them is important, they have frequently power to supersede and subvert the motives, by which the ordinary actions of the same animals are regulated, and suspend the ordinary laws of their mental constitution, so as to induce an animal to persevere in actions attended with privation and fatigue and positive suffering. " It ought not to be forgotten," says Paley, " how much the instinct often costs the animal that feels it; how much (e.g.) a bird gives up by sitting on her nest, — how repug- nant it is to her organization, her habits, and her pleasures. An animal formed for liberty * See Kirby and Spence, Introd. to Entomology, vol. ii, p. 468. IRRITABILITY. 29 submits to confinement at the very season when every thing invites her abroad ; an animal de- lighting in motion, made for motion, all whose motions are so easy and so free, — hardly a mo- ment at other times at rest, — is for many hours of many days together fixed to her nest as closely as if her limbs were tied down by pins and wires. For my part, I never see a bird in that position, but I recognize an invisible hand, detaining the contented prisoner from her fields and groves, for a purpose, as the event proves, the most worthy of the sacrifice." C W. P. Alison.) INTESTINAL CANAL. See Stomach and Intestinal Canal. IRRITABILITY; etym. irrito, to irritate, stimulate, excite; Syn. contractility, Dr. Bos- tock ; the vis insita, as distinguished from the vis nervosa, of Haller; Germ. Reizburkeit ; that peculiar vital power in the muscular fibre by which it contracts on being stimulated. The term irritability is certainly not the best which might have been devised to express this vital power, for it only expresses the suscep- tibility of being irritated ; the term contractility is equally inadequate, for it only expresses the result or effect of irritation in peculiar textures; the designation irrito-contractility, if not ob- jectionable by its length, would in my opinion express the fulness of this property in the mus- cular fibre of animal bodies. The term irritability was employed by Glisson, and some of its phenomena were not unknown to Harvey, Peyer, Baglivi, and other early physiologists ; but it is to Haller that we owe the accurate distinction of this principle from other principles in the animal ceconomy, its full development, and its application to physiology. Many were the disputes in his own time as to the degree of his originality and merit in this mattter, and Whytt proved a steady and persevering opponent to his claims ; but posterity has done him the justice which his contemporaries pertinaciously withheld; and now whenever there is a doubt as to the meaning or acceptation of the term irritability, that doubt is at once dispelled by adding the epithet Hallerian. The best test of the Hallerian irritability is the electric influence. It is by means of this agent that we detect the presence and the per- sistence of this vital power. Generally the parts which are originally most irritable pre- serve their irritability longest ; but we are not prepared to say that this is an invariable rule. As galvanism is the best test of irritability, so a muscle, endowed with a high degree of irritability, becomes in its turn an excellent test of electricity ; and it was by the irritability in the muscles of the frog that Galvani first detected that form of electricity which has since borne his name, or that of galvanism. It is an important question, whether the property of irritability belongs to the pure and isolated muscular fibre, or whether it belongs to this, combined with thenerves — the nervo-mus- cular fibre. The two textures cannot be separa- ted, the muscular fibres cannot be isolated from the fine fibrillar of the muscular nerves, and therefore the question cannot be determined by distinct experiment. But many facts, anatomi- cal and analogical, would lead us to attach the term irrito-contractility, at least, to the compound texture ; the nervous portion receiving the stimulus, the muscular undergoing the contraction. Why are the muscles which perform involuntary functions so richly endowed with nerves? Some of the disciples of Haller, and especially Behrens, contended, indeed, that the muscular structure of the heart, for example, was not supplied with nerves. The anatomist whom I have just quoted wrote a treatise entitled, " Dissertatio qua demonstratur Cor Nervis carere," in which he asserted that the cardiac nerves were distributed entirely to the bloodvessels; to this the celebrated Scarpa triumphantly replied in his " Tabula; Neurolo- gies Cardiacorum Nervorum," &c. Dr. A. P. W. Philip has placed himself at the head of the Hallerian school of the present day : Legallois had asserted that the spinal marrow was the constant and essential source of the action of the heart, which accord- ingly ceased when the influence of the spinal marrow was removed. But Dr. Philip de- tected a source of fallacy in Legallois' experi- ments, and discovered that although to crush the spinal marrow suddenly, as in those experiments, suspended the action of the heart, yet that the spinal marrow might be slowly and gradually destroyed, and the action of the heart still remain uninterrupted. Similar ex- periments were afterwards made with similar results by M. Flourens, and published in his admirable " Recherches sur le Systeme Ner- veux," p. 18. But though Dr. Philip has the merit of detecting the error of Legallois and of establishing the fact that the circulation may continue after the destruction of the spinal marrow, he has totally failed in proving that the action of the heart is independent of the nervous system, and that the irritability of Haller is exclusively a muscular power. It should be remembered that, after the removal of the brain and spinal marrow, the grand centres of the nervous system, the ganglionic or subsidiary nervous centres, remain, and that even after the removal of the heart from the animal body altogether, — in which case I have proved that its povverof mainfainingthe circulation remains, — * there are still probably as many nervous as muscular fibres ; and we know that the nerves themselves possess, independently of the ner- vous centres, the vis nervosa, or power of exciting under the influence of stimuli, the muscular fibre to contraction. I have also positively ascertained that after the destruction of the brain and spinal marrow in the eel, the heart is susceptible of being impressed through the medium of the ganglionic system. " In an eel, in which the brain had been carefully removed, and the * See my Essay on the Circulation of the Blood, p. 121. 30 IRRITABILITY. spinal marrow destroyed, the stomach was violently crushed with a hammer. The heart, which previously beat vigorously sixty times in a minute, stopped suddenly and remained motionless for many seconds. It then con- tracted;— after a long interval it contracted again, and slowly and gradually recovered an action of considerable frequency and vigour."* Dr. W. C. Henry has added an argument in favour of the theory of neuromyic action of ano- ther kind. It is known that certain narcotics, applied to nerves, destroy the vis nervosa of that part. Dr. Henry found that " a solution of opium injected into the cavities of the heart, or introduced into the intestine, immediately arrested the actions of these organs. "f It seems difficult to imagine that this effect of the narcotic was not produced through the medium of the nervous fibrillar, the muscular being defended by the internal lining of these organs respectively, in the latter organ, a mucous membrane. After much consideration given to this subject, we should be disposed to conclude that in the phenomena of muscular action, the stimulus acts upon the nervous fibre, and that the contraction is an effect and the property of the muscular fibre. If this view be correct, we are necessarily led to consider the vis insita, or muscular power, in connection with the vis nervosa. This latter power is peculiar to certain parts of the nervous system. It is not possessed by the cerebrum or cerebellum, or by the ganglia; but it exists in the tubercula quadrigemina, the me- dulla oblongata, the medulla spinalis, and the muscular nerves. The heart itself has recently been observed by Burdach to contract on sti- mulating the cardiac nerves by galvanism. We owe the discovery of the distinct limita- tion of the vis nervosa, or, as he terms it, the " excitabilite," to M. Flourens.J The following were the supposed laws of action of the vis nervosa by Haller, Bichat, and Professor Midler, before I began my own researches on this subject: Haller observes, " Irritato nervo, convulsio in musculo oritur, qui ab eo nervo ramoshabet." " Irritato nervo, multis musculis communi, totiveartui, omnes ii musculi convelluntur, qui ab eo nervo nervos habent, sub sede irritationis ortos. Denique medulla spinali irritata, omnes artus convelluntur, qui inf ra earn sedem nervos accipiunt ; neque contra artus, qui supra sedem irritationis ponuntur." He concludes, " conditio ilia in nervo, qua? motum in muscu- lis ciet, desuper advenit, sive a cerebro et me- dulla spinali, deorsum, versus extremos nervo- rum fines propagatur." And — " ut adpareat causum motus a trunco nervi in ramos, non a ramis in truncum venire."^ Bichat observes, " l'influence nerveuse ne se propage que de la partie supdrieure a l'in- ferieure, et jamais en sens inverse. Coupez un * Op. cit. p. 160. t Abstracts of papers read before the Royal Society, vol. iii. p. 65. $ Op. cit. p. 16, &c. § Elementa Physiologic, Lausannoe, t. iv. p. 335. nerf en deux, sa partie inf<;rieure irritee fera contracter les muscles subjacens ; on a beau exciter l'autre, elle ne determine aucune con- traction dans les muscles superieurs ; de meme la moelle, divisee transversalement et agacee en haut et en bas, ne produit un effet sensible que dans le second sens. Jamais l'influence nerveuse ne remonte pour le mouvement, comme elle le fait pour le sentiment." * Lastly, Professor Muller observes, " the motor power acts only in the direction of the primitive nervous fibres going to muscles, or in the direction of the branches of the nerves ; and never backwards ;" and " all nervous fibres act in an isolated manner from the trunk of a nerve to its ultimate branches." f It is a singular circumstance, that an esta- blished fact in experimental research, an esta- lished principle of muscular action in the animal ceconomy, should be without application to physiology. Yet such has been the case. For what is the application of the vis nervosa to the explanation of the functions of the animal ceconomy ? Before any such application could be made, it was necessary that other modes of action of this power should be ascertained. I have, by a series of experiments, determined new laws of action of the vis nervosa, and have thus been enabled to make an extensive application of the principle to the functions of life. The head of a river tortoise being separated between the third and fourth vertebrae : 1. The dorsal portion of the spinal marrow was laid bare to the extent of one inch below the origin of the brachial nerves ; the spinal marrow was then excited by means of the probe and by galvanism ; both anterior and posterior extremities, with the tail, were moved. 2. A lateral intercostal nerve was then laid bare, and stimulated in the same manner ; the same effects were produced as in the former experiment. These experiments have been repeated many times, and I performed them in the presence of M. Serres and other gentlemen at Paris, in the month of August, 1839. They establish the following new laws of action of the vis nervosa : — 1. That it does act in the direction from branch to trunk ; 2. That it is in a retrograde direction in the spinal marrow. The application of these new laws to phy- siology— the first application of the vis nervosa to physiology — is very extensive, co-extensive indeed with all the acts of ingestion and egestion in the animal oeconomy. But it does not belong to our present article to treat of this important and extensive subject. We now return to that of irritability in general. The degree of irritability is not the same in every organ of the body. Haller and Nysten have investigated this subject, and the follow- ing are their statements respectively : Haller observes, " Tenacissima virium insi- * Anatomie Generale, 2de partie, t. iii. p. 277- 278, ed. 1801. t Handbuch der Physiologie, i. 656. IRRITABILITY. 31 tarum intestina sunt, quae et evulsa pergunt se contrahere et frigida demum ; etiam his tena- cius cor, si omnia conputaveris, in pullo etiam evidentissime et in frigidis animalibus." * The observations of Nysten are more exten- sive, and his inferences were deduced from expe- riments made upon the human subject imme- diately after decapitation. They are as follow : " 1. La contractilite du ventricule aortique 6tait eteinte 49 minutes apres la mort ; " 2. L'aorte n'a offert aucun mouvement de contraction ; " 3. Cinquante-six minutes apres la mort, la contractilite de l'estotnac, des intestins et de la vessie etait eteinte ; mais ces organes n'ont pu ttre soumis assez promptement au galvan- isrne pour connaitre la duree relative de leur force contractile ; " 4. Le ventricule pulmonaire perdit sa con- tactilite une heure 58 minutes apres la mort ; " 5. Deux heures 2 minutes apres la mort, le diaphragme ne se contractait plus ; les mus- cles de Pappareil locomoteur perdirent succes- sivement leur contractilite a mesure que le contact de Pair agissait sur eux ; mais ceux qui ne furent exposes a l'air que tard, par exetnple au bout d'environ 4 heures, ne cesserent de se mouvoirque 4 heures 15 minutes apres la mort ; " 6. Les oreilletes du cceur, qui etaient exposees a Pair depuis le commencement de Pexperience, tie cesserent de se contracter que 4 heures 40 minutes apres la mort."f But if there be a difference in the irritability of different organs in the same animal, there is a still greater difference in the different animals themselves of the zoological scale. It maybe stated in general terms, that the degree of the irritability in the different parts of the animal series, as tested by galvanism, is inversely as the quantity of the respiration ; so that in the reptile tribes, in which the respiration is exceed- ingly low, the irritability of the muscular fibre is such as to afford a delicate test of galvanism ; and in birds, in which the respiration is at its maximum, the irritability exists in its lowest degree. This important subject deserves the fullest development. We shall here, therefore, insert some observations which were read to the Royal Society, and published in the Philoso- phical Transactions in 1832. The due actions of life, in any part of the zoological series, appear to depend upon the due ratio between the quantity of atmospheric change induced by the respiration, and the degree of irritability of the heart: if either be unduly augmented, a destructive state of the functions is induced ; if either be unduly di- minished, the vital functions languish and eventually cease. If the bird possessed the degree of irritability of the reptile tribes, or the latter the quantity of respiration of the former, the animal frame would soon wear out. If, on the contrary, the bird were reduced to the quantity of respiration appropriate to the * Haller, Primae Lineae, 1767, p. 207. t Rccherches de Physiologie, 1811, p. 312. reptile, or the latter to the degree of irritability which obtains in the former, the functions of life would speedily become extinct. Various deviations from the usual proportion between the respiration and the irritability, however, occur, but there is an immediate tendency to restore that proportion ; increased stimulus ex- hausts or lowers the degree of irritability, whilst diminished stimulus allows of its aug- mentation. The alternations between activity and sleep afford illustrations of these facts. Changes in anatomical form in the animal kingdom present other illustrations of the law of the inverse proportion of the respiration and irritability. The e?g, the foetus, the tad- pole, the larva, &c. are respectively animals of lower respiration, and of higher irritability, than the same animals in their mature and per- fect state. Changes in physiological condition also illustrate the same law. The conditions of lethargy, and of torpor, present examples of lower respiration, and of higher irritability, than the state of activity. It may be remarked that whilst changes in anatomical form are always from lower to higher conditions of existence, changes in the phy- siological condition are invariably from higher to lower. These views are further illustrated by a re- ference to the quantity of stimulus and the degree of irritability of each of the parts and organs of the animal system. The oxygen of the atmospheric air is the more immediate and essential stimulus of this organ. Taken up in respiration, it is brought into contact with the heart, by means of the blood, which may be considered as the carrier of this stimulus, as it is of temperature and nutriment, to the various parts of the system. As oxygen is the principal stimulus, the heart is the prin- cipal organ of irritability, in all the verte- brated animals; if the contact of oxygen be interrupted, all perish in a greater or less pe- riod of time. The extraordinary differences which exist in animals which occupy different stations in the zoological scale, have long excited the atten- tion of naturalists. Nor have the differences which obtain in the various ages and states of its existence, in the same animal, escaped the attention of the physiologist. A similar re- mark applies to that singular state of existence and of the functions of life, designated hyber- nation. But it appears to me that a sufficiently comprehensive view has not been taken of the subject, and that many facts, with their mul- titudinous relations, still require to be deter- mined. I. Of the jmcumutometer . — The principal of these facts is that of the quantity of respi- ration. 'Phis is greater in proportion as the animal occupies a higher station in the zoolo- gical scale, being, among the vertebrated animals, greatest of all in birds, and lowest in fishes ; the mammalia, the reptiles, and the amphibia occupy intermediate stations. The quantity of respiration is also remarkably low in the very young of certain birds which are 32 IRRITABILITY. hatched without feathers, and of certain animals which are born blind ; and in hybernation it is almost extinct. To ascertain the quantity of respiration in any given animal, with extreme minuteness, was a task of great difficulty. It was still more difficult to determine this problem, so as to represent the quantities of respiration in the different kinds, ages, and states of animals, in an accurate series of numbers. The changes induced in a given volume of air made the subject of experiment, by changes in the tem- perature and pressure of the atmosphere, and by variations in the height of the fluid of a pneumatic trough, which it is so difficult to appreciate minutely ; the similar changes in- duced by the humidity of expired air, and by the heat of the animal itself, were so many and complicated, that it appeared almost im- possible to arrive at a precise result. These difficulties, in fine, were such as to lead one of the first chemists of the present day to give up some similar inquiries in despair. Fortunately I have been enabled to devise an apparatus which reduces this complex pro- blem to the utmost degree of simplicity. I now beg the indulgence of the reader whilst I give a detailed description of its construction and mode of operation. This apparatus, which I shall designate the pneumatometer, consists of a glass jar (Jig. 1» a, b,) inverted in a mercurial trough (c, d,) so grooved and excavated, as accurately to receive the lower rim of the jar and the lowest part of the tube (e, f, g,) and also to admit of the ani- mal which is made the subject of experiment, being withdrawn through the mercury. This jar communicates, by means of the bent tube {e,J\ g, //,) with the gauge (i, j,) which is in- serted into a larger tube (k, I,) containing water. A free communication between the jar and the external air is effected and cut off, at any time, by introducing and withdrawing the little bent tube (»?, n,) placing the finger upon the ex- tremity {in,) whilst the extremity («) is passed through the mercury. If the jar be of the capacity of one hun- dred cubic inches, the gauge is to contain ten, and to be graduated into cubic inches and tenths of a cubic inch ; so that each smallest division shall be the thousandth part of the whole contents of the jar. Attached to the same mercurial trough is placed a little apparatus (o, p,) termed an aerometer, and consisting of a glass ball (<>,) of the capacity of ten cubic inches, commu- nicating with a tube (p, 9,) bent at its upper part, of the capacity of one cubic inch, di- Fig. 1. IRRITABILITY. 33 vided into tenths and hundredths, and in- serted into a wider tube containing water, precisely in the manner of the gauge (?', j.) In order to secure the exact proportion between the capacity of the pneumatometer and that of the aerometer, it is only necessary to add more or less of mercury to the trough. The whole apparatus is inclosed in a glazed frame so as entirely to obviate the influence of partial currents of air. It is plain that changes in external temperature and pressure will affect both these parts of the apparatus equally ; and that the fluids in the gauge and in the tube (p, q,) will move pari passu. It is there- fore only necessary to compare them, and to take the difference, for the real alteration in the quantity of the gas in the jar. Previously to noticing this difference, the fluids in the outer and inner tubes are to be brought accurately to the same level, by raising or depressing the outer tube (k, I,) and the inner one (p, q.) In order that the air within the jar and that in the aerometer may be in the same state of humidity, a little water is introduced into the glass ball (o) of the latter. When the animal is to be removed, the fluid in the inner and outer tubes of the gauge are to be brought to a precise level ; the animal is then to be withdrawn through the mercury, by a cord attached to the little net or box in which it is secured ; a quantity of fluid will immediately rise in the inner tube, (i, j,) equal to the bulk of the animal; the bent tube (m, n) is now to be passed through the mercury into the jar so as to effect a communication with the atmospheric air ; a portion of air equal to the bulk of the animal rushes into the jar, whilst the fluids in the gauge regain their level. To avoid the error which would arise from the influence of the temperature of the animal upon the air within the jar of the pneumato- meter, the first observation of the degree upon the gauge must be made the instant the ex- periment is begun, and before the tempera- ture of the animal can have been communi- cated to it ; and the last, so long after the animal has been withdrawn as to allow of its restoration to the temperature of the atmos- phere. In this way all calculations for the varied temperature and pressure of the external air, for augmented humidity and temperature of the air of the pneumatometer, and for the changes in the height of the fluid of the trough, are at once disposed of in a manner the most accurate and simple. It novv remains to determine the quantity of change induced upon the air of the pneumato- meter, by the respiration of the animal. Two views may be taken of this change; that of Messrs. Allen and Pepys, that the oxygen which disappears is replaced by a precisely equal bulk of carbonic acid ; or that of M. Edwards, that there is generally an excess of the oxygen which disappears over that of the carbonic acid evolved. In either case the quantity of respiration is ascertained by the VOL. III. gauge of the pneumatometer in the following manner. A frame made of glass rods {r, s) is placed within the jar (a, b) suspending por- tions of calico, imbued with a strong solution of pure potassa, and provided with a small dish of wood, so as to prevent the caustic liquid from dropping upon the animal beneath. By this means the carbonic acid is removed as it is evolved, or after the animal is with- drawn. The rise of the fluid in the gauge of the pneumatometer gives the quantity of oxygen which disappears, — whether this be entirely ex- changed for carbonic acid, or only partly ex- changed for carbonic acid, and partly absorbed, — and denotes the precise quantity of the respi- ration. The question itself, of the entire or partial exchange of the oxygen gas which disappears, for carbonic acid gas evolved, is at once de- termined by employing the same apparatus without the solution of potassa: in the entire exchange, there is no alteration in the bulk of the air of the pneumatometer; in the case of a partial exchange, the alteration in the bulk of the air gives the precise excess of oxygen gas which disappears, over the quantity of carbonic acid evolved. But this question, and that of the absorption and evolution of nitrogen, with the influence of night and day, of season, &c. are reserved for a future stage of this inquiry. It is important that the animal should be left for a considerable time in the very situation in which it is to remain during the experiment, before that experiment is begun, and before the jar is placed over it. In this manner the effect of timidity or restlessness is allowed to subside, and prevented from mingling with that of the natural state of the respiration. A bit of cork must also be attached to the mercurial trough, so as to float upon the mercury at t, and pre- vent the disturbing effect of the contact of this fluid with the animal. It is also well, after having placed the jar in the groove of the mercurial trough, to pour a little water over the mercury exterior to the jar. The apparatus is thus rendered perfectly air-tight, which is not always effected by the mercury alone. By means of this apparatus we readily and accurately determine the quantity of the re- spiration of any given animal, in any given circumstances. II. Of the measure of the irritabili/i/. — The problem to be next determined is that of the degree of irritability of the muscular fibre, and especially of the heart. The question is beset with scarcely fewer or less difficulties than that of the quantity of respiration, whilst it involves far greater errors and more dis- crepancy of opinion on the part of physio- logists. Even Baron Cuvier has fallen into these errors. It will be shortly demonstrated that the degree of irritability is, in every instance, inversely as the quantity of respiration. Yet M. Cuvier, in a remarkable paragraph, states the very contrary, and even speaks of that which is the exhauster, as the repairer, of the n 34 IRRITABILITY. irritability ; whilst, on the other hand, he makes statements which appear to me at va- riance with this very opinion. In the Ana- tomie Comparee (tome i. p. 49,) this cele- brated writer observes, " Les experiences modernes ont montre qu'un des principaux usages de la respiration est de ranimer la force musculaire, en rendant a la fibre son irrita- bilite epuisee." See also tome iv. p. 301. Similar observations are made in M. Cuvier's more recent work, the Regne Animal : " C'est de la respiration que les fibres musculaires tirent I'energie de leur irritabilite," (tome i. p. 57, 2me edit.) " C'est la respiration qui donne au sang sa chaleur, et a la fibre la sus- ceptibilite pour l'irritation nerveuse," (tome ii. p. 1.) On the other hand, speaking of the moUusca, (tome iii. p. 3,) M. Cuvier observes of those animals of low respiration, " L'irri- tabilite est extreme dans la plupart." The same term is, in fact, used in two distinct senses, in these paragraphs. No further proof can be necessary of the extreme vagueness and incorrectness of the prevailing notions and expressions of physio- logists in regard to this subject. All this will appear still more extraordinary, when the law, that the quantity of respiration and the degree of the irritability are, in fact, inverse throughout all the series, stages, and states of animated being, is clearly established. It is well known that the irritability of the heart and of the muscular fibre in general is greater in the mammalia than in birds, and in reptiles and amphibia than in the mammalia, whether we judge of it by the force and dura- tion of the beat of the heart, exposed to the stimulus of the atmospheric air, or by the con- tractions of the other parts of the muscular system. Now this is precisely the order of the quantity of respiration in these animals, as ascertained by the pneumatomer, inverted. It is essential, in accurately determining the ques- tion of the irritability of the muscular fibre, to compare animals of the same class inter se ; birds and the mammalia, reptiles and amphibia, fishes, the moUusca, &c. must be compared with each other, both generically and specifi- cally. It is especially necessary to compare the warm-blooded, the cold-blooded, the air- breathers, and the water-breathers, in this man- ner. However the different classes may differ from each other, there are differences in some of the species of the same class, and especially that of fishes, scarcely less remarkable. Great differences in the duration of the beat of the heart are observed in foetal, early, and adult states of the higher animals ; this dura- tion being greater in the first, and least in the last of these conditions. The order of the quantity of respiration is inverse. The law of the irritability being inversely as the respiration, obtains even in the two sides of the heart itself, in the higher classes of animals. The beat of the heart removed from the body does not cease at the same time in the wall of all its cavities, or of its two sides : but, as Harvey observes, " primus desinit pulsare sinister ventriculus ; deinde ejus auricula; de- mum dexter ventriculus ; ultimo (quod etiam notavit Galenus) reliquis omnibus cessantibus et mortuis, pulsat usque dextra auricula."* Even in this case the irritability is greatest in the part in which the respiration is least. It was shown by Hook, in the early days of the Royal Society,f that if, the respiration being suspended, an animal appeared to be dying, the beat of the heart and the signs of life were speedily restored, on performing arti- ficial respiration, or even by forcing air through the trachea, bronchia, and pulmonary air-cells and allowing it to escape through incisions made through the pleura. It was, in the next place, clearly shown by Goodwyn, in one of the most beautiful spe- cimens of physiological inquiry in any lan- guage,;]; that in suspended respiration, it is the left side of the heart which first ceases to contract, the right side still continuing its function for several minutes, until the supply of blood may be supposed to fail. The facts detailed by Harvey had shown that the left side of the heart was endued with less irritability than the right ; the experiment of Hook, that respiration restored the action of the heart, if it had previously ceased ; that of Goodwyn, that this cessation and restoration of functions were observed in the left side of the heart. It was obvious, on the other hand, that the respiration belongs, as it were, to the left side of the heart. It appears plainly deducible from these facts, that in circumstances and structures the most similar, the respiration is accurately inversely as the irritability. For the sake of a comparison with the hy- bernating animal, the object of which will be explained hereafter, I thought it right to repeat this experiment. Before I proceed to detail the result, I may just describe an easy method of performing that part of it which consists of artificial respi- ration. A quill is firmly fixed in the divided trachea : a small hole is then cut into that part of the quill which is external; Read's syringe is then adapted to the other end of the quill. At each motion of the piston downwards, the lungs are distended ; whilst the piston is raised, the air escapes through the opening in the quill, producing expiration. The experiment, there- fore, only requires the common action of the syringe. The experiment itself answered my expecta- tion. During the cessation of respiration, the left ventricle ceased to beat, the right ventricle retaining its function ; on renewing its respira- tion, the left ventricle resumed its beat. It appears from this experiment, that from want of a degree of irritability equal to that of the right ventricle, and its own proper stimulus of arterial blood, the left ventricle ceased its con- tractions. The function of the right ventricle * Opera Omnia, Collegio Medicorum Londinensi edita, 1766, p. 28. t Phil. Trans, vol. ii. i On the Connexion of Life with Respiration : London, 1788, p. 72, 82 note. IRRITABILITY. 35 must soon cease in consequence, from want of a supply of blood. These facts prove that arterial blood is the necessary stimulus of the left side of the heart, its irritability being low ; but that venous blood is a sufficient stimulus of the right, from its higher irritability : the phenomena plainly flow from the law, that the quantity of respiration and the degree of irritability observe an in- verse ratio to each other, and from the facts on which that law is founded. In this double sense, besides that of distinct cavities, the mammalia have, therefore, two hearts ; and as the highly aerated blood of the left is the pecu- liar property of birds and the mammalia, so the highly irritable fibre of the right may be compared to that of the heart of reptiles and the fishes. Except for the objection to new terms, the left side of the heart might be termed arterio- contractile, and the right veno-contractile ; the first being stimulated by arterial, the second by venous blood. It is quite obvious that the heart will bear a suspended respiration better, the more nearly its irritability approaches to that which may be designated veno-contractile. The power of bearing a suspended respiration thus becomes a measure of the irritabditij '. It is expressed, numerically indeed, by the length of time during which the animal can support a sus- pended respiration ; a conclusion of the highest degree of importance in the present inquiry. Birds die almost instantly on being sub- merged in water ; the mammalia survive about three minutes, the reptrles and the batrachia a much greater length of time. The unborn foetus, the young animal born with the foramen ovale open, the reptile, the mollusca, having all a state of the heart ap- proaching to the veno-contractile, bear a long- continued suspension of the respiration, com- pared with the mature animal of the higher classes. But the most remarkable fact deducible from this reasoning is the following : if such a case existed as that of the left side of the heart being nearly or absolutely veno-contractile, such an animal would bear the indefinite suspension of respiration ; such an animal would not drown though immersed in water. Now there is pre- cisely such a case. It is that of the hyberna- ting animal. It may be shown that in the state of perfect hybernation the respiration is nearly suspended ; the blood must, there- fore, be venous. See Hybernation. Yet the heart continues to contract, although with a reptile slowness. The left ventricle is, there- fore, veno-contractile, and in this sense, in fact, sub-reptile. The case forms a solitary excep- tion to the law pointed out by Harvey, that the left ventricle ceases to contract sooner than the right. If in the hybernating animal the left ventricle does cease to beat sooner than the right, it is only in so slight a degree as to be referred to the greater thickness of its parietes, and the slight degree in which respiration still remains. It is obvious that the foregoing state- ment must be taken with its due limitations. Venous blood is unfit for the other animal pur- poses, even though it should stimulate the heart to contraction. Another mode of determining the degree of irritability, is the application of stimuli, as galvanism. A muscular fibre endued with high irritability, as that of the frog, and the galvanic agency are mutually tests of each other.* A third criterion and measure of the irrita- bility is afforded by the influence of water at temperatures more or less elevated, in in- ducing permanent contraction of the muscular fibre. There are two other properties of animals which depend upon the varied forms of the inverse ratio which exists between the respira- tion and the irritability. The first is activity, the second, tenacity of life. The activity, which, I believe, M. Cuvier has confounded with the irritability, is generally directly proportionate to the respiration, and intimately depends upon the condition of the nervous system resulting from the impression of a highly arterial blood upon its masses, and not upon the degree of irritability of the muscu- lar fibre. It is the pure effect of high stimulus. To show that M. Cuvier has blended the idea of the irritability of the muscular fibre with that of the activity of the animal, it is only necessary to recur to the passages already quoted from that author, and to adduce the observations with which they are connected. " On vient de voir a quel point les animaux vertebrcs se ressemblent entre eux ; ils offrent cependant quatre grandes subdivisions ou classes, caracterisees par l'espece ou la force de leurs mouvements, qui dependent elles- memes de la quantite de leur respiration, at- tend u que c'est de la respiration que les fibres musculaires tirent l'energie de leur irritabilite."t " Comme c'est la respiration qui donne au sang sa chaleur, et a la fibre la susceptibility pour l'irritation nerveuse, les reptiles ont le sang froid, et les forces musculaires moindres en totalite que les quadrupcdes, et a plus forte raison que les oiseaux ; aussi n'exercent-ils gutre que les mouvements du ram per et du nager; et, quoique plusieurs sautent et courent fort vite en certains moments, leurs habitudes sont gentralement paresseuses, leur digestion excessivement lente, leurs sensations obtuses, et dans les paysfroids ou tempercs, ils passent presque tous l'hiver en lethargic." f It is extraordinary that M. Cuvier should have associated the elevated temperature of the blood with a high irritability of the muscular fibre, when they are uniformly separated in nature, and are, indeed, absolutely incompa- tible in themselves. The muscular fibre of the frog is so irritable, that it would instantly pass into a state of rigid contraction, if bathed with a fluid of the temperature of the blood of birds. § * Bostnck on Galvanism, pp. 4, 14. t Le Regne Animal, tome i. pp. 56, 57. 2de edit. % Ibid, tome ii. pp. 1, 2. 2dc edit. § See an Essay on the Circulation, chap. vii. pp. 180, 181. D 2 36 IRRITABILITY. The same confusion of ideas on the subject of the activity of the animal and the irritability of the muscular fibre prevails, I believe, amongst our own physiologists ; at least, in conversation with two, who may rank amongst the first, I found that they had uniformly con- sidered the respiration and the irritability to be directly, instead of inversely, proportionate to each other. That singular and interesting property of the lower orders of animals termed tenacity of life is, on the other hand, distinctly associated with a high degree of irritability of the mus- cular fibre. The property may be defined as consisting of the power of sustaining the pri- vation of respiration, the privation of food, various mutilations, divisions, &c. It is greater as we descend in the zoological scale. As activity depends upon the presence and condi- tion of the spino-cerebral masses acted upon by arterial blood, tenacity of life depends upon the diminution or absence of these masses and of this highly artenalized blood, being greatest of all in those animals which approach a mere muscular structure. Almost the sole vital pro- perty then remaining is the irritability; and this property does not immediately suffer from division. It is possible to reduce some of the reptile tribes to a state approaching that of animals still lower in the scale, by removing, by very slow degrees, successive portions of the ner- vous masses. This is most readily done in animals in which the respiration is already low, and the irritability high, as in the foetus, in the very young animal, in the reptile, &c, as in the experiments of Legallois,* M. Series,! myself,! &c. There is, even in animals most tenacious of life, one kind of mutilation — one kind of in- jury not well borne. As the blood is in its lowest condition of stimulus, it cannot be withdrawn with impunity ; even frogs soon perish if their blood be allowed to flow. As the irritability, on the other hand, is high, certain stimuli, as galvanism, slightly elevated tem- peratures, &c. are speedily fatal. The batra- chia are promptly destroyed by immersion in water of a temperature of 108° of Fahr., and some fish and Crustacea perish in great num- bers under the influence of a thunder-storm. It is a singular fact, that the fish alone, whose food is found amongst animals of a high irrita- bility, should possess an electrical organ for the destruction of its prey. The application of stimulus has uniformly a tendency to reduce the degree of irritability. The exclusion of all stimuli allows its augmen- tation. During active exercise the irritability is diminished ; during sleep it is proportionally augmented. We are now led to take another view of this sub- ject of irritability. W hat is its source ? How is it renewed when it hasbeen exhausted ? These ques- tions-lead us to take up another of great interest, to * Experiences sur le Principe de la Vie. t Analomie Comparee du Cerveau, tome ii.p. 224. } Essay on the Circulation, chap. iii. § 1. physicians especially, viz. what is the condition of the muscular irritability in those cases in which the influence of the cerebrum, or of the spinal marrow, or both, isremoved respectively? We cannot discuss this subject more clearly than by adducing the following observations, read before the Royal Medico-Chirurgical Society and published in its Transactions, in the year 1839. The utmost discrepancy of opinion prevails amongst physiologists and medical writers upon this subject. Prochaska, Nysten, and Legallois state, that the irritability of the muscular fibre remains in paralytic limbs ; whilst Professor Miiller and Dr. Sticker assert the contrary. No attempt has been made to reconcile a contra- diction not very honourable to our science. To explain this discrepancy of opinion is one of the objects of this communication. The authors to whom 1 have referred, misled by the generic term and idea of paralysis, have not sufficiently distinguished between its dif- ferent species. Yet it will be found, as we pro- ceed, that this distinction is of the utmost im- portance in the explanation of the phenomena. In fact, cerebral paralysis, or that which re- moves the influence of the brain, and spinal paralysis, or that which removes the influence of the spinal marrow, are in totally opposite conditions in reference to the irritability of the muscular fibre in the limbs severally affected ; facts equally obvious in experiments and in clinical observations. I must make quota- tions of some length, for these are necessary to show the present state of the science. I shall then proceed to the detail of my own investi- gations. The first distinct notice of this subject which I think it necessary to adduce, is contained in the following extract from the Opera Minora of Prochaska:* " Vis nervosa quai in nervis a commercio cum cerebro separatis superest, non una alterave musculi contractione, quam irri- tati cient, exhauritur, sed millenis plane con- vulsionibus excitandis par est; quod expertus sum in rana, cui medullam spinalem in dorso abscidi. Supervixit huic vulneri aliquot die- bus; interim irritando medulla; spinalis partem earn, quae erat infra sectionem, convulsiones in artubus inferioribus excitavi toto tempore, quo supervixit, plane mnumeras ; neque extremi- tates inferiores prius inortuje sunt, quam tota rana ; Dein quod vis nervosa in nervis diu persistere possit citra cerebri auxilium probare videntur musculi paralytici, in quorum nervis ob compressionem aliquam prate naturalem to- tum commercium cum cerebro sublaturn est, nihilominus tamen a stimulo electricte scintillas longo jam tempore paralytici musculi convel- luntur." More detailed remarks were made by Nysten, and these, from being founded upon very dis- tinct post-mostem experiments on the human subject, have excited more attention. This ce- lebrated physiologist observes, " Chez deux apoplectiques qui avaient succombe au bout de * Ed. 1800, p. 84. IRRITABILITY. 37 quelques jours, l'un a la premiere attaque et l'autre a la seconde, le galvanisme a determine" des contractions aussi fortes dans les muscles du cote sain que dans ceux du cote paralyse : les iris des deux cotes sont egalement contrac- tees." " Cette propi'iete n'a 6te corripletement aneantie dans les organes musculaires des deux sujets qu'environ 12 heures apres la mort; et on n'a observe aucune difference dans les mus- cles paralyses."* Legallois makes similar remarks, founded upon experiments made upon animals. He observes, " M. Nysten a montre que dans les paralysies les plus completes, l'irritabilite se conserve dans les membres paralyses tout aussi bien que dans ceux qui ne le sont pas. J'ai obtenu un resultat semblable d'un experi- ence que j'ai souvent repetee. Elle consiste a detruire la moelle lombaire dans un lapin age de moins de dix jours ; il faut le choisir de cet age, pour que la circulation ne soit pas ar- retee, et qu'il puisse continuer de vivre. Quoi- que dans cette experience, le train de derriere soit frappe de mort, et que ses nerfs ne puis- sent plus recevoir aucune influence de la mo- elle epiniere, l'irritabilite s'y conserve, et Ton peut, pendant fort long-temps, faire contracter les cuisses, en irritant les nerfs sciatiques. II paraitdonc qu'il se fait dans toute l'etendue des nerfs une secretion d'un principe particu- lier/'f From these quotations from Nysten and Le- gallois we should be led to the conclusion that the muscles of paralytic limbs, in all cases of hemiplegia and of paraplegia, simply retain their irritability. From another series of ob- servations, made by philosophers equally worthy of our confidence, we should be led to an op- posite conclusion. Some interesting experiments on this point have been recently performed by Professor Muller and Dr. Sticker. The former cele- brated physiologist observes,}; " It was known that, after the division of a nerve, the portion cut off from communication with the brain retains, for a certain time, its excitability; but the question, how far the continuance of the connection with the brain and spinal marrow is necessary for the longer preservation of the irri- tability of the nerves, and whether the muscles retain their irritability when their nerves no longer communicate with the central parts of the nervous system, could not hitherto be an- swered with certainty, and had indeed been seldom mooted. Nysten had asserted that the muscles of patients who died a short time after an apoplectic seizure preserved their irratibility, and contracted under the influence of the gal- vanic stimulus, although the functions of the brain had been paralyzed. " I had good reasons, however, for believing * Rccherches Physiol ogiques, 1811, p. 369; com- pare p. 377 and 419; and Cuvier, Histoire des Sciences Naturelles, tome i. p. 213. t CEuvres de Legallois, ed. 1824, p. 23 and 24. t See the excellent translation of the " Handbuch der Physiologie," by William Jialy, M.D., vol. i., p. 631—633 ; and compare p. 663, 724, 727, 898, &c. and Grainger on the Spinal Cord, p. 96, 97. that, in such cases, the nerves retain their power only for a short time, losing it entirely after a longer interval ; for, in experiments on the re- production of the nervous tissue in a rabbit, I had once observed, that the lower portion of the nervus ischiadicus, which I had divided some months previously, had lost all its exci- tability; and a similar fact had been before ob- served by Fowler. I have since performed, in conjunction with Dr. Sticker, new experiments, which have completely confirmed that suppo- sition. To prevent the regeneration of the nerves, and to withdraw more effectually the lower portion from the influence of the brain and spinal cord, a portion of the nerve (the ischiadic) was entirely removed. The experi- ments were made only on two rabbits and a dog; yet the results were so constant, that they are quite worthy of dependence. " Eleven weeks after the division of the nerve in the first rabbit, it was laid bare in its course between the biceps and semitendinosus muscles. Contrary to expectation, and to our mortification, the continuity of the nerve was found to be restored. It was divided anew below the cicatrix ; and it is remarkable that, although the animal uttered a loud cry, the section excited no contraction of the muscles. The lower portion of the nerve was now ex- posed to the galvanic stimulus of a single pair of plates, was cut and pulled in every possible way, but not the slightest muscular contraction was excited. " For the sake of comparison, the nerve of the opposite side was divided, when the animal showed signs of suffering the most severe pain, and violent muscular spasms took place ; and, after the division, very slight irritation of the nerve itself, that is to say, of the lower portion of it, or merely of the muscles, excited strong twitchings, even after death. " Ten weeks after the division of the nerve in the dog, the ends were found to be reunited. The experiment was performed exactly as in the rabbit, and the result, as to the effect on the nerve, was entirely similar : it had lost all its excitability; but the muscles still contracted slightly when stimuli were applied directly to them immediately after death : however, this remaining irritability was gone, while, in the muscles of the opposite leg, the strongest con- tractions could be excited. " Five weeks after the nerve had been di- vided in the second rabbit, we proceeded to examine its state, and were the more interested on account of the short time that had elapsed since its division. The ends were not united ; they were somewhat swollen, and connected with the surrounding cellular tissue. In the other instances, the portion of nerve removed measured about four lines only; here its length was eight lines. No contraction of the muscles could be excited by irritating the nerve either mechanically or by a chemical stimulus, caustic potash, or by galvanism ; nor by irritating the muscle itself, although the rabbit had plenty of vital power. On the left side the muscles were found irritable, as in the other cases, both before and after death. 38 IRRITABILITY. " The foregoing experiments prove, at least, that when the communication of the nerves with the brain is wholly cut off, they gradually lose the power of exciting the muscles to con- traction, while the muscles lose their irritability. The result would, however, have been still more decisive if, in place of a single pair of plates, a small galvanic battery had been em- ployed to stimulate the nerves and muscles. That, and that alone, would have enabled us to determine with certainty whether all the power of the muscles, in two of the cases, had been lost. The experiments as they were made, however, prove distinctly enough the necessity of communication with the brain for the pre- servation of nervous and muscular power. We may from them conclude also that if, after the division of a nerve, the excitability of the lower portion, and the irritability of the muscles are restored, the nerve has itself been completely reproduced ; and that this has not been the case if the nerve and muscle do not retain their vital properties." I may here observe, that an experiment, si- milar to those of Piofessor Miiller and Dr. Sticker, in which Sir Astley Cooper assisted the late Dr. Haighton, was made in this coun- try many years ago, but never published. The sciatic nerve was divided in a dog. In a few days the lower portion had lost its power of exciting muscular contraction. These statements appear, then, sufficiently opposed to each other ; how shall we explain or reconcile them ? Before I proceed to discuss this question, I must beg the attention of the reader to a third series of observations and experiments, in a certain sense at variance with both those which have been detailed. My own attention was first drawn to this interesting point by the fact, well known to physicians, that if we administer strychnine to patients affected with paralysis, it is frequently the paralytic limbs which first manifest the pe- culiar influence of this powerful remedy. M. Fouquier has, I believe, too hastily generalized this effect of strychnine on the muscles of pa- ralytic limbs. And how well do I remember the same remark being made by M. Louis, as, in our visit round his wards at La Pitie, we came to a case in point. From that moment I did not cease to revolve the question in my mind, and to devise modes of observation and experiment to solve it. Certainly the conclu- sion of M. Segalas d'Etchepare, in regard to it, is any thing but satisfactory. M. Segalas ob- serves :■ — " Ces experiences reunies autorisent done a conclure que le tetanos produit par la noix vo- mique a pour condition premiere de son deve- loppement la presence du poison dans le sang, et que les phenomenes qui l'accompagnent sont dus a Taction anormale de ce fluide sur le sys- teme nerveux. " Cette maniere de considerer Faction de la noix vomique donue un moyen simple d'expli- quer les effets de cette substance chez l'homme, et particulierement ce fait si remarquable de la contraction des muscles paralyses plus prompte et plus cnergique que celle des muscles sains, fait observe d'abord par M. Fouquier,* et con- state depuis par tant de praticiens du premier ordre. II est facile, en effet, de concevoir que les muscles sains, soumis a la fois a Tempire du cerveau et a Taction du poison, resistent a celle-ci plus que les muscles paralyses, qui, soustraits a Tinfluence cerebrate, ne sont plus commandes que par le poison." Upon these observations of M. Segalas, M. Ollivier remarks — " Mais s'il en est ainsi, com- ment se rendre raison d'un fait observe depuis long-temps par tous les praticiens, et sur lequel je viens d'appeler Tattention, c'est que la noix vomique cause souvent de violentes douleurs dans les membres paralyses, sans apporter aucun trouble dans les parties saines ? Pour- quoi cette action speciale sur les seuls organes paralyses ? et, d'un autre cot<§, la douleur percue ne prouve-t-elle pas que les parties paralysers ne sont point isolees entierement du centre nerveux, et qu'ainsi ce ne peut etre a cette inconstance qu'on doive attribuer la locali- sation singuliere des effets de la strychnine ? " + It will soon be seen that this view, like a former one, is far too general, far too indiscri- minate— that it is not in every case of paralysis, that the strychnine would first display its in- fluence on the paralytic limbs. Meantime, however, I figured to myself the fact of the strychnine acting on the spinal marrow, and diffusing its power equally along the nerves, to the right hand and to the left, to the muscles to which they proceed respectively: and I asked myself the question — Is the difference observed in its ultimate effects on those muscles, the power being obviously the same, owing to a difference in the degree of the irritability of the muscular fibre itself? Is the irritability of that fibre actually angmented ? If so, the pheno- menon would be explained ! I waited with anxiety for opportunities of submitting this question to the decision of ex- periment. This I entrusted, in the first in- stance, to my young friend and intelligent pupil, Mr. Dolman. The result was as I an- ticipated. A little child, aged two years, was perfectly paralytic of the left arm. The slight- est shock of galvanism was directed to be ap- plied which should produce an obvious effect. It was uniformly observed that the paralytic limb was agitated by a degree of galvanic energy which produced no effect on the healthy limb. A similar patient, with paralysis of one leg, was subjected to the same experiment by my friend and former pupil Mr.W. F. Barlow, and with the same result. I repeated the trial on several patients af- fected with hemiplegia, at my own house, uni- formly with the same event: the paralytic limbs were always moved by an influence which was lower than that required to affect the healthy limb, or if both limbs were agitated, it was uniformly the paralytic limb which was more shaken than the other. * Memoire sur 1'emploi de la noix vomique dans les paralysies, par M. Fouquier, 1815. t Traite de la Mo'e'lle Epiniere, 1827, p. 841. IRRITABILITY. 39 I next repeated my observations upon a more extensive scale, at the St. Mary-le-bone and St. Pancras Infirmaries. There were two exceptions to the rule ; whilst the numbers in which the phenomena as already described were observed were considerable. These exceptional cases I shall notice parti- cularly hereafter. I must now remark that these observations seem, even more than those of Prochaska, Nysten, and Legallois, at vari- ance with the experiments of Professor Miiller and Dr. Sticker. Before I proceed to discuss this question, I must, however, detail some ex- periments of my own. They were made on six frogs. I divided the spinal marrow immediately below the origin of the brachial plexus ; and I removed a portion of the ischiatic nerve of the right posterior ex- tremity. I had immediately, or more remotely, the following interesting phenomena. 1st. The anterior extremities alone were moved spontaneously; both posterior extremi- ties remaining entirely motionless, when the animal, placed on its back, made ineffectual efforts to turn on the abdomen. 2d. Although perfectly paralytic in regard to spontaneous motion, the left posterior extre- mity, that still in connexion with the spinal marrow, moved very energetically when sti- mulated by pinching the toes with the forceps. 3d. The right posterior extremity, or that of which the ischiatic nerve was divided, was en- tirely paralytic, both in reference to sponta- neous and excited motions. 4th. After the lapse of several weeks, whilst the muscular irritability of the left posterior ex- tremity was gradually augmented, that of the right was gradually diminished, phenomena ob- served when the animal was placed in water, through which a slight galvanic shock was passed accurately in the direction of the mesial plane. In this interesting experiment we have, then, first the phenomena of loss of spontaneous mo- tion on removing the influence of the brain, the excited or reflex actions remaining ; and the loss of these on removing the influence of the spinal marrow; secondly, in the case of mere cerebral paralysis, we have augmented irritabi- lity, and in that of the spinal marrow we have the gradual diminution of this property. 5th. Strychnine being now administered, the anterior extremities and the left posterior extre- mity, or that still in connexion with the spinal marrow, became affected with tetanus ; but the right posterior extremity, or that severed from all nervous connexion with the spinal marrow, remained perfectly flaccid. 6th. Lastly, the difference in the degree of irritability in the muscular fibre of the two limbs was observed when these were entirely separated from the rest of the animal. In a word, the muscles of the limb para- lysed by its separation from both cerebrum and spinal marrow, had lost their irritability; whilst those of the limb separated from its connexion with the cerebrum only, but left in its con- nexion with the spinal marrow, not only re- tained their irritability, but probably possessed it in an augmented degree. The next question came to be, — Do these phenomena obtain in the human frame? I visited a patient affected with hemiplegia, including paralysis of the face, and I passed a slight galvanic shock through two pieces of metal, of which one was placed over each cheek. The muscles of the paralytic side were most affected. I repeated the expe- riment with the same result. I now compared with these, two cases of injury of the facial nerve, passing the galvanic shock in the same manner, through the fibres of the orbicularis : it was now the muscle of the healthy side which was affected by the galvanism, the eyelid of that side being closed, whilst that of the para- lytic side gaped as before. I next compared the effect of galvanism in two cases of complete paralysis of the arm, one hemiplegic, the other the result of dislocation of the shoulder. The muscles of the former were more, those of the latter less, irritable than those of the healthy arm respectively, as were also those of the arm of a patient affected with the paralysis induced by lead. Lastly, I compared the cases of pa- ralysis of the lower extremities, one arising after pertussis, and therefore cerebral, the other, I think, from disease within the lumbar verte- bra? : in the former there was augmented, in the latter, diminished irritability. By means of these experiments and observa- tions we are enabled, I believe, to explain all the apparent discrepancies between the state- ments of former authors, and between each of them and my own. The observations of Nysten and others deter- mined that the irritability of the muscular fibre still existed in ordinary hemiplegia ; but they did not extend far enough to determine the comparative degree of irritability of the para- lytic and of the healthy limbs, or the question whether, in the former, the irritability was dimi- nished— -the event probably expected — or aug- mented, a result, I believe, never anticipated. Prochaska and Nysten and Legallois failed in their experiments, too, by not allowing time for the change in the condition of the irritability of the muscular fibre to take place. Professor Miiller and Dr. Sticker, on the other hand, did not distinguish between para- lysis arising from separation from the cerebrum merely, and paralysis arising from separation from the spinal marrow, a distinction of the utmost importance in every point of view, and that which explains the phenomenon under discussion. The term paralysis has been used by all the authors whom I have quoted in too general a sense. This is so true that I may affirm that in one kind of paralysis, that which removes the influence of the cerebrum, and which is therefore paralysis of spontaneous or voluntary motion, there is augmented irrita- bility; whereas in the other, that which severs the influence of the spinal marrow, the irrita- bility is diminished or even annihilated. We may conclude that in cerebral paralysis the irritability of the muscular fibre becomes augmented from want of the application of the stimulus of volition; in paralysis arising from disease of the spinal marrow and its nerves this 40 IRRITABILITY. irritability is diminished, and at length becomes extinct, from its source being cut off. We may further deduce, from the facts which have been detailed, that the spinal marrow and not the cerebrum is the special source of the power in the nerves of exciting muscular con- traction, and of the irritability of the muscular fibre ; that the cerebrum is, on the contrary, the exhauster, through its acts of volition, of the muscular irritability. As a further deduction from the same facts, we may infer the diagnosis between cerebral and spinal paralysis : mere cerebral paralysis is attended by augmented irritability, whereas spinal paralysis is that which is attended by diminished irritability. This fact will prove useful in many obscure cases. Having thus cleared up the physiological question, I proceed to the application of the principle to pathology ; and I may here observe that there is a whole series of phenomena which admit of explanation by its aid. And, first, the exception to the rule of aug- mented muscular irritability in paralytic limbs, is obviously dependent upon its existing in the cases of paralysis from the severed influence of the spinal marrow, as distinguished from those arising from the severed influence of the cere- brum merely. Secondly, we understand at once why the influence of strychnine is first and most seen in cerebral paralysis in the paralytic limbs. But there are still some other points which I must bring before the notice of the reader. The first of these is the influence of emotion in paralytic limbs. The second is the similar influence of certain acts of respiration ; as yawning, sneezing, coughing, &c. The third, the similar influence of the tonic power. It must have occurred to us all to observe the influence of surprise or agitation on the arm and hand, and perhaps on the leg, of a patient long affected by hemiplegia, whilst the limbs of the healthy side remained unaffected. In this case the influence of the emotion is, like that of strychnine in the case formerly discussed, exerted equally upon the limbs of both sides; but it is the muscles of the paralytic limbs which are most irritable, most susceptible of the stimulus ; it is, therefore, these limbs which are most convulsively affected. The same phenomenon is not observed in paraplegia, because the influence of the emotion is cut off from the affected limbs. Case 1. — I was called to a patient a short time ago, affected at that moment with bron- chitis. He was forty-three years of age, and at the age of twenty-four had been seized with hemiplegia. Recovering from the immediate danger of the attack, he remained hemiplegic, scarcely regaining the use of the hand and arm at all, and only partially that of the leg. Whenever this patient is excited by meeting an acquaintance, or in any similar way, he has a little strabismus, and the hand and arm are contracted and convulsed in the most extraor- dinary manner: whenever he coughs, the leg is thrown involuntarily upwards. The arm is severed, as it were, from volition, but affected by emotion. Similar facts have been observed in regard to the influence of certain respiratory acts, but especially those of yawning, sneezing, &c. Dr. Abercrombie details the following inte- resting case in a note to the late Mr. Shaw. " 1 think the following case will be interest- ing to you and Mr. Bell. I had some time ago under my care, a man affected with hemi- plegia of the left side ; the palsy complete, with- out the least attempt at motion, except under the following circumstances : he was very much affected with yawning, and every time he yawned the paralytic arm was raised up, with a firm steady motion, until it was at right angles with his body (as he lay in bed on his back), the fore-arm a little bent inwards, so that his hand was above his forehead at its greatest elevation. The arm was raised steadily during the inspiration, and when the expiration began seemed to drop down by its own weight, witli considerable force. He continued liable to the affection for a considerable time, and it ceased gradually as he began to recover the natural motion of the limb." — That is, as I conclude, as the state of augmented irritability was re- moved by the returning acts of volition. Not less interesting are the effects of the tonic power. In cases of hemiplegia of long duration, the paralytic limbs, but especially the arms and hands, are drawn into a state of chronic, rigid, contraction. This phenomenon is owing to the principle of tone constantly acting upon muscles now possessing augmented irritability, whilst they are never, or rarely, relaxed by acts of volition. A similar effect is seen in idiots born with atrophied cerebrum : the influence of volition is wanting; that of the spinal marrow, the source, at once, of the tone and of the irrita- bility of the muscular system, is in constant action, and induces chronic contraction, an effect which must, however, be distinguished from that of spasm, which is excited imme- diately by some disease of the spinal marrow itself. I may now resume the subject of the action of strychnine on paralytic limbs. It is obvious that the generalization of M. Fouquier, M. Se- galas, and others, that the strychnine attacks the paralytic rather than the healthy limbs, was too hasty. This is only true in those cases of paralysis in which the muscles still remain in nervous connexion with the spinal marrow ; the opposite result is observed in those other cases in which such connection between the muscles and the spinal marrow is intercepted. I would here make another observation. The arms and hands, generally speaking, are more under the influence of the cerebrum than the lower extremities; and these, on the other hand, are more under the influence of the spinal marrow than the arms and hands. The superior extremities are more and more fre- quently affected by hemiplegia than the inferior; these are more influenced by tetanus, by strychnine, &c. than the former, a fact which IRRITABILITY. 41 I have observed, in regard to strychnine, in some cases of hemiplegia. These facts must be borne in mind in making our observations. Another circumstance must also be noticed. The more perfect the paralysis, generally speaking, the more the irritability of the mus- cular fibre is augmented. In hemiplegia, the arm is generally at once more paralytic and more irritable than the leg. In chronic cases, however, the irritability becomes impaired, together with the nutrition. I will now adduce a few cases which, how- ever succinctly detailed, will exemplify and substantiate the preceding observations. Case 2.— On January the 16th, 1839, I visited a patient who had been seized with hemiplegia nine months before : the arm was perfectly paralytic, the leg less so, the face less so still. On passing the galvanic influence through the arms, the left or paralytic arm was much more affected than the right, and dis- tinctly affected by a force which induced no effect whatever on the right, the tendons start- ing on each completion of the galvanic circle; the contraction of the muscles of the left side of the face was seen in its effect on the features ; and that of the left gastrocnemius, in its effect on the tendo Achillis, when no effect was per- ceptible on the right side of the face, or in the right leg. In this patient other and very interesting phenomena were observed : 1st. The arm has, from the beginning, been much more paralytic than the leg or the face : 2d. The influence of strychnine was observed in the paralytic arm and leg only, in the latter more than in the former : 3d. Any sudden noise, or other causes of emotion, affect the paralytic side only — the leg, however, more than the arm : 4th. Yawning and sneezing move the para- lytic limbs ; the former the arm, the latter the leg, principally : 5th. The act of stretching, and the act of raising the right arm above the head, induce unconscious movements of the left or paralytic arm : 6th. During sleep, the left or paralytic arm and hand are greatly contracted and painfully pressed to the side : 7th. The paralytic arm shrinks from the application of cold, as the sudden contact of a cold hand ; an example of the reflex action in hemiplegia : 8th. Lastly, the paralytic hand and arm are constantly in a state of contraction. I repeated the trials with the galvanic shock, with the same results, on February the 14th. Case 3. — On January the 15th and 22d, 1839, 1 passed a slight galvanic shock through the orbicularis of each side of the face, in a patient affected with paralysis of the left facial nerve from exposure to cold, of six weeks' duration. Here the right eyelid was forcibly closed, the left or paralytic eyelid being totally unaffected. Case 4. — On February the 13th, I passed the galvanic shock through the two orbiculares in a patient whom I visited with Mr. Burford, and in whom the facial nerve was partially paralyzed by the removal of a considerable branch of the nerve, together with a tumour which had formed in its course along the cheek. The muscle of the paralytic side was un- affected, whilst that of the healthy side closed the eyelids on every application of the galvanic influence. Case 5. — I have more recently performed the same experiment on a patient affected with paralysis of the facial nerve, from otitis and disease of the temporal bone, with precisely the same result. Case 6. — On February the 9th, I compared the galvanic influence in two patients at the St. Pancras Infirmary : both were affected with complete muscular paralysis of the arm ; the first case was cerebral, being hemiplegia; the second was an injury of the brachial plexus, having resulted from dislocation of the shoulder; the results were what I had anticipated ; in the case of hemiplegia, the irritability of the muscles of the paralytic limbs was greater than that of the muscles of the healthy limb ; in the case of injured brachial plexus, the opposite state of things was observed, the irritability of the muscles of the paralytic hand and fore-arm being greatly diminished. Case 7 — On January the 23d, 1839, 1 passed the galvanic shock through the hands of a patient who had been gradually affected with paralysis of the right, from handling leaden types, as a compositor. Here, again, the para- lytic muscles were unaffected by a degree of galvanism, which induced an evident effect on the muscles of the healthy limb. Cases 8 and 9. — On January the 10th, 1839, I galvanized a little boy with paralysis of the left leg; the muscles were more irritable than those of the healthy leg ; the affection had fol- lowed pertussis, and I concluded that it was cerebral. This conclusion was confirmed by a fact which I learnt afterwards, viz. that in the commencement there was imperfect closure of the eyelids during sleep. On the same day I tried the galvanic influence in a case of partial paraplegia in a little girl, a patient of Mr. Bur- ford ; in this case the muscles of the paralytic limbs were less irritable than those of the healthy limbs; I concluded that the disease was seated in the course of the nerves, and probably within the lumbar vertebra. Case 10. — It has been suggested to me that the loss of irritability in the cases of spinal paralysis might be owing to the defective nutri- tion of the muscles. I therefore tried the effect of galvanism in a case of chronic cerebral paralysis, or hemiplegia, with much emaciation of the paralytic muscles. I found these muscles, as before, much more irritable than those of the unaffected limb. I must repeat, that I am perfectly aware of the sketchy manner in which these notes of cases are given ; but I have thought it better to leave the further details for another form of communication. In the meantime we may conclude, that by the test afforded by the galvanic trough, we are enabled to effect a diagnosis between the cases to which I now allude. Disease of the cere- 42 IRRITABILITY. brum itself, — disease of the dorsal portion of the spinal marrow, — induces cerebral paralysis, hemiplegia, or paraplegia; disease compressing or destroying the facial nerve, or the cauda equina in the lumbar region, induces both cerebral and spinal paralysis. In the former case we shall observe augmented, in the latter diminished irritability of the muscular fibre. I may now resume the points of this article, and observe, 1st. That the spinal marrow, exclusive of the cerebrum, is the source of the muscular irritability : 2d. That the cerebrum is, in its acts of voli- tion, an exhauster of that irritability : 3d. That in muscles separated from their nervous connexion with the brain we have augmented irritability : 4th. That in muscles separated from their nervous connexion with the spinal marrow we have, on the contrary, diminished irritability : 5th. That the degree of the irritability of the muscular fibre of paralytic limbs, compared with that of the muscles of the healthy limbs, will afford us a source of diagnosis between cerebral and spinal paralysis, and especially between. 1. Hemiplegia of the face, and 2. Paralysis of the facial nerve; 3. Hemiplegia of the arm or leg, and 4. Disease of the nerves of these limbs ; * 5. Disease of the spinal marrow in the dorsal region, and 6. Disease of the cauda equina in the lumbar region ; &c. 6th. That the greater influence of emotion, of certain respiratory acts, of the principle of tone, &c. on the muscles of certain paralytic limbs than on those of healthy limbs, depends on their augmented irritability : 7th. That the same principle explains the greater susceptibility of the muscles in certain cases of paralytic limbs, to the influence of strychnine : 8th. That, in the conclusions of M. Fouquier, Professor Miiller, &c, a sufficient distinction was not made between the influence of the cerebrum and of the spinal marrow, which in this, as in so many other respects, have such different properties : 9th. From these and other experiments and observations, I conclude, too, that sleep restores the irritability of the muscular system, by arresting the acts of volition which exhaust or diminish it; muscular efforts, on the other hand, diminish the irritability and induce fatigue. Before I conclude, I must beg my reader's attention to some experiments of that able phy- siologist, Dr. J. Reid, of Edinburgh, which appear, at first sight, to be contradictory to those which I have just detailed. Dr. J. lleid's paper is published in the * In disease of the cervical vertebras the arms are sometimes paralyzed without paralysis of the legs; this probably arises from compression of the brachial plexus. See Sir B. Brodie's paper in the Medico-chirurgical Transactions, vol. xx. p. 130 ; the galvanic trough would determine the question. Fourth Report of the British Association for the Advancement of Science, p. 671. It is as follows : — " Although physiologists are still divided in opinion as to the question whether nerves fur- nish a condition necessary to the irritation of muscles, (i. e. whether every stimulus which excites a muscle to contraction acts on it through the intervention of nervous filaments,) they have now very generally abandoned the once prevalent theory, that the irritability of muscles is derived from the brain or spinal cord, i. e. that muscles are continually re- ceiving, through their nerves, from those larger masses of the nervous system, supplies of a certain influence or energy, which enables them to contract ; and that some of the state- ments of Dr. Wilson Philip, in particular, are generally regarded as decisive against this theory. " Dr. Wilson Philip found by experiment, that the irritability of a muscle of which the nerves were entire, was exhausted by applying a stimulus directly to the muscular fibres (sprinkling salt on them) even more quickly than that of a muscle of which the nerves had been cut, and where all communication with the supposed source of nervous influence or energy had been cut off ; and he states gene- rally that a muscle of voluntary motion, if ex- hausted by stimulation, will recover its irritabi- lity by rest, although all its nerves have been divided. " But in opposition to this statement, and in support of the old theory of nervous influ- ence continually flowing through certain of the nerves into the muscles, it has lately been stated by Mr. J. W. Earle, that when the nerves of the limb of a frog were cut, the skin stripped off, and the muscles irritated by sprinkling salt on their fibres, until they had lost their power of contraction, although they did not lose their power much more quickly than when the nerves were entire, yet they did not regain their power, although left undisturbed for five weeks; while the muscles of the limbs of another frog, simi- larly treated, but of which the nerves were left entire, completely recovered their irritability. " It occurred as a fundamental objection to the experiment of Mr. Earle, that in the case where the nerves had been divided, the mus- cles had become inflamed ; being found at the end of the five weeks ' softer in their texture than natural, a good deal injected with blood, and with some interstitial deposition of fluid in them ;' while in the limb to which the salt had been applied, but of which the nerves were left entire, and where the irritability was recovered, ' although the colour of the muscles was rather darker than natural, their texture remained un- changed, and there was no interstitial deposi- tion of fluid in them.' " In these circumstances it might evidently be supposed that it was the inflammation and disorganization of the muscles, not the section of the nerves, which prevented the recovery of the irritability in the case where the nerves had been cut; and it became important to have the experiment repeated, with care to avoid such IRRITABILITY. 43 injury of the limb of the animal as should cause inflammation to succeed the section of the nerves. " With this view, Dr. Reid performed a num- ber of experiments on frogs, in which the irrita- bility of the muscles of both hind legs was ex- hausted or greatly diminished by galvanism, after the nerves of one leg had been divided, and the lower part of the limb rendered per- fectly insensible and incapable of voluntary motion, (but without stripping off the skin,) while the nerves of the other had been left entire. The state of the muscles of both limbs was examined after some days. The results of these experiments were not uniform ; but in several, where every attention to accuracy seems to have been paid, the irritability of the mus- cles in the palsied limbs appeared to be re- stored as perfectly us in others ; contractions being excited in them, in several instances, by the galvanism from four or even two plates, whereas they had formerly been irritated until they were no longer excitable by that from fourteen plates. " That the muscles which thus recovered their irritability had lost all nervous connexion with the brain or spinal cord was proved, not only by their obvious insensibility, but by after- wards cutting off the heads of the animals and forcing a probe along the spinal canal, which excited forcible contractions in all parts, ex- cepting the palsied limbs. " Dr. Alison's paper contained the details of several of these experiments ; and he stated, in conclusion, that as a positive result in such an inquiry must always outweigh a negative one, (particularly where a source of fallacy at- tending the latter can be pointed out,) these experiments appear fully to justify the assertion of Dr. Wilson Philip, that a muscle of volun- tary motion may recover its irritability by rest, although all its nerves be divided ; and that they afford, perhaps, more direct evidence than any others in support of the doctrine of Ilaller, now generally admitted in this country, that the property of irritability in muscles is independent of any influence or energy con- tinually flowing from the nervous system, although, like every other endowment of living animals, it is subjected to the control of causes which act primarily on that part of the living frame. " Dr. Allen Thomson expressed a doubt whether these experiments warranted the con- clusion drawn from them, not because he ac- quiesced in the theory to which they are op- posed, nor because he called in question the accuracy of the results described to have been obtained, but because he knew that former ex- periments had failed in producing such dimi- nution or exhaustion of the irritability of mus- cles as had been found by Dr. Keid ; and con- ceived it possible that some of the numerous fallacies to which such experiments are liable might not have been sufficiently guarded against. " The accuracy of Dr. Reid's statement as to the great diminution or apparent exhaustion of the irritability of the muscles under the in- fluence of galvanism, and the subsequent reco- very of the power, notwithstanding the division of all their nerves, was satisfactorily established. It is to be remarked, however, that in these experiments, as usual in such cases, the limbs to which the galvanism was applied were kept moist by the same saline solution with which the galvanic trough was charged ; and Dr. Thomson has observed, that when they are moistened with pure water, the diminution of the irritability under the excitement by galva- nism is much less obvious. Hence he was led to suspect that the apparent loss of power in the muscles under that process might depend, not on the circumstance of repeated excitement, but on a degree, however slight, of injury to their texture by the action of the salt. This inquiry he proposes to prosecute further; but in the meantime it is certain that by the usual process of galvanizing a living muscle moist- ened by a saline solution, a very great diminu- tion of its irritability may be effected, which may subsequently be regained, notwithstanding the division of all its nerves ; and as the fact of its recovery, not the cause of its diminution or exhaustion, is the point on which the infe- rence drawn from these experiments rests, that inference maybe held to be sufficiently justi- fied." The first question is, — what is the nature of that effect produced upon the nervous and mus- cular system by such agents as those employed in these experiments temporarily to diminish or suspend their powers? The immediate effect of an attack of hemiplegia, the immediate effect of an injury done to the spinal column, by acci- dent, or in an experiment, the immediate effect of galvanism, or other stimuli, applied to the nerves or muscles, is to suspend, for a time, the phenomena of the excito-motory power of the nerves, and of the irritability of the muscles, respectively; which, however, repose renews. What is the nature of these changes ? Do they not consist in the sudden reduction and more gradual removal of some physical effect, diffe- rent from the diminution and restoration of a purely vital property of these textures, widely different from the slowly induced loss of irrita- bility resulting from the removal of its source, the natural physical condition remaining un- changed ? At any rate we must agree with Legallois. " II faut se souvenir que deux faits bien constates ne peuvent jamais s'exclure l'un 1 'autre, et que la contradiction qu'on croit y remarquer tient a ce qu'il y a entre eux quelque intermediaire, quelque point de contact qui nous echappe." * I must here adduce two experiments of my own, performed and published many years ago.f " In an eel, in which the brain had been carefully removed, and the spinal marrow de- stroyed, the stomach was violently crushed with a hammer. The heart, which previously beat vigorously sixty times in a minute, stopped suddenly and remained motionless for many seconds. It then contracted ; after a long in- * CEuvres, Paris, 1824, t. i. p. 21. t See my Essay on the Circulation of the Blood, 1831, p. lo'O, 188. 44 NORMAL ANATOMY OF THE KNEE-JOINT. terval it contracted again, and slowly and gra- dually recovered an action of considerable fre- quency and vigour." " A frog was made perfectly insensible by the application of laudanum or alcohol. Its respiration ceased. It did not move on the application of any irritant. The circulation in the web was carefully observed. When it had long continued in the same enfeebled state without change, the thigh was crushed. The circulation in the minute and capillary vessels ceased at once, and never returned. The sto- mach was now crushed in the same manner. The heart ceased to beat for many seconds. Its beat then returned, but never regained its former force." In these experiments we have the sudden influence of shock and its gradual subsidence. The experiment is peculiarly interesting in many points of view : — 1. it is the only one on record of the effects of shock induced solely and exclusively through the medium of the ganglionic system ; 2. it exemplifies the effect of shock or excessive stimulus on the heart, with its gradual though incomplete subsidence. The connexion of the ganglionic system with the irritability of the visceral muscles, — the heart, the stomach, the intestines, &c. forms the subject of an experimental investigation, in which I am at this moment engaged, and the results of which I purpose to give under the head of vis nervosa and vis insita. It is pro- bable that the ganglia are to the internal mus- cular organs what the spinal marrow is to the muscles of the limbs, viz. the power of irritabi- lity, &x. This inquiry is founded on a fact first ascertained by myself, that, in spring, we may, by portions at a time with considerable intervals, totally destroy the brain and spinal marrow in the frog, eel, &c. leaving the circula- tion in the web or the fins and tail.* We have thus isolated the ganglionic from the rest of the nervous system, on which we may therefore proceed to experiment, watching the effect of various agents tin the circulation and on the action of the heart, the stomach, the intestines. We have thus passed in review in its anato- mical, physiological, zoological, pathological, and those peculiar relations, the question of the irritability of the muscular fibre. It only remains for us to advert, once more, to the ex- treme importance of this principle in physiology : all physiology is involved, indeed, in the topic of the nervous system and the vascular system, and the principle of irritability seems, with its various and appropriate stimuli, to be placed between those two. (Marshall Hall.) JOINT. — See Articulation, and the arti- cles under the headings of the several joints for both the normal and abnormal anatomy. KIDNEY.— See Ren. KNEE-JOINT (normal anatomy of the). Gr. yo'w ; Lat. genu; Fr. genou ; Germ. * Op. cit. p. 136'. Kniegelenk ; Ital. ginocchio. The knee-joint, the largest joint in the body, results from the articulation of the os femoris with the tibia below and the patella anteriorly. It admits of extensive motion as a ginglymus, to which is added an arthrodial motion, or a small degree of rotation of the leg and foot, when the joint is partly flexed. The articular surfaces are large and complicated, the ligaments numerous, and the joint chiefly superficial ; circumstances necessary to the freedom, stability, and sym- metry of the limb, but exposing this important articulation to frequent accident and disease. It is intended here to describe so much of, a, the bones entering into the formation of this joint, and, b, the cartilages, ligaments, &c, as may be necessary to the elucidation of, c, the mechanical Junctions. (a.) Bones. The shaft of the os femoris, which in the middle of the thigh is triangular, becomes of a four-sided form as it approaches the knee, in consequence of the bifurcation of the linea aspera. This rough ridge, which in the middle of the bone forms a prominent pos- terior angle, divides on entering its inferior third into two diverging lines which terminale at the convex articulating eminences called condyles ; a flat triangular surface of bone is thus left, where the popliteal vessels lie. The outer line is most strongly marked, and gives origin to the vastus externus and short head of the biceps flexor cruris : the inner line is deficient near the upper part, over which the femoral vessels pass into the ham ; it gives attachment below to the vastus internus and adductor magnus. The internal condyle is narrower and more pro- jecting behind than the external ; and in rela- tion to the shaft of the bone, it appears to extend further downwards; but the natural oblique position of the os femoris brings the condyles nearly horizontal. The greater width of the pelvis in women gives, ceteris paribus, a greater obliquity to the os femoris than in men. The condyles are separated behind by a deep fossa, out of which the crucial ligaments take their origin ; their articulating surfaces are con- vex both in the transverse and in the antero- posterior directions, until in front they coalesce into one pulley-like surface over which the patella plays in the motions of the joint: this trochlea is convex from above downwards, but concave from side to side ; its outer half is more prominent than the inner, and extends higher up the corresponding condyle. Above the trochlea there is a flattened or slightly depressed surface, upon which the patella partly rests during complete extension of the joint. The thickness of the os femoris from front to back undergoes little change till the condyles sud- denly jut out behind, and the edges of the trochlea rise up in front ; but from side to side the shaft of the bone increases in breadth as it approaches the knee, the two postero-lateral surfaces winding gradually round to become antero-lateral, at the same time diverging ra- pidly to form a smooth slope on the side of each condyle. Towards the posterior part of each of these sloping surfaces, there is an irregular prominence called the tuberosity, {ox the attach- NORMAL ANATOMY OF THE KNEE-JOINT. 45 merit of the lateral ligaments ; below which, on the outer condyle, there is a pit for the origin of the popliteus tendon, and a fossa leading upwards and backwards from it which lodges the tendon when the joint is fully flexed. In the lateral aspect of the bone we best see the peculiar curvature of the articulating surface. In two adult, but rather small, specimens before me the inferior part of the outer condyle is a segment of a circle of fourteen lines radius, while the radius of the posterior portion is only seven lines; similar measurements of the curves of the internal condyle give radii of six and twelve lines respectively : the centre of the smaller circle coincides precisely with the point of attachment of the lateral ligament on each side, and the advantages of this arrangement will appear when we come to consider the functions of the joint. The smooth articulating surface of the trochlea and condyles is, in the recent state, covered with cartilage. Above this surface and in the fossa between the con- dyles are numerous foramina for the transmis- sion of the nutrient vessels of the bone, the internal structure of which is here made up of minute cancelli. The lower extremity of the os femoris is cartilaginous at birth, becomes ossified from a separate centre, and long conti- nues to form an epiphysis ; but it is ultimately joined to the shaft by perfect bony union. The thigh-bone exposes the largest extent of surface in the knee-joint ; that of the tibia is the next in size. Its superior extremity is ex- panded into the same kind of cancellated struc- ture as the os femoris possesses at its lower part ; and the width from side to side equals that of the condyles, which rest upon its upper surface. That surface is nearly horizontal, in the erect position of the body ; it is irregularly oval, the long axis passing from side to side, and is marked in the centre by a rough promi- nence or spine, in front of which is a depression, and at the back part a notch. On each side of these inequalities there is a smooth articular surface; the inner one the larger, especially from before backwards, and slightly concave ; while the outer one is flat round the margin and raised at the inner side by the base of the spine. Viewing the bone in its anterior aspect we observe that below the articular surface it slopes downwards and forwards to the tubercle ■which stands out at the upper part of the shin or crest of the tibia; this tubercle gives insertion at its lower part to the strong ligament of the patella, a bursa being interposed between that ligament and its upper smooth portion. Nu- merous foramina are to be observed round the head of the bone for the purposes of its nutri- tion. Below the tubercle a section of the tibia shows it much reduced in size and somewhat triangular in shape ; the outer side forming, in conjunction with the fibula, a large fossa for the tibialis amicus and other muscles; and the inner, facing also anteriorly, being a portion of that surface of bone which is covered only by skin and periosteum; except at its upper pari, where three fiat tendons pass upon it to be inserted by the side of the tubercle in the follow- ing order; that- of the semitendinosus lowest, the gracilis next above, and the sartorius the highest up and most anteriorly. The posterior surface of the tibia at the supposed place of section has advanced considerably forwards, so as to leave a hollow for the popliteus muscle which lies obliquely on this part of the bone. A few lines below the great articulating surface on the head of the tibia there are two things to be noticed on its posterior aspect ; at the outer side a small articular surface for the head of the fibula, and at the inner side a shallow pit where the tendon of the semimembranosus is inserted. The patella is a flat disk of bone placed in front of the knee-joint; it equals in width the trochlea of the os femoris to which it is applied, the posterior surface being for that purpose covered with cartilage and divided into two slight cavities by a prominent vertical line ; the articular surface is oval from side to side and does not reach to the lower edge of the bone. Anteriorly, the patella is convex, and its hori- zontal slightly exceeds its vertical measure- ment, particularly in the female ; into its upper edge are inserted the united tendons of the rectus, cruralis, and vasti muscles ; into its lower edge the strong ligamentum patella? which joins it to the tubercle of the tibia ; it is covered only by skin, fascia, and some ten- dinous fibres, to which latter may be attributed the appearance of vertical stria; observable on the bone. (b.) Curtilages, ligaments, t)-c. — The whole of tlie bony surfaces which come into contact with each other or with the interarticular carti- lages during the movements of the knee-joint are covered with " cartilages of incrustation " (see Articulation); and the extent of these on the condyles and trochlea of the os femoris, on the head of the tibia and the posterior sur- face of the patella, is well marked even in the dry bones by their smooth and compact ap- pearance and the total absence of foramina on the parts so covered. Besides these pure car- tilages there are two fibro-cartilages of a semi- lunar form lying upon the head of the tibia, which serve to deepen the articulating surfaces for the reception of the condyles. These seini- Innar cartilages, (cartilagin.es falcatte, s. lu- natic) as they are named, are thickest at their convex edges which are attached rather loosely to the circumference of the head of the tibia ; the concave edges are thin and sharp, and lie unattached between the condyles and the tibia. The two semilunar cartilages differ slightly from each other in the two following points ; the inner one is falciform, decreasing in breadth from behind forwards ; the greatest width being at the inner and back part, five-eighths of an inch, whilst in front it is hardly more than one quarter of an inch ; the anterior and posterior cornua are separated to the distance of an inch, whilst those of the outer semilunar cartilage approach to within three-eighths of an inch of each other; and, besides that the ring is thus more nearly completed, the breadth of the outer one is more uniform, being about three-eighths of an inch throughout the greater part. The thickness of either of them barely exceeds one- 46 NORMAL ANATOMY OF THE KNEE-JOINT. sixth of an inch, at the outer margin or thickest part. They are both composed of concentric fibres, the extremities of which are fixed to the central parts of the head of tiie tibia, before and behind the crucial ligaments, with whose fibres they intermingle ; the anterior extremities are usually joined together by a transverse liga- ment, but this is sometimes wanting. The ligament um patella, of vast importance in the actions of the knee-joint, is yet the most distant from its articular surfaces ; it extends, broad and flat, from the lower somewhat point- ed portion of the patella to the inferior part of the tubercle of the tibia, being in the adult about two inches in length. It forms a strong inelastic but inflexible bond of union of the patella with the tibia, and may with propriety be looked upon as a continuation of the ex- tensor tendons which are inserted into the upper and lateral margins of the former bone; some fibres indeed pass over Us anterior sur- face, but it is only through this bone and its ligament that the extensor muscles can act upon the leg. The patella is thus seen to be placed in a situation analogous to that of the sesamoid bones, in the tendons which play over bony surfaces, in the hands and feet. The ligament of the patella is covered anteriorly by dense integument, and the fascia of the leg : posteriorly a cushion of fat is interposed be- tween it and the joint at the upper part, while below it is separated from the bone by a bursa, whose situation was pointed out in the descrip- tion of the tibia. (See fig. Ill, b, vol. i. p. 252.) More closely applied to the joint are the lateral ligaments, the posterior and the crucial liga* ments; and portions of the synovial capsule which are described by some anatomists as alar and mucous ligaments. The lateral ligaments have a vertical direction at each side of the knee, and are placed nearer to the posterior than the ante- rior boundary of the joint ; the upper attach- ment is in fact to the tuberosity at the centre of the smaller curve which the articular sur- faces of the condyles form at their back part. The internal lateral ligament descends from the tuberosity of the internal condyle of the os femoris to beneath the head of the tibia ; it is nearly three inches in length, of a flattened form, narrow at its commencement, but en- larging considerably opposite the joint, to the synovial membrane of which as well as to the internal semilunar cartilage it adheres; infe- riorly it again contracts in width. Its upper attachment is covered by the fascia lata ; below, it is inserted into the shaft of the tibia just beneath the head of the bone, and anterior to its inner angle ; and the tendons of the sarto- rius, gracilis, and semitendinosus cross over it. The external lateral ligament (lig. laterale externum ) arises from the tuberosity on the external condyle of the femur, and descends, inclining backwards, partly covered by the tendon of the biceps, to be inserted with it into the head of the fibula ; the attachment of its upper extremity is immediately above the origin of the popliteus tendon, which it crosses in its descent, so that this tendon enveloped by its synovial sheath is situated between the liga- ment and the joint. The deviation of this ligament from the perpendicular direction is perceived most distinctly in the state of exten- sion ; when the joint is flexed, the upper at- tachment of the ligament is brought more into the perpendicular over its fibular attachment, the ligament is relaxed and assumes the per- pendicular direction ; hence, in the flexed con- dition of the joint, the external condyle of the femur, or the tibia on it, admits of a more free motion. This ligament is contrasted by its less length and more rounded form with the internal lateral, and is composed like it of shining tendinous fibres ; a still shorter set of fibres sometimes passes more posteriorly from the condyle to the head of the fibula, or from the sheath of the popliteus tendon, and has been called the short external lateral liga- ment. The posterior ligament (lig- posticum Win- slow/i) is a portion of the tendon of the semi- membranosus muscle which is given off near its insertion at the posterior and inner margin of the head of the tibia ; the portion under con- sideration forms a flat and dense fascia which passes upwards and outwards to the external condyle, where it becomes adherent to the sy- novial capsule and minglingwith the tendinous origin of the outer head of the gastrocnemius : posterior to it lie the popliteal vessels, and in front of it there is a quantity of firm granulated fat, into which some of its fibres penetrate. When the posterior ligament and the fat just spoken of are removed, and the joint is ex- tended, the two crucial ligaments (ligamenta cruciata* ) are brought into view ; they may be seen on the anterior aspect by dissecting down the patella from the fore part of the joint, and putting it in a state of flexion ; in the former view, the posterior crucial ligament is best seen ; in the latter, the anterior : the upper extremities of both are fixed in the fossa be- tween the condyles of the os femoris; their lower extremities are attached to the head of the tibia between the two articular surfaces. The anterior crucial ligament passes from the inner and back part of the outer condyle downwards and forwards to the depression in frontof the spine of the tibia, where some portion becomes continuous with the anterior extre- mity of the internal semilunar cartilage. The posterior extends from the fore and outer part of the internal condyle downwards and back- wards to the notch at the posterior margin of the head of the tibia, where it becomes like- wise attached to the posterior extremity of the external semilunar cartilage. The crucial liga- ments thus derive their name from decussating one another like the strokes of the letter X ; the crossing is, however, considerably above their centre : the anterior passes to the outer side of the posterior. The synovial capsule^ entirely surrounds the * [It is useful to bear in mind that these ligaments are called anterior and posterior with reference to their insertions into the tibia, the one in front of, the other behind, the spine of that bone. — Ed.~\ t [Weber recommends as a good way of demon- strating the fall extent and connexions of the NORMAL ANATOMY OF THE KNEE-JOINT. 47 joint, and there are good reasons for affirming that it is continued in a highly attenuated state over all the interarticular and incrusting carti- lages, giving them their smooth and secreting surfaces. (See Articulation.) The remain- der of its extent may be traced in the following manner : from the upper edge of the patella it ascends behind the common extensor tendon, and is loosely reflected upon the thigh-bone two or three inches above the trochlea in the extended position of the limb; from each side of the patella it passes backwards in a broad sheet, whose lower margin is attached to the edge of the semilunar cartilage, and thence goes to the tibia, while above it is loosely reflected on to the condyles of the os femoris, at the distance of nearly an inch from their cartila- ginous surfaces ; from the back part of the con- dyles these two lateral portions pass into the fossa and join to cover the anterior surface of the crucial ligaments. From the lower edge of the patella the synovial membrane descends to cover the fatty body which is placed in that part of the joint, and it accompanies a small prolongation from that body which frequently passes across the joint to the lowest portion of the trochlea of the os femoris, forming what has been named the mucous ligament; this structure however is not always present. There is some discrepancy in the descrip- tions of different anatomists as to the alar ligaments, which are described as folds at the sides of the patella, and it seems altogether unnecessary to distinguish these lateral portions by name from the other parts of the synovial capsule. They are simply folds of the syno- vial membrane projecting into the articular cavity, and obviously destined to increase the extent of synovial surface for a greater amount of secretion. This membrane has a dense cel- lular tissue on its outer surface, by which it is connected firmly to the posterior surface of the extensor tendons and fascia lata. It possesses some degree of elasticity, but its chief power of accommodation to the motions of the joint is derived from its lax connection with sur- rounding parts. (c.) The mechanical functions of this joint, or the movements of which it is capable within certain limits, and the resistance which it op- poses to motion beyond those limits, are plainly deducible from a knowledge of the parts of which it is composed. To say that the knee is a hinge-joint with a slight arthrodial or sliding motion, gives a very faint idea of the complex problem which has been solved in its construc- tion : to procure firmness without the aid of bony processes interlocking with one another (as in the ankle and elbow); and yet to com- bine free power of flexion with impossibility of over-extension ; to oppose large surfaces of bone to one another, so as to ensure stability in the erect posture, without making the joint synovial membrane of the knee-joint, to distend it by injecting some coagulating fluid, as size, through a hole bored through the centre of the patella. — Mechanik der menschlichen Gehwerkzeuge, p. 195. unsightly by its size, are some of the indica- tions most admirably fulfilled. In the straight or extended position of the leg, the joint is firmly locked so as to admit of no lateral or rotatory motion ; the pointing of the toes in and out in this position is effected by moving the hip-joint. The portions of the condyles forming the segments of large circles are, during complete extension, applied to the tibia and form a broad surface of support ; the patella is drawn to the upper or deepest part of the trochlea; and the lateral and crucial ligaments, being attached nearer to the poste- rior than to the anterior surface of the thigh- bone, are together with the posterior ligament put upon the stretch. If the curve of the arti- cular surfaces of the condyles had been uni- form, with the lateral and crucial ligaments fixed to the centre of that curve, the posterior ligament only could have acted to restrain the leg from being flexed forwards upon the thigh, and it would be quite insufficient for that pur- pose: whereas, by the present arrangement, the centre of motion being placed nearer to the posterior surface of the condyles, the lateral and crucial ligaments cooperate with the pos- terior in opposing a strong check to over- extension. In flexion the joint admits of mo- tion to the extent of about 140 degrees, when it is arrested by the crucial ligaments. During this movement the condyles offer a diminishing surface to the head of the tibia, and the semi- lunar cartilages have their ends brought closer together, so as to deepen the cavities for their reception: in extension, the reverse takes place, the semilunar cartilages are pressed out from betwixt the bones to their greatest extent. The adjustment of these fibro-cartilages during flexion is effected partly by their elastic power of resuming their shape when pressure is re- moved, and in some degree by the atmospheric pressure urging these moveable parts between the ends of the bones, to prevent the formation of a vacuity in the joint. During the motions of the knee, the patella undergoes important changes of relative position both with regard to the os femoris and the tibia ; it plays over the whole extent of the trochlea, being drawn in extreme extension half its diameter above that pulley, whilst in extreme flexion it has moved through a quarter of a circle and is found at right angles with the os femoris, forming in that situation the surface which comes to the ground in kneeling, and so de- fends the joint from injury. In relation to the tibia, the patella always keeps the same dis- tance from the tubercle, being joined thereto by the ligamentum patella; but as the con- dyles recede during flexion, the patella follows them ; so that a line passing over its anterior surface and that of the tubercle will, if pro- longed, reach the point of the great toe, though a similar line in the extended position will fall through the ankle-joint. The necessity for this advancing and receding movement of the pa- tella explains why it is a separate bone instead of forming a process of the tibia, as in the elbow-joint the olecranon forms a part of the ulna; and may also suggest the use of the 46 ABNORMAL CONDITIONS OF THE KNEE-JOINT. bursa behind its ligament. It has been said above that besides its ginglymoid motion, the knee-joint has a slight arthrodial motion in the bent position : this is strictly a rotation of the tibia on its axis, and the effect is to point the toes more or less to the outer side, rotation in- wardly to any great extent being prevented by the crucial ligaments. During this movement of rotation, the inner articulating surface on the head of the tibia advances forwards, while at the same time the outer one recedes ; the lateral ligaments allow of this motion, in con- sequence of their inferior attachments being a good deal below the margin of the joint ; and the crucial ligaments permit the successive, though not the simultaneous, advance or re- cession of the cavities on the head of the tibia. In all positions of die joint the arrangement is such that the attempt to thrust forwards the whole head of the tibia is resisted by the ante- rior crucial ligament, whilst the posterior pre- vents it from being driven backward.* The * [The following experiments, which may easily be tried, illustrate the respective offices of the se- veral ligaments. If the external fibrous investment of the joint be completely removed, taking care that the lateral and crucial ligaments shall be free from injury, the motions of the joint will be in no degree af- fected; but if the opposite experiment be tried, and the lateral and crucial ligaments be cut, leav- ing the external fibrous investment uninjured, excepting a small hole made for getting at the liga- ments, it will be found that the integrity of the joint is completely destroyed, the bones are but loosely connected to each other, their apposition is destroyed, and they move about indifferently in every direction. A°ain, if after dissecting off the external fibrous investment both crucial ligaments be cut, leaving the lateral ligaments as the only bonds of con- nection between the two bones, it is found that during extension, the fixedness of the joint is un- impaired, but if flexion be made gradually, the bones becomes less in apposition and more move- able, and in the completely bent state of the limb, they become quite loosely connected and may rea- dily be moved from side to side, and the only limit to flexion is from the tibia coming against the femur. If the lateral ligaments be cut, leaving the cru- cial uninjured, the bones remain firmly connected when the joint is in the state of complete flexion, and the crucial ligaments still, as in the natural state, oppose any further flexion. In the gradual diminution of the flexion, the junction of the bones becomes less complete, and when the extension has been carried to its full extent, the bones may be separated from each other, and admit of lateral motion ; and if the joint be held up so as to allow the tibia to hang from it, the foot will become everted by its own weight, and the two crucial liga- ments, instead of their crossed and oblique position, will assume a parallel and vertical direction. These expeiiments are described by Weber, but there are few anatomists in this country, formany years back, who have not frequently tried them. The office of the semilunar cartilages is three- fold : 1. filling up the empty space which the arti- cular surfaces leave around their point of contact, they distribute the pressure over a greater surface ; 2. they serve to distribute the tension of the liga- ments in the movements of the joint more uni- formly, and thereby to oppose any jarring of the bones against each other; and, thirdly, they deaden the vibrations which in the various movements of mucous ligament and fatty body of the joint change their situation in some degree during its motions and may serve to fill spaces which which would otherwise be left vacant: the idea that they are peculiarly concerned in secreting the synovia has been satisfactorily refuted un- der " Articulation." The bursas in the neighbourhood of the knee- joint are numerous and not unimportant, from the circumstance that some of them often open into the joint itself. In the layers of fascia anterior to the patella, one or more exist, im- perfectly formed and very liable to inflame and suppurate. The situations in which the more perfect specimens are found are as follow, viz. behind the ligament of the patella; between the cruralis and fore-part of the os femoris; beneath the internal lateral ligament ; at the insertion of the semitendinosus, gracilis, and sartorius ; underneath each head of the gemel- lus; and around the tendons of the semi-mem- branosus and popliteus respectively; the last- named bursa is continued down some distance between the popliteus and the tibia, and it often communicates below with the superior tibio-fibular articulation, as well as with the knee-joint above. This joint is supplied with blood from the popliteal artery by five different branches, viz. two superior articular, which wind round the lower part of the os femoris; one mid- dle articular which passes through the posterior ligament to the central parts of the joint; and two inferior articular, which take their course round the head of the tibia, and anastomose freely with each other, and with the two upper; the returning veins go to the popliteal. The comparative anatomy of the knee-joint gives for the most part the same essential struc- ture as we have described in man, though va- riously modified. In most animals, when in a standing pos- ture, the knee maintains habitually a state of flexion, and this arrangement conduces much to fleetness and agility of motion. In the ele- phant, however, the bones of the hind leg form an upright pillar of support, and the knee is ex- tended as in the human subject. The elephant also resembles man in the circumstance of the knee being brought to the ground in kneeling ; whereas, in most genera, the true knee is placed much nearer to the body of the animal. ( Alfred Higginson.) KNEE-JOINT, ABNORMAL CONDITIONS of. — The abnormal conditions of the knee- joint may be arranged under those which result from disease and accident. The deviations oc- casionally met with as the consequence of con- genital malformation are fortunately rare. Disease. — The abnormal appearances in the knee-joint resulting from disease are those which spring from some specific irritation, such as struma, gout, rheumatism, syphilis, or malig- nant disease, or from direct violence. Most of these irritations affect all the structures of the the limbs, especially in standing, walking, or run- ning, are propagated along the bones. — VideWeber, Mechanik, &c. p. 193. Ed.J ABNORMAL CONDITIONS OF THE KNEE-JOINT. 49 articulation, and are associated with some form of inflammatory action, either acute or chronic. Simple acute inflammation of the knee-joint, or acute arthritis genu, may be the result of a contusion, a sprain, or a wound; or there may be no assignable cause. In the latter case it may have been preceded by rheumatic fever, erysipelas, or diffuse inflammation, which had previously engaged distant organs and other structures. The symptoms are usually strongly marked. Considerable pain, which comes on very suddenly, is felt in the knee ; the leg in most cases soon becomes flexed and reposes on its outside ; and the patient cannot bear the slightest movement to be communicated to the knee-joint. There is considerable increase of temperature in the skin over the affected arti- culation, together with tension of it from in- ordinate effusion of synovial fluid into the joint. Although the usual phenomena of red- ness as an accompaniment of phlogosis may not be observed externally, there can be but little doubt that the capillary vessels pervading the different structures of the interior of the joint are in a state of hyperemia. The patient has but little sleep, and this is frequently inter- rupted by unpleasant dreams and1 painful spas- modic startings of the affected extremity. (Ede- ma of the lower part of the limb now occurs, and in severe cases sometimes extends up the whole leg and thigh, even to the groin. The sympathetic fever may run so high, and the swelling and other local symptoms proceed so rapidly as to deprive the surgeon of any oppor- tunity of proposing or performing amputation to save the patient's life. The fever in well-marked cases of acute ar- thritis genu is sometimes symptomatic of the local disease ; sometimes it has preceded the local affection, and has been ushered in by a very severe rigour followed by profuse perspi- ration. Like the disease, the fever will vary in its character. Erysipelas, rheumatic fever, and diffuse inflammation, as has been mentioned, will each occasionally. present in their progress examples of the disease of the knee-joint now under consideration, and the accompanying fever will bear the character of the disease with which the inflammatory affection of the joint is associated. The local phenomena presented by an acute arthritis genu do not, however, vary so much, except in degree and severity. Acute arthritis genu may supervene as a consequence of wounds. Sometimes these wounds are very small. We have known one case in which a puncture made with a fine sew- ing needle, which was accidentally driven with force into the knee-joint, at the inside of the patella, was the cause of a fatal inflammation of the joint: the point of the needle probably penetrated the bone. The - patient, a young woman, was under the care of Mr. Colles many years ago, in Steevens's Hospital. In some instances we have known inflammation of the synovial membrane of the knee to have been the result of a wound of the subcrureeal bursa. A countryman had received a trans- verse wound by the cut of a broadsword just above the patella, and fatal inflammation VOL. Ill, extended from this bursa, which was opened, to the synovial sac of the knee-joint. Acute inflammation of the knee-joint has been the result of surgical operations, such, for instance, as that occasionally undertaken for the extraction of moveable bodies which form in the joint and interfere with the due perform- ance of its functions. This operation, we be- lieve, is now very seldom recommended. We have heard and read of many cases in which it has been performed with complete success ; on the other hand, we have reason to know that many have died of the inflammation con- sequent on it, and that others have narrowly escaped with their lives, having ever after- wards an anchylosed knee-joint. It is rather singular, but we believe it to be true, that the inflammation resulting from a valvular opening having been made in the knee-joint has not come on for six or seven days after the moveable cartilage has been extracted ; but in- flammation being once set up, its course is ge- nerally acute and dangerous. We consider the observations and experience of Mr. Guthrie on the subject of wounds of the knee-joint to be too valuable to be here 'passed over. " Wounds of the knee-joint," he remarks, " however simple, should always be considered of a dangerous nature, infinitely more so than of the shoulder, the elbow, or the ankle." " I could," he adds, " relate an infi- nite number of cases on these points, termi- nating fatally or in amputation, where the in- jury was severe, or apparently at first but slight, and but few cases where the capsular ligament was opened into by a musket-ball, where the patient has preserved the use of the limb. In every case where the wound was known to be serious, I have invariably been disappointed in the hope of saving the limb." He then adduces the following case as an instance of apparent simple injury that frequently occurs. "This case," he adds, " will shew the danger of all these wounds, and the very great care and at- tention that are necessary for their cure. Co- lonel Donellan, of the forty-eighth regiment, was wounded at the battle of Talavera in the knee-joint by a musket-ball, which gave him so little uneasiness, that when a roller had been put on his leg, with some simple dressing, he could scarcely be persuaded to proceed to the rear. At a little distance from the fire of the enemy we talked over the affairs of the mo- ment, when, tossing his leg about on the saddle, he declared he felt no inconvenience from the wound, and would go back, as he saw his corps was very much exposed. I explained to him the dangerous nature of the wounds of the knee-joint, and after he had staid with me a couple of hours, I persuaded him to go into the town. This injury, although at first to all appearance so trifling, and under the best sur- gical care, caused the death of this officer in a very short time, and proceeded so rapidly as to prevent any relief at last being obtained by amputation." Some years ago MM. Larrey and Garriques, in France, recommended the amputation of the leg immediately below the tuberosity of the e." . 'r'*>-'V 50 ABNORMAL CONDITIONS OF THE KNEE-JOINT. head of the tibia, instead of amputation of the thigh, where it was found impracticable to re- move the leg at the ordinary place of election — four inches below the knee-joint. But Larrey made an addition to this operation, namely, the extraction of the head of the fibula. He says, " when the fibula is left short, which is usually the case, it is to be extirpated as useless, and troublesome in the application of the artificial leg, and the skin is to be left as long as pos- sible, to cover the stump." Mr. Guthrie gives Larrey much praise for drawing the attention of the profession to this " great improve- ment," and adds the weight of his high autho- rity by recommending the removal of the head of the fibula. In alluding to this subject we may appear to be departing from the proper object of this article, — the abnormal appear- ances presented by the knee-joint ; but having known some melancholy examples of acute in- flammation of the knee-joint to follow the operation here recommended, we take this op- portunity of warning the profession against it. Mr. Guthrie himself says, '' it is possible, how- ever, that a case may occur (perhaps one in a thousand) in which the head of the fibula com- municates with the general cavity of the knee- joint ; in such a case amputation must be done above the knee." Independently of this com- munication between these two contiguous joints which Mr. Guthrie considers so rare, we have found, by repeated anatomical examinations of the relation existing between the synovial sacs of the knee-joint and that of the superior tibio- fibular articulation, that these two sacs are so close as to have but a thin transparent wall separating them. We consider it, not abso- lutely, but very nearly impracticable to cut out the head of the fibula in the living subject without making a communication with the pos- terior and back part of the synovial membrane of the knee-joint, so delicate is the thin trans- parent membrane which is interposed between the synovial sac of the knee-joint and the little synovial sac which partially envelopes the head of the fibula. Besides, in the living subject it must always prove to be a difficult matter to remove the head of the fibula without in- terfering with the tendon of the popliteus muscle, as we know the tendon to be enve- loped by a synovial production sent down along it, like that which in the shoulder-joint invests the tendon of the biceps. This synovial production is not confined to the tendon of the popliteus, but is also reflected over the groove formed for the reception of this tendon, and must be in danger of being opened in every operation which we can devise for the removal of the head of the fibula ; and conse- quently, although there may be many cas'es in which it may be advisable to amputate the leg a little below the tubercle of the tibia, in no case, in our opinion, should the surgeon attempt to extirpate the head of the fibula. The idea that this small portion of bone, when left, is " useless and troublesome in the application of the artificial leg," may be true, but it is not the less true that in the majority of cases acute arthritis of the knee-joint will be very likely to succeed to this operation ; and we feel satisfied that, as soon as these anatomical relations be- tween the synovial sac of the knee-joint and that of the superior tibio-fibular articulation are reflected on, this modern proposal will be re- jected. Among the causes of acute arthritis genu, exposure to cold is very frequently referred to by the patient, and apparently with reason. The knee-joints being less covered by muscular parts than any other of the large articulations, are more subjected to the influences of cold, and on this account are perhaps more generally affected by acute and chronic inflammation than other articulations. It must be admitted, how- ever, that we have met with cases of acute inflammation of the knee-joint for the origin of which we could assign no cause, having come on, as we are accustomed to say, spontaneously. Acute arthritis genu sometimes arises as a symptom in the course of different diseases. Thus in diffuse inflammation and in phlebitis it is quite usual to find the joints visited by most severe attacks of inflammation. We have seen examples of acute arthritis supervening suddenly in the course of a severe attack of erysipelas ;* and in rheumatic fever and puer- peral rheumatism we can see little else than an inflammation of the joints, the nature of the in- flammation in these cases, however, being very different. Although we have here spoken of three different forms of disease, diffuse inflammation, phlebitis, and puerperal rheumatism, we have ourselves long entertained the opinion expressed by Mr. Arnott, Velpeau, Dance, Cruveilhier, our friend Dr. Beatty, and others,t that the three forms of disease in which the acute arthri- tis we are here treating of occurs, are the same, and that the arthritis in all three is similar, and proceeds from the same common cause, viz. phlebitis and its consequences. The peculiar form of acute arthritis here adverted to has in almost all cases been found to have been preceded by phlebitis. This may have come on spontaneously, or in consequence of a wound, or of the vessel having been in- cluded in a ligature. The form of acute arthri- tis which has been called puerperal rheumatism has also been found, in many cases, coincident with or preceded by phlebitis of the veins of the. uterine system, or of some other veins.J We have seen many cases which we consi- dered to be examples of diffuse inflammation in very young subjects, engaging the periosteum of the femur and tibia, and terminating in the complete destruction of the bone, in the short space of three days. Sometimes the periosteum of the femur, for example, formed a complete cylindrical sac containing the detached shaft of the bone. The symptoms of acute arthritis which occur in the course of a case of diffuse inflammation * See Dublin Journ. vol. xvii. p. 336, and in this article p. 55. t See Dublin Journ., and Mr. Arnott's valuable observations in the Med. Chir. Trans. t See Dance's, Beatty's, and Mr. Harrison's cases, Dublin Journ. ABNORMAL CONDITIONS OF THE KNEE-JOINT. 51 are usually ushered in by a severe rigor followed by perspiration. The patient is remarkably restless and depressed in mind. If the phle- bitis be external, as in that occasionally succeed- ing to venesection, which has preceded the acute arthritis, the inflammation along the course of the wounded vein will be observed for several days before the attack of arthritis shall come on. Whatever may have been the cause of the inflammation of the joints, the disease does not, as in rheumatic fever, pass successively from joint to joint, completely leaving one joint to visit another. Although varieties may of course be noticed in the local symptoms which this dangerous disease presents, it very con- stantly happens that a joint once visited by it seldom or never completely recovers its effects. Usually many joints are successively or simul- taneously affected, and we very generally dis- cover that one or more of the internal organs is also implicated. Whatever joint is attacked in the course of the disease, it presents the ordinary characters of an acute arthritis. The integu- ments covering the articulation sometimes wear a pink hue, and always have an elevated temperature. The affected limb is powerless. The patient complains of very considerable pain, more particularly, as it appears to us, in puerperal arthritis than in the affections of the joints which attend on the ordinary forms of diffuse inflammation. The swelling, when first examined, is soft and fluctuating. After a time the effusion of synovial fluid and pus increases, giving rise to the distension of the synovial sac. If at this advanced period we carefully examine the parts immediately surrounding the inflamed joint, we can discover that the integuments and subjacent parts feel somewhat indurated and cedematous, reminding us of the hardened basis which we find circumscribing; an abscess. It is probable that this condition of the surrounding parts arises from diffuse inflammation and the infiltration of its digested purulent matter. The arthritis in these cases is seldom the cause of death ; either some internal vital organ be- comes violently inflamed by which the death of the patient is accelerated, or abscesses form in the subcutaneous or intermuscular cellular membrane in various parts of the body, which, although more slowly, as certainly lead to a • fatal issue, for when the evacuation of the pus takes place, the quantity of matter which is dis- charged and continues to be secreted is so excessive as greatly to reduce the patient's strength, and the exhaustion from this source and from the diarrhoea which usually attends are sufficient to prostrate the powers of the youngest and strongest individuals. Most writers indeed have observed that in the majority of cases the subjects of this disease had been in a bad state of health at the time the exciting cause came into action, — a cachectic condition produced by over-exertion of mind or body, and that from these circumstances the susceptibility or pre- disposition^ to this disease most probably arose.* These observations are, we believe, fully borne out by experience, and it may not * Sec Dr. Beatty, Dublin Journal, &c. perhaps be uninteresting to adduce some remarks published by an author nearly forty years ago, which prove that he was practically acquainted with the complaint denominated by the moderns puerperal rheumatism or puerperal arthritis, and that he took a similar view of the predisposing causes of this disease. Mr. Russell in his work on the knee-joint, in treat- ing of acute cases of what he calls white swelling, says : " in those cases which proceed most rapidly, the disease will reach its acme" in the course of a few weeks." The very rapid and acute cases seem to be connected with some state of great relaxation and weakness. He adds, " the most remarkable instances of this variety which have fallen under my observation, have occurred in the cases of women in child- bed." In the Richmond Hospital (Dublin) we had had many cases of this form of acute arthritis, from which we select the two following as serving to illustrate some of the foregoing observations. Both these individuals were in a delicate state of health when the disease attacked them, and the swelling of the knee-joints and other articulations formed a very small part of their diseases. Andrew Turner, 28 years of age, was ad- mitted into the Richmond Hospital on the 7th of May, 1836. He had much abused his health and constitution. Five days after having been bled in the right arm to relieve the con- sequences of a severe beating, a superficial dif- fused redness appeared on the skin of the fore- arm ; the venesection wound was swelled and inflamed ; a severe rigor occurred, followed by profuse perspiration and fever ; erratic erysipelas characterized by a faint red mottling of the skin in patches appeared ; a blush of inflammation in the form of a patch showed itself on the shoulder, but not continuous with that on the fore-arm ; a pink patch next appeared over the right knee, then on the left arm, and afterwards on the left lower extremity ; and while this dis- ease invaded the body part after part, those once occupied remained engaged as before. On the 15th May, the ninth day from his ad- mission, there was observed effusion into the right knee and into the bursa which is subjacent to the cruroeus muscle. Although considerable, this effusion escaped the patient's attention ; he complained of no pain, and to our enquiries always replied that he was going on " gaily." On the 18th the left knee-joint was tumefied, but not to the same extent as the right. He died on the 26th, his death being preceded by the ordinary symptoms of pneumonia, pleu- ritis, &c. On the post-mortem examination the anatomical appearances of pneumonia, pleuritis, and bronchitis were seen ; there was also effu- sion into the cavities of the pericardium and peritoneum. In the right knee-joint and sub- cutaneous bursa, which freely communicated with it, there was a large quantity of yellowish green fluid, which seemed to be formed of the mixture of purulent matter with the synovial fluid : flakes of lymph floated in it. The syno- vial lining of the subcruroeus bursa was very red, as was also that of the joint itself. The synovial membrane was elevated above the level £ 2 32 ABNORMAL CONDITIONS OF THE KNEE-JOINT. of the cartilages by subsynovial infiltration. The ligamentum mucosum, as it is called, was very vascular. The capillary system of the semilunar cartilages was. injected with minute red vessels. The left knee-joint, which had been but lately attacked, contained an inordinate quantity of synovial fluid, of a greenish-yellow hue, and of a thicker consistence and a deeper colour than natural. The synovial membrane was pale, and there was no infiltration in its subsynovial structure. The vein in which venesection had been performed was contracted in the neighbourhood of the wound, and lymph adhered to its lining membrane. Above the right elbow-joint and internal to the course of the vein, there was a small collection of matter between the skin and fascia. Susan Brett, set. 24, was brought into the Richmond hospital on 26th February in great distress and pain. On the 14th February she was suddenly seized with convulsions, being seven months pregnant. She was bled in the right arm and her head shaved. Two days after the operation the arm became very painful and swollen. The pain increased, and on the 21st labour-pains came on and continued during the day. In the evening she was again attacked with convulsions, and blood was drawn from the left arm. The child (her first) was not expelled until early the next morn- ing ; the evening of the same day she had a severe rigour, which lasted half an hour, and was succeeded by profuse perspiration; this soon went off, but she remained cold and chilly for the remainder of the night. On the following morning (23d) she was seized with what she called severe rheumatic pains in her hips and right shoulder, which left her " all sore" and completely powerless. On the 24th the pain in the right shoulder-joint became most intense, and a severe stitch seized her in the same side, which prevented her drawing her breath. The pain in the arm also was now very severe, extending upwards from where ve- nesection was. originally performed. The wound was found not yet healed. When brought to the hospital, the fifth day from her lying-in, she was in great distress and pain. Her pulse was 140, with some fulness, but still compressible. She preferred lying on her right side bent forwards, with her knees drawn up. Her respirations were fifty-two in a minute, and greatly oppressed. At each effort of inspiration the aire nasi were much dilated. Her countenance was anxious, and there was a bright circumscribed flush on each malar emi- nence. For the last week she has raved con- stantly at night, and has been more ill at cer- tain hours of the day, very early in the morn- ing, and again at half-past five, p.m. At the latter hour she was generally found perspiring copiously. Her bowels were too free. She complained of pain chiefly in the right shoulder and the lower part of the back ; also in both her knees and metacarpal joint of the index- finger of the left hand. She also complained of her left hip. The right arm was swollen but not discoloured, edematous, and pitting on pressure. The original wound made for vene- section was gaping, with unhealthy everted edges ; no matter exuded from it. She kept the arm in the flexed position ; to herself it felt quite powerless, and when the least movement was communicated to it, she suffered great tor- ,. ment. There was a hard line up the arm cor- responding to the course of the basilic vein, and when even the slightest pressure was made in this line, she suffered pain. Immediately above the elbow-joint the skin was hard ; the subcutaneous cellular structure seemed more or less oadematous as if infiltrated with fluid ; the skin and subjacent parts seemed to be matted together and somewhat cedematous, and pres- sure here also gave the patient much uneasiness. There was a suffused pink blush on the skin covering the metacarpal joint of the index finger ; the joint was much swollen, and she complained of much pain in it. Her princi- pal suffering was from dyspnoea. An exami- nation of the chest by auscultation and percus- sion furnished all (he evidence of extreme bronchitis in both lungs, pleuritis with inci- pient pneumonia: it was also inferred that effusion had taken place into the right side of the thorax. On the 28th February some of those deceit- ful appearances of amendment not unusual in the course of acute disease discovered them- selves. It was reported that she had passed a better night ; her pulse fell to 128; her respi- ration was reduced to forty in the minute; but in the evening a pain, which she referred to the situation of the diaphragm, came on with great severity. Her cough was troublesome and in paroxysms ; she expressed great anxiety about herself, inquiring whether there were any hopes for her, and complained of pain in her left elbow, where, however, there was no swelling. The original wound made in the right arm for the first venesection was still open, but there was no inflammation about it. The wounds made in the left arm for two sub- sequent bleedings healed perfectly. She now had pain in all her joints, particularly in the metacarpal joint of the index finger of the left hand. The shoulder-joints were swelled, and she could not bear the slightest movement of them. Her knees were very painful, chiefly the left, which was greatly swollen, but its in- teguments were not discoloured. Diarrhoea was very troublesome. On the 2d of March profuse perspiration broke out over the whole body, and oedema of the feet came on. The next morning her pulse was 128 ; respiration was jerking and very much hurried ; and her countenance be- trayed great internal distress. She had raved all night. There was complete orthopnoea, and the swelling of the knees increased. She died at four o'clock. On an examination of the body twenty-two hours after death, the shoulder-joints were found to contain a viscid greenish imperfectly formed pus. Matter of the same appearance, but less viscid, was met with on cutting down to the right shoulder-joint among the muscles external to it. The cartilages in both these articulations had lost their colour and seemed ABNORMAL CONDITIONS OF THE KNEE-JOINT. 53 thinner than natural, but were not ulcerated. The elbow-joints were in a normal condition. The joint of the index ringer contained a thin greyish coloured matter, which was not con- fined to the joint, being also found in the mus- cles external to it. The cartilages on the head of the metacarpal bone and corresponding sur- face of the index finger were much ulcerated and partially removed. The knee-joints con- tained a large quantity of a viscid greenish matter like lime-water and oil. Behind the right knee-joint, and extending down to the gastrocnemii muscles, matter of somewhat a similar character, except that no synovial fluid was mixed with it, occupied the interstices of the muscles and the cellular tissue of the lower part of the poplitceal region. The hip-joint did not contain any matter. The basilic vein of the right arm was plugged up with a dense coagulum, which closely ad- hered to its internal tunic, and was not easily separable from it. There was no pus in the vein; its exterior presented an unusual red co- lour. On opening the cavity of the chest a quan- tity of serum escaped. There was a great quantity of a very yellow lymph effused on the surface of the pleura of both lungs, principally the right. In many places it was very thick, rough, and consistent. On the diaphragm and in the right side of the chest the lymph was soft, of a greenish colour, being in shreds easily removed, and leaving the subjacent mem- brane highly vascular. There were also evi- dences of interlobular pleuritis having existed : all division into lobes had been effaced. The lungs presented specimens of pneumonia in its three stages. A very small portion of the apex of the left lung alone seemed healthy, but even here the bronchial membrane was en- gaged and presented evidences of bronchitis having existed. In the substance of the lungs there were also found small abscesses present- ing near their surface like little gangrenous abscesses surrounded byecchymosed red spots ; these contained some grumous dark-coloured fluid, which, however, was inodorous. In others was found an ill-digested purulent matter ; and leading to one of these disorganized portions of the right lung near its apex, the minute veins on very careful dissection were found thickened, with yellow parietes ; and many of those present at the examination satisfied them- selves that these minute veins contained puru- lent matter. The heart and pericardium were natural. The most careful examination could discover nothing abnormal in the uterus. The large intestines throughout presented numerous ulcerations on their mucous surface ; the neigh- bourhood of the ileo-ccecal valve being most beset by them. The mucous membrane was in a state of hyperemia. The prognosis in cases of acute arthritis genu is in general very unfavourable except when the disease accompanies what has been usually termed rheumatic fever. In this case the syno- vial system of all the articulations is visited in succession, until the inflammatory disease ex- hausts itself as it were in three or four weeks, often leaving no trace behind. It is, however, well known to medical men that in the course of these fevers fatal metastasis may occur from the synovial membrane of the knee or other joint to the pericardium or peritoneum.* In some few cases, after the general rheumatic fever and acute specific arthritis had subsided, we have known the chronic rheumatism, or nodosity of the joints, to set in, remaining permanently to interrupt the patient's health. Not long ago there was a young woman in the Richmond Hospital, under the care of Dr. Hutton, having acute arthritis of the right knee-joint, which had remained after a severe attack of general rheumatic fever. All the joints in succession had been visited by in- flammation. The fever, with its debilitating accompaniments, profuse perspirations, &c. subsided, but the local symptoms of acute arthritis of the right knee-joint continued, and increased even to suppuration, nor did ampu- tation of the limb save the patient's life. These unfavourable results of acute arthritis, of the rheumatic form, may be considered as excep- tions. In general the form of inflammation of the joints, commonly called rheumatic fever, terminates favourably ; on the contrary, in cases where the knee-joints and other articulations are engaged during an attack of diffuse inflam- mation, puerperal arthritis, or phlebitis, the prognosis is most unfavourable, the disease in all these cases being generally fatal whether the joints be implicated or not. Anatomical characters of the acute arthritis of the knee. — On examining the interior of a knee-joint which had recently been the seat of acute inflammation, we find that the synovial fluid has accumulated in the cavity of the joint, and that it is mixed with purulent matter; when this is removed, we perceive that the synovial sac has been widened and enlarged, and that the subsynovial tissue is much infiltrated, causing the synovial mem- brane to be raised up above the level of the articular cartilages. We have seen the syno- vial membrane or subsynovial tissue as red as the conjunctiva oculi in acute purulent ophthal- mia. In these cases the articular cartilages lose much of their natural white silvery lustre, become yellowish, and are found softened at their edges or circumference, where the ele- vated and inflamed synovial membrane is in contact with them. VVe have found the carti- lage of the patella softened and partially de- tached from the bone, even in very recent cases. In cutting down to the joint we have noticed an alteration in the natural colour of the muscles ; and outside the synovial sac we often encounter abscesses containing true pus. Generally speaking this sac is of an intensely red colour, and covered here and there with a green but not very consistent layer of organi- z^ible lymph. Some fragments of thinned shreds of exfoliated articular cartilage, with serrated edges, hang into the cavity of the joint, and some portions are altogether free, * Sec Dublin Hosp. Rep. vol. ii. p. 321. vol. iv„ p. 365. 54 ABNORMAL CONDITIONS OF THE KNEE-JOINT. and float about loose in the interior. We have found the minute capillary vessels of the car- tilages faintly traced in red lines, and have also discovered that these vessels admit the colour- ing matter of our injections. The vascularity of the cartilages under the influence of acute inflammation seems to be fully proved. We have it on the authority of Sir B. Brodie that he had been able to detect with the naked eye vessels in articular cartilage filled by blood ; and it is fresh in the recollection of the profes- sion that Mr. Liston has lately laid before the Medico-Chirurgical Society important obser- vations on this subject. — The periosteum of the bones in the immediate vicinity of the knee is usually found to be of a red colour, thicker than natural, and easily detached from the bone ; the bones themselves occasionally pre- sent a reddish or pink hue externally, and a section of them shews, by its bright red colour, an increase in the number or size of the capil- lary vessels, admitting red blood, which per- vade their medullary membrane and cancellated structure. Example of acute arthritis genu. — Michael Roche, twenty-seven years of age, was admitted into the Richmond Hospital in April 1832. He had an emaciated appearance, a dry tongue, and some fever. He complained of severe pain in the left knee, which completely inter- rupted sleep, and of frequent spasmodic stag- ings of the limb. The limb was so much swollen that measurement of it showed an in- crease of six inches in its circumference over the sound one. The superficial veins were di- lated, the patella was thrown much forwards, and the leg and foot were cedematous ; the in- teguments were red and thinned, and a fluctu- ation of matter in the joint was very .evident. He stated this violent attack to be of five weeks' duration, having commenced with a very severe rigor, and attributed it to his having lain for some hours on wet grass. Three years previ- ously he had had an attack of acute inflamma- tion of the knee, which, however, quickly sub- sided, but leaving a stiffness of the joint. An opening was made with a lancet into the part of the knee-joint which was red and thinned, and eight ounces of purulent matter were let out, but no relief was afforded. Some super- ficial inflammation was observed, in the course of the lymphatics to the groin, from the wound, as also swelling of the inguinal glands. The spasmodic startings of the limb became more urgent, and the cedema increased. On the 17th of April Dr. M'Dowel amputated the limb. The incision passed through a sinus which he thought it necessary to dissect out. The muscles did not retract. On the following day the report from the man was that he rested well at night. But on the fourth day after the operation his countenance was flushed, his pulse feeble — 96, and he complained much of the pain of the stump. On the 22d of April, the fifth day after the amputation, he had a rigor followed by a hot and sweating stage : his pulse amounted to 144. For some days subsequently he had frequent rigors. The stump was not doing well ; the muscles were shrinking away daily and leaving the bone un- covered. The edges of the wound had a sloughy appearance, and towards the end of the month he was attacked with diarrhoea which in a few days proved fatal. On an examination of the knee-joint all the structures entering into its composition exhi- bited evidence of their having been the seat of recent high inflammatory action. The bones and synovial membrane presented a very great degree of vascularity and redness; purulent matter and flakes of lymph were contained in the interior of the joint ; a fragment of one of the semilunar cartilages alone remained, and the articular cartilages were in many places removed altogether ; in other situations these latter were thinned very much, and in one or two places a number of minute perforations were seen in the articular cartilage investing the lower end of the outer condyle of the femur. The minute vessels of the joint were rendered evident by a previous injection of fluid size coloured by vermdlion. The syno- vial membrane was much thickened and raised above the level of the cartilages ; it presented a red pulpy appearance, and productions from it passed from the side of the femoral condyles and were loosely folded over the articular carti- lages ; and wherever this loose membrane was in contact with the articular cartilages, these seemed to have been absorbed. Depressions in the cartilages exactly corresponded in form with this vascular membrane, which was lodged in these superficial depressions. The articular cartilages were thinned, and when elevated from the bone a red pulpy membrane, very similar in appearance to the free surface which the synovial membrane presented, was seen. The minute pores and perforations in the articular cartilages already noticed were evidently formed by the action of a pulpy membrane subjacent to them, and causing their absorption, evidently in the same manner, it appears to us, as we find an exfoliation from a flat bone of the cranium to be perforated by the absorbing powers of the granulations proceeding from the bone beneath it. In examining this preparation, and reflect- ing on the history of the case, it would appear that when the limb was amputated, the com- plete destruction of the articular cartilage was in progress. On the free surface towards the cavity of the joint, the cartilage was evidently absorbed by the villous productions from the inflamed synovial membrane; on the osseous surface the cartilage was acted upon by a pulpy membrane, which existed here also, and it was this membrane which was produced from the bone and caused the number of minute perfo- rations already alluded to, having partially removed the articular cartilage.* The bones were in a condition of hyperemia. This newly formed membrane seems to be endowed with a power of absorbing, by its villi, the cartilage with which it comes in contact ; for we must agree with Mr. Key that these vascular fimbriae or tufts are often buried into excavations in the * The preparation is preserved in the museum of the Richmond Hospital. ABNORMAL CONDITIONS OF THE KNEE-JOINT. 55 cartilage, and the convexity of the villous mem- brane seems sunk into foveae formed in the cartilage, so as to leave no doubt of the vital mechanism, if we can so say, of the process, which seems quite analogous to the absorption of the sequestrum of a cylindrical bone, or the exfoliating piece of a flat bone. The writer presented to the Pathological Society of Dub- lin a recent specimen and a drawing of the knee-joint of a man aged seventy, William Walsh, who died the day previously (13th Dec. 1839) in the House of Industry, of an attack of acute arthritis genu which had supervened on a chronic disease of the joint of long standing. The synovial sac of the joint had been much distended and was more capacious than usual. It was greatly thickened, and presented on its internal surface an intense scarlet colour. Ex- tensive deposits of a yellowish green lymph were noticed over the entire of the synovial sac : the strong contrast in colour between the green lymph and the red villous synovial mem- brane is well seen in the preparation. The cru- cial ligaments were partially removed, and it was found on dissection that the internal and external lateral ligaments had lost all their dis- tinctness as fibrous bands ; both seemed to be resolved and spread out into thin membranes or fasciae, which but little restrained the move- ments of the knee, and allowed of a motion of rotation being communicated to the joint. The articular and semilunar cartilages were removed, and the denuded porous surfaces of the bones of the tibia, femur, and patella presented nu- merous small red spots, as if they had been sprinkled with red sand. An abscess contain- ing about two ounces of yellowish green pus, of a laudable consistence, was found under the cruroeus muscle, just above the synovial sac of the joint: this abscess was isolated, and had no communication whatever with the interior of the sac of the joint. The fluid in the interior of the articulation was more of a thin sanies than pus, but was abundant in quantity, and had made its way externally by a large sloughy- looking opening in front of the leg, about two inches below the knee. Michael Smith, 58 years of age, was admitted into the Richmond Hospital in 1838, labouring under erysipelas of the head. During the course of the disease, one of his knee-joints became hot and swollen, the patella seemed to float, and on each side of it a fluctuation be- came evident. He was more or less insensible from the erysipelas of the head, but when the knee-joint was moved, he exhibited signs of suffering. On the eighth day after the knee- joint was first affected, he died of the erysipelas of the head. The knee-joint was carefully inspected, fine red injection having been previ- ously thrown into the femoral artery. The synovial sac of the articulation was distended by a turbid yellowish-green fluid, apparently composed of a mixture of pus and synovia. When this was washed away, the synovial membrane was found not so much thickened as in the former case, nor had it so much of the vivid scarlet colour as the last specimen alluded to; and reminded those who examined it of the appearance which the conjunctiva presents in subacute conjunctivitis. This membrane ap- peared to be thickened and pulpy where it had already advanced somewhat over the external condyle of the femur. The subsynovial tissues were more or less infiltrated. The cartilages had lost their normal whiteness and brilliancy, and were of a murky yellowish hue ; they were somewhat softened in their substance, and the cartilaginous covering of the patella was slightly elevated, in patches, and one spot of ulceration was seen at the circumference of its external edge. The cartilage covering this bone was so soft that the blunt probe easily penetrated into its structure. Many would call this a case of simple synovitis genu, but it is manifest that, although the acute disease in the knee originated in the synovial membrane, the other structures of the joint very soon became implicated, and that, at the period of the patient's death, which was only a few days after the first attack of the joint, the term of synovitis of the knee-joint was not sufficiently comprehensive. We have had many opportunities of examining the knee- joints of those who have died of diffuse inflam- mation, which has occurred in females some short time after parturition, and in those cases denominated puerperal rheumatism, and in cases where the arthritis of the knee or other joints was concurrent with phlebitis ; and in such cases we have found the most remarkable phenomena to be, — great effusion into the knee- joint of a fluid which would seem to be com- posed of equal parts of pus and synovial fluid. This was viscid, of a sea-green colour, and of the consistence of honey. In cutting down to the joint in these cases we frequently met with ill-digested matter in and amongst the muscles surrounding the affected articulation. The synovial membrane was of a pink colour. The articular cartilages presented an appearance which was rather peculiar. We have found them generally to preserve their normal adhesion to bone, to be smooth on their surface, but to be evidently thinned, and so reduced as to form a stratum covering the condyles of the femur scarcely half a line in thickness. The inter-articular cartilages externally preserve their normal appearance, but we can occasionally discover that after an attack of acute arthritis of the description now under consideration, these structures shew that they are permeated inter- nally by capillary vessels containing red blood. We have had many, — too many examples lately verifying the above description of the anatomical appearances presented on the examination of the knee-joints of those who have died of dif- fuse inflammation. Simple chronic arthritis of the knee. — The symptoms which denote the existence of simple chronic inflammation of the knee-joint are very similar to those belonging to the acute affection of this articulation, being only slower in the different stages of their developement and milder in their character. The simple chronic arthritis genu commences with a pain which the patient usually refers to the inner side of the joint. This pain is not sufficient to prevent him from following his .56 ABNORMAL CONDITIONS OF THE KNEE-JOINT. ordinary occupation, and is at first usually un- accompanied by swelling, or if swelling exist at this early period, it is inconsiderable. There is more pain and less swelling than in the ordi- nary case of scrofulous white swelling. The swelling, too, is different, that in the strumous being more elastic, more of a globular form, and situated at first more at the lower and ante- rior part of the joint around the ligamentum patellae : in the strumous also the ham is sooner filled up. Moreover, the simple chronic ar- thritis of the knee is a disease of adult life, and the strumous of the younger subject. As the simple chronic arthritis of the knee proceeds, the limb wastes somewhat, a preternatural effu- sion of synovial fluid into the joint takes place, and pain on motion becomes so severe as to confine the patient to the house ; he complains of a constant, deep, boring pain, which is usu- ally referred to the inner condyle of the femur or tibia, and is accompanied by some spasmodic starting of the muscles of the limb, by which his sleep is disturbed. When pressure is made on the knee over the situation where uneasiness is experienced, the pain is increased ; and the integuments of the affected articulation have a higher temperature than natural. In the early stage of the disease the popliteal space is not filled up. As the inflammatoryaction proceeds, the patient's strength and spirits become ex- hausted by continued pain and confinement; the constitution becomes engaged, suppuration occurs in the interior of the joint, and matter makes its way to the surface, oedema of the instep manifests itself, and the disease now runs very much the same course as does the chronic strumous white swelling, partial dislocation of the tibia outwards or backwards occurring, and amputation becoming necessary to save life. The two following cases may serve as exam- ples of the simple chronic arthritis genu. The first presented us a rare opportunity of witness- ing the anatomical characters of the disease in a very early stage ; the second in the advanced form, as amputation could no longer be deferred with safety. J. M'Cann was admitted into the Richmond Surgical Hospital on the 13th Dec. 1836, for an affection of his left knee-joint. The attack was about six weeks coming on, but he remem- bered that about ten years previously he had fever, and that the left knee-joint was at that time severely visited by inflammation. Since that period, however, he remained well until he got cold, which ended in the present attack of the knee, and at this time no other joint was affected. The joint appeared to be much en- larged when compared with the right and healthy knee ; the prominences of the bones were no longer evident ; the swelling was soft and fluctuating, and extended up the front of the thigh, but the ham was not in the least filled up; the knee was slightly flexed, and the ten- dons of the hamstring muscles were remarkably tense ; he referred the pain to the internal side of the joint. Hoping to be released of these symptoms he sought admission into the hospi- tal. He was ordered twenty-four leeches and fomentations to the knee-joint, and to take three times a day a pill containing two grains of calomel and half a grain of opium. On the fourth day of this treatment he complained of scalding when passing urine, and of acid eruc- tations from his stomach. For the latter mag- nesia and lime-water were given. On the fifth day diarrhoea, probably mercurial, set in, which was very severe and did not yield to the treat- ment, which consisted in the administration of an emollient enema containing forty drops of tincture of opium, and of a pill every third hour, containing two grains of acetate of lead and one grain of opium ; and warm fomenta- tions with turpentine to the abdomen. After the fourth pill had been taken the diarrhoea ceased. It is proper to mention that the fore- going symptoms were accompanied at the com- mencement by a good deal of fever of the sthenic type ; the patient's face was greatly flushed, his eyes glistened, the lips were Ver- million red, the pulse was one hundred and strong, and there was much increase of heat of the surface. When the diarrhoea ceased, a new phenomenon, hasmaturia, presented itself,accom- panied by great pain across the lumbar region, along the course of the ureters, and in the testi- cles. The calls to pass water occurred hourly, and half a pint of urine and blood mixed would pass, which had not any urinous odour. These calls became less frequent, but the fluid passed became more and more red ; his countenance changed, and he had the general symptoms of loss of blood. Added to this his stomach was in a continued state of erethism ; he had urgent desire for cold drinks, but nothing, not even cold water, would for one moment remain on his stomach. His countenance was sunken and exsangueous ; his pulse, one hundred and forty, could scarcely be counted. His surface became cold, and he complained of the greatest sense of exhaustion. At this period most urgent singultus set in and added much to his other sufferings. The hematuria continued, the sto- mach rejected every species of nutriment, and medicine failed altogether to relieve his symp- toms. He died exhausted on the fourth day from the diarrhoea setting in, and on the seventh from his admission into hospital. It is remark- able that during the last three days of his illness he did not feel any uneasiness in his knee, and the swelling of the joint had greatly dimi- nished. On a post-mortem examination the kidneys were found much enlarged and friable, with some purpuric spots (petechias hemorrhagica;) on their surface. The spleen was very small and of a healthy consistence. On opening the bursa beneath the rectus and vasti, it was found to be distended with synovial fluid of the ordinary character; no communication existed between this bursa and the knee-joint. When the proper synovial membrane of the joint itself was opened, the quantity of synovial fluid was found to be very scanty. The semi- lunar cartilages were normal, but the articular cartilages which invest the tibia and femur were of a yellowish hue, and here and there appeared softer than natural. In one spot the cartilage covering the convexity of the internal condyle ABNORMAL CONDITIONS OF THE KNEE-JOINT. 57 of the femur was superficially removed for the size of a sixpence. To this softened, ulcerated, or abraded point the principal pain was referred, by the patient during life. There were not any loose and vascular synovial fringes hanging into the interior of the joint, but examining at the circumference of the cartilage, where it invests the external condyle of the femur, this mem- brane and its subsynovial tissue were very red, vascular, and villous-looking. The outer edge of the cartilaginous covering of the femoral condyle was thin and minutely serrated, and the eye of the probe could be placed under this edge. John Nugent, set. 19, was admitted into the Richmond Hospital, January, 1839. He had been under treatment in the country for six months for a disease of the left knee-joint which originated in a blow on the joint from the handle of a printing-press. He fainted at the time of the accident, and the pain never ceased from that day up to this period of his admission. He was reduced a good deal in flesh. He had occasional perspirations during the night, parti- cularly about the head, and starting pain shoot- ing up and down the leg. He could not bear the joint to be moved but kept it semiflexed, and the limb lying on the outside. He stated that before his admission he had never been altogether confined for the complaint. There was some little swelling of the knee, which was tender on pressure. There was no swelling in the ham, nor enlargement of the inguinal glands. The calf of the leg was wasted, and the thigh also was less than the other by an inch in the measure of its circumference above the knee. He remained much in thisstate until March 14th, when he complained of suffering a constant " dead pain" across the joint below the patella ; besides this there was occasionally a throbbing sensation which was more distressing to him than any other, even than the spasmodic starting of the limb. On the 2nd of April a valvular opening was made with caution into an abscess on the inside below the articulation; thin curdy matter came away. This gave him some relief. On the 4th another opening was made in the outside above the joint, where also the abscess showed itself: matter of a similar description came away. Previous to these punctures hav- ing been made, amputation was proposed to the man as the only means of escape from this disease, but he preferred to have the abscesses opened. Fever did not follow upon this first or second operation, but subsequently it set in, and ran very high for four days, during which he perspired largely and had much pain and starting of the limb, with head-ache and anxiety of manner, and for two days he was in a con- fused state bordering on delirium. Nor did the evacuation of the purulent, matter prevent the enlargement of the cavities of the abscesses connected with the diseased joint, as appears by the following report, dated May 10th, made by our clinical clerk, Dr. Bradshaw. " The abscess has ascended up the thigh, running high up the popliteal region. The hectic fever is severe; his pulse in general 120, small and compressible; emaciation had advanced and is still advancing ; his strength is giving way under the disease, and he must soon sink if amputation be not consented to." On the 10th May the report was, " Diarrhoea still con- tinues, but without abdominal pain or tender- ness. The emaciation is very great. Pulse 120, small, and compressible. Tongue red, moist, and morbidly clean. The flexion of the leg on the thigh becomes every day more and more considerable, so that the angle becomes daily more acute." On the following day amputation high up was performed. The disease of the knee had much affected the cartilaginous struc- tures of the joint, the absorption of which seemed to have been effected by a vascular pulpy mem- brane. The parts that had suffered most were the external condyle of the femur, the inner head of the tibia, and the inner and posterior surface of the patella. Along the trochlea of the femur there existed longitudinal grooves or furrows in the cartilage, which was not removed. A highly vascular and pulpy membrane was found filling the parts wherever the cartilage had been absorbed, and this membrane could be traced insinuating itself beneath the edge of the remaining portions of the cartilage, by which means the process of absorption seemed to have been effected. In the interior of the joint there were much pus and flakes of lymph, and where the cartilages had been removed the porous surface of the bones had been covered by soft layers of lymph of very recent formation. Chronic rheumatic arthritis of the knee. — In the articles Hand, Hip, Elbow, &c. in this work we have treated of a chronic disease affecting other articulations, which we have denominated chronic rheumatic arthritis; we shall now give an account of the symptoms and anatomical characters of this disease as we have found it in the knee-joint. When this articulation is affected with it, other joints in the same individual will also be found more or less implicated. The commencement of this disease of the knee is marked by evidences of subacute inflammation, such as pain, heat, con- siderable swelling. This is followed by a second period, in which the heat and swelling diminish, but the pain continues. This pain is usually referred to the inner eondyle of the femur and tibia. The patient may for a long period be able to walk, but every movement produces considerable pain, and at length he becomes incapable of walking or even of stand- ing. The limbs diminish in size, but become remarkably firm to the feel. The patient having at last lost the power of flexing or extending the limb, the hamstring muscles gradually become more tense. The knee-joints from the com- mencement incline slightly inwards, and the tibia outwards, and this bone is at the same time rotated in this last direction, so that the foot is everted ; if the limb then be kept in the semi-flexed position, and the tibia be thus rotated outward, carrying with it the 1 igameiitum patella;, it is easy to account for the circumstance which we have in some examples witnessed in the disease, — viz. that the patella leans towards the outer condyle, and further, that it is then sometimes thrown completely over it, so as to represent the external dislocation of this bone. 53 ABNORMAL CONDITIONS OF THE KNEE-JOINT. When the distension of the synovial sac of the articulation is at its maximum, we usually notice in this disease a prominent tumour about the size of a small hen's egg projecting into the popliteal space (fig. 3). This tumour leans towards the inner head of the gastro- cnemius ; it disappears when the knee is flexed, and becomes more tense and hard when the limb is in the extended posture, as when the patient stands erect. We have known several cases of this disease of the knee-joint, where the synovial sacs of the knees have been much distended, and have on these occasions almost uniformly observed this popliteal tumour formed. From its situation, and from negative evidence, we can readily infer that the swelling consists of synovial fluid contained in a bursa, which has a communication widi the interior of the knee-joint. We have witnessed very many cases of this chronic rheumatic arthritis of the knee, in which this dropsical condition of the popliteal bursa existed, and some of these having had this chronic disease in both knee-joints, the bursa? were seen in both popliteal spaces, — presenting in these cases on a superficial inspection the resemblance to a case of double popliteal aneurism. We have also enjoyed an opportunity of ascertaining by anatomical examination the real condition of this synovial sac in this disease, and its relation to the synovial membrane of the joint itself, to which we shall have occasion just now to revert. When the palm of the hand is applied over the patella in the early stages of the affection, a sensation of a preternatural degree of heat is felt ; and when pressure is made on the patella, and a lateral movement across the condyles is communicated to it, a very evident roughness is perceived, either on the articular surface of the patella itself, or the corresponding surface of the trochlea of the femur ; and when the knee-joint is fully flexed, a characteristic arti- cular crepitus becomes manifest. In the later stages of the disease, the subacute inflamma- tion, with the phenomena which it presents, subsides, the synovial fluid becomes absorbed, and the patella falls down on the trochlea of the femur ; the popliteal bursa also disappears, and the grating produced by rubbing surfaces is perceived by the patient himself in all his movements, and can even be heard by the by- standers. If the joint be now examined care- fully by the surgeon, he feels satisfied that the smooth cartilage has been removed, either par- tially or completely, from the articular surfaces. Crests of ossific deposit may even be per- ceived, and, almost invariably, foreign bodies may be felt in the interior of the joint. Some of these are superficial, small, and moveable ; others are evidently situated more deeply in the interior of the joint. Some are small, some large, and we have known one case, which we learned to be of forty years standing, in which numerous bodies* of this description * The case mentioned by Morgagni in which he saw twenty -five of these bodies in the left knee- could be felt, some literally as large as the patella, floating about in the interior of the knee-joint, and which, we doubt not, were exactly of the same nature as those we have described in the elbow-joint. The prognosis in this disease must be un- favourable, as it seldom yields to medicine, but it does not appear to us to shorten life. We have seen an example in which the knee-joints had been affected with this disease, as the patient herself reported, for forty years. We are not prepared to say, however, that medicine and proper treatment may not occasionally cut short the disease, and we are sure the sufferings of the patient may be palliated at least by appropriate treatment. The following case is a good example of this disease. Case of chronic rheumat ic arthr itis. — Patrick Donohoe, aged 38, a carter, admitted into the Richmond Hospital, (Dublin,) Nov. 24, 1836, complained of chronic pains in all his joints, but the principal source of his uneasiness was the diseased condition of his knee-joints, which prevented his earning his livelihood. Both knee-joints were greatly swollen ; he com- plained of stiffness of them, and of some pain at the inner condyle of the tibia, which in- creased when he stood up ; yet he was able to walk a considerable distance. The limbs could be fully extended, and when in bed he kept them pretty constantly in this position. He could not fully flex them backwards. The swelling of the knees differs from that of an ordinary white swelling, although it might cor- respond much to the characters which a case of chronic synovitis of the knee might present, or to a case which the older writers denominated hydrops articuli. The swelling viewed in front is of an irregular globular form, involving the patella, its ligament, and the hamstring ten- dons in one uniform tumour ; on the contrary the ligamentum patella can be felt, with its edges as yet sharp and well defined, when the patient is desired to exert the extensor muscles of the leg. The tibia at the side of the liga- ment, as far as the insertion of the internal lateral ligament, can be plainly felt through the skin to be rough and scabrous, and it can be perceived that this part of the bone is beset with bony vegetations. The breadth of the head of the tibia is increased ; the synovial membrane contains a redundant secretion, which elevates the vastus internus and forms a swelling here which measures about seven inches in its vertical diameter, and which seems to be some- what constricted transversely in its centre (/?g-2). The swellingof the knee on the outside is evident enough, but is not so well marked as that on the inner side. It presents no transverse band, subdividing it into two tumours. The out- line of the hamstring tendons is seen, when the joint is viewed in profile, either from without or within, and a very well defined ovoid projection from the popliteal space is observed (fig. 3). Its centre is on a level with the up- joint of an old woman who died of apoplexy, we think must have been a case of the chronic disease we are now describing. ABNORMAL CONDITIONS OF THE KNEE-JOINT. 59 Fig. 3. Left knee- joint, front view. The prominent swelling on the left, A, is from the en- larged head of the tibia; that on the rig/it, H, is the soft globular swelling resulting from the effusion into the synovial membrane. per and projecting margin of the inner condyle of the tibia : it leans to the inner hamstring muscle. The rest of the popliteal space pre- sents a normal appearance. When the limb is fully extended, and the muscles are allowed to remain in a passive state, the patella may be moved from side to side with much freedom. It appears to float as it were on the surface of an accumulated quantity of synovial fluid. When pressed against the trochlea of the femur, this fluid is moved laterally, and the patella strikes against the femur, and if a lateral movement be now communicated to this bone, a grating of rough surfaces may be perceived. If we grasp the leg and flex it on the thigh, we find we can elicit a peculiar articular crepitus. In this case it is quite audible, and resembles much the noises which electric sparks make when dis- charged in quick succession from an electrical apparatus. When the limb is much flexed, the swelling of course feels remarkably hard and solid, but when the limb is again brought back to its ordinary state of extension, fluctua- tion may be felt very evidently in it over its whole surface. The popliteal bursa, however, is felt very tense in the extended position of the joint, as when the patient stands and throws his weight on the limb. If we feel this bursa, and then cause the patient's limb to be flexed, we can follow the fluid, as it were, with our fingers into the articulation. As the patient lies in bed, the limb left in the extended posi- Left knee-joint, side view, shewing the enlarged bursa in the popliteal space. tion, and the synovial sac as flaccid as possible, moveable bodies may be detected in its interior. Some appear to be adherent, and situated more particularly in the upper portion of the sub- crural bursa. When we elevate the leg, and preserve it still in the fully extended position, the patient, without any apprehension of pain, will permit us to press it firmly against the femur, and does not experience the least suf- fering even if we strike the heel forcibly. (See Hip, abnormal condition of.) Both knee-joints in this case are affected with this disease, but the left is more distended by fluid than the right. The inner condyles of the femur and tibia of this limb are thrown somewhat inwards, and form a salient angle in this direction, which, the patient says, is cer- tainly the result of disease, as his limbs were perfectly straight before he was visited by his present illness. Although his knee-joints are more affected with this chronic disease, his other joints pre- sent very evident traces of this afflicting malady. The disease in him followed a rheumatic fever, which was brought on in consequence of his having lain a whole night asleep on a wet road, having fallen unobserved from his cart when in a state of intoxication. Although this is not the place to speak of treatment, we may be permitted to say that under the influence of rest in bed and a mild mercurial course, followed by a long-continued use of sarsaparilla with large doses of the hydriodate of potass, this man left the hospital, by no means cured, but much improved and tolerably well able to follow his occupation. 60 ABNORMAL CONDITIONS OF THE KNEE-JOINT. He found it necessary, however, after the lapse of three years, to seek re-admission into the hospital, where he now is. The right knee- joint is now enlarged, and in a condition simi- lar to that of the left on his first admission. The latter, on the contrary, has nearly resumed its normal condition ; the dropsical effusion of synovia has disappeared ; he does not com- plain of pain in it ; but if the joint be accu- rately examined, the bony irregularities which were noticed on the head of the tibia will be found, as might be expected, still to exist. If we move the patella transversely, an articular crepitus is perceived, plainly shewing that the cartilages have been removed from the patella and corresponding trochlea of the femur. The edges of the trochlea can also be felt through the skin to be elevated into rising crests. The peculiar crackling noise which is elicited when the joint is flexed and extended is infinitely more remarkable in the left knee-joint now, when it is comparatively well, than formerly, when it was much swollen, and when the syno- vial membrane was in what has been called a dropsical condition. Anatomical characters. — When we have an opportunity of making an anatomical examina- tion of a knee in which the disease had been fully established, we find the synovial fluid increased in quantity, and but little altered in its sensible qualities. The membrane is thicker than natural, and opaque. Sometimes vascular synovial fimbria; are formed, and hang into the synovial sac* We also find moveable carti- laginous bodies in the interior, similar to those noticed in the elbow-joint. f (See Elbow, ABNORMAL CONDITIONS OF.) In the line of flexion and extension we observe narrow sulci formed by the removal of the cartilages. On examining the popliteal tumour, we find it to be, what we might have surmised, an enlargement and dropsical condi- tion of the bursa, which naturally exists at the point of decussation of the semi-membranosus tendon with the tendon of the internal head of the gastrocnemius. This bursa communicates normally with the synovial sac of the knee- joint by a very small circular aperture. It is not an uniform ovoid sac, but evidently has semilunar septa irregularly thrown across its interior, making the bursa a small multilocular cavity. When the joint is much distended by synovial fluid, the bursa admits some of this fluid, and takes upon itself the same morbid process which affects the proper synovial mem- brane of the joint itself. As we examine the disease when it has existed for some time, we find that the cartilage has been removed in grooves, and its place supplied by a porcelain- ous or ivory deposit. The bones of the knee- joint, however, present appearances charac- teristic enough : they generally appear to be enlarged. This is obviously the case with the patella : it is broader than natural, excavated, and grooved vertically. All the bones seem enlarged and porous on all those parts of the * See Cruveilhier, liv. 9. pi. 6. t See Morgagni's case, in note above. articular surfaces which have not been worn by use into porcelainous polished surfaces and sulci. The cavities of the head of the tibia for the reception of the condyles of the femur are much deepened, and exuberant nodules or vegetations of bone are thrown out around the circumference of this head. When we examine the femur, we find here also bony vegetations, arranged along the lateral margins of the con- dyles, similar to those which we noticed around the corona of the head of the femur.* The part of this bone called the trochlea, upon which the patella moves, is also grooved verti- cally, and the trochlea has rising edges to it, or crests, which will be found to correspond to the lateral margins of the patella when this bone is laid upon the trochlea of the femur. The anatomical characters of this disease when it has existed long, will of course be still more strongly marked. However, the dropsical effusion into the synovial sac will be found to be much less as the disease is of longer dura- tion. The joint becomes more and more flexed, the tibia has a tendency to be partially dis- placed outwards, and the toe is everted : the patella under such circumstances is dislocated on the external condyle, giving us another example of this luxation from disease. In the interior of the joint foreign bodies are found, while the articular and semilunar cartilages are altogether absorbed. White swelling, or chronic strumous arthritis of the knee. — The knee-joint is more liable to the disease commonly called white swelling than any other articulation. This disease, though utterly insidious in its attack and slow in its progress, nevertheless presents some of the characters of an inflammatory complaint during its whole course. The first symptom generally is reported as a deep-seated dull heavy pain unattended by swelling and not increased by motion, but in children the swell- ing is often the first symptom noticed. This is followed by pain, which, although it comes only occasionally, is severe, and is referred almost uniformly to the inside of the knee. Some increase of temperature of the affected joint on comparison with the other knee, can be ascertained. The swelling does not at first encompass the whole joint, but first appears on the anterior and lower part of the knee, occupying in general the two little hollows on the different sides of the ligament which joins the patella to the tibia. This swelling is elastic, and on examination by the finger conveys a sense of softness and fluctuation, as if it contained a fluid, although no fluid to any amount ieally exists. The skin over the knee becomes pale and shining, as if thinned. The subcutaneous veins dilate and become very evident. The muscles of the leg waste, so that the volume of this portion of the affected extremity is con- siderably reduced, and the inferior part of the thigh just over the knee suffers a characteristic diminution in the measure of its circumference. * See Hip, abnormal condition of, Jig. 310; also Cruveilhier, liv. 9. pi. §u3^^Flie external appearance of the eye- browsJHPw well known to require any lenticu- lar desewptjon. Their prominence is produced partly by the superciliary arches of the frontal bone over which they lie, but principally by a cushion of cellular and adipose tissue under- neath the skin, together with the roots of the hairs and muscular substance. The hairs of the eyebrow are, generally speaking, directed from within outwards, but internally, especi- * Cilia, quia oculos celent ac tueantur. ally where they exist over the root of the nose, they are inclined in the opposite direction. Those immediately over the root of the nose indeed cross each other. Besides the general direction from within outwards of the majority of the hairs of the eyebrows, it is to be re- marked that the uppermost ones are inclined downwards and the lowermost ones upwards, so that they are raised into a kind of ridge along the middle line of the eyebrow, an ar- rangement which presents a pleasing appear- ance of regularity. The eyebrows are capable of very free motions, and these are in close connexion with the affections of the mind ; hence the eyebrows have always been con- sidered a very important physiognomonical feature. The movements of the eyebrows are effected by muscles inserted into their skin. These muscles are: the frontalis, which elevates the eyebrows ; the upper and outer fibres of the orbicularis palpebrarum, which depress them, and the corrugatorsupercilii, which draws them inwards. For their description, see article Face. The eyelids act in conjunction with the iris on many occasions ; thus, in a weak light and in the act of looking at distant objects, the eyelids are widely opened at the same time that the pupil is dilated ; when the eye is exposed to a strong light, on the contrary, or in looking at near objects, the palpebral fissure is con- tracted along with the pupil. In sleep com- plete closure of the eyelids is associated with very great contraction of the pupil.* Fig. U. The eyelids of the left side widely opened, seen from without. ( From Soemmerring. ) a a, The broad free margins of the eyelids, with the mouths of the Meibomian follicles. b, Outer canthus. c, Inner canthus. d, Lacrymal papilla and lacrymal point of upper eyelid. e, The same of the lower eyelid. f, Lacrymal caruncle, and g, semilunar fold, at the bottom of the lacus lacrymalis, which is the space within the fissure of the inner canthus. h h, The orifices whence the eyelashes have been plucked out. i, Eyebrow. * See farther on this subject, Tourtnal.Ueber die Function der Augenlider beim Sehen. in Muller's Archiv, No. iii. 1838. LACRYMAL ORGANS. 81 Internal structure of the eyelids. — The tar- sal cartilages may be looked upon as the skele- ton of the eyelids, and the membraneous ex- pansion intervening between them and the mar- gins of the orbits as connecting ligaments. The latter, indeed, are called the tarsal ligaments, although they do not in reality possess a liga- mentous structure, but consist merely of dense laminar cellular membrane. On the inner sur- face of the tarsal cartilages and tarsal ligaments the palpebral conjunctiva adheres. On the outer surface are the palpebral and ciliary por- tions of the orbicularis palpebrarum muscle, over which is the skin. Moreover, incorporated with the superior tarsal ligament is the expan- sion of the tendon of the levator palpebral supe- riors muscle. Imbedded in the substance of the tarsal cartilages lie the Meibomian follicles. Underneath the skin and the ciliary portion of the oroicularis palpebrarum muscle, the roots of the eyelashes lie close on the tarsal cartilages. Tarsal* cartilages.- — Tarsi; ¥r.,Les Tarses; Ital., / tarsi; Germ., l)er Augenliedknorpel. These are thin plates of fibro-cartilage, convex on the outer surface, concave on the inner, to be adapted to the front of the eyeball. The upper is the larger. One of their margins is thick and straight, the other thin and curved, especially so in the upper, which therefore re- presents in some degree a segment of a circle, whilst the lower is little more than a narrow stripe. The thick and straight margin, called the ciliary, forms the margin of the eyelid ; the thin and curved margin, called orbital, degene- rates into the membraneous expansion already mentioned under the name of tarsal ligaments. Towards the outer canthus the orbital margins of the tarsal cartilages run into the ciliary ones at an acute angle, whilst towards the inner can- thus they form an obtuse angle by their junc- tion. The transverse length of the tarsal carti- lages is somewhere about an inchj the breadth of the upper cartilage at its broadest part about one-third of an inch, the breadth of the lower cartilage only half as much. At the inner can- thus the tarsal cartilages extend no farther than the lacrynial points, and at the outer canthus they stop close to the commissure of the two lids. As to the intimate composition of the tarsal cartilages, they consist of what is called fibro- cartilage, a microscopically fibrous substance, without any of the corpuscles of common carti- lage. In the human lower eyelid, the thickness of this substance is inconsiderable, and its con- sistence not so great as in the upper. In the lower animals it is in the same state in both eyelids. This is what has led Zeissf to say that he never found a real cartilaginous tarsus in the human lower eyelid, nor among the lower mammifera in the upper eyelid either. "In * Tarsus, propter siccitatem quod tarnis sit ex- pers. t Anatnmische Untersuchungen der Meibornis- cnen Druscn des Menschen und der Thieren mit besondere Beriicksichtigung ihrer Verhaltniss zum larsus. In Amnion's Zeitschrift der Ophthalmo- logic Bd. iv. p. 249. VOL. in. the sow only," says he, " there is a nearer ap- proach to a tarsal cartilage than is to be found in any other of the lower animals." Miiller* has very well explained away all this difference of opinion, by snowing that the dense cellular tissue which, according to Zeiss, occupies the place of tarsal cartilage in the human lower eyelid, and in both those of the inferior mammi- fera, is the same tissue, as the more consistent fibro-cartilage of the human upper eyelid, only in a less condensed state. The Meibomian glands are commonly de- scribed as being situate between the palpebral conjunctiva and tarsal cartilage. Winslow, Haller, and Zinn describe them as lying in grooves on the posterior surface of the tarsal cartilages. The Meibomian glands are seen very distinctly from the inside of the eyelids, as if they were immediately underneath the con- junctiva. But if the skin and orbicularis muscle be removed from the outside, these glands be- come equally visible there. "Where, then," asks Zeiss,f"do they lie,— before or behind the tarsal cartilage 1" Examination of sections of the cartilage shows that the Meibomian glands lie in the substance of the tarsal cartilage itself; and in the human lower eyelid and in both those of the lower animals, in the less consistent fibrous structure which there composes the tarsus. At the outer canthus the cellulo-membra- neous expansions called tarsal ligaments are stronger, and form bands which decussate and thus tie the tarsal cartilages to each other and to the outer margin of the orbit. These bands compose what is called the external palpebral ligament. The internal palpebral ligament is the tendon of the orbicularis palpebrarum muscle, — tendo ocu/i, or tendo palpebrarum. This, to adopt the description of Professor Harrison of Dub- lin, " is a small horizontal tendon, nearly one quarter of an inch in length. It is inserted in- ternally into the upper end of the nasal process of the superior maxillary bone ; thence it passes outwards and backwards to the internal com- missure of the eyelids, where it forks into two slips which enclose the caruncula lacrymalis, and are then inserted each into the tarsal carti- lage and the lacrymal duct." J Orbicularis palpebrarum muscle. — This is de- scribed in the article Face, vol.ii.p. 221. Here we shall only advert to some particular points in its history. The fibres of the orbicularis pertaining to the upper eyelid arise from the internal angular process of the frontal bone, and from the upper edge of the tendo pal pefcra and proceed, forming a curve, at first^tj ,uds and outwards, and then downwards j5la,$3ut- wards, within the upper eyelid and along and over the upper edge of the orbit towards the temple and outer angle of the eye. Here they meet those of the lower eyelid which have come from the nasal process of the upper jaw-bone, * Archiv, 1836. .Tahresbericht, p. xxxviii. t L. c. p. 240, and op. cit. Bd. v. S. 216. See also Sichel in Lancette Fiancaise, Gazette des Ho- pitaux, No. 53, 55, and 57. Paris, 1833. X Dublin Dissector, 4th ed. p. 6. G 82 LACRYMAL ORGANS. and from the lower edge of the palpebral ten- don, curving at first downwards and outwards, then upwards and outwards, within the lower eyelid and along the edge of the orbit, extend- ing some way down over the cheek.. The part of the orbicularis more immediately contained within the eyelids, sometimes called the palpe- bral and ciliary portions, in contradistinction to the outermost fibres, which are without the eye- lids, and encircle the base of the orbit, therefore called the orbital portion, consists of pale thin fibres, of which those at the margin of the eye- lids are collected into a considerable fasciculus, having interposed between them and the tarsal cartilage the roots of the cilia. At the outer canthus the upper and lower fibres intercross and adhere to the external palpebral ligament. That many of the fibres of the orbicularis are inserted into and exert their action in a great degree on the skin of the eyelids, may be easily ascertained in the living person, by observing, during the action of closing the eye, the traction of the skin of the eyelids towards the nasal can- thus. By this traction, the skin, especially in the lower eyelid, is very much corrugated. This corrugation of the skin of the lower eyelid by the action of the orbicularis is greatest right over the lower part of the lacrymal sac, — that part which we commonly press upon when we want to evacuate any accumulation of mucus or tears, — that part where abscess of the sac gene- rally bursts and leaves a fistulous opening, — that part which we open in the operation for so- called fistula lacrymalis. This part of the lacrymal sac must therefore be immediately affected by the contraction of the muscle, and the pressure thus produced, together with that on the upper blind end of the sac by the supe- rior fibres, will promote the transmission of the tears and conjunctival mucus into the nasal duct. The great use of the orbicularis palpebrarum is to close the eyelids; but in effecting this it acts at a disadvantage, inasmuch as its action on the eyelids is not direct, but oblique ; there- fore they are brought together only by being drawn horizontally inwards, though it is the lower eyelid alone which yields to this latter movement. We may imitate in some degree the mode of action of the orbicularis, but in an opposite direction, by pressing the skin imme- diately outside the outer canthus, towards the temple. Levator palpebra svperioris muscle. — This is the antagonist of the upper part of the orbicu- laris. It is a weak slender muscle, but then it has the advantage of exerting its action in a di- rect manner. It extends from the bottom of the orbit to the superior tarsal cartilage, lying im- mediately underneath the roof of the orbit. It is the longest of all the muscles of the orbit. Thin and triangular, it rises by its apex, which is a short tendon, from the upper edge of the optic foramen. The fleshy body of the muscle gradually increases in breadth as it proceeds forwards ; then bending downwards over the eyeball, its insertion takes place by a broad thin tendinous expansion, the base of the triangle, into the upper margin and anterior surface of the superior tarsal cartilage, being incorporated at the same time with the so-called tarsal liga- ment. It is by the action of this muscle that the upper eyelid is drawn up and retracted within the orbit. Having thus described the skeleton and mus- cles of the eyelids, it remains to consider their investments and appendages. The investment of their inner surface, the palpebral conjunctiva, will be described farther on, along with the rest of the conjunctiva. The skin of the eyelids lies over the fibres of the orbicularis „palpebra- rum. It is very fine and destitute of hairs, but contains minute sebaceous follicles. The latter are sometimes, especially in. the lower eyelid, enlarged, and give out a morbid secretion, which is hard, and forms those horny excrescences occasionally met with in old persons. Cellular tissue of the eyelids. — The conjunc- tiva investing the inner surface of the tarsal car- tilages adheres without the intermedium of any cellular tissue. The connection between the two structures is immediate and intimate, as in the compound membranes called fibro-mucous. The rest of the palpebral conjunctiva adheres by cellular tissue. The palpebral and ciliary portions of the orbicularis muscle are connected on the one hand to the tarsal cartilages and other subjacent parts,, and on the other to the superjacent skin, by a laminar cellular tissue, which, like that in some other parts of the body, is not combined with the adipose tissue. Being rather loose, the cellular tissue of the eyelids becomes readily infiltrated by effused fluids, as in adema and emphysema. It is not unfrequently the seat of abscess. Roots of the eyelashes. From the anterior edge of the free margins of the eyelids, the eyelashes spring. They are inserted three or four deep, especially in the middle. The cap- sules of the bulbs of the eyelashes lie close on the tarsal cartilage under the ciliaris muscle and skin, extending to the depth of about one- eighth of an inch. One of the operations for trichiasis is to extirpate the roots of the eye- lashes, but it is very difficult to remove them all, the oozing of blood is generally so great. When the part has healed after the operation, and the case seems doing well, a hair or two will often be found here and there sprouting out again. Connected with the roots of the eyelashes, as with other hairs, are small sebaceous glands, consisting of minute but distinct lobules or grains closely surrounding the capsule, into which they send one or more excretory ducts.* Meibomian glands. Glandula Meibo- miana s. palpebrarum sebacea ; — Fr. Les glandes de Meibom ; — Ital. Le glandule Mei- bomiane ; -Germ. Die Meibomschen Dr'usen. * Gurlt, Vergleichende Untersuchungen uber die Haut des Menschen und der Haussaugethiere, besonders in Beziehungauf die Absonderungsorgane des Haut-talges und des Schweisses. In Muller's Archiv, 1835, p. 399. t Zeiss. Fortgesetzte Untersuchungen uber die Anatomie und Pathologie der Augenlider von Dr. E. Zeiss in Dresden. In Ammon's Zeitschrift, &c. B. 5, p. 216. LACRYMAL ORGANS. 83 These are elongated more or less compound follicles, secreting a peculiar sebaceous matter intended as an ointment to protect the delicate integument of the margins of the eyelids from any irritation which might result from friction, or the frequent contact of the tears, and also to preserve to it that peculiar degree of sensibility which, like all other transition structures from skin to mucous membrane, it possesses. The Meibomian glands lie imbedded in the sub- stance of the tarsal cartilages. They are ar- ranged close and parallel to each other, and ge- nerally speaking in a direction at right angles to the ciliary margin of the eyelids, where they open in that row of minute apertures already mention- ed. Thereare between thirty and forty Meibomian glands in the upper eyelid, but not so many in the lower, in which also they are shorter in consequence of the difference in breadth be- tween the upper and lower tarsus. Sometimes two glands are united towards their orifice ; sometimes, on the other hand, at their end. Frequently the tail of the gland bends laterally and describes an arch. The structure of the Meibomian glands consists essentially in a central canal running from one extremity to the other, like the duct of the pancreas, and around that canal glandular loculi or cryptas opening' into it directly, or through the medium of each other. The duct suddenly contracts before opening on the margin of the eyelid. In a transverse section of the Meibomian glands this canal is seen, according to Zeiss, as a small hole around which are placed from five to six glandular grains. The Meibomian glands of the sow are small ; representing merely a short cyst subdivided into several loculi. The glands of the eye- lashes in the same animal are, on the contrary, large. The Meibomian glands of the sheep, dog, and fox, are long very thick-walled bodies, in the middle of which there is a wide canal. Ranking next in complexity of structure are the human Meibomian glands. Those of the horse, ox, goat, and cat, Zeiss found still more complex, consisting of lobes, lobules, and granules.* The secretion of the Meibomian glands is a mild, yellowish, unctuous substance, of the consistence of lard. Occasionally the external orifice of one or more of the Meibomian ducts becomes covered by a thin film, apparently of epidermis. This prevents the escape of the secretion, which accumulating raises up the film into a small elevation, like a phlyctenula. This does not actually cause pain, but gives rise to uneasiness in the part when the eyelids are moved : the film is easily broken, and the accumulated secretion removed on the point of a pin. Hordeolum, or stye, according to some, is abscess of the Meibomian glands ; according to others, a small boil implicating the cellular tissue at the margin of the eyelid. Zeissf sus- pects it has its seat in the capsule and glands * Zeiss's papers in Amnion's Zeitschriff, B. iv. and v., already quoted. - - " t Locis citatis. of the roots of the eyelashes. Abscess of the Meibomian glands does occur, and gives rise to a tumour on the edge of the eyelid like a stye, but the nature of the case is seen on everting the eyelid. There can be no doubt that the roots of the eyelashes are involved in the disease, because the hairs at the part affect- ed generally fall out at the end. Dr. Zeiss proposes to anticipate this result by plucking them out at once, and he says that by this pro- cedure the progress of the complaint is arrested, a thing, certainly, occasionally very desirable. In a small inflammatory tumour at the root of a hair on the cheek, I have obtained such a result from plucking out the hair. Fig. 12. The eyelids of the right side seen from within. ( Modified from Soemmerring.) a, a, Inner surface of orbicularis palpebrarum muscle. b, Palpebral fissure. c, c, c, Upper mass of lacrymal gland. d, Lower mass of lacrymal gland. e, e, Conjunctiva, the palpebral portion is smoothly spread on the inner surface of the eyelids. The portion which has been dissected from off the. eyeball is in folds. /, Hairs inserted into the orifices of the ducts of the lacrymal gland. These orifices are on the conjunctival surface of the upper eyelids towards its temporal extremity. g, q, Meibomian glands of both eyelids seen shining through the conjunctiva and the thin layer of tarsal cartilage covering them on the inside of the eyelids. h, Lacrymal papilla and point of the upper eyelid. i, The same of the lower eyelid. k, Lacrymal caruncle. I, Semilunar fold pressed aside to show the caruncle. II. The conjunctiva, semilunar fold, and lacrymal caruncle. The conjunctiva in general. — Tunica con- junctiva seu adnata. Fr. La Conjunctive. Ital. La Congiuntiva. Germ. Die Bindliaut. The conjunctiva is that membrane which lines the posterior surface of the eyelids, and covers the front of the eyeball to the extent of about a third of its whole periphery. This disposition has given rise to the distinction of a palpebral and ocular conjunctiva. Towards the margin of the orbit, all round the circumference of the eyeball, a cul-de-sac is formed by the reflection 84 LACRYMAL ORGANS. and continuation with each other of these two portions of the membrane. It is by this conti- nuity that the eyelids and eyeball are held in connexion, hence the name conjunctiva, and that the orbit is closed in and cut off from all communication with the space between the eyeball and eyelids. The space between the eyelids and eyeball we shall distinguish by the name of oculo-pulpebral space oj' the conjunctiva, a name, the necessity for which appears from this, that in common language, when it is said a foreign body has got into the eye, it is only meant that it has got into the oculo-palpebral space of the con- junctiva. The propriety of the name moreover will become more evident when the space in Serpents and Geckoes comes under considera- tion, for in them it is a closed cavity, (in ser- pents already designated by Jules Cloquet* oculo-palpebral sac of the conjunctiva,) re- ceiving the lacrymal secretion and communi- cating with the exterior only by the connexion it has with the nose through the nasal duct. What are called the superior and inferior palpebral sinuses of the conjunctiva are those parts of the oculo-palpebral space under the upper and lower eyelids respectively, where the ocular and palpebral portions of the con- junctiva are reflected and continued into each other, forming a cul-de-sac. The conjunctiva is here loosely attached to the subjacent cellular and adipose tissue, &c. of the orbit, and forms folds constantly varying with the motions of the eyeball and eyelids. The superior palpebral sinus of the conjunctiva is deeper than the lower, the reflection of the conjunctiva from the eyelids upon the eyeball being when the eyelids are passively closed : above, at the distance of about seven-tenths of an inch from the margin of the upper eyelid, and below, at about three- tenths of an inch from the margin of the lower. The cul-de-sac formed by the reflection of the conjunctiva does not lie very deep within the outer canthus, speaking in reference to it alone, though as near the edge of the orbit as above or below. The looseness of the folds formed by the conjunctiva at the upper and lower palpebral sinuses and within the outer canthus, together with the peculiar nature of its disposition at the inner canthus, presently to be noticed, allows of the free motions of the eyeball in all direc- tions. These folds may be readily seen on everting either eyelid, as also the continuity of the conjunctiva from the eyelid to the eyeball by requesting the person to look upwards, if it is the lower eyelid which is everted, downwards in the contrary case. In operations on the eyeball when the eyelids are held apart unskilfully, the folds are thrust out between the eyelids by the action of the orbicularis muscle, so that they almost bury the front of the eyeball and consequently im- pede the operator. By long-continued catarrhal ophthalmia and the abuse of blue stone and similar escharotics, * Memoire sur l'existence et la disposition des voies lacrymales dans los serpens. Paris, 1821. the conjunctiva is apt to become contracted and thickened, and to acquire at the same time a callous articular surface. In such cases the contraction tells very much upon the looseness of the folds of the conjunctiva at the upper and lower palpebral sinuses, which may indeed be said to be obliterated. The consequence of this is great restriction in all the movements of the eyeball. Foreign bodies which may have entered the oculo-palpebral space sometimes get lodged in the palpebral sinuses of the conjunctiva, especially the upper, and may be retained there for a length of time without causing much or any irritation, the conjunctiva being there so loose and the adjacent cellular and adipose tissue of the orbit so soft that the body is not much pressed upon by the opposing surfaces. The contrary is the case when the foreign body lies between the eyeball and the firm part of the eyelid, for here its irritation excites the orbicularis muscle to stronger action which serves but to aggravate the distress. Disposition of the conjunctiva at the inner canthus.— Under this head falls to be consi- dered the semilunar fold, the notice of which it will be advantageous to premise by a descrip- tion of the lacrymal caruncle. In consequence of the prolongation of the palpebral fissure at the inner canthus into a secondary one, the lacrymal caruncle and semilunar fold are so exposed that their external conformation can be readily and indeed best studied in the living eye. Lacrymal caruncle, caruncula lacrymalis. Fr. La caroncule lacrymule. Ital. La carun- cula lugrimale. Germ. Die Thrunenkarunhel. Tuis is a small reddish yellow eminence having a slightly tuberculated surface, beset with very delicate scarcely visible hairs. It is situated, as has been said, within the secondary fissure of the inner canthus, and inclosed between the two slips of the tendo palpebrarum. To see the lacrymal caruncle in its whole extent, it is necessary to evert slightly the lower eyelid, when it is observed running into a point down- wards and outwards. The lacrymal caruncle consists of a mass of loose fibro-cartilaginous tissue, similar to that of the tarsal cartilages, in which are imbedded follicles, secreting a fluid of the same nature as that of the Meibomian glands, and pouring it out by twelve or fifteen excretory orifices on its surface, which is in- vested by the conjunctiva. Anciently the la- crymal caruncle was thought to be the secreting organ of the tears, and the lacrymal points the excretory orifices. Semilunar fold, plica semilunaris. Fr. Le repli scmilunaire. Ital. La piega semilunar e. Germ. Die halbmondfurmigen Falte. In passing from the caruncle to the eyeball, the conjunctiva forms a vertical semilunar fold which encloses at its free edge a minute cartilage of a nature similar to the tarsal cartilages. This part of the conjunctiva is distinguished from the ocular portion by its reddish colour and greater thick- ness, indeed it resembles more the palpebral conjunctiva than the ocular. The concavity of the crescent, which is also the free edge of the LACRYMAL ORGANS. 85 fold, is towards the cornea. The rolling of the eyeball outwards has a tendency to undo the fold, which on the contrary is rendered more distinct when the cornea is turned towards the nose. In quadrupeds the semilunar fold is much more developed, and contains within it a more distinct cartilaginous plate. It consti- tutes what in them is called membrana nictitans. The third eyelid in birds is the same structure carried to its highest pitch of development. In man, in whom it is very small, its component structures are readily developed to a consider- able size by inflammation. According to Soem- merring the semilunar fold is larger in the negroes. We shall have occasion to recur to the membrana nictitans of quadrupeds and the third eyelid of birds. The intimate nature of the connexion between the tarsal cartilages and the conjunctiva which lines them has been already noticed. Beyond the tarsal cartilages the adhesion of the palpe- bral conjunctiva becomes looser and looser until its transition into the ocular conjunctiva. The ocular conjunctiva is smoothly spread over the front of the sclerotica, where it first passes on the latter. The interposed cellular tissue is loose enough to allow it to slide upon the sclerotica, or even to be raised up in wrin- kles according to the motions of the eyeball, which are thus facilitated. But as the con- junctiva approaches the cornea it is more and more closely applied to the sclerotica and con- sequently less readily falls into wrinkles. The debated question of a conjunctival covering of the cornea will be considered when speaking of the intimate structure of the conjunctiva. The cellular tissue between the conjunctiva and sclerotica is sometimes the seal of extrava- sations of blood, subconjunctival ecchymosis, sometimes the seat of an accumulation of se- rous fluid, as in the oedema attending erysipela- tous ophthalmia. It is sometimes the seat of a more serious form of oedema, that known by the name of chemosis, and common in the purulent inflammation of the conjunctiva. It may also be the seat of emphysema, and is occasionally so of phlegmon. Nuture of the conjunctiva. — -The conjunctiva forms part of that membraneous system, conti- nuous with the skin at all the natural apertures of the body, which lines the interior of the respiratory and digestive canals, and to which, as to that lining the genito-urinary passages, the generic name of mucous membrane is given. Of course different parts of this system present specific peculiarities in structure and function, and this is the case even in regard to the palpe- bral and ocular parts of the conjunctiva, though so near each other. Some of the Germans have unnecessarily involved this subject. Thus Walther viewed the conjunctiva as mucous in the eyelids, tcgumentary over the sclerotica, and serous over the cornea. Whence we some- times meet in their ophthalmological works such expressions as " the conjunctiva considered as a mucous membrane," and " the conjunctiva considered as a serous membrane." In refe- rence to these opinions of his countrymen, Miiller* has thought it necessary to remark that the conjunctiva is as certainly a mucous membrane as any other of which the character has not been doubted. * * * On the other hand it has nothing in common with the serous membranes either in secretion, for the limpid secretion of the eyes is derived from the lacry- mal gland, or in its form, which is not that of a shut sac. Within the upper eyelid towards the outer canthus (Jig- 1 2./'), the conjunctiva presents the minute mouths, nine or twelve in number, of the ducts of the lacrymal gland. At the inner canthus the conjunctiva is continuous through the lacrymal points with the membrane lining the canalicules, and so through them, the la- crymal sac and nasal duct, with the mucous membrane of the nose. At the margin of the eyelids its continuity with the skin is seen. The oculo-palpebral space of the conjunc- tiva receives the tears much in the same way that the mouth receives the salivary secretions. Like other mucous membranes the conjunctiva secretes a mucous fluid which lubricates its surface and serves to protect it from the irri- tating action of external agents, and even from that of the lacrymal secretion which is naturally poured out on it. Intimate structure of the conjunctiva. Palpebral conjunctiva, conjunctiva palpe- brarum.— The conjunctiva lining the eyelids is thicker and more vascular than that which invests the sclerotica. On the posterior surface of the eyelids, about one-twelfth of an inch from and parallel with the posterior acute edge of the margin, there is a very slight groove. Between this and the edge of the eyelid the conjunctiva is sufficiently distinct by its moist shinins; surface and its vascularity, from the more integument-like though delicate invest- ment of the margin of the eyelids with which it is continuous. But it is immediately in the groove and especially beyond it that the con- junctiva, as pointed out by Eble,f first shows itself truly as a mucous membrane, that is, pre- sents all the characters commonly ascribed to mucous membranes. The palpebral conjunctiva consists of a chorion, the free surface of which presents papilla?, constituting what is called the papillary both/, and the whole is covered by an epithelium. The chorion of the palpebral conjunctiva is intimately incorporated with the tarsal fibro- cartilages, so that the latter and their investing conjunctiva might be considered together as constituting a compound or fibro-mucous struc- ture. Beyond the cartilages the chorion ap- pears in its independent and separable form as a felt-work composed of an interlacement of filamentous cellular tissue, and is the nidus for the ramification of the vessels and nerves. Papillary body. — If the upper eyelid be * Handbuch der Physiologic des Mensclien, Bd. i, S. 429, Coblenz, 1838, or Translation by Baly, p. 436. t Ueber den Bau und die Krankbciten der Bindc- haut des Angcs, p. 9. Wien, 1828. 86 LACRYMAL ORGANS. everted and examined, the moisture being first wiped off from its suiface, under different direc- tions of the light, an appearance is observed as of a shining surface beset with small brilliant grains, as if minutely shagreened. This ap- pearance is more or less distinct in different individuals and most so after death. The appearance described is produced by numerous papillae, considered nervous by Ruysch,* and small glands by Muller,f and, after him, by most other authors. Eble+ objects to this view of the matter, and asserts that the papillae are quite distinct from mucous glands, and are the same as the papilla found on other mucous surfaces, and that they particularly resemble the papillae of the mucous membrane of the gums and inner surface of the alae nasi. Eble, however, adds that these papillae present themselves in all the mucous membranes in a manner quite analogous to glands, and he thinks that the mucus of mucous membranes is the product of the secretion of the papillary body. And this is equally applicable to the secretion of the palpebral conjunctiva, whence it would appear that Miiller and Eble really do not differ in opinion, but only in the terms they employ to express it. The part where the papillary body appears least distinctly is between the edge of the eyelid and the groove on the posterior surface above mentioned. The palpebral conjunctiva all beyond the groove presents the papillary body in a more decided form, and the development of it goes on increasing to some distance beyond the orbital margin of the tarsus. The con- junctiva covering the lacrymal caruncle, as also the greatest part of the semilunar fold, present no papillary body. Towards the lacrymal points there is found a great number of pretty apparent papillae. The papillary body is very vascular. It is the morbid development of it which constitutes the so-called granulations of the eyelids in the puro-mucous ophthalmiae ; of which indeed the papillary body appears to be the peculiar seat. An inflammation suddenly affecting a healthy conjunctiva from atmospherical causes is what is conventionally called a catarrhal ophthalmia. If this be allowed to fall into a chronic state, or if the conjunctiva has been affected by a less marked inflammatory action ,for a time, the papillary body becomes hypertrophied. In this state it forms as it were a new organ ready to be affected by a form of disease which a healthy conjunctiva is not all at once so prone to as- sume. Mere congestion caused by over- exertion of the eyes, or by heavy caps and high tight collars, as Dr. Vleminckx thinks, together with fatigue, exposure, want of cleanliness, abuse of stimulating liquors, &c, may give * 10th Thesaurus. t Erfahrungssatze liber die contagibse oder agyptische Augenentzundung. Mainz, 1821. { Op. cit. p. 19, 29, pi. i and ii. Or the Belgian- French translation, " De la Structure et des Mala- dies de la Conjonctive. &c. Traduit de l'Allemand par Ed. de Losen de Seltenhoff, M.D. Publie par ordre du Ministre de la Guerre. Bruxelles, 183rji. rise to this unnatural development of the papil- lary body of the conjunctiva, and so predispose in a particular manner, on the occurrence of any atmospherical influence, to an attack of con- junctivitis, and that rather of the form of the Egyptian ophthalmia than of a simple ca- tarrhal. Epithelium of the palpebral conjunctiva. — " It is extremely difficult," says Eble,* " to distinguish this on so fine a membrane. Al- though I have succeeded, by maceration in boiling water, in detaching it in part from the eyelids of an ox, I have not again been able to convince myself of the exactness of the obser- vation as I could have wished." J. F. Meckel doubted the existence of an epithelium. Eble says again that he would, however, admit its presence on the conjunctiva rather from analogy than from observation. Here is a good example of the assistance derivable from the microscope, two such observers as Meckel and Eble unable with the naked eye to determine the existence of a structure which later observers with the microscope have fully established. We shall return to the subject in speaking of the epithe- lium of the conjunctiva bulbi. Sclerotic conjunctiva, conjunctiva sclerotica. As far as vascularity goes, there is a decided difference between this and the preceding. The sclerotic conjunctiva is composed of a chorion or vascular basis of the membrane covered by epithelium. Valentinf describes between the chorion and epithelium another structure which he calls papillary. The chorion of the sclerotic conjunctiva con- sists of irregularly stratified fibres of cellular tissue interwoven with bloodvessels and nerves. " Do the conjunctiva sclerotica and the conjunctival pellicle of the cornea also preserve a papillary body or not?" asks Eble,}; in re- ference to Valentin's assertion of one. Eble admits the structure described by Valentin under the name of papillary body between the chorion and epithelium of the conjunc- tiva bulbi, but thinks, and correctly, that it is a very different thing from the papillary body of the palpebral conjunctiva as described by himself. Valentin's papillary body of the con- junctiva bulbi is a matter of the microscope — Eble's papillary body of the palpebral con- junctiva, though minute, is still in some de- gree cognisable to the naked eye. Hypertrophy of the papillary body of the palpebral conjunc- tiva constitutes, as has been said, what is called granular conjunctiva. We never see such a gra- nular state of the sclerotic conjunctiva. The following is Valentin's description of what he calls the papillary body of the conjunc- tiva bulbi : — It is best seen in the human eye, " when, after several days' maceration, the loosened and swollen epithelium is carefully * Loc. eit. t Repertorium fur die Anatomie &c. Bd. 1 ; pp. 142—300. Berlin, 1837. J; In medicinischen jahrbiicher des k. k. Oester- reicliischen Staates. Neueste Folge, xvi. Band, p. 73. LACRYMAL ORGANS. 87 removed and the papillary body then separated by a shaving cut through the surface of the conjunctiva. The papillae are seen under a microscope magnifying three hundred diame- ters, as yellowish red corpuscles standing close together, of an arched conical shape and pre- senting a round nucleus in their interior. Many of the papillae have short pedicles. Many present at their extremity a small point or fila- mentous prolongation which runs towards the epithelium. Henle* thinks Valentin's papillae are nothing but the corpuscles of the epithe- lium, presently to be noticed, distorted by the action of the compressorium. Itappears to me that Valentin's papillary body constitutes a structure of the same nature as the corpus Malpighianum of the skin. We know that such exists in the sclerotic conjunctiva from the circumstance that in negroes and many of the lower animals it is tinged of a black or brown colour, whilst in Isabella horses and in Swiss races among oxen it appears yellowish. Epithelium of the conjunctiva. The dis- covery of a characteristic structure in epithe- lium enables us to determine its existence even when so delicate as not be separable as a dis- tinct layer. It may appear merely as a tena- cious mucus little more than perceptible to the naked eye, but examined under the microscope it is found to consist of minute polygonal cells, flat and containing a central nucleus. These corpuscles aggregated together more or less closely and in greater or less quantity con- stitute the substance of epithelium. The epi- dermis is essentially of the same structure; as also the corpus Malpighianum, only when this is coloured, the cellules are found to contain colouring particles, as is remarkably the case in the black pigment of the eye, the small hexagonal bodies composing the membrane of which belong to the same category as the cor- puscles of the epithelium or corpus Malpi- ghianum. According to Valentin the epithelium of the conjunctiva consists of rhoinboidal or quad- rate cells lying close together, the boundaries of which are formed by simple lines. In every cell there is found without exception a some- what darker and more compact nucleus of a round or largish form. The average diameter of these cells, in the human eye, is about the two-thousandth of an inch. The nuclei are about half the size. Thickening of the epithelium takes place in ectropium and callous granulations. What is called cuticular conjunctiva is at the same time a general contraction of the whole conjunctiva with a thickened and dry state of the epi- thelium. Does the conjunctiva extend over the cornea ? Every one admits the existence of a layer on the anterior surface of the cornea, quite dif- ferent from its proper substance, and apparently a continuation of the conjunctiva covering the sclerotica, but this layer on the anterior surface * Symbol*: ad Anatomiam Villorum intestina- lium, imprimis eoiurn epilhclii ct vasorum ]ac- tcoriim, p. 8. 4to. bcrolini, 1837. of the cornea does not present exactly the same or at least all, the anatomical and chemical characters as the sclerotic conjunctiva. What of it can be raised is like epidermis or epithe- lium, coagulated and rendered white by the heat applied to separate it, and moreover it is not vascular, the vessels seen ramifying on the surface of the cornea in some inflammations being situated underneath it. What is the nature of the superficial layer of the cornea? It is composed of two lamellae. The more superficial constitutes a very fine but firm epithelium. According to Valentin, after sixteen or twenty-four hours' maceration, the epithelium separates from the cornea. The cells have in this case lost a little in transpa- rency and are somewhat distended. The nuclei appear more or less swollen by the action of the water. The other lamella situated under- neath the epithelium is more loose in its co- hesion, and is what Valentin considers the same structure as the papillary layer described by him in the ocular conjunctiva. Valentin says that a chorion or fibrous layer does not exist in the conjunctival extension over the cornea. The bloodvessels derived from the sclerotic conjunctiva run merely betwixt the papillary body and the surface of the proper substance of the cornea. They are very deli- cate and extremely difficult to inject. Rumor' has described the arteries of the con- junctiva cornea; from injections. The fine twigs of the arteries of the sclerotic conjunctiva unite together around the margin of the cornea into a vascular wreath or circle. From this there arise very numerous branches which run from the circumference towards the centre of the cornea, and in their course make two or three very fine subdivisions. Their ends bend distinctly inwards, and appear to penetrate the proper substance of the cornea. Having thus shown on the surface of the cornea the existence of an epithelium and a structure, called by Valentin a papillary body, similar to what is found on the surface of the sclerotic conjunctiva, as also a stratum of blood- vessels, we must admit a cellular support for those vessels, however delicate. If so, the bloodvessels and cellular tissue would consti- tute the essential elements of a chorion. f We can only explain the development of those ex- tensions of membrane like sclerotic conjunctiva, over the cornea by supposing an irregular and undue development or hypertrophy of these elements. The question, "Does the conjunctiva ex- tend over the cornea?" may be considered as answered in the affirmative by the above ana- tomical demonstration. Morbid anatomy now comes in advantageously with its corro- borative evidence. " Nothing is more in favour," says Eble, " of the existence of a con- * In Amnion's Zcitschrift lid. v. p. 21, Tabic 1 Fig. 9 and 11. Sec also Miiller's Archtv, 1 83f> ; Jahrcsbeiicht, p. 28; and Hcnle Dc Membrana Pupillari, &c. Bonnas, 1832. + Medico-Chirurgical Transactions, vol. xxi. p. 414, London, 1838; London Medical Gazette, vol. xxiii. pp. 571, 702, 815. 88 LACRYMAL ORGANS. junctival layer on the cornea than the microsco- pical structure of this membrane, for there is the greatest resemblance between the structure of the sclerotic conjunctiva and the investment of the cornea."* Eble thus retracts the opinion he formerly expressed against the existence of a conjunctival layer of the cornea. Externally the sclerotica overlaps or en- croaches on, more or less, the edge of the cornea. In certain constitutions, and especially in old persons,! I have observed that the overlapping part of the sclerotica is thicker and more opaque than usual — perhaps also en- croaching more extensively on the cornea. The conjunctiva covering the overlapping sclerotica, especially when the latter is to any considerable extent, appears in its independent form with its chorion fully developed, and although it ad- heres to the subjacent overlapping part of the sclerotica very closely by cellular tissue, it by no means presents the same intimate union with the subjacent structure and the same rudi- mentary state which the conjunctival extension over the transparent cornea has. In an eye before me in which the overlapping sclerotica is to some considerable extent at the upper edge of the cornea, I easily raised up in a fold and then separated by dissection the perfectly developed conjunctiva from over the part. The conjunctiva covering the overlapping part of the sclerotica has a vascular connexion with the latter no otherwise than by the anastomoses of the proper vessels of each — a vascular con- nexion, which indeed subsists between the scle- rotica and conjunctiva elsewhere. The dispo- sition just described is connected with a point in the pathology of the eye, viz. the bluish white ring which is observed to encircle the cornea more or less completely in certain inter- nal inflammations of the eye, and so frequently in what is called arthritic iritis that it has been considered a diagnostic of it, but certainly with- out just grounds. Before explaining the cause of the appear- ance, I would request it to be remembered that the insertion of the ciliary ligament is at some little distance from the apparent margin of the cornea; that the vessels which form the red zone of the sclerotica in the internal inflammations of the eye, and in inflammation of the proper substance of the cornea, are vessels which send branches inwards to the iris, opposite the ciliary ligament, branches outwards to anastomose with those of the conjunctiva, and lastly, branches which, following the original direc- tion, go to be distributed to the proper sub- stance of the cornea. These vessels are not apparent in the healthy state, and one set of them only may become apparent in inflamma- tion. Thus in inflammation of the iris, they will be apparent only as far as opposite the in- sertion of the ciliary ligament. Between this and the clear part of the cornea is the opaque overlapping part of the sclerotica, which of * Mcdicinische Jahrbiicher des k. k. oester- reichischen Staates ; Neueste Folge. Band xvi. t The arcus senilis, it is to be remembered, is not here the question. course not being in the way of the progress of the vessels towards the inflamed part, remains white as usual, and the cornea not being affected the minute branches to its proper sub- stance remain unenlarged and unseen. Hence the overlapping part of the sclerotica is seen in contrast between the abruptly terminating red sclerotic zone on the one hand, and the trans- parent cornea (appearing dark on account of the dark structure behind it) on the other, forming the bluish white ring. From this explanation the bluish white ring round the cornea ought to exist more or less in all internal inflammations of the eye, unless obscured by vascularity of the conjunctiva in inflammation of the cornea. So it does; but in persons of otherwise sound constitution and not of advanced age, the overlapping sclerotica is so transparent and sometimes also to so small an extent, that it is not strongly contrasted by the transparent cornea. It is otherwise the case, however, in certain persons, especially such as are advanced in life, in whom the encroach- ment of the sclerotica and fully developed con- junctiva on the cornea exists to a great degree and in a very opaque state, that the bluish white ring appears in the exaggerated distinct- ness which has commonly attracted the notice of surgeons. The condition of the eye necessary for the distinct appearance of the bluish-white ring round the cornea occurring principally in old persons of bad constitution, and these being the very persons in whom an internal inflamma- tion of the eye very often presents what is called the arthritic character, are circumstances which readily explain the error of supposing the bluish white ring round the cornea diagnos- tical of arthritic iritis.* III. — Lacrymal organs properly so called. Under this head are comprehended : 1. The secreting lacrymal organs, or the lacrymal gland and its excretory ducts. 2. The derivative la- crymal organs, or the passages by which the secretions of the lacrymal gland and of the conjunctival surface are drawn off into the nose, viz. the lacrymal points, the lacrymal canalicules, the lacrymal sac, and nasal duct. The lacrymal gland and its ducts may be considered as a branched diverticulum of the conjunctiva; the derivative lacrymal organs, to use the expression of M. Ue Blainville, as nothing but the continuation of the conjunctiva and its anastomoses with the olfactive mem- brane. 1. Secreting lacrymal organs. Lacrymal ghnd,— Glandula lacrymalis ; Fr. Laglande lacrymale; Ital. La glandula lagri- male; Germ. Die Tlirdncndr'use. When the lacrymal caruncle was supposed to filtrate the succus lacrymalis, and the lacry- mal points to excrete it, the lacrymal gland was called glandula innominata. The lacrymal gland ( Fig. 13) consists of two masses, an upper and a lower. The upper mass, or glandula lacrymalis supe- rior, lies in the lacrymal fossa, a depres- * London Medical Gazette, vol. xxiii. p. 817. LACRYMAL ORGANS. no sion of a size sufficient to receive the point of the thumb, situated in the roof of the orbit at its upper and outer angle, just within the overhanging outer extremity of the superciliary arch. The superior lacrymal gland is of an oval or triangular shape about three-fourths of an inch in its longest diameter and about half an inch across. It is flattened from above downwards. Its upper surface is convex; its lower plane or concave. The thickest edge of the gland is turned outwards. The gland is of a reddish colour and is en- veloped in a thin but dense cellular coat. The lower mass of the lacrymal gland, or glandula lacrymalis inferior, is a loosely connected ag- gregation of lobules of the same glandular substance as the above. It was first described by the second Monro, who called the lobules, for distinction's sake, glandula congregate.* The lower mass of the lacrymal gland is smaller than the upper, with which it is in con- tact above, whilst below it extends to the outer part of the upper margin of the tarsal cartilage of the upper eyelid. It lies indeed in the substance of the upper eyelid at the outer part. It is seen shining through the conjunctiva in everting the upper eyelid. Fig. 13. Lacrymal ylund, left side. a a, Superior mass ; h b, inferior mass ; c, part t>f inferior mass lying towards the outer canthus. Intimate structure of the lacrymal gland. — The lacrymal gland is what is commonly called conglomerate. It belongs to Miiller's com- pound glands with canals of the ramified type. " In the arrangement of the secreting canals of the lacrymal glands," says Muller,f " two principal forms are observed : the one is that which I discovered in the chelonian reptiles ; the other, that which prevails in birds and Mammalia. In the chelonia, the gland is formed of a number of club-shaped lobes, united together by means of the different ducts which run in their interior. The duct of each lobe is pretty uniform in diameter, and into it open an innumerable quantity of microscopical tufts of cceca, which are arranged around it * Monro's Observations, Anatomical and Phy- siological, wherein Dr. Hunter's claim to some dis- coveries is examined, p. 77. Edinburgh, p. 77. Rosenmuller, Partium Externarum oculi lnimani, imprimis organorum lacrymalium descriptio anato- mica, &c. § 109. Lipsia:, 1810. t Handbuch der Physiologic des Mcnschen, Bd. i. S. 438. Or, Translation by Baly, p. 445. See also " De glandularum secernentium penitiori structura, p. 51, 52, tab. v. figs. 8, 4, 5, & 8. at right angles like the foliage of a moss on its stem." In birds, in which the lacrymal gland is very small and situate at the posterior angle of the eye, and Mammalia, the secreting ca- nals of the lacrymal gland are regularly branched and terminate in each acinus in a number of small cells. In birds these cells are very large ; and in them, and likewise in the horse, the cells can be filled with mercury from the efferent duct. Efferent or excretory ducts of the lacrymal glands. — The lacrymal glands pour out their secretion by nine or twelve very slender excre- tory ducts which proceed from above down- wards and open on the surface of the con- junctiva on the inside of the upper eyelid. The orifices of the ducts are placed at about one-twentieth of an inch apart from each other in a row extending about half an inch from the outer canthus inwards, parallel to but a little above the outer part of the upper margin of the tarsal cartilage, that is, at the inferior boun- dary of the lower mass of the gland. The excretory ducts of the lacrymal gland were first discovered on the 11th of November, 1665, by Nicolaus Steno,* in the eyelid of a sheep. He delineated them from the eye of the calf. Moreover it appears that Steno de- scribes vasa lacrymalia discovered in man, which opened in the membrane of the upper eyelid.f Admitted by some and doubted by others from the time of Steno, the ducts of the lacry- mal gland became a subject of dispute between Dr. William Hunter}; and the second Monro,§ the one claiming to have observed them in the human eye before the other. The best way to demonstrate the ducts is to stretch the upper eyelid, turned inside out, upon the finger; then wipe clean the surface of the conjunctiva, and having by close in- spection at the place where the ducts open, as above described, discovered the orifices, take a short piece of human hair in the point of a forceps, and entering it at the orifice, push it on in the direction of the duct. From the orifices on the surface of the conjunctiva the ducts run nearly parallel with each other upwards. Of two eyes before me I have in this way inserted hairs into nine orifices of ducts in the one and into twelve orifices of the other, a work which did not occupy five minutes for each eye. In both eyes there is one orifice of a duct exactly within the external commissure, * Obscrvationes Anatomica?, quibus varia oris, oculorum ct narium vasa describuntur, novique salivne, lacrumarum et muci fontes deteguniur et novum Bilsii commentum rcjicitur. Leidie, 1662. See also Bibl. Anat. Clerici ct Mangeli. Genev. 1699. fol. torn. ii. p. 787. t Thorn. Bartholoni epistolarum medicinalium a dortis et ad doctos scriptarum centuria iii. & iv. Hafnias, 1667-8. Epist. 53. cent. iv. \ Monro's Observations, Anatomical and Phy- siological, wherein Dr. Hunter's claim to some discoveries is examined, p. 77. Edinburgh, 1758. § Dr. William Hunter's Medical Commentaries, p. 1, containing a plain answer to Professor Monro. London, 1762-4. 00 LACRYMAL ORGANS. and another1 rather within the lower eyelid. See figs. 12 & 14. Fig. 14. A loft eye with the eyelids cut in the middle, and the outer halves everted to show the orifices of the ducts of the lacryraal gland, into which hairs are inserted. The preceding description of the lacrymal gland and its ducts shows that the latter and the lower mass at least of the former may be readily wounded along with the upper eyelid, and that in Crampton's operation for entro- pium, the lower mass of the gland, together with some of the lacrymal ducts, must neces- sarily be wounded, if the eyelid be cut through near the outer angle and to any height. In cases in which 1 have performed the operation, however, I have not observed any lacrymal fistula or other bad consequence follow. Tears. — Lacrythee, Fr. Les larrnes ; Ital. Le lugrime; Germ. Die Thr'dnen. The lacry- mal secretion like the salivary appears con- stantly to flow, though in no greater quantity than is sufficient to moisten the surfaces of the conjunctiva. The derivative lacrymal organs are in this case equal to the removal of it; but when the tears are poured out in unusual quantity, as they are, like the salivary or uri- nary secretion as well as that of the skin, in certain affections of the mind, they run over the margin of the lower eyelids and drop down the cheeks. According to Fourcroy and Vauquelin there remains after evaporating the tears, about one per cent, solid substance, which consists chiefly of common salt and a yellow extractive matter perfectly soluble in water. Before drying, this appears quite similar to mucus. 2. Derivative lacrymal organs. Previously to describing the passages by which the tears are drawn off into the nose, it will be advantageous to take a glance at the osseous groove and canal in which the prin- cipal part of those passages is lodged. Osseous groove for the lodgement of the lacrymal sac. The lacrymal groove, sulcus la- crymalis, is situated at the fore part of the inner wall of the orbit. It is directed from above downwards, extending from the junc- tion of the frontal bone with the nasal process of the superior maxillary and with the lacrymal bone, on the one hand, and to the inner and lower angle of the margin of the orbit on the other. Here it runs into the osseous canal for the nasal duct. The lacrymal groove is pretty deeply scooped out, and is about eight-tenths of an inch long and five-twentieths broad. The outer aspect of the nasal process of the superior maxillary bone is divided by an as- cending ridge, the continuation of that forming the lower margin of the orbit, into two sur- faces. The posterior surface, which is the narrower, forms the anterior half of the lacry- mal groove. The posterior half of the groove is formed by that narrow grooved part of the orbital surface of the lacrymal bone in front of its vertical crest. The line of junction ( shin- dy lesis ) between the posterior margin of the nasal process of the superior maxillary bone and the anterior margin of the lacrymal runs down longitudinally in the bottom of the groove. The anterior margin of the lacrymal groove formed by the ascending ridge subdividing the outer surface of the nasal process of the supe- rior maxillary bone, is thick and rounded. The posterior margin, formed by the crest which subdivides vertically the orbital surface of the lacrymal bone, is thin and sharp. Inferiorly the crest of the lacrymal bone forms a small curved prolongation directed for- wards and outwards, which serves to form the commencement of the posterior wall of the osseous canal for the nasal duct. The process, which is called hamulus ossis lacrymalis, arti- culates with the orbital plate of the superior maxillary.* The osseous canal for the nasal duct. — The osseous nasal canal, about half an inch in length, extends from the lower extremity of the lacrymal groove to the lowest meatus of the nose, at the anterior part of which it opens. Its orifice is overhung by the anterior extremity of the lowest spongy bone. The osseous nasal canal is directed a little obliquely from before backwards^ and from within outwards. It is somewhat narrower in the middle than at either extremity. It is compressed from within out- wards, hence a horizontal section is rather elliptical than circular. The anterior and outer walls of the osseous canal are formed by a groove inclined down- wards and backwards on the inner surface of the body of the superior maxillary bone, the continuation of that on the nasal process which contributes to form the lacrymal groove. The posterior wall of the canal is in great part formed above by the hamular process of the lacrymal bone, where it articulates with the orbital plate of the superior maxillary. The lowest part of the posterior wall is formed by the meeting together of the lacrymal process * In man the lacrymal bone does not always form a single piece. '* In a great number of cases," says M. Rousseau, " the lacrymal bone is found divided into two unequal parts, even in aged sub- jects. The larger contributes to form the inner wall of the orbit, the smaller is situated below and outside the preceding on the floor of the orbit ; its exposed surface does not measure more than two millimetres in extent, but it dips under the vertical crest of the first portion, and contributes to form the lacrymal canal." See " Description d'un nouvel os de la face chez 1'homme," in An- nates des Sciences Naturelles. Paris, 1829. LACRYMAL ORGANS. 91 of the lowest spongy bone and the posterior margin of the groove in the superior maxillary, constituting the anterior and outer walls. The internal wall of the osseous nasal canal is formed superiorly by a continuation of the osseous surfaces composing the lacrymal groove. Below, it is formed, in front, by a farther con- tinuation of one of these surfaces, viz. that of the superior maxillary bone, and behind by a thin plate of the lowest spongy bone, the nasal or lacrymul process of the lowest spongy bone, which rises to join the inferior edge of the lacrymal. The anterior edge of this process of the spongy bone joins the posterior edge of the lower part of the lacrymal surface of the nasal process of the superior maxillary. The line of junction is thus the continuation of that at the bottom of the lacrymal groove. Lacrymal papilla, points and canalicules. — ( Fig. 15. ) At the inner extremity of the ciliary Fig. 15. Continuation of Figure 11, showing the relative situa- tion of the upper mass of the lacrymal gland, and t/ie exact shape of the derivative lacrymal passages. (From Soemmerring. ) a, b, c, d, superior and inferior lacrymal canali- culi; a, a, lacrymal points; b,b, the small blind dilatations presented by the lacrymal canalicules, where they bend inwards to the lacrymal sac ; c, c, continuation of the lacrymal canalicules ; d, d, their entrance into the lacrymal sac ; e,f,g, lacry- mal sac ; e, blind end of the lacrymal sac ;f, middle part of the lacrymal sac ; g, its termination ; h, i, nasal duct i, opening of the nasal duct into the nose. margin of each eyelid, where the fissure of the nasal canthus begins, there has been already de- scribed a small papillary eminence, lacrymal papilla, papilla lacrymalis, in the summit of which is a small orifice, lacrymal point, of such a size as to admit a thick bristle. The lacrymal points, puncta lacrymalia ; Fr. Les points lacryrnaux ; Ital. I punti lugrimali ; Germ. Die Thrdnenpunkten ; are from their size and situation sufficiently conspicuous as not to be confounded with one of the orifices of the Meibomian follicles. In the natural state the lacrymal papilla: are inclined towards the lacus lacrymalis. The lower papilla is somewhat more prominent than the upper, and situate some- what more towards the temple. The lacrymal canalicules, canaliculi lacrymales, s. cornua limacum ; Fr. Les conduits lacryrnaux ; Ital. I condotti lagrimali ; Germ. Die Thrunen- kandlchen; lead from the lacrymal points into the lacrymal sac. From the superior lacrymal point the superior canalicule proceeds upwards and outwards within the papilla a little way, then suddenly bending at an acute angle and forming at the same time a small dilatation, it runs downwards and inwards, inclosed in the fold of skin and conjunctiva forming the upper border of the fissure of the nasal can- thus, to the lacrymal sac. The course of the inferior canalicule is the counterpart of the above. From the lower point it runs a short way perpendicularly downwards and outwards within the corresponding papilla, then bend- ing abruptly and like the upper forming a small dilatation, it proceeds upwards and in- wards, inclosed in the fold of skin and con- junctiva forming the lower border of the fissure of the nasal canthus, to the lacrymal sac. The canalicules having met each other at the commissure of the fissure of the nasal canthus, pass under the tendon of the orbicularis mus- cle, and open by separate orifices, close to each other however, into the anterior and outer part of the lacrymal sac. These orifices indeed are separated merely by a duplicature of the mucous membrane composing their walls. The lacrymal canalicules have pretty firm walls of mucous membrane, which do not col- lapse, but when cut across are seen gaping open. The calibre of the canaliculi is about the thirtieth of an inch in diameter ; that of the points is less, but these are capable of being dilated. The canaliculi are immediately surrounded by the fibres of the internal palpebral ligament, and those of the tensor tarsi muscle. Lacrymal sac ; saccus lacrymalis ; Fr., Le sac lacrymal ; Ital. II sacco lagrimale; Germ., Der Thrdnensack. — (Fig. 16). This is a membra- neous reservoir of a vertically elongated form, and externally compressed, nine-twentieths of an inch long, and two-tenths broad externally. Fig, 16. Derivative lacrymal passages of the left side, seen from the side of the nasal cavity. Here it is seen that the nasal duct is much broader viewed from the side than from before, a, h, superior and inferior lacrymal canaliculi ; c, d, lacrymal sac ; e, f, nasal duct ; /, nasal orifice of the nasal duct, seen quite in its natural state. 92 LACRYMAL ORGANS. It lies, by its inner and posterior surface, in the lacrymal groove, with the periosteum of which it is closely incorporated. Its an- terior and outer surface, which lies without the groove, is immediately covered by a strong aponeurosis derived from the upper and lower edge of the horizontal tendon of the orbicularis muscle, which passes across the la- crymal sac a little above the centre. This apo- neurosis adheres to the margins of the bony groove in which the sac is lodged, and there becomes continuous with the periosteum. More superficially, the anterior and outer surface is covered by the muscular fibres of the orbicu- laris and by the skin. Above the lacrymal sac forms a cul-de-sac or blind end, — -finis ccecus sacci lacrymalis. Be- low it passes into the nasal duct. This transi- tion is marked by a slight contraction, some- times inside, by a circular fold of the mucous membrane, of which both are formed. At its anterior and outer part, a little below its upper blind end, and immediately behind the internal palpebral ligament, the lacrymal sac receives the canalicules. Overhanging the orifices of these there is a small semilunar fold of the mucous membrane of the sac* The nasal duct ; ductus nasalis ; Fr., Le canal nasal ; Ital., II condotto nasale ; Germ., Der Nasenkanal, is a laterally compressed canal, about three-quarters of an inch in length, and readily admitting the passage of a probe the fifteenth of an inch thick, continued from the lower part of the lacrymal sac. It runs downwards, backwards, and a little outwards in the osseous canal already described, of which it is indeed nothing but the membraneous lining. The nasal duct is more contracted in its middle than at either extremity. It opens in the anterior and upper part of the lower meatus, at the lateral wall of the nasal cavity, and about one inch from the entrance of the nostril. Its ori- fice, which is overhung by the lower spongy bone, is a long fissure, oblique from above downwards and from within outwards. The obliquity of the orifice of the nasal duct is owing to the circumstance that the posterior or external wall of the membraneous part of the nasal duct descends farther than the osseous canal, and forms, by means of the folded pitui- tary membrane, a semi-canal, which descends in the external wall of the lower meatus, whilst the internal wall of the membraneous part of the nasal duct is shorter, and terminates where the osseous canal stops. The lacrymal sac and nasal duct are com- posed of a thick soft mucous membrane, which must be considered as productive of that of the nose. Externally, this mucous membrane is united with the periosteum of the osseous sur- faces in connection with the lacrymal sac and nasal duct, and as far as concerns that part of the lacrymal sac not in the osseous groove, by the aponeurosis derived from the tendo palpe- brarum. Internally, the mucous membrane of the la- crymal sac and nasal duct forms various small * Rosenmiiller, op. cit. § 125. plica? or rugse. Red and villous, it is quite different from the white and smooth mucous membrane of the canalicules. Like the pitui- tary membrane of the nose, it secretes, in the healthy state, a clear, mild, fluid mucus. Lacrymal or tensor tarsi muscle. — Here is perhaps the proper place to notice a muscle which was discovered many years ago by M. Duverney,* delineated and described by Rosen- miillerf in 1805, and more recently re-described by Dr. Horner,! an American anatomist, with whose name it is now commonly associated. To get a view of this muscle, Professor Hor- ner directs us to cut through the eyelids and separate them from the ball, except at the inner canthus ; then turn the lids over the nose, re- move the semilunar fold and the conjunctiva in the neighbourhood, with the fatty matter, when the muscle, such as it is represented in the fol- lowing description, will be seen. " The tensor tarsi arises from the posterior superior part of the os unguis, just in advance of the vertical suture between the os planum and the os unguis. Having advanced three lines, it bifurcates ; one bifurcation is inserted along the upper lacrymal canalicule, and terminates at its punctum, or near it ; and the lower bifur- cation has the same relation to the lower lacry- mal canalicule. The base of the lacrymal caruncle is placed in the angle of the bifurcation. The superior and the inferior margins of the muscle touch the corresponding fibres of the orbicularis palpebrarum, where the latter is connected with the margin of the internal can- thus of the eye, but may be readily distin- guished by their horizontal course. The nasal face of this muscle adheres very closely to that portion of the sac which it covers, and also to the lacrymal canalicules. The lacrymal sac rises about a line above its superior margin, and extends in the orbit four lines below its inferior margin. The orbital face of the muscle is covered by a lamina of cellular membrane, and between this lamina and the ball of the eye are placed the semilunar fold of the conjunctiva, and a considerable quantity of adipose matter. As the bifurcated extremities of the muscle fol- low the course of the canalicules, they are co- vered by the conjunctiva. The muscle is an oblong body, half an inch in length, and about one quarter wide, bifurcated at one end ; and it arises much deeper from the orbit than any ac- knowledged origin of the orbicularis. The su- * (Euvres Anatomiques de M. Duverney, torn. ii. 4to., Paris, 1761. After speaking of the fibres of the orbicularis which lie over the lacrymal sac, it is said (torn. i. p. 130), " Entre ces fibres, il y a un petit muscle an dedans du grand angle qui prend son origine de la partie anterieure de l'os planum et s'insere a la partie interne du tendon mitoyen ou commun a l'appose de l'orbiculaire ; e'est un petit muscle que j'ai observe il y a long-temps." f Rosenm'uller, Icones Chirurgico-Anatomicse. Wiemar, 1805. See also Mackenzie in Medical Gazette, vol. xi, 1 Medical Repository for July, 1822. See also, A Treatise on Special and General Anatomy, by William E. Horner, M. D., Professor of Anatomy in the University of Pennsylvania, &c. vol. ii. p. 498. Philadelphia, 1826. LACRYMAL ORGANS. 93 perior fork, however, has a few of its fibres blended with the ciliaris." The action of the muscle appears to be to direct the lacrymal papilla? and points in to- wards the lacus lacrymalis, and to assist in keeping the edges of the eyelids properly ad- justed to the eyeball. Nerves. — The parts of the organ of vision which have been just described receive their nerves from the fifth and seventh pairs ; the former communicating sensibility, the latter the power to move. See articles, Fifth pair of Nerves, and Seventh pair of Nerves. The first division of the fifth pair gives nerves not only to the accessory parts of the eye, but supplies also the eyeball ; hence it is called ophthalmic. The second division of the fifth sends filaments to the lower eyelids. Nerves from the first division of the fifth distributed to the accessory parts of the eye.— The first division of the fifth pair or the oph- thalmic divides into three nerves, \he fron- tal, the nasal, the lacrymal. 1. Frontal nerve. The sapra-trochlear branch of this nerve gives filaments to the upper eyelid and inner canthus. The continu- ation of the frontal nerve sends filaments to the upper eyelid and external canthus. 2. Nasal nerve. The infra-trochlear branch of this nerve supplies the parts at the inner canthus, the conjunctiva, the lacrymal caruncle and lacrymal sac ; it also gives filaments to the orbicularis palpebrarum. The tensor tarsi* receives two twigs from it. The infra-trochlear sends branches upwards, which anastomose with those of the supra-trochlear. 3. Lacrymal nerve. — After supplying the lacrymal gland the branches of this nerve emerge from it, and ramify in the conjunctiva, orbicularis muscle, and skin of the eyelids. The lacrymal nerve forms anastomoses with other branches of the fifth. Nerves from the second division of the fifth pair distributed to the accessory parts of the eye. — The principal of these is the inferior palpebral branch of the infra-orbital. The in- ferior palpebral nerve divides into two branches, an external and an internal, which indeed may be separate from the first. The external branch runs in the substance of the lower eyelid, distributing branches in its course, to the outer canthus, where it anasto- moses with the inferior palpebral filaments of the lacrymal nerve. The internal branch supplies the part of the lower eyelid towards the nose, and terminates in the parts at the inner canthus, anastomosing with a branch of the infra-trochlear. The facial orportio dura of the seventh pair. — Of the accessory parts of the eye, the orbi- cularis muscle is that which receives branches from the portio dura of the seventh pair; per- haps, also, the tensor tarsi muscle, as Mac- * Rosenmiiller, Icones chirnrgico~anatomicCKr$%ov, Hipp.§ Ligula, Gal. Operculum, Cic. || Cartilugo epiglottidis. Epiglotte, Ft. Kehldeckel, Germ. The epi- glottis is a cartilaginous valve, situated at the base of the tongue, and covering the opening of the larynx. The direction of the epiglottis is vertical, except during the act of deglutition, when it becomes horizontal. In form it has been compared to a cordate leaf, (fig. 23,) or that of the artichoke. The di- mensions vary with the volume of the larynx. The anterior aspect of the epiglottis is convex, the posterior concave ; it is partly free and partly connected : the free portion projects above the level of the base of the tongue. It is lined by the mucous membrane : the centre of its superior margin is very slightly notched. Inferiorly it terminates by a kind of pedicle, very thin and delicate, which is attached to the angle of the thyroid immediately above the plane of the thyro-arytenoid ligaments. Nu- merous foramina are observed, perforating its substance (f f, fig. 23), rendering the struc- ture of this cartilage less dense than that of the thyroid or cricoid cartilage. It is consi- dered to be more brittle, in consequence of the cohesion of its particles being affected by these perforations. Its elasticity, however, is augmented by each perforation admitting some fasciculi of the yellow elastic ligament which is expanded, and, as it were, rivetted on its an- terior aspect. In the larger Ruminantia, such as the ox, this structure is very conspicuous, the thickness of the elastic tissue being nearly equal to that of the epiglottis itself. This ligament is disposed so as to secure perma- nently the return of the epiglottis after its de- * Anat. Descript. t Lemons Anat. Comp. % De organo vocis Mammaliura. § In Lib. Morb. 1. || De Nat. Dcor. ii. p. 54. Fig. 23. A posterior angular view of the cartilages of the larynx, exposing the rugged and perforated structure of the epiglottis after the removal of the mucous membrane and tlie yellow elastic ligamentous tissues. ( Drawn from a preparation in tlie Museum of King's College, London.) a a, the arytenoid cartilages ; b b, the superior cornua; c, the right inferior cornu ; d, the posterior surface of the cricoid catilage; e, the foramen for the transit of the superior laryngeal nerve ; f f, the perforation of the epiglottis ; i, the superior margin of the thyroid; t, the trachea; h, the right inferior tubercle. pression in the act of deglutition, indepen- dently of any muscular fibres. Its perforations have been described as giving lodgement to " muciparous follicles," but their office seems not to have been hitherto thoroughly investi- gated. Articulations and ligaments of the larynx. — The articulations are divided, first, into those connecting the larynx with surrounding struc- tures, called extrinsic articulations ; and, se- condly, those peculiar to the larynx itself, termed intrinsic articulations. Extrinsic articulations. — The hyo-fhyroid 104 NORMAL ANATOMY OF THE LARYNX. articulation. The thyroid cartilage is united to the os hyoides by three ligaments : the mid- dle and two lateral. 1st. The ligamentum thyro-hyoideum medium is a lax yellow tissue arising from the superior margin of the thyroid, and inserted into the inner margin of the os hyoides : it is thicker and denser at its middle part ; its lateral borders are involved with the surrounding cellular membrane. The anterior surface in its middle is situated immediately under the integuments, having its sides co- vered by the thyro-hyoidei muscles, (g, fig. 25) and its posterior surface corresponding with the form of the epiglottis. 2d. The ligamenta hyo-thyroidea lateralia are small round liga- ments on each side of the larynx, connecting the tubercles of the great horns of the os hy- oides with the extremities of the superior cor- nua of the thyroid cartilage (c c, jig. 24). In the substance of these ligaments there are often found small osseous or cartilaginous bodies. The articulations of the thyroid cartilage Fig. 24. A mesial section of the larynx, from Lauth. The mucous membrane and muscles are removed to expose the elastic ligaments. a, the epiglottis; b, the hyo-epiglottic ligaments; c c, the lateral thyro-hyoid ligaments ; e, a portion of the glosso-epiglottic ligament ; f, the crico-thy- roid ligament; g i, the junction of the crico-thy- roid, and lateral crico-thyroid ligament ; ri , the attachment of the lateral crico-thyroid ligaments to the base of the arytenoid cartilage ; n, the elas- tic ligament lining the bottom of the ventricles; o, the superior inner margin of the cricoid cartilage ; the lateral ligamentous connection with the inferior vocal coid ; I, the superior vocal cord ; the right arytenoid cartilage. with the os hyoides are furnished with syno- vial membranes. The ligatnents of the epiglottis. — The epi- glottis gives attachment to three ligaments, which contribute to its elasticity and the stabi- lity of its position. 1. The ligamentum thyro-epiglottideum arises from the mesial line below the notch of the superior angle of the thyroid, and is inserted into the base of the epiglottis. It binds the epiglottis to the thyroid cartilage. 2d. The ligamentum hyo-epiglottideum arises from the inner surface of the base of the os hyoides; its fibres passing horizontally are inserted into the anterior surface of the epiglottis ; its action tends to keep the position of the epiglottis per- manently vertical. 3d. The ligamentum glosso- epiglottideum. arises from the base of the tongue ; it lies in the median mucous folds be- tween the tongue and epiglottis, and is inserted into the anterior surface of the epiglottis im- mediately above the ligamentum hyo-epiglot- tideum. Its action is nearly the same as that of the last-named ligament, but it is also con- nected with the motions of the base of the tongue. The tracheo-cricoidean articulation. — The lower margin of the cricoid cartilage is arti- culated with the first ring of the trachea by a series of the same ligamentous fibres which connect the rings of the trachea with each other. At the anterior mesial base of the cricoid there are found additional ligamentous fibres. The elastic tissue which connects the larynx with the trachea permits considerable freedom in the multiplied movements of the neck without im- peding the regular transmission of the atmos- phere. In these movements the first ring of the trachea passes within the inferior margin of the cricoid cartilage. The intrinsic articulations of the larynx are, 1st, the crico-thyroid ; 2d, the crico-arytenoid. Besides these may be included the articulation of the arytenoid with the cartilages of Santorini. The cuneiform cartilages are generally unarticu- lated in man. The crico-thyroid articulation. — The inferior cornua of the thyroid are curved forwards and inwards. Their extremities present oblique planes directed inwards and downwards, which are firmly attached by a capsular ligament to the oblique discs on the sides of the cricoid, directed upwards and outwards. The ligament of this joint is of an orbicular form, radiating in oblique fasciculi, the pos- terior fibres of which extend nearly to the crico- arytenoid articulation. The crico-thyroid ligament. Syn. Pyrami- dal, or conoid ligament. Lat. Ligamentum crico-thyroideum. Fr. Membrane, ou liga- ment thyro-crico'idien moyen. The crico- thyroid ligament is a very thick, strong, yellow elastic ligament, arising from the mesial line of the inferior margin of the thyroid ; it then crosses the crico-thyroid space, and is inserted into the superior mar- gin of the cricoid. This ligament supports the anterior part of the cricoid cartilage, and NORMAL ANATOMY OF THE LARYNX. 105 trachea in conjunction with the crico-thyroid muscle. The nature and position of the arti- culation of the thyroid, with the cricoid, render the force of this ligament of great utility and importance. The Intend crico-thyroid ligament, lig. crico- thyroid laterale, arises immediately at the side of the crico-arytenoid articulation. Some fas- ciculi, according to Cruveilhier and Lauth, are attached to the bases of the arytenoids, others are reflected horizontally forwards to the in- ferior margin of the cricoid. It is bounded externally by the thyro-arytenoideus and crico- arytenoideus lateralis, and lined internally by the mucous membrane of the larynx. The crico-arytenoid articulation. — The ob- lique articulating convex surface of the cricoid is received in a corresponding channel or groove at the base of the arytenoid cartilage. The ligament arises from the cricoid, and ra- diates both anteriorly and posteriorly round the base of the arytenoid cartilage; a fasciculus is reflected along the base of its anterior mem- brane behind the attachment of the thyroary- tenoid ligament. The crico-arytenoid liga- ment is thick and strong, yet sufficiently loose to permit a diversity of motion. Some anato- mists divide the ligament into anterior and posterior. The articulation is lined and lubri- cated by a synovial membrane. The thyro-arytenoid ligaments. Syn. Chor- da vocales, Ferrein. Slimmb'dnder, Germ. These ligaments, as their name implies, con- nect the thyroid with the arytenoid cartilages, and are instrumental in the production of voice. There are on each side two vocal cords, a su- perior and an inferior; the cavities between these ligaments are termed the ventricles of the larynx. The inferior thyro-arytenoid ligaments, or, as they are often denominated, " the true ligaments of the glottis," are much thicker and stronger than the superior : they present the form of nearly rectangular parallelograms, and are stretched horizontally across the long axis of the larynx, from the anterior horizontal tubercle of the arytenoids, to the angle formed by the junction of the wings of the thyroid ( c, fig. 27). On their outer side these ligaments are connected with the thyro-arytenoid mus- cles ; their anterior extremities are inserted into the thyroid, the posterior to the arytenoid car- tilages ; the internal margins are free to vibrate. On exposing them by the removal of the mu- cous membrane they are found less than their apparent volume. Immediately after death they are semi-transparent, very elastic, and composed of parallel fibres. They are con- nected with, and form a continuation of the ligamentum crico-thyroideum lateralis (k,ftg. 24). The length of the vocal ligaments varies with the general dimensions of the larynx : in the adult male they are much longer than in the female. In infancy they are very short, and increase from that period to the age of puberty in an arithmetical ratio. Thus, if at one year old their length in parts of an inch is 0,2500, at five years they will be 0,3333, at nine 0,4166, and at fourteen 0,4999: these are close approximations. The superior thyro-arytenoid ligaments or superior vocal cords are, in contra-distinction to the inferior, denominated (though incorrectly) the false ligaments : they are of less thickness and strength than the inferior ligaments, and are further removed from the axis of the larynx (/, fig. 24). They arise from the internal angle of the thyroid, and are inserted into the middle of the anterior superior prominence of the arytenoid cartilages (fig. £4); they are composed of a few slender fasciculi of elastic fibres, approaching less nearly the mesial plane than the inferior ligaments ; they appear more prominent, in consequence of their form- ing the roof of the ventricles. They are in the same plane as the aryteno-epiglottic muscle, and are connected with the fibres of the lateral crico-thyroid ligaments. According to M. Lauth there is a connexion between the crico-thyroid, the lateral crico- thyroid, and thyro-arytenoid ligaments by three fasciculi, one of which is vertical, one hori- zontal, and one ascending (g, k, n, fig. 24), the first of these being the crico-thyroid ; the second the lateral ; the third connects the thyro- arytenoid with the superior thyro-arytenoid ligaments, and lines the bottom of the ventricles. M. Lauth considers also that the - thyroepi- glottic, the hyo-epiglottic, and glosso-epiglottic ligaments are composed of the same elastic tissue. Muller and Cruveilhier concur in these views. They certainly appear of the same colour and texture under the microscope, and undergo the same change by exposure to the atmosphere : they also possess the same cohe- sive elastic properties. The strength of the inferior thyro-arytenoid ligaments is so great that they will tear away the cartilage to which they are attached without being injured, and will support the force of many pounds weight. Muscles. — The motions of the larynx are exceedingly complex, and are performed by two sets of muscles, which are divided into two classes: — 1, the extrinsic; and, 2, the intrin- sic muscles. The muscles which elevate the larynx are the digastrici, stylo-hyoidei, mylo- hyoidei, genio-hyoidei, and hyo-glossi, and those pharyngeal muscles which are inserted into the cricoid and thyroid cartilages. The muscles which antagonize these and lower the larynx are the sterno-hyoidei, the omo-hyoidti, the sterno-thyroidei, and the thyro-hyoidei. The os hyoides is the centre of motion for the action of these muscles. (See Neck, Muscles of the.) We shall here confine our description to the Intrinsic muscles of the larynx, Syn.; mus- cles intrinsiques, Cruveilhier. — The muscles of this division comprise those acting exclusively on the larynx itself. There are four pairs and one single: 1, the crico-thyroidei ; 2, the crico-arytenoidei postici; 3, crico-arylenoidei laterales ; 4, tliyro-urytenoidei ; and, 5, aryte- noideus, which, from a difference in the direc- tion of certain of its fibres, is divided into the oblique and transverse. Independently of these, there are some muscular fasciculi, named the thyro-epigluttidei and the aryteno-epiglotlidei. The crico-thyroidei. — These are very short, 106 NORMAL ANATOMY OF THE LARYNX. thick, almost quadrangular-shaped muscles, situated on each side of the anterior part of the larynx : they arise from the anterior and inferior surface of the cricoid cartilage, on each side of the median line. The fibres are fleshy : the most internal directed obliquely upwards and outwards ( m, fig. 25), the central very Fig. 25. A side view of the larynx with the os hyoides attached. a, the thyro-hyoideus muscle ; b, the middle thyro-hyoid ligament; e, the pomum ; d, the crico- thyroid ligament; m, the crico-thyroid muscle; O N, the direction of the inferior fibres of the crico- thyroid lying nearly perpendicular to the axis of the crico-thyroid articulation ; f, the trachea ; re re, the insertion of the thyro-hyoid muscle and mem- brane to the inner margin of the os hyoides. obliquely, and the inferior almost horizontally to the inferior margin of the thyroid and to the inferior horn : others are inserted into the pos- terior surface of the thyroid. A portion of this muscle is prolonged to the inferior constrictor of the pharynx. Each crico-thyroid muscle is covered by the sterno-thyroideus, and lies external to the crico- arytenoid lateralis and the thyro-arytenoideus. The triangular space between the crico-thyroidei is occupied by the crico-thyroid membrane. The action of the crico-thyroidei is to rotate the cricoid on the thyroid. The superior and middle fibres are at the greatest distance from the axis of rotation (N, Jig. 26), and conse- quently acting as if at the arm of a long lever. In this action the anterior superior margin of the cricoid is elevated towards the inferior edge of the thyroid from f to f (Jig. 26), by which the posterior upper margin of the cricoid is carried backwards from B to B' indicated by the dotted line 1, 2, 3, 4, 5, (Jig. 26), and as the space is greater from A B' than A B, it is manifest that the space in the mesial plane Fig. 26. A view of the left side of the larynx to illustrate the functions of the thyro-arytenoid, the sterno-thyroid, and crico-thyroid muscles. The dotted line 1, 2, 3, 4, 5, shows the position of the cricoid cartilage when the crico-thyroid mus- cles have closed the crico-thyroid space ; m, the crico-thyroid muscle ; N, the crico-thyroid articu- lating axis; A B and B A, the directions of the force of the thyro-arytenoideus muscle ; R S, the direction of the force of the sterno-thyroideus muscle meeting that of the thyro-arytenoideus in R ; R N, the resultant of the combined muscular forces R P and RS; ON and P N are perpendi- cular lines drawn from the directions of the forces of the thyro-arytenoideus and sterno-thyroideus muscles to the common axis of rotation ; they are also the'cosines of the angles R N O, R N P, and B N P, and show the amount of force on the axis of the sterno-thyroideus and thyro-arytenoideus muscles respectively; R' and A' are the points which R and A must pass through when the thy- roid is rotated forwards on the cricoid ; A, the point opposite which the thyro-arytenoideus is in- serted into the posterior angle of the thyroid carti- lage ; B, the point on which the thyro-arytenoid acts in rotating B towards A ; the crico-thy- roid space ; h, the trachea. must be enlarged to an amount equal to the difference of the distance A B and A B' (fig. 26). The action of this muscle, therefore, is to stretch the thyro-arytenoid ligaments. The direction of the force of the inferior horizontal fibres of the crico-thyroid which are lying parallel to the line O N (fig. 25 and 26) being nearly perpendicular to the axis of rotation, can have, consequently, little or no effect, until the superior fibres have (by raising the cricoid) pro- duced an angle with the axis N (fig. 25) ; they assist only when the crico-thyroid space is diminished. It has been commonly supposed that it is the thyroid which is drawn forwards on the cricoid, and Cruveilhier adopts this sup- position ; but it has been refuted by Magendie, and not only do we observe that the attach- ments of the crico-thyroidei are mechanically directed to produce a rotatory motion of the cricoid, but the latter has no fixed point of NORMAL Fig. 27. A side view of the larynx, the left wing of the thyroid and the mucous membrane removed, and the fibres of the arytenoid imiscle depressed to expose the liga- ments and chink of the glottis. a, the internal surface of the right wing of the thyroid \b b, the arytenoid cartilages ; c, the thyro- arytenoid ligament ; d, the thyro-arytenoideus muscle ; d', the thyro-arytenoideus superior vel minor ; e e, the crico-arytenoidei postici ; f, the crico-arytenoideus lateralis ; n, the cricoid carti- lage ; h, the trachea ; I, the external prominence of the arytenoid cartilage. attachment or muscles appropriated to fix it as a fulcrum for motions in an opposite sense. The crico-arytenvideus lateralis is an irregu- lar quadrilateral muscle, arising from the supe- rior margin of the cricoid, from thence passing upwards and backwards, (f,jig- 28). It is in- serted into the posterior surface of the external prominence of the arytenoid cartilage by a tendon common to it and the thyro-arytenoid muscle. It is deeply seated under cover of the thyroid car- tilage and crico-thyroid muscle. The action of this muscle has caused much diversity of opi- nion. Cowper, Ilaller, Magendie, and others consider that it opens the glottis ; but Bichat and Soemmering that it closes it. Its action has, however, been mechanically solved in the following manner by Willis. The arytenoid cartilage is loosely fixed to the cricoid by liga- ments already described at B (jigs. 28 and 29). The direction of the force of this muscle is represented by the line N X (fig. 30), having its point of insertion into the cricoid about X. The fibres in passing thence to the arytenoid (f, fig. 28) lie nearly parallel to the projection of the axis of motion, G C ; the tension of this muscle in the direction N X (figs. 29 and 30) ' OF THE LARYNX. 107 Fig. 28. A section of the larynx similar to that of fig. 27, with the thyro-arytenoideus muscle removed to give a full view of the thyro-arytenoid ligaments, and the rima glottidis lying in the direction of A and B. The line G C is the vertical projection of the crico- arytenoid articulating axis ; cc,f, g,h, represent the same parts as in Jig. 27. tends to bring N X B into the same straight line and approximate the point V to the mesial plane; and as N is above the line joining B X, it will depress N and still more V, because the cartilage turns on the articulating surface be- neath Q. The action, therefore, of this muscle is to approximate the anterior arytenoid promi- nences and depress them. The arytenoideus (obliquus and transversus). Modern anatomists consider this as one muscle, but owing to the obliquity of the fibres of one of its fasciculi with respect to the other, some have made a division of it into arytenoideus obliquus and a transversus. It is a very short thick muscle, occupying the concavities on the posterior surface of the arytenoid cartilages and the interval between them. It consists of two layers; the superficial layer, which is composed of the oblique fibres, which arise from the base of the right arytenoid, and crossing the fibres of the deep-seated layer, are inserted into the summit of the left arytenoid cartilage : this is the arytenoideus obliquus of Albinus. The deep-seated layer is thicker and stronger than the superficial ; its fibres, which are directed transversely from one arytenoid to the other, constitute the arytenoideus transversus of Albi- nus. The arytenoid muscle is covered pos- teriorly with mucous membrane, which is con- nected to it by loose cellular substance, in which some mucous follicles are found; anteriorly it NORMAL ANATOMY OF THE LARYNX. corresponds with the posterior surfaces of the arytenoid cartilages, and is connected by some muscular fibres and membrane with the supe- rior margin of the cricoid cartilage and with the whole length of the internal margins of the arytenoid cartilages. The immediate effect of the contraction of the arytenoid muscles is to approximate the posterior internal surfaces of the arytenoid cartilages, but their action, at the same time, tends to separate the anterior pro- minences, and to open the chink of the glottis. To counteract this effect the action of the crico- arytenoideus lateralis is called simultaneously into play, and the joint effect of these two muscular forces, represented by the lines N X and NY (Jig. 30,) produce a resultant in the direction of W N ; hence the crico-arytenoideus lateralis and the arytenoideus muscle acting together tend to close the glottis posteriorly. The thyro-arytenoideus. — This is one of the most important, most complicated, and perhaps least understood of any of the muscles of the larynx. It arises from the side of the angle of the thyroid cartilage, occupying about two-thirds of its height, and reaches within two or three lines of its superior margin. The central fibres are directed horizontally back- wards and outwards, slightly inclined upwards, and inserted into the prominence and concavity on the lateral surface of the arytenoid^ I, fig. 27). The superior fibres terminate in the external ridge of the arytenoid ; some of them pass round the arytenoid, and enclose the arytenoid muscle like a sphincter.* The inferior fibres which arise near the median plane (k, 29) are inserted, at a greater distance from it, into the arytenoid cartilages (f\ fig. 30) ; some ex- ternal fibres are directed more eccentrically Fig. 29. i Rj si I A view of the larynx from above. f From Mr. Willis.) The mucous membrane is removed to shew the ligaments and muscles of the glottis. N F, N F, the arytenoid cartilages; TV, the vocal ligaments ; N X, the right crico-arytenoideus lateralis, the left is removed ; X« L, the ring of the cricoid capable of rotating on the axis RS; e e, the crico-aryte- noidei postici ; E, the junction of the wings of the thyroid. * Lauth, Mem. de l'Acad. deMed. 1835. Fig. 30. Y 1 A portion of fig. 29 enlarged to demonstrate the di- rection and result of the forces of the muscles of the larynx. O P, the horizontal projection of the axis of articulation ; T V, the vocal ligament ; g h, the direction of the force of the thyro-arytenoideus ; N X, of the crico-aiytenoideus lateralis ; N W, of the crico-arytenoideus posticus ; N Y, of the arytenoideus transversus. upwards and backward, corresponding to the superior ligaments and ventricles, where, ac- cording to Lauth, they terminate without reaching the arytenoid. Some fibres of the thyro-arytenoid take an oblique direction back- wards and downwards, arising immediately below the superior internal margin of the angle of the thyroid, and are inserted into the ver- tical prominence of the arytenoid cartilage; they are sometimes detached from those passing horizontally, as in d, (fig 28,) constituting the thyro-arytenoidei superiores of Albinus, but they are sometimes described as one muscle. The thyro-arytenoideus corresponds to the internal surface of the thyroid cartilage, from which it is separated by some loose cellular and adipose tissue. Internally it is in contact with the inferior vocal ligament, which lies in contact with the thickest part of this muscle, the bulk of which causes the vocal ligaments on each side to project towards the mesial line and contracts the aperture of the larynx. Some anatomists consider that the thyro-arytenoid ligaments consist of nothing more than the tendons of these muscles; it is not difficult, however, to prove the contrary by dissection. The functions of the thyro-arytenoidei, con- cerning which there has been much diversity of opinion, produce several changes in the rela- tive position of the internal mechanism of the larynx, and therefore they require rigid inves- tigation. The effects of these muscles may be considered, first, with respect to the tension of the vocal ligaments ; secondly, to the aper- ture of the glottis. We observe that the points of attachment (at dd' I, fig. 27) of the thyro- arytenoid are situated within those at A B, (fig. 28); and, as the arytenoid cartilage is tied by ligamentous fibres to the point B, it follows that the contraction of thismusclewill drawupon the point B, through the interposed arytenoid cartilage : if A be made the fixed point, the contraction of this muscle will draw the point B towards A by rotating the cricoid on the thy- roid. If, on the contrary, B be fixed, then A will approach B by the rotation of the thyroid on the cricoid. In both these cases the dis- tance from A to B is diminished, and as the vocal ligaments are situated in a direct line NORMAL ANATOMY OF THE LARYNX. 109 passing through A and B, this muscle must consequently relax them. The closing of the anterior and central por- tion of the glottis by these muscles, or that part lying between T and V (fig. 29), is effected, according to Mr. Willis, partly by the approach of the point V of the arytenoids towards T arising from the obliquity of the axis of rota- tion, and partly by the swelling of the muscle whilst contracting to approximate the arytenoid cartilages tending to fill the space T N X V (fig. 29), and to close tightly the sides of the passage below the vocal ligaments; thus clos- ing the anterior and central portions of the glottis. The question as to how A is made a fixed point, in the above demonstration, remains to be solved. Mr. Willis remarks that while all writers agree that the crico-thyroidei serve to approximate the cricoid cartilage to the thyroid, either by raising the cricoid or by depressing the thyroid, none of them have shown how the cartilages are to be separated again. Let us investigate this proposition. In order that the motions necessary to dilate the crico-thyroid space be effected by mus- cular motion, it is obvious that A must be made a fixed point, so that B' may be drawn to B ( fig. 26), by which f" ascends to f, the object in question (fig. 26). It is clear that the crico-thyroid muscle cannot be employed in this instance, as it has been already shewn that its action is to force B to B' and /'to J"; whereas we have now to reverse the direction, and to bring back B' to B, so that f may de- scend to J. The sterno-ihyroidei are the only muscles, which by their origin, insertion, and direction of force are calculated to effect this purpose; the insertion of one of these muscles being about the point R at an angle with the axis R N (fig. 26), its force in the line R O S ( fig. 26) cutting the right line O N at O ; the effect of which will be to draw forwards and downwards the thyroid cartilage from A to A', and the point R R'; these muscles have the advantage of acting on the extremities of a lever equal to the line O N. When any force equal to that in R S is acting simultaneously with that of the thyro-arytenoideus, in the di- rection ARPB perpendicular to R S, the composition of these forces R S and ARPB will produce a resultant in the diagonal R N, which will cut the axis N ; and as by hypo- thesis the forces R O and R P are equals, R and consequently A will be fixed points; but the attachment of the thyro-arytenoid at B makes an angle with the axis in the line B N, and the perpendicular cutting the direction of the force of this muscle produced to the axis is P N ; thus whilst the sterno-tliyroid has, by its action on the lever O N, fixed the points A and R, the thyro-arytenoid may act with an equal force at the point B on the lever P N ; but as the force P N is produced on the cricoid (which is free to move by the relaxing of the crico-thyroid), the result will be to rotate the point B towards A, and depress the point /' to f, and thus the question is solved. In the preceding demonstration it must be remem- bered that the point R is assumed to be that in which the whole of the sterno-thyroid is in- serted, whereas it is expanded upon the surface around the oblique ridge, but any of its fibres below R will have the same effect as if at R, provided they are in the line O S. It must also be borne in mind that the thyro- hyoid prolongs the action of the stei no-thyroid to the os hyoides ; but in this instance the os hyoides itself descends simultaneously with the expansion of the crico-thyroid space, and we know that the sterno-thyroid is always in action during the descent of the larynx. There is, however, very little muscular force required for rotating the cricoid in the direction in ques- tion. It is therefore evident that the sterno- thyroid is the antagonist to the thyro-arytenoid, and that, in this instance, during the rotation of the cricoid on the. thyroid in the direction B B P A must be the antagonist to the crico- thyroid. From the preceding demonstrations we con- clude that when the crico-thyroidei, the thyro- arytenoidei, the crico-arytenoidei laterales, and the arytenoid muscles are acting simultane- ously, the chink of the glottis is entirely closed. Another function of the thyro-arytenoidei re- lates to their effects during the production of vocal sounds, which will be considered in the article Voice. In order that the glottis may be closed in the manner just described, it is necessary that the crico-thyroid assisted by the sterno-thyroid should have fixed the fulcrum for the play of these muscular motions. The crko-urytcnoidei postici. — The intrinsic muscles of the larynx already described tend, more or less, to affect the antero-posterior di- ameter of the laryx, the tension of the thyro- arytenoid ligaments, or the contraction of the chink of the glottis. The crico-arytenoidei postici have altogether a different tendency. They are a pair of muscles arising at the pos- terior surface of the cricoid (e e, figs. 27 &28); the superior and middle fibres ascend obliquely, the inferior nearly vertically to be inserted into the lateral prominences at the bases of the ary- tenoid cartilages, anterior to the crico-aryte- noidei laterales. These muscles lie under the mucous mem- brane of the pharynx, and upon the posterior surface of the cricoid. The contraction of these muscles is gene- rally said to draw the arytenoids backwards, outwards, and downwards, and to open the glottis posteriorly. This view is in a great degree, but not strictly, accurate. The crico- arytenoideus posticus being inserted into the arytenoid cartilage at N has the effect of acting as on the arm of a short lever at N, and of rotating it upon the axis O P, in the direction of N VV, which is directly opposed to the direc- tion of the force of the crico-arytenoideus late- ralis, which is represented by W N, therefore the effect of this muscle is to separate the vocal ligaments, and consequently to open the chink of the glottis. Mr. Willis remarks that the thyro-arytenoidei postici do not draw the ary- tenoids backwards, as described by anatomists, which implies that the posterior fasciculi of the 110 NORMAL ANATOMY OF THE LARYNX. ligamentous fibres of the crico-arytenoid arti- culation at B (fig. 30) are relaxed ; for, al- though some fibres lying nearest the mesial plane are directed to draw the arytenoids to- wards B, they are counteracted by the fibres lying furthest from it, and by assuming the whole to act together, the resultant will be as nearly as possible perpendicular to the axis of articulation O P, which would open the glottis ; and therefore he concludes that the force of the thyro-arytenoidei postici in a direction back- wards may be neglected. Bichat erroneously considered that they assist the thyro-aryte- noidei and crico-arytenoidei in drawing the thyro-arytenoid ligaments very tense.* The thyro-epiglottidei.- — These are a pair of small muscles situated between the anterior sur- face of the thyroid cartilage and epiglottis; they arise from the internal surface of the thyroid near its middle, and not far from the origin of the thyro-arytenoidei ; their fibres are directed upwards and forwards to the base of the epi- glottis, to which they are inserted behind the ligamenta thyro-epiglottidea. Their action is to depress the epiglottis. The aryteno-epiglottidei are two small mus- cles, arising from the superior pyramid of the arytenoid cartilages posterior to the arytenoid muscles, or from the fibrous raphe situated vertically behind them ; they pass upwards and forwards to the sides of the epiglottis, and upon the posterior border of the thyro-epiglottic membrane. Action. — Owing to the direction of their fibres, the thy ro- and aryteno-epiglottidei tend to depress the epiglottis, or rather to effect the tension of the aryteno-epiglottic mucous folds. The action of the intrinsic muscles of the larynx may be briefly recapitulated as follows : The crico-arytenoidei postici open the glottis; all the other muscles close it. The arytenoideus obliquus and arytenoideus transversus approximate the arytenoid cartilages posteriorly. The crico-arytenoidei laterales and the thyro-arytenoidei bring them in contact anteriorly. The thyro-arytenoidei close the centre of the glottis, and with the crico-thyroidei, assisted by the sterno-thyroidei, regulate the tension, position, and vibrating length of the chords vocales. The crico-thyroidei and sterno-thyroidei an- tagonise the thyro-arytenoidei, and in stretch- ing the crico-thyroid ligament, the sterno-thy- roidei with the thyro-arytenoidei antagonise the crico-thyroidei. The crico-arytenoidei laterales, and thyro- arytenoidei, and the arytenoideus obliquus and transversus antagonise the crico-arytenoidei postici. These last-named muscles likewise may be said to antagonize all the muscles which close the glottis. The genio-glossi, the liuguales, the stylo- pharyngei, and crico-pharyngei, and hyo-glossi, are muscles associated in common with the mo- * Quand les thyro-arytenoidiens c.t crioo-aryte- noidiens lateraux d'une part, et los ciico-arytenoi- diens posterieurs d'une autre part agissent simul- tanement, les ligamens ihyro-arytcnoidicns sont fortement tendus. tions of the tongue, pharynx, and larynx, and belong rather to the structure and functions of the two former of these organs than to the larynx, and consequently are considered only as auxiliary. The motions of the internal mechanism of the larynx being effected by muscles, whose forces are directed, with respect to each other, in various degrees of obliquity, and in different planes, and producing by their combination results which can only be demonstrated on me- chanical principles, it has been deemed desira- ble to introduce them into the preceding inves- tigations to insure greater precision of detail and accuracy of result, and the more especially as we find in the works of our best anatomical writers the most discordant opinions, based ap- parently upon mere hypothesis or superfical observation, and without reference to any data or principle from whence their conclusions are drawn. The perusal of the works of Albinus,* Hal- ler,f Cowper,! Soemmering,§ Meckel, || Bi- chat,H Magendie,** and Bell,tf confirm these remarks ; exceptions to these observations are found in the works of Borelli,J| Barthez,§§ E. and W. Weber,|||| Bernoulli i,M Barclay,*** and Willis ;fft from the invaluable investiga- tions of the latter much assistance has been de- rived. Bloodvessels. — The arteries of the larynx are derived from the superior thyroid, a branch of the external carotid and from the inferior thyroid, a branch of the subclavian. Small veins accom- pany the arteries and empty themselves into the neighbouring trunks. Structures called glands. — The arytenoid gland. Syn. Glandulff. arytenoidea, Mor- gagni, Bichat, Cloquet ; cartilago cunei- J'ormis, Wrisberg, Bandt. The arytenoid gland is an inappropriate designation given to the cuneiform cartilage by Morgagnian whose views of the structure of this body are adopted by Bichat,§§§ Cloquet,|||||| and Cru- * Historia Musculorum, lib. ii. t Elem. Phys. torn. iii. | Anat. of the human body. De Corporis Hum. Struct. Traite Generate, torn. x. Traite d'Anat. desc. torn. ii. ** Physiol. ft Anat. of the human body. it De motu animalium. Lugd. Batav. 1685. Nouvelle mechanique des mouvemens l'Homme et des Animaux, 1798. Illl Mechanik der Menschlichen Gehwerkzeuge, mit xvii Taf. Gott. 1836-8. H 11 De motu musculorum. **» 'j-jjg muscular motions of the human body. ttt Cambridge Phil. Trans. 1833. |jj Constant glandulae arytaenoidaea? ex granosa substantia e livido albescenle, de qua utilem oblini- endo laryngi succum maxime inter edendum, aut vociferandum, appressa epiglottis ; vel contracti vicini musculi exprimunt. §§§ II apparoit que les deux glandes aryteno'ides ne sont que des glandes muqueuses plus prononcees que celles qui entourent le reste de la membrane laryngee, mais qu'elles ont absolument le meme usage. Op. cit. p. 386. || Illl Les glandes sont formees de petits grains arrondis, asscz consistans, d'une couleur grisatre. Op. cit. de NORMAL ANATOMY OF THE LARYNX. Ill veilhier.* The description given of it by Morgagni is, that it consists of a granular sub- stance of a livid whitish colour, from which under the pressure of the epiglottic or neigh- bouring muscles a fluid is poured out. Wris- bergf described it as a cartilage under the name of cuneiform. Cuvier and Wolff, as before stated, have confounded it with the cartilage of Santorini. Morgagni appears to have mistaken for glandular the yellow elastic tissue pene- trating its body. Lauth describes some mucous follicles about its base and internal surface, but he opposes the views of Morgagni on the constitution of this body. This body is some- times absent in the human subject, but scarcely ever in the quadrumana. Its structure is de- cidedly cartilaginous. The epiglottic gland. — Syn. glundnla epi- glottidis, Fab. Cass. Morg. The epiglottic gland is a name given to a mass of yellow ligamentous adipose and cellular substance, situated in the triangular space between the anterior surface of the epiglottis and the angle of the thyroid cartilage ; it is bounded anteriorly by the thyro-hyoid membrane, above by the thyro-epiglottic mucous membrane and ligament ; below, by the union of the epiglottis with the thyroid cartilage, and on each side by the mucous membrane passing from the thyroid to the epiglottis. Berengarius speaks of it as a fleshy gland : Steno and many others as com- posed of granules, whose ducts perforate the epiglottis and open on its posterior surface. Fabricius, Casserius, and Morgagni J have de- scribed and figured these supposed granules and ducts. Bichat,§ Cloquet,|| Quain,U and most modern anatomists adopt the same views. Morgagni, upon the same supposition as he had formed of the nature of the elastic tissue, considers the composition of the epiglottis to be chiefly glandular. Cloquet and Bichat admit the difficulty of detecting any follicular structure, nor could we discover any under the microscope ; and from what has been already stated on the structure of the epiglottis, we conclude, as of the arytenoid, that the structure which enjoys the name of epiglottic gland is not glandular. Mucous membrane.— -The mucous membrane of the larynx is continuous with that which covers the mouth and pharynx. The posterior surface of the larynx is bounded by the pharynx, and is lined by mucous membrane both on its • Traite d'Anat. t Prima; lineae phys. anat. a de Hallcr, cd. Wris- berg. Gotting. 1780-8. p. 157. % Morg. advers. anat. om. tab. ii. p. 48. § " Cet espacc estoccupepar un corps manifeste- ment celluleux, et graisseux, dans sa plus grande partie, mais qui est inferieurement recouvre de petits grains glanduleux, tantot agglommeres, tantot isoles, lesquels envoient sensiblement dcs prolonged mens dans les trous dont est percee l'epiglotte : les prolongemens paroissent s'ouvrir stir sa surface laryngee, aux orifices qu'on y distingue. Quelque- fois les petits corps glanduleux sont tellcment masques par cette graisse jaunatre, qu'on ne peut les distinguer." Traite d'Anat. descript. torn. ii. p. 385. |l Anat. descript. p. 245. % Klein, of Anat. p. 858. anterior and posterior surfaces. If the state- ment of Cruveilhier be correct, this singular duplication is not to be found elsewhere in the animal economy ; afterwards it is reflected over the surface of the base of the tongue, and lines the interior surface of the epiglottis ; in this space it forms threefolds, catted glosso-epiglottic, often described as the middle, and two lateral, which adhere closely to the surface of the epi- glottis. The mucous membrane being reflected over the free part of the epiglottis, to which it rather closely adheres, then lines its posterior surface and dips into the larynx. A duplication called the ari/teno-epiglottic fold passes from each side of the lateral mar- gin of the epiglottis to the vertical apophysis of the arytenoid cartilage. This membrane is connected posteriorly with the mucous coat of the pharynx, and lines the posterior surface of the larynx ; it is reflected over the arytenoid cartilages, and with the aryteno-epiglottic fold forms the posterior and lateral superior margin of the larynx ; covers the superior thyroaryte- noid ligaments, penetrates to the bottom of the ventricles ; from thence, after lining the inferior thyro-arytenoid ligaments, it passes through the chink of the glottis, covers the thyro and crico- arytenoideus lateralis muscles, and the internal surface of the cricoid cartilages, and becomes the investing membrane of the trachea. The laryngeal membrane is perforated by numerous mucous orifices of a peculiar pale rose-colour, and is remarkable for its great sen- sibility, more especially in the region above the rima glottidis. The rima glottidis. Syn. cavum seu sinus la- ryngis The chink of the larynx is an aperture directed horizontally, connecting the supra and infra-laryiigeal regions, and allowing the free transmission of air in respiration. It is bound- ed posteriorly by the arytenoid cartilages, ary- tenoid muscle and mucous membrane ; laterally by the arytenoid cartilages and the thyro-aryte- noid ligaments, which, with the mucous mem- brane reflected over them, present nearly rect- angular-shaped valves, attached on three sides, leaving one, bounding the glottis, free; ante- riorly by the angle of the thyroid. Immedi- ately above it are the ventricles, one on each side. The intrinsic muscles of the larynx not only contribute to its functions in the produc- tion of voice, but determine its form. The form of the chink of the glottis is variable; in the state of repose, or that of ordinary respiration, it is triangular, the aperture dilating during inspiration and contracting during expiration. When the arytenoids are separated to the great- est extent by the crico-arytenoidei postici, it assumes a lozenge form ; if the posterior bases of the arytenoids are closed by the arytenoid muscles it becomes an ellipse ; if the anterior apophyses of the arytenoids meet by the action of the crico-arytenoidei laterales, the chink may be divided into two parts. The length of the chink of the glottis is very variable, and bears a relation to that of the thyro-arytenoid ligaments ; like the latter, it increases with age in an arith- metical proportion until the period of puberty ; at that time its length in the male sex under- 112 NORMAL ANATOMY OF THE LARYNX. goes a sudden development, whilst in the female it remains stationary. The comparative length of the chink in the male and female is proportional to the relative lengths of the vocal ligaments already detailed. The length of the rima glot- tidis bears no relation to the stature of the indi- vidual. In the adult male it is about eleven lines, of which the boundaries formed by the arytenoid cartilages are four, and the thyro-ary- tenoid ligaments seven lines. In the male and female it is on a mean average as three in the former to two in the latter. In a female, M. Lauth however found the rima glottidis to mea- sure from ten lo eleven lines, whilst that of a tall male extended only from eight to nine lines ; but this is a rare instance. The pomum Adami on the thyroid has a corresponding concavity within, which affords a greater length in the mesial section of the larynx, and which tends to increase the longi- tudinal dimensions of the glottis. In several of the ruminantia the concavity is very con- spicuous.* The breadth of the glottis is much less than its length. In a state of repose its transverse section is not more in the adult than about two or three lines, or with respect to its length as two to eleven, but the diameter varies with the intensity of the forces of the intrinsic muscles of the larynx. The ventricles. Venlricule ou sinus du larynx. Cruv. — These are oval or elliptical cavities directed from before backwards, between the superior and inferior ligaments. The depths of the ventricles are effected by the distance from the free margin of the vocal ligaments to the internal surface of the thyroid, or rather to the thyro-arytenoid muscles, which constitute the bottom of the ventricles. The internal part of the posterior cavity of the ventricles is enlarged and deepened by a duplicature of the mucous membrane passing external to the arytenoid cartilage, which has been described by Mor- gagni, and recently more particularly by Mr. Hiltonf under the name sacculus luryngis. The ventricles are prolonged anteriorly, extend- ing along the vocal cords on each side of the epiglottis. In size the ventricles vary with the general dimensions of the larynx ; they are each divided into an interior and posterior cavity by a transverse ridge. The ventricles afford greater freedom of motion to the inferior thyro-arytenoid ligaments. Nerves. — The larynx is exquisitely sensible, and, as we have seen, combines complex and delicate motions with secreting surfaces. These properties result from its nervous endowment, which is derived from two branches of the pneumo-gastric nerve, namely, the superior and the inferior laryngeal nerves. It will be unnecessary to enter into any de- tailed description of these nerves here. Their distribution will be fouhd fully described in the article Par vagum, to which we refer. Let it suffice to mention, that the superior la- ryngeal nerve by its external branch gives fila- ments, 1, to the inferior constrictor of the pha- * Vide Pallas Spicil. Zool. Trans, xii. t Guy's Hosp. Reports, No. v. Fig. 31. A view, from Mr. Swan, of the superior and inferior laryngeal nerves. a, a portion of the tongue ; b, the epiglottis ; c, the thyroid cartilage'; d, the posterior arytenoid muscle divided for show- ing a branch of the recurrent nerve passing to the oblique and transverse muscles ; e, the lateral crico arytenoid muscle ; f, the thyro-arytenoid muscle ; g, the arytenoideus obliquus ; h, the ary- tenoideus transversus ; i, the crico-thyroid ; j, l.the superior laryngeal nerve; 2, a branch of this nerve to the membrane connected with that covering the epiglottis ; 3, a branch of the superior laryngeal to the membrane placed between the superior extremities of the arytenoid cartilage ; 4, the recurrent nerve ; 5, a branch of the recur- rent given off to the membrane lying between the larynx and pharynx ; 6, a branch of the recurrent nerve to communicate with a branch of the supe- rior laryngeal nerve ; 7, a branch of the recurrent to the posterior crico-arytenoid muscle ; 8, a branch to the crico-thyroid and crico-arytenoid muscles ; 9, a branch giving filaments to the posterior crico- arytenoid, and passing between this muscle and the arytenoid cartilage, to terminate in the oblique and transverse arytenoid muscles. rynx; 2, to the thyro-hyoid muscle and mem- brane ; 3, to the laryngeal plexus ; 4, to the crico-thyroid muscle ; 5, to the thyroid gland. The internal branch of the superior laryngeal nerve supplies filaments, 1, to the epiglottis; 2, to the adipose and mucous membrane ; 3, to the arytenoid muscles ; 4, to the thyro- arytenoideus; 5, to the crico-arytenoideus late- ralis; 6, a descending anastomotic branch to the NORMAL ANATOMY OF THE LARYNX. 113 recurrent; and, 7, to the aryteno-epigloltic mucous folds and muscles. The inferior laryngeal or recurrent nerve gives filaments, 1, to the pneu mo-gastric and cardiac plexus; 2, to the pharynx; 3, to the trachea ; 4, to the oesophagus ; 5, to the crico- arytenoideus posticus ; 6, to the arytenoideus obliquus and transversus ; 7, to the crico- arytenoideus lateralis and thyro-arytenoideus ; 8, an anastomosing branch to the superior laryngeal. Our knowledge of the anatomical distribu- tion of the laryngeal nerves, and of the func- tions of the intrinsic muscles of the larynx, are sufficient, independently of experiment, to demonstrate the inaccuracy of the well known assertion of M. Magendie, supported by Clo- quet, Pinel, Percy, and several others, that the recurrent nerve presides over those actions which open the glottis, whilst the superior la- ryngeal influences those muscles which close the glottis. The principal facts opposed to this theory of M. Magendie may be briefly stated as follows, 1. It was well known long- before the promulgation of Magendie's views that the inferior laryngeal nerve gave to the arytenoid muscle a filament which had been described by Andersch,* Bichat,f and Mec- kel,} and subsequently by Schlemm Bischoff, Swan, Cruveilhier, Dr. Reid, and others, there- fore it has been sufficiently demonstrated that the recurrent nerve supplies the muscles that close, as well as those which open the glottis. 2. M. Magendie has stated that the crico- arytenoideus lateralis and thyro-arytenoideus opened the glottis, whereas in the preceding details it has been proved that these muscles close it. 3. The loss of voice which follows the section of the recurrent nerves results from the paralysis of all the muscles (except the crico-thyroid) which both open and close the glottis, a fact proved by the experiments of Le Gallois and Dr. Reid. The limited space allotted to this article will only permit us to notice the conclusions to which recent expe- rimenters have arrived respecting the functions of the laryngeal nerves. The external branch of the superior laryngeal is composed chiefly of motor fibres, and it controls the action of the crico-thyroid and the other muscles to which it gives filaments. The internal branch of the superior laryngeal is composed of sensi- tive fibres, which confer the most exquisite sensibility on the mucous membrane of the larynx, more especially in its supra-glottideal region. It is therefore the. sensitive and the excitor nerve of the larynx. The inferior la- ryngeal supplies the muscles that both open and close the glottis, and is chiefly a nerve of motion when it reaches the larynx, but a few of its fibres go to the mucous membrane. The union of the superior with the inferior laryngeal branch by an anastomosing filament, preserves a reciprocal play in the functions of these * Fragmentum descr. nervor. t Traite d'Anal. torn. iii. p. 216. } Man. d'Anat. torn. iii. p. 66. VOT.. i/j. nerves: whilst the branches anastomosing with the sympathetic, connect the larynx with the ganglionic system ; the pulmonary and cardiac branches connect it with the respiratory and circulating systems, and thus associate the larynx with those vital functions. The laryn- geal nerves also belonging to the reflex system, impressions made on the sensitive filaments of the larynx are reflected to the medulla ob- longata, and propagated by a circuitous route to the motor filaments of the recurrent, so that a long interval is traversed in circulating an impression from the sensitive to the motor nerves of the larynx; but according to the esti- mate made of the speed with which an impulse is propagated along a nerve, which is assumed to be equal to that of electricity, the time occu- pied to transmit an impression from the fila- ments of sensation to those of motion must be inappreciable to our senses. Other important physiological considerations result from recent experimental researches, those of Le Gallois and Dr. Reid in particular. 1. With respect to the motions of the glottis during respiration, the dilatation during inspiration, and contrac- tion during expiration, are the effects of the play of muscular force in opposition to the direction of the current of air in its passage to and from the lungs, the tendency of which is to produce the reverse action.* There is a constant periodical oscillatory motion of the arytenoid cartilages, revolving upon the axis of articulation, O P, (fig. 30,) at every expiration and inspiration ; hence the necessity of a syno- vial membrane to lubricate the crico-arytenoid articulation. 2. When the recurrent nerves are diseased, compressed, or cut, so as to para- lyse the crico-arytenoideus posticus, the power of muscular action in opposition to the direction of the inspired air is lost. The valves of the glottis are drawn downwards with the air, the anterior apophysis of the arytenoid cartilages rotated inwards, the chink closes, symptoms of suffocation supervene, and asphyxia results. When spasmodic closure of the chink of the glottis occurs, the obstacle to the ingress of air is increased by convulsive attempts to draw in the breath, which causes a rarefaction of the air below the glottis, and augments the atmos- pheric pressure above it ; and the chest thus, says Dr. Ley, " becomes hermetically sealed." If the aperture of the glottis be partially open, the air rushing through it causes a stridulous sound (laryngismus stridulus J, whilst in ano- ther position of the glottis the crowing inspi- ration is produced ; this effect arises (accord- ing to Dr. Ley) from the chink of the glottis being partially open for the admission of air, and remaining so until an explosive expiration such as screaming, coughing, or belching, me chanically bursts open the floodgates, and terminates the paroxysm. * In the production of these periodical move- ments, the action of the muscles is involuntary, but in their action for the purposes of voice, they be- come subordinate to the will, and therefore belong also to the voluntary system. I 114 ABNORMAL ANATOMY OF THE LARYNX. Asphyxia is often delayed by the posterior chink of the glottis being retained partially open, in consequence of the coincident para- lysed force of the arytenoid muscles, and by the great inclination of the crico-arytenoid articu- lating axis, with respect to its vertical section, preventing the approximation of the arytenoid cartilages by which the posterior part only of tlie chink can be closed. When any irritation is produced on the exquisitely sensitive mucous membrane of the lary nx, it transmits a reflex action to the motor filaments of the recurrent, and the glottis is spasmodically closed, without any such morbid condition of the recurrent nerve as Dr. Ley supposed necessary. The larynx, when dissected out, and cleared of its extrinsic structures, presents on its ante- rior aspect the free margin of the epiglottis, the notch of the thyroid, the pomum Adami, its mesial line, the crico-thyroid space, and liga- ment, and the anterior border of the cricoid cartilage. On each side of the larynx are observable a portion of the wings of the thyroid, the crico- thyroid muscle, the great arid lesser cornu, the superior and inferior tubercles, the oblique ridge, the superior and inferior margins of the thyroid, the side of the cricoid, with a portion of the lateral crico-thyroid ligament, and the superior, inferior, and posterior margins of the cricoid. On the posterior aspect are observable, the posterior free surface of the epiglottis, the ary- tenoid cartilages and muscles, the aryteno- epiglottic mucous folds, the crico-arytenoidei postici muscles, the vertical ridge of the cricoid, the posterior margins of the th_\roid,and the posterior surface of the cricoid cartilages. In the internal surface, from above, we ob- serve the superior margin of the thyroid carti- lage and great cornua, forming the superior boundary of the larynx, the superior margin and notch of the epiglottis, the cornicula la- ryngis, the arytenoid and cuneiform cartilages, the aryteno-epislottic mucous folds, the supe- rior and inferior vocal ligaments, the ventricles, the rima glottidis, and the mucous membrane. Looking from below upwards, we perceive the inferior circular margin of the cricoid, the membrane lining its internal surface, the infe- rior aspect of the thyro-arytenoid ligaments, and the rima glottidis. The preceding outline of the general anatomy of the larynx will give the reader an idea of its manifold structures, its exquisite sensibility, its complex motions, its connection with the process of deglutition, and its admirable adapt- ation for the production of sound, and may- serve to impress a conviction that it is one of the most elaborate and perfect specimens of mechanism in the human body.* Bibliography. — Galeni Opera, de locis affectis, lib. i. cap. 6, p. 6. Vesalius, De corp. humani fabrica, Basiliae, fol. 1555. J. Casserius, de org. vocis et auditu, Ferrara, 1600. Riolanus, Opera. Anat. Paris, fol. 1649. Bidloo, Anat. Humani Corp. * For the description of the vocal functions, see the Article VOICE. Amstel. fol. 1685. 3/alpighi, Opera omnia, Lond, fol. 1687. Cowper, Myotomia reformat-*, Lond. 8vo. 1694, p. 80. Dodart, Mem. de l'Acad. Roy. des Sciences, 1700. Morgagni, Advers. Anat. omnia, Lugd. 1718. Santorini, Obser> ationes Anat. Venice, 4to. 1724. Albinus, Hist. Muscul. Hominis, Leida? Batavorum, 4to., 1734. Ferrein, Mem. de l'Acad. Royale, 1741, p. 400. Pic- cohmini, Anat. Int. Veronae, fol. 1754, p. 15, 45, 53. Duverney, Onvres Anat. Paris, 8vo. 1761, p. 91. Wmslow, Anat. Edinb. 8vo. 1763. Vieg d'Asyr, Mem. de l'Acad. Royale. 1779. Holler, El. Phvsiol. Soemmering, De corp. humani struct, vol. vi. Tra- jecti ad Mcenum, 8vo. 1801. Savart, Ann. de Chimie et de Physique, Paris, 8vo. 1825. Ben- nati, Recherches sur la Mechanisme de la Voix, 8vo. Pans, 1832. Willis, Camb. Phil. Trans, vol. iv. p. 323, Camb. 1832. Cloqwt, Traite d'Anat. descrip. Paris, 8vo. 1834. Louth, Mem. de l'Acad. Royale de Med. 1835. P. Broc, Traite d'Anat. descrip. Paris, 1837, p. 527. The prin- cipal systems of anatomy. (J. Bishop. y LARYNX. (Morbid anatomy and patho- logy.)— The importance of this organ to life, and even when existence is not actually en- dangered, to the comfort and well-being of the individual, must render any deviation from its healthy and normal condition in the hig!. est de- gree interesting to the pathologist : nor will that interest be diminished by reflecting on the paramount value of a knowledge of these de- viations to every practical physician. Small in size and composed of few and apparently sim- ple structures — its functions so obvious that any imperfection in their performance could be quickly perceived and readily understood — it would appear only reasonable to suppose that its various pathological conditions should have been observed, and the symptoms connected with them ong since collected and arranged. Yet, such is not the history of the pathology of the larynx : on the contrary, it presents itself to us with all the interest of a new discovery, and whatever is known on the subject is the result of investigations made within the last few years. We have the opiniou of the late Dr. Cheyne, (no mean authority on the subject,) that in the year 1800, " perhaps there was not in Britain more than one individual, namely Monro, who was acquainted with the true na- ture of the disease of which General Wash- ington died — acute laryngitis ; " and the same writer goes on to shew that in ten years subse- quent to that general's death, Dr. Baillie, then at the head of the medical profession in Eng- land, admitted that he was ignorant of the nature of the same malady. But without reverting so far back, I may be permitted 1o state, that within a comparatively recent period I can personally remember the lack of know- ledge that obtained amongst medical practi- tioners in this particular, and the deplorable results that too frequently ensued : and al- though it may be gratifying to reflect on the altered condition of things at present, yet it must be obvious that a subject so short a time under investigation cannot be expected to have been thoroughly worked out. Much as has been brought forward — perhaps more remains behind, and any person now attempting to give ABNORMAL ANATOMY OF THE LARYNX. 11.5 an exact and adequate description of the pa- thology of this organ, may probably find it ne- cessary to bespeak a very considerable degree of indulgence. Accustomed to consider laryngeal disease practically, and more particularly with refe- rence to operation, I find it difficult to bind myself down to mere pathological arrangement, or to attempt a satisfactory classification. True, like other organs, the larynx is composed of different structures, in each of which disease will assume the character peculiar to itself, and exhibit the appropriate appearances in an exa- mination after death, but it rarely happens that morbid actions are so limited in extent, as to exist and produce their proper results in one tissue without the participation more or less of the others. This will produce confusion, and render it a matter of difficulty to connect symp- toms with the existing pathological conditions that occasion them, and may be adduced as an objection to any attempt at arrangement founded upon structure alone : yet there really can be no classification altogether exempt from the same or a similar observation, and there- fore 1 shall adopt this one as having the merit of the greatest simplicity. Following this view then, I find the larynx to be composed of the following structures, viz. : — 1. Mucous membrane, exhibiting all the va- rieties of inflammation that are observed in that tissue when situated in other organs. Thus inflammation here may be acute or chronic, phlegmonous or erysipelatous, idiopathic or symptomatic, and attended by fever of a ty- phoid or an inflammatory type. And these varieties producing different effects or results. Thus we have examples of acute idiopathic in- flammation with fever of a sthenic kind in the croup of children, producing the adventitious membrane, and in the laryngitis of adults, that terminates so frequently in oedema ; and of the same local disease with asthenic fever in the diphtherite and in erysipelas: whilst accident furnishes numerous instances of the results of symptomatic inflammation in the consequences of burns, scalds, penetrating wounds, and the swallowing of caustic poisons. As happens so constantly in other structures, chronic in- flammation is here best known by the changes it induces, and furnishes us with abundant specimens of hypertrophy or thickening of the membrane, and of the different forms of ul- ceration. 2. Submucous tissue, which is the seat of cedematous effusions, and of the sloushy and pu- trid matter produced by diffuse inflammation. 3. Cartilage, in which we remark great and important varieties of disease, such as inflam- mation, ulceration, mortification, degeneration into an earthy unorganized material, atrophy, hypertrophy, and some alterations of shape and structure probably depending on scrofula or other constitutional taint. 4. Muscle, the seat of those spasmodic ac- tions so frequent and so perilous in larvngeal affections, and perhaps occasionally of gout and rheumatism also. .5. Ligaments. I know not whether disease ever originates in these structures, but there can be no doubt that they are sometimes removed by ulceration, and there is reason to believe that great inconvenience and even 'danger may be occasioned by a preternatural relaxation of some of them. 1. Acute inflammation of the mucous mem- brane is alwavs in the first instance attended by a change of colour more or less intense ac- cording to its situation, being comparatively pale where it is closely attached to a subjacent cartilage, but of a deep and concentrated red tint, verging on purple, where it is more loosely connected by the intervention of cellular tissue or muscle. The membrane is also swollen, soft and pulpy, these characters being likewise influenced by the nature of its connection to subjacent parts, and I believe the usual symptom of inflammation, "pain," is not ab- sent, although the mental agony attendant on obstructed respiration renders this a secondary consideration to the patient : certainly in the laryngitis of the adult, pressure on the pomum Adami is very sensibly felt. In connexion with these changes the functions of the organ are interrupted and impaired. The usual secretion of the membrane is diminished in quantity, or perhaps ceases altogether, and hence the sen- satiou of dryness or huskiness in the throat, and the peculiar solitary ringing cough that uniformly is present. The voice is also in- jured, beinsc occasionally nearly if not altose- ther lost, and there is difficulty of breathing accompanied by a harsh stridulous sound ; this latter being caused by the mechanical obstruc- tion to the passage of air produced either by tumefaction or by spasm. Having continued a given time, — and the first stage of inflammation of the larynx if very acute is usually but short, — certain results or effects are developed, which, differing in the child and the adult, require a brief separate notice for each. The acute laryngitis of the child, or croup, although generally commencing in the larynx alone, and sometimes altogether confined to it, is by no means uniformly so : on the contrary, it not only may commence in or extend to the trachea, but possibly have its origin in the bronchial cells, and pass thence upwards along the tubes. It may also perhaps not be strictly correct to arrange croup amongst the diseases that are preceded or accompanied by inflam- matory fever, for occasionally it makes its at- tack without any previous warning whatever, and a child that had retired in apparently per- fect health may arouse and alarm its attendants in the middle of the night with the sounds of that dry, harsh, and incessant cough, and that loud and stridulous respiration which afford to the practised ear the painful but unerring evi- dence of the nature of the mischief present. In either case, however, the disease hastens to its second pathological state, in which the evi- dences of increased vascularity begin to disap- pear, and are succeeded by the secretion or effusion of a viscid tenacious lymph, which, assuming the form of a membrane, has ob- r 2 ABNORMAL ANATOMY OF THE LARYNX. tamed the name of the false or adventitious membrane of croup. This substance is of a pale yellow colour, viscid and tenacious ; more generally found in the larynx than the trachea ; seldom occupying the entire circumference of the tube ; unorganized ; incapable of becoming the medium of union between opposing sur- faces, and with a strong disposition to separate from the surface on which it was originally formed. It usually commences in the larynx, and travels downwards along the trachea; more rarely it seems to begin in the ramifications of the bronchial cells ; and again, still more sel- dom is the entire of the mucous membrane attacked at once, and the adventitious mem- brane thrown out over its whole extent. Con- sidered as a pathological production, this false membrane of croup presents some curious and interesting subjects for observation, for although so generally met with that by some it has been regarded as the essential characteristic of the disease, yet perhaps it is not invariably or ne- cessarily so ; at least I have seen cases so far resembling croup in all their stages, that they could not be distinguished from it during life, in which dissection subsequently shewed the mucous membrane swollen, and soft, and pulpy, with copious submucous effusion, yet without the formation of a single flake of lymph. Possibly in the few cases of this de- scription that came under my observation, the disease had proceeded with a rapidity which proved fatal before the membrane had time to have been formed. Again, it is the only* instance of lymph beins; produced on a mucous surface as the result of active acute inflamma- tion. In chronic affections membranous layers of lymph are often formed, and in different situations, as in the bronchial cells and the mucous coat of the intestines, but the acute produces it alone in the structures that are the seat of croup. And lastly, it appears that this effect of inflammation is restricted to patients under twelve years of age. Mr. Ryland, in his excellent treatise on the larynx, has published a table from Bricheteau, by which it is shewn from the experience of fourteen distinguished authors, that croup " has never occurred at a later age than twelve years, and very rarely at that age." My friend, Dr. W. Stokes, con- siders the cases published as examples of croup occurring in the adult as not being inflamma- tory croup at all, but analogous to the diphthe- rite of Bretonneau, which will be shewn to be a very different disease indeed. Such is the pathological condition of the parts in the second stage of croup — a condition indicated by the increased difficulty of breath- ing— the pale and swollen countenance — the straining eye — the dilated nostril and the purple lip ; by the occasional expectoration of some portions of the false membrane; and (as hap- pens in every affection of the larynx) by severe and protracted spasms of the glottis. If the patient still continues unrelieved, the third and * For an apparent exception to this rule, see a case published in the Dub. Journ. of Med. Science, September 1838, No. 40, vol. 14. last stage supervenes. The child still breathes with difficulty, but with increasing languor : its countenance is pale; its lip bloodless; there are generally convulsions, in one of which the fatal event may take place ; or else he sinks gradually, exhausted and worn out, and dies comatose. And we are to look for the actual and immediate cause of death not to the larynx but to the lungs and brain. No matter how much the membrane may be swollen, or how extensively the false mem- brane may have been formed, the rima is not completely closed, and the patient dies, not because there is an absolute insufficiency of air to provide for the arterialization of the blood, but because some change has taken place in the organ by which this most important func- tion is performed. When the thorax is opened the lung does not collapse under the influence of atmospheric pressure : when the lung is cut into, it is found to be loaded with dark blood and with frothy serum, the effusion of which latter is often so abundant as nearly to fill the trachea. The brain, if examined, is found congested, and not unfrequently is there an effusion of serous fluid into its ventricles. The acute inflammation of the mucous mem- brane of the larynx bears no resemblance in the adult to that in the child, excepting only in the agonizing difficulty of respiration and the fatality of the result, but the pathological con- ditions are different, and therefore is the disease in the adult far more manageable. I can scarcely conceive, much less describe the ex- istence of acute laryngitis to any dangerous extent in the membrane alone without the participation of the submucous tissue, in which the perilous tumefaction is generally, if not al- ways, seated ; I shall, therefore, as I have hi- therto done, consider this affection in connec- tion with its principal pathological result — the formation of an oedematous effusion. Mucous membranes in every situation seem to be connected to the adjacent tissues by that species of cellular membrane termed reticular, as a provision that the courses of the canals of which they form so important a part should not be impeded by any accumulation of fat : and this reticular membrane is more or less lax according to the nature and consistence of the subjacent structure. Where mucous mem- brane is attached to bone, the nature of the connecting medium is so short and close, that in many instances it is scarcely observable, and the membrane, in addition to its own func- tions, appears to perform that of a periosteum, whilst in other situations, as in the intestine, it is so lax as to allow the organ to become dis- tended to an almost unlimited extent. The usual effect of inflammation on this reticular tissue is an effusion of a serous fluid within its cells, and the production of oedema ; but this is of little consequence where the tissue is dense and close, and perhaps of still less where the organ is widely distensible. The larynx, however, presents an organ of a mixed character — the mucous membrane is here at- tached to muscle and to ligament, and these ABNORMAL ANATOMY OF THE LARYNX. nr again are supported and restrained by resisting cartilages externally, so that if the submucous tissue which is here so loose as to allow the membrane to be thrown into natural folds, should become the seat of infiltration, the swelling so produced cannot take a direction outwards, but must tend to compress and close the aperture of the glottis. This is the cedema of the glottis, a formidable and too often a fatal affection, but nevertheless present- ing very considerable pathological varieties. Thus it is sometimes attended by fever, and forms only part of a more extended inflamma- tion, involving tonsils and fauces, pharynx and larynx : again, it is purely local, confined to the larynx alone, and so entirely free from any accompanying fever, that the patient only com- plains of the difficulty of breathing and the cough. It is often idiopathic, but may be produced by injury, and is a common result of swallowing caustic poisons and boiling water ; nor is it in this latter respect confined to the adult, for I have thus seen the superior aper- ture of the glottis, in a very young child, pursed up and closed as if by the drawing of a running string. It may be situated only in a part of the larynx, the rest remaining free ; thus it is no uncommon occurrence to see only one side of the glottis puffed and swollen, and the slit-like aperture thus converted into a curve; but the most interesting because the most prac- tical illustrations of partial cedema will be found in cases published by Sir Henry Marsh, in which the disease appeared to be confined to the epiglottis alone.* Lastly, I believe it is possible to have this cedema produced without any external evidence of inflammation. In the Museum of the School of Park-street there is a preparation shewing it as apparently occa- sioned by the vicinity of a large carcinomatous tumour. Considering the pathology of this affection, the degrees of inconvenience and of danger likely to result from it will be easily under- stood. The symptoms will be, a loss or imper- fection of voice, which is generally very well marked, the utmost effort at articulation amount- ing to no more than an indistinct whisper ; and difficulty of respiration, including cough and other signs of local irritation. The danger will probably be in proportion to the rapidity with which the effusion is formed, for life may be maintained with a wonderfully diminished supply of air to the lungs, provided the dimi- nution takes place gradually and slowly: but it may not arise solely from this cause, for here, as in every other form of laryngeal disease, spas- modic exacerbations are painfully frequent, and place the patient's life in momentary danger. Dissection, therefore, developes three different causes of death. One, the most infrequent where the patient has perished by spasm : the glottis, although swollen, is still pervious — perhaps apparently sufficiently so for the ordi- * See Dub. Journ. of Med. Science, March 1838, v. 13, no. 37. This excellent paper of Sir H. Marsh's contains many illustrations of the same fact. nary purposes of respiration ; but in order lo observe the relaxation after spasm, several hours must be allowed to elapse between death and the post-mortem examination, for the bodies of those who die of laryngeal disease become ex- tremely rigid, and remain in this state a consi- derable time. A second, in which the effusion having been poured out with great rapidity, the rima is found mechanically blocked up, and immediate suffocation occasioned : in this case neither the lungs nor brain are engaged, at least not necessarily. The third is, where the dis- ease has lasted three or four days or more, the cedema has been developed but slowly, and the diminution of the supply of air been less sudden : in these cases, besides the symptoms of strangulation, others, indicative of a con- gested condition of the lung and brain, are observed during the latter periods of existence, and corresponding morbid appearances are dis- coverable after death. Very severe inflammatory affections of the mucous membrane of the larynx are unfortu- nately too frequent to admit of doubt or to create difficulty ; but a good deal of confusion has arisen from an attempt to identify them, or some of them, with croup, because an exuda- tion takes place from the surface in some re- spects resembling the adventitious membrane formed in the latter disease. One of these has been described with graphic accuracy by M. Bretonneau of Tours, by him supposed to be the same with croup, and named Diphtherite : but although the differences between these af- fections have been observed and pointed out, the name is still frequently applied (1 fear) without very precise ideas attached to it. The exact disease described by Bretonneau I do not profess to have ever seen, neither have I heard of it, unless in one instance in a family in this country which lost four of its young and inte- resting members by a visitation at least bearing- some resemblance to it. In hospital 1 have heard the name applied to some throats which I never should have thought of identifying with that described by the French writer, and I feel satisfied that the attempt, to mix up different and it may be opposite diseases under one generic name has done anything but simplify the study of pathology. If, however, by asthenic croup or diphtherite is meant the peculiar local disease which accompanies the eruption of scarlatina anginosa, or which is frequently met with without any cutaneous eruption, especially in adults— which is ac- companied throughout by low and typhoid fever, and is often propagable by contagion — then is the affection well known and its de- scription easy: but it bears no similitude what- ever to inflammatory croup. For besides that the constitutional affections are totally oppo- site, a circumstance of the greatest importance as influencing the progress of the respective cases, the local symptoms and appearances have marked and distinct characters. Thus the as- thenic angina is always ushered in by shivering and other precursors of fever ; the soreness of the throat is intense from the very commence- 118 ABNORMAL ANATOMY OF THE LARYNX. ment, and the part is even painful on pressure externally; every attempt to swallow is so dreadfully distressing that patients will suffer to be half-famished rather than attempt to get down a spoonful of fluid. In attempting to examine the throat there is often great diffi- culty, because the patient either cannot, or from the pain it occasions, will not open his mouth; but if it can be seen, it is observed to be of a deep red colour, verging on purple, sometimes diffused over the surface, sometimes in patches, and even from an early period abundantly covered by a thick glairy tenacious mucus that it is difficult to wipe from it. If the disease is severe, the membrane soon be- comes sloughy : " the colour of the slough is grey or ashey : in some few instances it appears brown; its edges are abrupt and well defined, and it is surrounded by inflammation of an intensely deep red colour. The slough is in general slow in separating, and when thrown off it appears to resemble a membrane of viscid lymph not unlike the adventitious substance formed in croup, and the surface underneath looks of a bright red colour, is nearly level with the adjoining parts of the membrane, and seems more like the blush of erythema than the relic of mortification. I believe that wher- ever croup has appeared to have been conta- gious it will be found that malignant scarla- tina has prevailed also ; and that the occur- rence of the laryngeal or tracheal disease was occasioned by the spreading of the inflamma- tion from the fauces to the windpipe, or per- haps by the actual presence of one of these sloughing ulcers in the immediate neighbour- hood of the glottis."* Such is the description of the effects of an- gina maligna on the mucous membrane written in the year 1825, but without any suspicion on the part of the writer that it could ever be ranged by the side of the affection termed croup : for besides the essentially opposite characters of the fever in each, which by them- selves would be all-sufficient, there are the following differences. The angina maligna, diphthente, or by what other appellation it is to be known, — for with respect to it we enjoy a most happy abundance of nomenclature, — com- mences always in the fauces, and when it at- tacks the windpipe, which is by no means very frequent, it does so secondarily by spreading to it; whereas croup seldom or never com- mences in the fauces unless when it appears as the sequela of some serious injury, such as the swallowing of boiling water. Cynanche ma- ligna even locally is not confined to the mucous membrane, as is evidenced by the intense pain in swallowing, the difficulty of opening the mouth, the enlargement, suppuration, and even gangrene of some of the adjacent glands; and it occasionally exhibits something like a me- tastatic transfer of disease to some important organ, such as the brain or liver. And even when recovery takes place, the difference is still remarkable: it is slow, often imperfect, * Potter on the larynx and trachea, p. 17. and followed by anasarca or some similar evi- dence of a broken and cachectic habit. This is not the place to enter more fully into the examination of these two diseases, which the reader will find admirably contrasted in Dr. W. Stokes' work on diseases of the chest, where the angina is spoken of under the name of secondary croup. There remain two other affections of the larynx to be noticed accompanied by asthenic fever, in both of which the pathological con- dition of the submucous tissue is of great im- portance, viz. erysipelas and diffuse inflamma- tion. I believe the larynx is very seldom the primary or original seat of an erysipelatous attack, at least such has not come under my observation ; but I have not infrequently seen it seized either by the spreading of the disease from the head and face, or by some species of metastasis. The constitutional symptoms during life are of a low and typhoid character; the local, those of painful and difficult deglutition and respiration, and the termination (as far as I know) always fatal. Nor are the appear- ances after death always satisfactory, for, as in other cases of erysipelas, the tumefaction often subsides and the colour fades very soon after death. In most instances, however, we find the mucous membrane of a pale yellow colour and apparently greatly thickened : the sub- mucous tissue filled sometimes with serum, sometimes with a gelatinous lymph, and some- times with a sloughy and putrid matter ; the natural folds of the organ obliterated, and the rima more or less blocked up and closed by the thickening and tumefaction of the adjacent parts. But one of the most curious affections to which the larynx is liable is that of diffuse in- flammation. I say " curious," because it is not necessary that the mucous membrane should be inflamed or thickened or otherwise engaged, or that there should be any remarkable swel- ling of the parts, and yet the breathing is harsh, sibilous, or croupy, as if from the presence of some mechanical obstruction. In these cases, which are always fatal, the cellular tissue is the seat of the disease, and is found filled with offensive purulent matter and flakes of unor- ganized lymph, sometimes around the larynx, trachea, and oesophagus, sometimes at the front of the throat, and not infrequently extending to a considerable distance down into the ante- rior mediastinum. Chronic inflammation of the mucous mem- brane of the larynx resembles in its effects a similar form of disease in other structures, ex- cept that as the aperture of the glottis is small, and its functions essential to life, the same de- gree of alteration or of disorganization cannot have place here that may occur in other situa- tions without the patient generally experiencing a degree of distress that will at least direct his attention to the subject. Still is this affection sufficiently insidious, and its progress in many instances so slow, that often irremediable mis- chief is produced before assistance is sought for: and thus it happens that we are obliged to speak of chronic inflammation, not with re- ABNORMAL ANATOMY OF THE LARYNX. 119 ference to its commencement or the early pe- riods of its progress, but to its effects or pro- ducts, which, exhibiting various forms of de- rangement and disorganization, shew to the morbid anatomist the length of time the work of destruction must have been in operation, and the extraordinary changes of shape and form and structure that may occasionally be endured consistently with the maintenance of a miserable existence. The simplest form of altered structure in the mucous membrane that I am aware of is that effected by a slow but progressive deposit (pro- bably of lymph) within its substance, which renders it firmer, thicker, and more solid ; and although this must occasion inconvenience and difficulty of respiration to a certain extent, and is troublesome from the dry cough and occa- sional spasmodic exacerbations that accompany it, yet perhaps, whilst restricted to this stage, it is seldom perilous to life. But these altera- tions of structure, particularly if neglected, are seldom quiescent, and however slow in their progress have a tendency to move forward either to a morbid or perhaps malignant change of the tissues, or to the partial removal of these by the process of ulceration. Thus, ulcers of the larynx, however heretofore overlooked by pathologists, are now found to be extremely common, and I know of nothing more diffi- cult than to subject the numerous varieties of them to any form of classification. They cannot be arranged according to structure, for they are very seldom so superficial or so insulated as to engage the mucous membrane alone ; neither can they be classed according to the symptoms they occasion, for the suffering of the patient or even his ultimate danger does not seem entirely to depend on their extent or character. The most practically useful division of these ulcers would be as to their exciting cause if it could always be discovered ; yet even here there is so much uncertainty of symptom during life and such diversity of appearance after death as to render the subject obscure and unsatisfactory. In some instances the larynx becomes the seat of idiopathic ulceration, that is, the dis- ease seems to have been occasioned by cold or other causes of local irritation — at least such is the only explanation to be offered. " Thus the laryngeal surface of the epiglottis and the in- ternal parts of the organ itself may be studded over with numerous minute aphthous ulcera- tions ; sometimes the edges are marked by a yellow line of superficial excoriation, bordered by a deep blush of inflammation; and in these cases I have always observed, during life, that great pain and difficulty of deglutition accom- panied the symptoms of dyspnoea, and often formed the most prominent feature of the case. Occasionally the ulceration is deep and foul, and spreads with an almost phagedenic de- structiveness : these sporadic sores, usually commencing above, either in the soft palate or the back of the pharynx and spreading down- wards, too often involve the destruction of the patient. Occurring as they constantly do in bad and cachectic habits, they are little under the control of medicine, and operation, how- ever it may prolong existence, scarcely holds out a hope of ultimate recovery." In other cases the ulceration seems to be sympathetic, and either precedes or follows certain affections of the lung. Thus in cases of tubercular consumption, aphonia is often a very distressing symptom, sometimes accom- panied by difficult respiration, and occasionally by painful deglutition. In these instances not only is the larynx studded over with specks of ulceration, but the trachea and bronchial tubes leading to the cavity in the lung present a similar appearance, as if the matter possessed some corrosive quality and its passage over the mucous membrane became the cause of its ulceration. These appearances have been too frequently observed not to have attracted the notice of the morbid anatomist, but still it is extremely difficult to connect them with dis- ease of the lung in the relation of cause and effect, for sometimes the loss or imperfection of voice precedes or at least is amongst the earliest symptoms of consumption, and in other instances it only becomes manifest in the very latest stages. It is easy to conceive that the presence of an ulcer in the larynx, by pro- ducing difficult breathing and occasioning a diminution of the supply of air, may deter- mine the development of an abscess in a scro- fulous lung already well disposed to such dis- ease; but when the ulceration has occurred at a late period, and the difficulty of swallowing, the aphonia, and stridulous breathing appear among the closing symptoms of consumption, it will be difficult to account for the appear- ances observed, unless by supposing them to be sympathetically produced. But of all the causes from which ulcerations of the larynx are known to proceed, some specific or constitutional taint seems to be the most influential, such as syphilis, scrofula, mer- cury, or a combination of two or more of these. As far as my own observation extends, I cannot say I have ever seen the larynx engaged in a case of venereal where no mercury had been used, but on the other hand there is scarcely any organ more likely to be attacked where the me- dicine has been imperfectly or improperly used, or in which the attack is more perilous and unmanageable. Sometimes the larynx becomes ulcerated in consequence of phagedena or other destructive form of the disease spreading down- wards from the throat or fauces, but more fre- quently is it engaged alone. The ulcers here are seldom solitary, but present several spots of ulceration, and in some cases are so extensive that the whole configuration of the organ is spoiled and lost, the epiglottis being partially or entirely removed, and the chordae vocales and ventricles carried away. The surface of this extensive ulceration is irregular, warty, and gives the appearance of uneven granulation, and there are chaps and fissures that pass deeply into the substance of the subjacent car- tilage, portions of which are removed. When the ulcers are more superficial they very often exhibit the herpetic appearance and the ten- dency to spread observed in mercurial sores, J 20 ABNORMAL ANATOMY OF THE LARYNX. healing in one situation whilst fresh ones break out in the neighbourhood, and cicatrizing with a depressed surface and evident loss of sub- stance. With respect to symptoms, the loss or imperfection of voice will very much depend on the situation of the ulcers; but the diffi- culty of breathing and general distress are by no means criteria by which the extent of de- struction of parts can be estimated, for some- times there is uncommon suffering where the ulceration is extremely limited. Very fre- quently these ulcers (particularly if the epi- glottis is engaged) produce symptoms of diffi- cult deglutition, exactly resembling those of stricture of the oesophagus : but this is only during the time the sores are actually open, for, when healed, swallowing is performed with astonishing facility, even although the greater part of the epiglottis may have been carried away. But the most interesting fact in connexion with these ulcers is, that by rest and proper treatment they are susceptible of cure, and for- tunate it is that by means of operation we are enabled to afford this important organ the requi- site degree of repose. Mr. Carmichael lias published two most interesting cases illustrative of this fact ; in which the patients recovered, and in which we have consequently a right to infer that the ulcerations healed. In the summer of 1838 I operated on a woman in the Meath Hospital, who had symptoms of such extensive destruction of parts as must have proved fatal, but who nevertheless recovered with a complete capability of breathing through the rima, but with nearly a total loss of voice. The healing of this kind of ulceration may be inferred from that case also, but it is proved by the following observation : " In the Museum of the School of Park-street, Dublin, is a preparation taken from a poor woman who had been an inmate of the Meath Hospital ten or eleven different limes for venereal ulceration of the larynx, and finally died there quite suddenly, as if from the effects of spasm. It shews where a large por- tion of the epiglottis had been removed, the ulcer having healed by a puckered cicatrix. From below the left ventricle a longitudinal scar extended a full inch and a half down into the trachea,' the contraction of which had di- minished the calibre of that part of the tube very sensibly The right ventricle was totally obliterated, and on different spots about the superior part of the trachea there were several small pale depressed cicatrices, evidently the results of former sores that had been open at different periods at which she had been in the hospital. The only ulcer that existed at the time of her death was a very small one, with ragged irregular edges, situated midway be- tween the natural position of the right ventricle and the root of the epiglottis." The softer tissues of the larynx are also occa- sionally liable to gangrene, circumscribed — con- fined to the organ itself and not exhibiting any tendency to spread. Of this I have as yet seen but one example, and that one under circum- stances that rendered it doubtful whether the disease should not be considered as sympathetic with a similar affection of the lung. It was the case of a man who died in hospital of gan- grene of the lung supervening on acute pneu- monia. Seven days before his death he was attacked with symptoms of laryngeal disease, hoarseness, with difficult and laborious breath- ing, which gradually increased until the voice was nearly lost and respiration quite stridulous. After death, besides the gangrene of the lung, a gangrenous ulcer was found, involving the chorda? vocales at the left side : its surface was about the size of a shilling, and of a dirty green colour ; its edges quite sloughy, and its centre excavated to a considerable depth : the mucous membrane around highly vascular and covered with a pellicle of lymph. 3. The cartilages of the larynx are subject to very important diseases, some of which seem to be peculiar to fibro-cartilage in this particular situation, and all of which are attended with in- convenience and danger by reason of their interfering with the function of the organ. I shall commence with that which I believe to be the most frequent, the most important, and the most fatal ; indeed, when allowed to run its own course it is always destructive, and when the patient's life is preserved by art, it is with the alternative of breathing for ever afterwards through an artificial aperture. In consequence of the similarity of symptoms between this and phthisis pulmonalis, it has obtained the name of phthisis laryngea. The exact manner in which this disease com- mences and the causes that lead to its produc- tion have not yet been so accurately ascertained as to admit of no farther doubt or question ; for instance, Mr. Ryland seems to think that " in most instances it is secondary to some inflam- matory affection of the laryngeal mucous mem- brane or its subjacent tisssue," whereas I have ventured to believe that the original morbid action was set up in the cartilage itself and was proper and peculiar to it ; at the same time it must be confessed that I have seen it apparently produced by the presence of an abscess in the immediate vicinity, and I believe there can be no doubt of its being an occasional sequela of typhus fever. Theessence ofthedisease seems to be a change of structure in some of the cartilages, followed by the death and disorganization of the newly formed material, and an attempt at its removal by abscess and ulceration. Thus on a post-mortem examination of one of these cases an abscess is always found in the situation of some of the cartilages — very generally of the broad posterior part of the cricoid : and this abscess has burst by one or more openings, one of them being very frequently just behind and above the rima. On cutting into the cavity of the abscess, besides the matter, which is green- ish, putrid, and abominably fetid, particles of a grey or white earthy material are found, and there are always portions of bone, thin, ragged at the edges, white and perfectly dead. When the disease has so far progressed, there is always other and more extensive mischief ; the exterior parts in the neighbourood are swelled and thick- ened, the mucous membrane ulcerated ; the arytenoid cartilages often detached ; and the ABNORMAL ANATOMY OF THE LARYNX. 121 epiglottis, in every case that I have seen, more or less removed by ulceration. The whole con- figuration of the organ is lost or spoiled, and scarcely bears a resemblance to the natural shape and appearance of a healthy larynx. We cannot even form a conjecture of the causes that occasion this formidable disease, or of the circumstances that dispose to its production. At some time beyond the middle period of life the cartilages of the larynx, except the epiglottis, and often of the trachea also, become converted into bone, and from the circumstance of carious bone being so constantly found in these ab- scesses, it would appear that it is either during the process of ossification or immediately after- wards that the disease commences. I have always imagined that it was at the former of these periods, and that the affection was pro- duced by some imperfection or irregularity in, or deviation from, the ordinary and natural pro- cess— in a word, that this earthy unorganized material was formed instead of healthy bone. I had once an opportunity of seeing a case which I regarded as an example of the commencement of this disease, in the person of a man who, having suffered from laryngeal symptoms for some months, suddenly died in the Meath Hospital, ap- parently from the effects of spasm. " On slitting up the larynx, the cricoid cartilage appeared to be highly vascular and organised. Its substance was internally as red as blood, and in three or four places there were specks of an earthy white substance that crackled under the knife, and was evidently of the same nature with that usually found in caries of the laryngeal cartilages." I am aware that one case can prove but little, particularly in pathological science, but oppor- tunities of seeing the incipient stages of such an affection as this must be very rare, and every case ought to be recorded that will in any man- ner tend to throw light on a disease the etiology of which is so extremely obscure. However occasioned, this earthy degeneration of the laryngeal cartilages is an extremely in- sidious disease, its approach being so gradual as scarcely to alarm the patient, and its progress slow. There is usually sore throat and difficulty of swallowing, although this latter is not neces- sarily a constant symptom ; hoarseness, and at first but trifiingly impeded respiration. These inconveniences in the commencement are not such as to produce much distress; fori have known one patient suffer for three months and another nearly nine, beforeeither applied for relief, and in both the disease had a fatal termination. Afterwards, however, the symptoms become much more aggravated, the difficulty of breath- ing is exceedingly distressing, and there are exa- cerbations that bring the patient to the point of death by suffocation. I have already noticed one case in which dissolution took place at a very early period, and when the occurrence could only be explained by the suddenness and severity of the spasm. At length, as the dys- pnoea becomes extreme, the patient suddenly experiences some partial relief; his cough, which was before teasing and troublesome, now becomes softer, and the expectoration free and copious. This latter has all the characters of purulent matter, and there are, mixed with it, particles of that white, gritty, earthy substance already described. Occasionally, pieces of the size of a pea of this unorganised substance are coughed up, and when they appear they leave very little doubt of the nature of the complaint. Towards the latter end of the disease the breathing be- comes loud and sonorous, with a whistling noise, so as to be heard at a considerable dis- tance. The cough is incessant ; the expectora- tion copious, with a peculiarly fetid gangrenous smell ; the patient's breath has this odour also, which may also be regarded as an unfavourable symptom. There is at all times convulsive struggling for breath, with occasional exacerba- tions. In most cases, but not in all, the chest becomes affected ; there is pain in some one part of it or other, with a sensation of tightness round the thorax as if the patient could not draw a full inspiration. His strength seems to give way rapidly under these symptoms; his body becomes emaciated ; he has night sweats accompanied with excessive restlessness ; and at last he sinks exhausted in the struggle and dies. Throughout the entire progress of the dis- ease there is seldom any well-marked paroxysm of fever, although the pulse is never much under 100; however, this may be attributed to the constant irritation under which the patient labours. The tongue is usually clean ; the ap- petite t;ood — in some instances ravenous ; and the general functions of the body, with the exception of respiration, seem to suffer but little. The countenance is always pale, with that sickly dirty hue that characterises hectic fever. The expression evinces great anxiety ; and this is so remarkable that patients suffering under this species of cynanche often seem to bear a strong resemblance to each other. It is now familiarly known to surgeons that even this dreadful condition is not utterly di- vested of hope, and patients in whom this dis- ease had wrought such ravages as to render the larynx quite unfit for the performance of its functions, nevertheless survived for years after an artificial opening had been practised in the trachea. Some of these patients have since died, and thus in a limited degree afforded op- portunity for examining the extent -of destruc- tion produced, as well as proving the all-im- portant practical fact, that ulcerations here, how- ever extensive, are capable of being cicatrized if the organ is only left in a state of repose. In the Museum of the Royal College of Surgeons in Ireland is the larynx of a patient who lived for more than two years after having been ope- rated on by Mr. Purdon of Belfast, and the following are the appearances exhibited by the preparation. About half the epiglottis had been carried away, and the edge of the remnant is cicatrized. The space between the root of the epiglottis and the rima, rough on its sur- face, irregular and warty. The ventricles altered in shape, diminished in size, but not ob- literated. The dimensions of the rima greatly diminished. The canal of the larynx is not more than one-third of its natural size, and is lined by a thick uneven membrane, evidently 122 ABNORMAL ANATOMY OF THE LARYNX. the product of cicatrization, and the place which should have been occupied by the broad por- tion of the cricoid cartilage exhibits an empty cavity, as if that structure had been removed by absorption or some other process, and nothing deposited in its room. One of the pa- tients on whom I operated in the year 1829 died about a year since in the Fever Hospital, and the larynx was examined by the surgeon of that institution, Mr. Trant; it presented ap- pearances so nearly similar to the above as not to require particular detail, and quite sufficient to shew that the original destruction had been such as totally to preclude the possibility of the organ ever being capable subsequently of performing the ordinary function of respi- ration. The cartilages of the larynx are also liable to mortification following on inflammation, and apparently produced by the causes that induce gangrene in other structures. I suppose this affection to be extremely rare, as I have met with but two cases, and have not heard of its being observed by others. In one of these cases a large abscess existed in front of the larynx and upper part of the trachea, in which the thyroid cartilage lay like a foreign substance entirely denuded, mortified, and abominably offensive, its appearance resembling that of wetted rotten leather. The front of the cricoid cartilage and of the two upper rings of the trachea had been removed by mortification also. The lining membrane of the larynx was thickened, corru- gated, and had a granular appearance ; part of it was ulcerated, through which the abscess had communicated with the pharynx. The remnant of this larynx is preserved in the pathological collection of the School in Park-street, and shews that at least five-eighths of the organ had been totally and entirely destroyed. It proves that such a disease must be utterly hopeless and irremediable, and that, quite independent of the constitutional derangement that must lead to its formation and accompany its progress, no chance could exist of cicatrization and subse- quent recovery. Occasionally, although I should suppose very rarely, the cartilages of the larynx are the sub- jects of an alteration of structure strongly re- sembling the ordinary product of scrofula. Of this I have seen but one specimen, for which I am indebted to the kindness of my friend Dr. Benson. December, 1838. A man, aet. 39, was received into the City of Dublin Hospital, under the care of Dr. B. for the treatment of what was considered to be chronic rheumatism. It was soon discovered that the pains were not rheumatic, but most probably depended on cerebral disease. The larynx presented a firm tumour externally, and there was an almost total loss of voice. He died, and after death scrofulous tubercles were discovered in the brain. The larynx was of a healthy structure in every part except in the thyroid cartilage, the ala: of which were converted into a firm scrofu- lous mass, about the size of a large chesnut on each side. The scrofulous or tubercular matter appeared to have been deposited originally in tire centre of each ala. The margins and cor- nua of the cartilage were unaltered, and the cartilaginous structure seemed to lose itself in- sensibly on the surface of the turnout. This very interesting preparation is preserved in the Museum of the Royal College of Sur- geons in Ireland. Besides these deviations from the ordinary healthy conditions of the cartilages of the la- rynx, it is certain that one at least of them pre- sents appearances of abnormal changes both of size and shape. Morbid thickening or hyper- trophy of the epiglottis, as well as its opposite state of contraction or shrivelling, have been spoken of by authors, but I have never been fully satisfied that the former of these was not rather the result of a thickened condition of the mucous membrane than of the cartilage itself, and I believe the latter never is seen unless as the consequence of previous ulceration. A de- viation from its usual shape is by no means very uncommon in this cartilage, most instances of which are trivial and unimportant, and are probably congenital ; but in some few instances the change is more remarkable. One of these has been noticed by Dr. Stokes in the chapter of his work which treats of diseases of the la- rynx and trachea, and by him it is termed the leaf-like expansion of the epiglottis. He de- scribes it thus : " This has not been described by any author, but a most remarkable preparation of the disease exists in the Museum of the School of Anatomy and Medicine in Park- street. The epiglottis is thinned and singularly elongated, and its form so altered as to repre- sent the shape of a battledore, the narrow ex- tremity being next the glottis. In the prepara- tion alluded to it is fully two inches in length, and coincides with double perforating ulcers of the ventricles. Nothing is known as to the history of the case, but I have seen more or less of a similar alteration in other cases of la- ryngeal disease." In a paper professedly devoted to abnormal anatomy, I know not whether I am warranted in noticing derangements of function, unat- tended by any lesion of structure discoverable by dissection, yet there are some of these ex- hibited by the epiglottis which seem deserving of the attention of the physiologist. The use ascribed to this cartilage of protecting the la- rynx during the process of deglutition is well known, yet observation has furnished us with examples of exceptions to this use, both posi- tively and negatively ; for, as when this valvular structure is altogether removed (by experiment in animals and by disease in man), the larynx is nevertheless often found able to protect itself, and the subject to swallow bothliquidsand solids without much, and occasionally without any in- convenience, so, on the other hand, it is a fact which cannot be controverted, that the epiglottis sometimes seems to be deprived of its protec- tive sensibility, and permits the free introduction into the windpipe of substances attempted to be swallowed. This latter fact I first noticed in the case of a Wapiti deer which was bronchoto- mized by Sir Philip Crampton : it frequently discharged portions of its food through the wound, and yet after death the larynx in all its ABNORMAL ANATOMY OF THE LARYNX. 123 parts was found apparently perfect in its orga- nization. But not to rely on observations made on the inferior animal, a case soon afterwards occurred in the Richmond Surgical Hospital, of a young female wounded in the trachea rather low down in the neck. From this wound por- tions of the ingesta frequently escaped, and yet after death the larynx was found healthy, its organization complete, and no unnatural communication whatever between the oesophagus and windpipe in any part or situation what- ever. I have since had a precisely similar case under my care in the Meath Hospital. These are instances in which the epiglottis seems inert, and the larynx is left patulous and unprotected; there are other cases in which it appears to be morbidly active, although it is difficult to ex- plain the agency by which such activity is pro- duced. In prosecuting some experiments on the subject of asphyxia, a stout middle-sized clog was let down into a brewing vat that had been emptied of the fermenting liquor about ten minutes previously; he was to all appear- ance perfectly dead in two minutes. After al- lowing the body to remain thus for twenty minutes, it was examined : the glottis was found to be of a very pale colour, and the rima completely shut up by the close approximation of the arytenoid cartilages. The epiglottis was shut down like a lid upon a box, so as perfectly to close the superior aperture of the larynx : this latter was a curious appearance, and I know not what muscles could produce the effect, but the fact was witnessed by Dr. Hart, now one of the professors of practical anatomy in the College of Surgeons, by Dr. Young, and others. I am also ignorant as to whether a similar condition of the epiglottis obtains in men who have been suffocated by carbonic acid ; human subjects are seldom examined so soon after falling into a state of asphyxia as to allow of the immediate appearances being ob- served, and yet information on this point would be of great value in determining the suitable means for attempting resuscitation. The most difficult part of the pathology of the larynx to contend with is that which has reference to muscular organization, and unfor- tunately it is that which has been least ex- amined, or on which examination has thrown the faintest and most unsatisfactory light. Furnished with an exquisitely delicate and beautiful arrangement of muscle, the normal actions of which are exemplified in the pro- duction of the different sounds of the voice, and in giving force to the exit of the air in coughing, sneezing, &c. it would appear only reasonable to suppose that the functional de- rangements of the larynx should be accom- panied by some appreciable corresponding le- sion of its muscular apparatus ; yet such does not seem to be the case, at least not invariably, and we sometimes find the voice impaired or perhaps lost, the muscles of the organ ex- hibiting their ordinary appearance, and again remarkable and seemingly important lesions without much injury to voice or respiration. Under these circumstances we must speak of the morbid appearances that have been ob- served in the first instance, and consider the irregularities of function afterwards. The muscles of the larynx are sometimes found in a state of extraordinary develope- ment amounting almost to hypertrophy. I know not how far this may be considered to be an abnormal condition, or whether it may not be the natural result of great and constant em- ployment of the organ : reasoning from ana- logy this latter seems more probable, but dis- section has hitherto thrown no light upon the subject. They are likewise subject to atrophy or wasting, the fibres appearing thin, pale, and attenuated. Andral mentions cases of loss of voice in which he sometimes found the fibres of the thyro-arytenoid muscle wonderfully atro- phied, and sometimes separated from each other by some morbid secretion, either of pus or tubercular matter. I have been informed by Sir P. Crampton that he has seen in the Mu- seum of the Veterinary College in London, several preparations illustrative of the disease termed " roaring" in the horse, which seems to be produced by an atrophy of the arytenoid muscles. A relaxation is thus effected which allows to the arytenoid cartilages an unnatural degree of mobility. Whilst the animal is at rest or moving slowly, the current of air passes gently, and there is no " roaring;" but when he is put to greater speed and respiration becomes more hurried or more forced, the little valves are acted on, the rima is proportionably closed, the breathing becomes stridulous, and that pe- culiar noise so well known to persons conver- sant with horses is produced. Lesion of function in the muscles of the la- rynx exhibits itself in the opposite conditions of atony and spasm. Examples of the former are to be found in some cases of partial pa- ralysis where the patients become totally in- capable of uttering any sound, however in- distinct and inarticulate; in the hoarseness and sometimes loss of voice that suddenly attacks young persons, particularly females, from ex- posure to cold and damp ; and perhaps fre- quently inthe sympathetic aphonia that precedes or attends on phthisis. On the pathology of these affections morbid anatomy has thrown but little light, nor is it surprising that the subject has attracted a minor degree of attention, when it is recollected that the more severe laryngeal symptom, that of difficult respiration, is seldom or never present. I have had two cases of aphonia attended with pain and soreness in the larynx, which, under an idea that the disease was either gout or rheumatism, I treated with colchicum with apparently favourable results. I know not whether the supposition that the la- rynx may be the seat of either of these painful affections is correct or not, but I see no reason why it should enjoy so fortunate an exemption. However, although atony of the muscles of the larynx may not be attended with much peril, a spasmodic action of them is always eminently perilous, sometimes destroying life with a ra- pidity that almost precludes the possibility of assistance. There can, therefore, be few sub- jects more interesting to the practitioner, and 124 ABNORMAL ANATOMY OF THE LARYNX. although, as might be expected, the causes that produce these terrific affections have not been explained, yet it may be desirable to examine into the symptoms and some of the circum- stances that occasionally precede or accompany them. Spasm of the glottis is either idiopathic or symptomatic. The idiopathic occurs, as far as I know, only in children, as in the " spasmodic croup," or laryngismus stridulus, unless we also choose to include within this class the hysteric dyspnoea that occurs in young females. The symptomatic occurs as indicative of, or in connexion with, 1. The application of some deleterious sub- stance to the larynx, as carbonic acid, boiling- water, or steam. 2. The application of some irritating mate- rial, as a paiticle of salt. 3. The presence of a foreign body within the trachea or bronchial tubes. 4. The presence of a foreign body in the oesophagus. 5. The existence (occasionally) of an aneur- ism of the aorta. 6. The existence of any other disease within the larynx or trachea. Any of these latter may be present in the adult or the child indif- ferently. Few diseases have attracted more attention than the spasmodic croup of children ; few have been more accurately described as to symptoms, and in none is our pathological in- formation more deficient; a fact that may al- most be proved by the number of different names by which it has been designated. It is the asthma of infants of Millar; the cerebral croup of Pretty; the spasm of the glottis of Marsh ; the spasmodic croup of other writers ; and the laryngismus stridulus of Mason Good and Ley. It occurs in very young children, with a peculiar difficulty of breathing, attack- ing for the most part suddenly, accompanied by a crowing sound, and oftentimes with a sus- pension of respiration for several seconds. This difficulty of respiration varies in intensity from a single crow to a more prolonged paro- xysm threatening suffocation, and terminates when in recovery by a long deep-drawn respi- ration, with a peculiar stridulous noise ; when in death, by such convulsive struggles as might lead, and indeed have led, to a belief that the cerebrum was engaged. Pallid and exhausted, the child falls lifeless upon the nurse's arm, and is then generally said to have died in a fit. In these cases there is no cough ; no raucal sound of voice; no continued stridulous breathing, except an occasional mucous rattle heard only while the infant sleeps be con- sidered as such ; there is no fever ; and on ex- amination after death no trace of inflammation, nor indeed any deviation from the ordinary healthy appearance of the organ, can be disco- vered. Under these circumstances, patholo- gists had no method of explaining the pheno- mena but by spasm, an irregular and invo- luntary contraction of the muscles of the larynx closing up the rima glottidis to a greater or less extent, and in proportion to such closure in- terfering with and obstructing respiration. But what is the cause of this spasm ? Some have supposed it to have an intimate con- nexion with an hydrocephalic tendency, be- cause it has been sometimes seen in children with large heads and sluggish dispositions, and because signs of cerebral congestion have been discovered after death ; but I have seen the di- sease prove fatal to the liveliest and apparently most healthy children, and the congestion may just as well be the consequence as the cause of the closure of the glottis. Others again have referred it to the general constitutional irri- tation that proceeds from painful dentition, and doubtless eases have occurred in which the crowing respiration was relieved by successive scarifications of the gums, according as each tooth became prominent underneath ; but this, although teaching an important practical lesson, leaves the pathological connexion between the facts in as much obscurity as ever. Accord- ing to others there is a constitutional tendency to this disease in some children, a fact which it must be conceded has been painfully exempli- fied in more families than one ; but this here- ditary disposition to disease, although abun- dantly obvious, is too imperfectly understood to be discussed with any thing approaching to pathological accuracy. Lastly, improper or un- wholesome food, indifferent clothing, a close and tainted atmosphere, and exposure to vicis- situdes of climate, have been regarded as in- fluential exciting causes, and change of circum- stances in these respects has often produced an almost magical amendment in the condition of our little patients ; but still we are at a loss to discover the immediate modus operandi of these pernicious influences, or why they should be determined to the larynx in the form of an in- voluntary spastic contraction of its muscles. Other causes have been assigned for the pro- duction of this disease, some of which are eminently deserving of attention ; at the same time it may be observed that its being attri- buted to such a number of influences shews that its real exciting cause is probably still unknown. For instance, either this disease or an affection bearing a strong resemblance to it, has been described by Dr. Kopp, and after- wards by Dr. Hirsch of Konigsberg, under the name of thymic asthma, and by them attri- buted to an hypertrophied condition of the thymus gland, which by its weight and volume presses on the heart, the lungs, the large arte- rial and venous vessels, and prevents the free exercise of their functions. Dr. Montgomery has published an interesting paper on this sub- ject, in which he attributes the sudden death to an enlargement of this gland, whether that arises from hypertrophy of its substance or an alteration of its structure from scrofula or other disease ; and explains how agitation or excite- ment may suddenly distend and increase the size of the organ in such a manner as to affect materially the condition of the surrounding parts. Again, in the work by Dr. Ley already referred to, a different explanation has been offered. Apparently relying on the experi- ABNORMAL ANATOMY OF THE LARYNX. 125 mental researches of Magendie and Le Gallois, he supposes that, if the recurrent nerves are compressed to such an extent as to have their functions impaired, the glottis, under the in- fluence of the superior laryngeal branches, would become and continue fast closed. The cause of the disease then, according to him, will be found in some tumour, scrofulous or otherwise, so situated as to create an injurious degree of compression on the recurrent nerves. That an enlargement of the thymus gland may, from its situation, produce great and serious in- convenience, it would be absurd to question, and perhaps there is sufficient evidence to shew that it may occasion the symptoms and results of this very disease : but it is far from being proved that spasm of the glottis may not occur, and even prove fatal in cases where no such enlargement existed. Alterations of size, shape, and structure, even if rapid, take place gradu- ally, and their results should be gradual also, whereas this disease has been known to destroy its victim in its first and only paroxysm ; and moreover, if structural change in the gland was its sole exciting cause, it would be difficult to account for its sudden disappearance on the removal of the child to the country and its diet being changed. Whilst therefore it may not be denied that hypertrophy of the thymus can occasion the phenomena by others attributed to spasm of the glottis, there is not sufficient proof of its being the general or even frequent cause of this peculiar disease. I shall have occasion to notice the supposed consequences of pressure on the recurrent nerves hereafter. It is questionable how far spasm occasioned by the contact of noxious or irritating sub- stances can justly be termed sympathetic, for they are the results of an application of a di- rect stimulus : it is immediate in its effects, and more or less complete according to the nature or quality of the exciting cause. Death from total submersion in carbonic acid gas occurs so quickly as almost to seem instan- taneous, and the spasm entirely occludes the glottis. The mildest form of spasm seems to be that occasioned by the accidental admission of some particle of food which is usually expelled again very quickly by a cough suf- ficiently distressing but seldom dangerous: yet instances have been known of the apparently trifling occurrence of the introduction of a par- ticle of salt being attended by a fatal result. However, when spasm is, or appears to be produced by the presence of a foreign body in the oesophagus or the trachea, or by the pres- sure of an aneurismal tumour, it is evidently sympathetic, and it may be interesting to in- quire into the evidence by which such relation of cause and effect is established. I had formerly entertained the opinion that spasm of the glottis should be the consequence of some irritation applied to the larynx itself, and not external to or at a distance from it, and therefore that the presence of a foreign body in the oesophagus ought not to hold a place amongst its exciting causes. I have since, however, altered my views on the subject, and indeed, when we consider the number of cir- cumstances under which this morbid action may occur, we cannot be justified in denying it in this case in opposition to most respectable testimony. Mr. Kirby has published a case in the Dublin Hospital Reports, in which death was apparently produced by spasm of the glot- tis in consequence of the lodgment of pieces of meat and bone in the oesophagus: and Dr. Stokes saw an instance in which a piece of money was lodged in the oesophagus and where croupy breathing and other laryngeal sym- ptoms were manifestly the result. In this lat- ter instance the foreign body was not lodged in the fauces or pharynx. I have myself seen cases to corroborate the above, but it is need- less to swell this article with proofs of a patho- logical fact that will probably not be called in question. It is protably a new observation — at all events it is one of great pathological interest, that spasm of the glottis may be produced by the presence of a foreign body lodged within the bronchi. In the month of May, 1836, a child was brought from the country and placed under the care of my friend Mr. Cu- sack : his father's account of the case was that he had swallowed a small pebble, was instantly seized with a violent paroxysm of cough, had croupy or sonorous breathing ever since the accident with occasional remissions and exacer- bations, but was sometimes brought to the verge of suffocation. The stethoscopic indi- cations were that the foreign body was loose and mobile within the trachea. I assisted Mr. C. in performing the operation of tracheotomy on this child ; but, although the aperture in the windpipe was made very large, no stone was expelled, and the size of the organ did not admit of the employment of any forceps with which we were furnished. Immediately on the opening into the windpipe being perfected the croupy breathing disappeared, neither was there a severe paroxysm of cough experienced afterwards, and the father, either doubting that the foreign body had ever obtained admittance, or dissatisfied at its not being removed, car- ried him off to the country contrary to the wishes and advice of his medical attendants. We afterwards heard that the little pebble had been coughed up in about three weeks after he left town, but have not been informed as to the ultimate termination of the case. On the 13th of September, 1839, a child, aged three years and a half, was brought to the Meath Hospital : he had, half an hour pre- viously, swallowed a small stone, and was in- stantly seized with a violent cough which con- tinued up to the period of admission. His breathing was quite stridulous — countenance expressive of great distress — face and lips lived — efforts at respiration hurried and gasp- ing. The left side of the chest heaved vio- lently, the right was comparatively quiet : re- spiration very weak and interrupted in the right lung, in the left loud and puerile : no dulness over either lung on percussion. I per- formed the operation of tracheotomy, but no foreign body was expelled, and yet the little patient experienced the greatest relief. The 126 REGIONS OF THE LEG. trachea was too small to allow of the intro- duction of any instrument for the extraction of the offending substance if such was there, so I merely satisfied myself with keeping the wound open, in the hope of its being coughed up. Whenever from any accident the wound in the throat became obstructed, the breathing became dreadfully oppressed, but he obtained instant relief when it was opened again and cleaned. Such were the phenomena of the case generally up to the 6th of October, when it was found that the wound had gradually closed and healed so as to leave the artificial opening very small, and on that day, in con- sequence of the increased difficulty of breath- ing, I was obliged to open up the whole wound anew. This second operation afforded im- mediate relief. On the Cth of December the wound being again nearly healed, in a despe- rate fit of coughing he expelled a small stone about half an inch long by about two lines broad, through the rima glottidis. There were many other interesting facts con- nected with this case, which I omit here, my object being only to show that the difficult re- spiration which rendered the operation neces- sary was not caused by the mechanical occlu- sion of the bronchi by the presence of the stone, but had its seat in the larynx. The child had always repose when not called upon to employ the rima in respiration, although the stone was present in one or other of the bron- chi, and in this case it was remarkable that it shifted its position, as proved by stethoscopic evidence. It is sufficiently well known that the pres- sure of an aneurism, and of course of any other tumour, on the trachea or bronchi will produce difficult respiration to such an extent as to simulate laryngitis and to place the pa- tient's life in imminent peril. This has been supposed to proceed from the mechanical ob- struction given to the passage of the air by the compression of the tumour, and I shall not deny that this cause may occasion inconveni- ence, but still may be allowed to doubt that it produces the stridulous breathing and other laryngeal symptoms — at least in the majority of cases. In the month of July, 1837, I was requested by another practitioner to see a case of acute laryngitis and to operate if I deemed it necessary. The case appeared to be seriously urgent : the man seemed to be on the point of suffocation ; and having made some inquiries as to the history, and particularly as to the con- dition of the chest as ascertained by auscul- tation, I operated immediately. The relief was as marked and as decided as I had ever seen in any laryngeal affection ; and, after allowing the patient two or three hours' repose, I had him removed to the Meath Hospital, in order to be under my own immediate care. He died on the fourth day afterwards from the bursting of an aneurism of the aorta within the chest, and on examination the larynx was found in a perfectly healthy and normal condition ; yet was it evident, from the relief experienced on the opening being made below it, that the ob- struction to respiration that existed during life had been caused within this organ. Those who, with Le Gallois and Magendie, explain spasm of the glottis by a compression exer- cised on the recurrent nerves, may possibly consider that the aneurism in this case pro- duced such pressure, and I am not in a con- dition to deny it, because the sac was collapsed and empty, and I could not say what pressure it might have created directly or indirectly when tense and full of blood. But the sac in no situation lay in contact with the nerve, or seemed to hold any relation to it that would lead to such a conclusion. I may add, inci- dentally, that I have seen aneurismal tumours which must have implicated this nerve, in which the spasmodic difficulty of breathing did not exist, and therefore whilst I believe that spasm of the glottis may be produced in consequence of, or in connexion with, the ex- istence of some tumour compressing the trachea or bronchi, I cannot (in the present state of our knowledge) yield to the opinion that refers it so entirely to a compression of the recurrent nerve. The ligaments of the larynx are, of course, liable to disease. Thus, during life, we argue on the possibility of an abnormal state of ten- sion or relaxation, from observing certain alte- rations of the tone of voice which are thus supposed to be capable of being explained : but the most frequent morbid appearance found after death is ulceration, although there is no evidence of its ever commencing in these struc- tures. In all cases of phthisis laryngea, the ligaments suffer severely and in some are actu- ally destroyed ; for the expulsion of the ary- tenoid cartilages by coughing is no infrequent symptom of that disease, and it could not other- wise occur. I have often imagined that this ulceration of the ligaments was one cause of the difficult respiration, particularly in cases where there is a marked difference between in- spiration and expiration, by allowing to the arytenoid cartilages too great a degree of mo- bility, and permitting them to be thrown down on the rima. When the connexions between the cricoid and arytenoid cartilages are cut across posteriorly, it is easy to lay the latter down in such a manner as nearly to obliterate the rima; and if a similar division be effected by disease, why may not these little bodies, become loose, be acted on by the current of air and shut like a valve in every act of in- spiration ? ( W. H. Porter.) LEG (Regions of the). — If the importance of a part, and the interest connected with the study of its structure and its diseases, be mea- sured by the general amount of suffering through it entailed upon mankind, by its ex- treme liability to accident and injury, and by its value in the general movements and well being of the body, certainly the leg would possess claims to our consideration greater than any other portion of the system of the same extent. From the integument to the bone, and from the knee to the ankle, every part of it is the frequent subject of disease, more or less REGIONS OF THE LEG. 127 interfering with the comfort, if not with the health, of the entire system. It is composed of two bones, the tibia and fibula, with accompanying masses of muscles both before and behind, which act upon the foot. If we divide the leg into anterior, external, and posterior regions, we find in the anterior the tibialis anticus muscle, the extensor coin- munis digitorum, extensor proprius pollicis, and peroneus tertius ; in the external region, the peroneus longus and brevis ; and poste- riorly, the two gastrocnemii, popliteus, plantaris, tibialis posticus, flexor longus digitorum, and flexor longus pollicis. Among these are run- ning the anterior and posterior tibial and pero- neal arteries, with their accompanying veins, nerves, and absorbents ; all these bound toge- ther, and supported by strong fascial coverings, and enveloped in the general integument. Be- tween this and the fasciae just mentioned, is an important layer of cellular tissue, (fascia super- ficialis,) enclosing the two saphenae veins, major and minor, and the superficial nerves and ab- sorbents. It may be well to make some few obser- vations upon the external form and characters of the leg, before describing the deeper seated parts. The leg, comprising all that part of the lower extremity between the knee above and the ankle below, is somewhat of a conoidal tapering figure, rather flattened on its anterior and outer aspect, full and round posteriorly. This shape renders permanent compression by means of a bandage very difficult. The con- traction of the gastrocnemii, especially during walking, rarely fails in a short time to separate the turns of the bandage below, causing the lower ones to overlap each other, and producing constriction, irritation, and excoriation of the skin, above the malleoli. If this difficulty were more considered, and the importance of the bandage in diseases of the leg duly appre- ciated, we should see more pains taken in ac- quiring the art of its application than is now common; though we are happy to find that the minor operations of surgery are now beginning to receive much more attention than formerly, and to form a part of the general system of demonstrative instruction. Assuredly the ag- gregate amount of suffering relieved would be far greater by attention to these minutiae of surgery, than by the more striking, though not more important details of operations, which to the mass of practitioners can occur but seldom, if at all. The projection of the muscles at the back part of the leg, produced by the two gastro- cnemii, and known under the name of the calf, forms a characteristic peculiar to man. No inferior animal possesses it, not even the ourang outang ; and the feeble and uncertain gait of these animals, when in the erect position, at once demonstrates the value of the muscles of the calf of the leg, and that this position is natural only to man himself. The form and expression of this part of the leg varies much according to age, sex, and general habit. In infancy the gastrocnemii, in common with the developement of the whole lower extremity, are small and feeble. The upper extremities are, in early infancy, even larger than the lower ; these latter do not acquire their full growth and proportions till adult age. In the female, the general form of the leg is less marked and prominent, and more rounded than in the male, while, in this last, the leg presents every pos- sible variety of proportion, according as habits of exercise on foot, robust health, or long conti- nued sickness, has invigorated or enfeebled the muscular system at large, or this portion of it in particular. The broad and rounded surface of the calf of the leg is contracting as it de- scends, and at the lower part projects like a kind of cord, representing the tendo Achillis. In contraction, the calf shows two portions, marked out by a double fissure, which indi- cates the situation where the gastrocnemius join the soleus, the lower elevation being formed by this last muscle, which extends lower down the leg than the gastrocnemius. This projection of the soleus is in some much more marked than in others, and is indicative of considerable power when it reaches lower down, much more so than when the whole prominence of the calf is high up. In persons celebrated for pedestrian powers we have observed this projection of the soleus in a marked degree. In the anterior region of the leg, the form is considerably flatter than in the posterior, and narrows as we proceed downwards, at the lower part becoming almost round. During extension of the foot, this region is marked by longitudinal elevations and depressions, indi- cative of the situations of the muscles, and of the connecting portions of aponeurosis. An examination of these points will assist us in cutting down upon the arteries here, as the depressions mark the exact boundaries of the muscles, being produced by the aponeurotic processes, which dip between them. The integument of the anterior region, gene- rally covered with hair in man, and of a some- what dense structure, enjoys sufficient mobility to admit of wounds being united by the first intention, provided the loss of substance be not great. Not being very extensible, abscesses, tumours, &c, have great difficulty in projecting externally in front of the limb, and consequently for the most part remain more or less flattened. The posterior part of the leg has an integument more soft and elastic, and possessing fewer hairs than the anterior, particularly on the inner side. The position of the skin, with relation to the parts which it covers, occasions a marked difference in the mode of repairing the ravages of extensive ulcerations or sloughings. On the front and outer part of the leg, where the skin is somewhat stretched over the tibia and fibula, the process of cicatrization can only draw together the sound parts to a small de- gree. In consequence the healing process is slower in completion, and the cicatrix less de- pressed in proportion than when it is situated posteriorly. On the contrary, in this latter situation, the skin being stretched only over soft parts, when a considerable portion of it has been destroyed, the contractile force of the new REGIONS OF THE LEG. skin has full opportunity to exert itself, and this it does sometimes to a degree that is re- markable, acting as a sort of ligature upon the back part of the leg. We have seen a case where, by the cicatrization of an old and very extensive ulcer, the lower part of the calf of the leg, viewed in profile, had an appearance as if more than half the entire leg had been cut away.* The most dense and strong part of the integument of the leg is over the inner side of the tibia where this forms the only covering of the bone, while at the upper and back part of the leg the skin is exceedingly thin and deli- cate, and devoid of hairs. We may here re- mark, in illustration of the properties of the integuments of the leg, important in relation to surgery, that the contractile property of the skin is usefully exemplified in amputation, when, should the flap of the integument be more extensive than we desire, even to a great de- gree, we always find that in the progress of the case it contracts so much as to exhibit no re- dundance in the end ; in fact that a large quantity of integument, however unsightly, is far less to be dreaded than the opposite defect. It is not our intention here to enter minutely upon the diseases of the parts we are now de- scribing, but we cannot refrain from alluding to a state of disease of the integuments which we have never seen but in the leg, and of which we have met with no account in books. It consists in a soft elastic swelling, generally occupying the entire circumference of the leg, for the lower third or fourth of its length, though often much less. The skin over it is considerably redder than natural, and of a somewhat dark colour. It is not at all tender to the touch, but is exceedingly painful when the foot is down and in exercise ; on pressing the finger firmly upon it no pit is left, but the skin is very white until the capillaries fill again, which they do slowly. Should the skin ulce- rate, the sore is very slow in healing, and gene- rally has a brownish unhealthy look, but the state in question often lasts for years without any ulceration occurring. The disease is very indolent, neither increasing nor diminishing in extent for many years. We have not been able to trace it satisfactorily to any cause more than too much standing. All the cases observed by us have occurred in females between the ages of twenty and forty, whose employment kept them very much on foot. It appears to us to consist in a varicose state of the capillaries of the cellular tissue and inner side of the cutis. No treatment that we have employed has had anything more than a temporary effect. Pres- sure, as long as it is continued, relieves it ; but all the morbid symptoms return upon the remedy being omitted. Immediately under the skin lies the cellular tissue, which is a part of the general cellular investment of the body, and is here known as the superficial fascia of the leg. It is gene- rally pretty thick, and is easily dissected back in amputations. Placed between two solid layers, the aponeurosis and skin, it easily in- * See article Cicatrix, flames and may become the seat of extensive inflammation and abscess. When the inflam- mation has terminated in gangrene, the slough- ing process in this cellular tissue is very rapid and often very uncontroulable ; and where this destruction has occurred to considerable ex- tent, in the after process of reparation the new cellular web is so short, close, and inelastic, as to materially impede the freedom of movement in the limb. When pus has been formed, the facility which the loose texture of the super- ficial fascia offers for its spreading in all direc- tions, points out the necessity for early and free incisions through the integuments ; and even before this stage of the inflammation, and while it is in its most active state, the same bold practice offers us the best means of arresting its progress. This cellular layer is the seat of the effusion in phlegmonous erysipelas, anasarca, phlegmasia dolens, and partially so in ele- phantiasis. The distension which this tissue and the integument over it undergo in the dis- eases just mentioned, is occasionally enormous, and affords a striking contrast between the elastic properties of the natural and adventitious structures. When anasarca distends a leg upon which an old cicatrix exists, the newly formed cellular web of this part is so little elastic and so little admits the fluid into its cells, that a considerable depression is seen here in the midst of the general swelling. Imbedded in this superficial fascia we find a number of veins which are various in size, none very large in the natural state, numerous, and here possessed of more surgical interest and importance than in any other superficial region of the body. They are principally ar- ranged in two sets ; one commencing about the inner ankle, and running along the inner side of the calf, terminates just below the knee by one trunk called the internal or major saphena. The other set form the saphena minor, by coming from the outer ankle, along the outer and back part of the leg, and termi- nating in the popliteal vein in the middle of the ham. This vein is superficial only in the lower two-thirds of the leg ; after this, it passes through the layers of the aponeurosis, and runs under it till its termination. This is the more ordinary course of them, but no part of the circulating system is more various than these superficial veins in their divisions and arrange- ment. These veins, by becoming varicose, frequently occasion great suffering to the pa- tient, and annoyance to the surgeon, by the difficulty of their cure. The saphena major is more liable to this state of disease than the minor; indeed few persons whose habits are to be much in the erect posture appear to attain middle age without being more or less troubled by it. The deeper seated veins, which accompany the arteries, lie imbedded among the muscles, and from them receive considerable passive support, in sustaining the weight of the column of blood above them, and still more in an active sense, when, in contracting, the muscles swell and press against their sides, and thus assist in forcing onwards their contents, But these REGIONS OF THE LEG. 1-29 superficial veins are without this important help. Their sides are supported, on one hand, by the yielding layer of the fascia and muscles, and, on the other, by the integument. When, therefore, any impediment presents itself to the free transmission of the blood through the femoral, popliteal, or iliac veins, or even by the mere weight of the ascending column of blood, in persons who stand much, it is the superficial veins that suffer most, and a perma- nently dilated state is the frequent result. The pathology of varicose veins has not re- ceived the attention which it deserves, and hence the conflicting opinions as to the precise nature of their origin ; we must even now con- fess with Delpech that the nature and causes of the disease are unknown. It is quite clear that that state of disease of the veins commonly termed varicose comprehends more than one pathological condition, and probably has more than one mode of origin. Every instance of an enlarged vein cannot be considered as a varix, unless we confound under the same denomination a condition of the vessel natural and healthy except in regard to its size, neither originating nor terminating in a morbid condi- tion, with every variety and degree of disease accompanied with enlarged capacity of the vein. We have seen the veins of the abdomen en- larged so as to fulfil the office of the vena cava inferior, which was obliterated. But there was not the slightest mark of disease in these super- ficial vessels. The uterine veins, also, in preg- nancy become enlarged in a similar manner, thus answering to the call for the increased circulation of blood in the uterus. This state of the vessels has been aptly termed hyper- trophy, and the term varix has been restricted to permanently dilated states of the veins, at- tended with the accumulation of dark blood, which more or less generally becomes coagu- lated and adherent to the parietes nf the vessels. Of this latter species Andral enumerates six varieties : 1st, simple dilatation without any other change, such dilatation affecting either their whole length, or occurring at intervals ; 2d, dilatation, either uniform or at intervals, with a thinned stale of the veins at the dilated points; 3d, uniform dilatation with thickening of the venous coats ; 4th, dilatation at inter- vals with thickening of the dilated points ; 5th, dilatation, with the addition of septa within the vein, whereby the cavity is divided into little cells in which the blood lodges and coagulates ; 6th, a similar disposition combined with per- forations in the parietes of the veins, which communicate with the surrounding cellular tissue in a more or less diseased state by nume- rous small apertures. From repeated observa- tion of its practical impoitance we should be inclined to add to this list one other variety, viz. when the varicose state had extended into, or existed distinctly in, the capillaries of the skin. We believe that in those troublesome ulcers known as varicose we shall frequently, if not generally, find this state of the minuter veins and capillaries, and we are more inclined to attribute the pain and the obstinate character of these ulcers to the pathological condition now vol. nr. mentioned than to the mere vicinity of an en- larged vein as it passes through the superficial fascia. The causes of the diseased state in question have been variously stated, nor do opinions yet agree upon it, some attributing it to mechanical influence, and others supposing a morbid tendency. Both these causes pro- bably act in different instances, or even co- operate in the same case ; we shall now only mention in illustration of the effect produce- able by the mechanical influence of too much standing, that it is not necessary to suppose that the valves are either destroyed or even materially injured in structure to nullify their agency in supporting the column of blood above them, since ever so small a communi- cation between the two columns, the upper and the under, is sufficient to destroy all the beneficial agency of the valves as supporters of the gravitating fluid in the veins. Therefore a dilatation of the vein merely enough to draw the opposed edges of the valve ever so little apart, or even a thickening of the valves pre- venting the accurate coaptation of their edges, will be sufficient to prevent their power of support to the superincumbent column, and as far through the vein as this defective state of the valves may exist, so far will the gravi- tating column of blood be virtually unbroken and entire, and in the same proportion will the tendency to the varicose state be increased. This reasoning will explain many, probably the majority of cases where the morbid dila- tation having once begun goes on to increase rapidly by the continued operation of this ex- citing cause. That there are other causes capable of producing this state of the veins cannot be disputed ; indeed the occurrence of it in parts not likely to be affected by the up- right position, and even in several different parts of the body of the same subject, shews that there is occasionally a morbid tendency in the venous system to this particular state, which acts independently of any mechanical cause; but we believe that this predisposing cause is not necessary to the production of the disease, and that the morbid tendency, when it is met with, should be regarded rather as the exception than as the rule. In considering the causes of the disease in question, we should not lose sight of the rela- tive proportion of the deep and superficial venous circulations of the lower extremities, a proportion varying in almost every individual. In one, the superficial veins are large and nu- merous, and lie immediately under the skin; in another, they are few and small. Tt is ob- vious, that in the first case the blood retained by this route bears a large proportion to that passing through the deep set, much larger than it would in the latter case. In the first in- stance, therefore, these vessels will have a greater proportional weight of blood to sustain and transmit, than in the second ; while, in those individuals who have the superficial cir- culation small, the blood is chiefly returned by the deep set, which, from circumstances before mentioned, are more equal to the task, and in such persons the diseased state in question K 130 REGIONS OF THE LEG. rarely occurs. This we conceive to be a ratio- nal and practical explanation of phenomena which are otherwise obscure. It seems probable that that most troublesome ulcer, the varicose, is kept up, and the difficulty of its healing produced not by the irritation occasioned by the mere vicinity of the enlarged veins, but from the actually varicose state of the capillaries of the skin at that part; at least we have found such a state of the vessels fre- quently, if not generally, to co-exist with this species of ulcer. The depth of the cellular layer (superficial fascia) in which these veins lie should be accurately understood and borne in mind in performing the operation of passing a needle under the vein for the cure of varices, according to Velpeau's plan (a method which we have adopted with considerable success.) Should the needle be passed so deep as to reach the fascia, the inflammation would pro- bably be severe, at any rate sufficient to com- plicate needlessly the operation. The thickness of the cellular layer varies in different subjects, according as it is distended more or less with fat or with accidental effusion ; it is rarely, however, less than two lines in depth, thus affording abundance of room for the transmis- sion of the needle. The size of these veins of the leg in the healthy state is at the most not larger than a small goose-quill, but when varicose they sometimes swell to the size of the finger, and we lately saw a varicose enlargement of the saphena major a little below the knee, of the size of a large hen's egg ; the quantity of blood that may in a short time be lost from them may hence be conceived. On the anterior region the veins are few, and varices but rarely occur compara- tively. On the inner region the saphena major lies close upon the bone in part of its course, and even indents it deeply when distention has continued long. In cutting upon the vein in this situation, we must bear in mind the conti- guity of the internal saphenus nerve, whose situation, with relation to the vein, varies much, sometimes being before, sometimes behind it. We cannot, therefore, lay down any rule for its avoidance, unless it be to open the vein parallel to its length. The saphena minor has a nerve running with it, which in phlebotomy must be avoided with the same precaution as the nerve on the inner side. The two nerves found imbedded in this su- perficial layer of the leg are, 1st, the internal saphenus, which is the largest, and is passing from the inner side of the knee to the inner side of the foot, accompanying the saphena major vein; 2d, the external saphenus or com- munkans tibialis from the tibial nerve, which runs near the saphena minor through the lower part of its course. Imbedded in the superficial fascia, we also find a set of lymphatics, principally on the inner side of the leg, receiving part of those from the sole and dorsum of the foot, while those absorbents which accompany the sa- phena minor are receiving their commence- ment entirely from the sole of the foot. All of these superficial lymphatics ascend to the inner side of the thigh, and terminate in the inguinal glands. Hence diseases of the sub- cutaneous cellular tissue of the leg exert their influence upon the superficial glands of the groin, and are not unfrequently the cause of disease in them, which, without due inquiry, might erroneously be attributed to disease of the genital organs. The aponeurosis of the leg forms an important part of its economy. It is a dense tendinous structure, which immediately invests the mus- cles, and partly affords them origin. In conse- quence of its strength and want of elasticity, it prevents swelling in deep-seated inflamma- tions, and we are consequently obliged to divide it early and freely, particularly when suppuration already exists, and when the mat- ter would otherwise burrow among the muscles. On the anterior region it is strong, very dis- tinct, and tense. In its superior fifth, it gives attachment to the fibres of the tibialis anticus, extensor communis digitorum, and peroneus longus. Below, it is pierced by the anterior tibial and musculo-cutaneous nerves. It is attached above to the heads of the tibia and fibula, and along the crest of the tibia, stretching from this to the anterior edge of the fibula. At the upper third of the leg, it sends processes backwards between the muscles, to be attached to the bones, thus forming sheaths for the muscles, and affording to their fibres a greater extent of origin. At the lower two- thirds of the leg, the fascia is closely attached to the intermuscular tissue, but has here no septa from its own structure. At the lower third, it binds the tendons firmly down in their places, and by its transverse fibres opposite the ankle forms the anterior annular ligament of that part.* From the anterior edge of the fibula, this fascia passes over the two peronei muscles, and is again inserted on the posterior border of the bone, forming a sheath for these muscles, and dividing them from the soleus. The observations made above on the surgical treatment of purulent collections refer especi- ally to this anterior portion of the fascia of the leg, on account of its greater strength, density, and inelasticity. At the back part of the leg, the aponeurosis is a continuation of that of the ham. We may consider it as formed of two principal layers ; one superficial, and the other deep. Attached to the posterior border of the fibula externally, and to the inner margin of the tibia internally, the first appears to arise from the expansion of the tendons of the sartorius, gracilis, and semi- tendinosus. Applied over the posterior surface of the calf, it is lost below in the fibro-cellular tissue surrounding the heel. This portion being thin and yielding, it allows deep-seated ab- scesses to become superficial with great facility. The second layer is a continuation of the apo- neurosis of the popliteal cavity, and descends between the two layers of muscles ; but split- ting into two, at the point where the soleus de- taches itself from the deep parts, one of its divisions follows the anterior surface of the * See Ankle-joint, Regions or. REGIONS OF THE LEG. 131 tendo Acbillis, of which it completes the fibrous canal, formed posteriorly by the super- ficial layer; the other remains applied over the posterior surface of the deep muscles, and both arrive at the heel. In its inferior third, this aponeurosis thus circumscribes three spaces. One is filled by the tendon of the muscles of the calf. The se- cond incloses the flexor muscles of the toes, and the vessels. The third, which separates the two others, lies between the tendo Achilhs and the posterior surface of the last-named muscles. The latter is remarkable, from being filled with fat and fibrous filaments, interlaced in various directions.* We have, for convenience of description, de- tailed the anatomy of the superficial parts of the leg, without particular reference to the re- gional divisions, which become more defined, distinct, and practical as we investigate the re- lations of the deeper seated parts, and to which we shall therefore now limit ourselves. In the anterior region, comprising all those muscles which rest upon the tibio-fibular fossa, we find, on dissecting the fascia from the upper part, only two muscles exposed, viz. the tibialis anticus and extensor communis digitorum. Lower down, we see in addition the extensor proprius pollicis ccming out between the two last, and the peroneus tertius a slip of the outer side of the extensor communis. These four are, as it were, bound down in a canal, formed anteriorly by the aponeurosis, posteriorly by the tibia, fibula, and interosseous ligament. The diiection of the tibialis anticus, its size, and boundaries should be borne in mind, as these form the surest guide for cutting down upon the anterior tibial artery. This muscle is of a prismatic form, tapering downwards, and its outer edge is indicated externally by a sulcus in the integuments made more apparent by extension of the foot. It is found more ac- curately by tracing a line from the middle of the space between the crest of the tibia and the fibula to the middle of the instep ; and here, between this muscle and the extensor communis, the artery runs. The external mus- cles are the peronei longus and brevis ; they are enveloped in a sheath of the aponeurosis, and are applied, for some extent, to the exter- nal surface of the fibula. They are completely separated from the extensors and from all the muscles of the posterior region by the two apo- neurotic septa attached to the anterior and posterior edges of the bone. The adherence of the muscular fibres continuing until just above the outer malleolus, a transverse section, in the two superior thirds, does not entirely destroy their action upon the foot, while, lower down, it would render abduction almost impossible. We have not heard of an instance of the entire rupture of any of these muscles, nor is it an accident likely to occur, as they are not, from their situation, likely to be called upon for any very great exertion of power; but these muscles are occasionally liable to the accidental rupture * See Velpeau's Anatomy of Regions, translated t>y Hancock. of some of their fibres, a circumstance attended with much more pain and distress in moving than the apparently slight nature of the accident might lead us to expect. We have had lately a case of this kind under our care, where the suffering and the injury to the movements of the foot were so great as at first to lead us to suspect a much more serious extent of injury than really existed. It was occasioned by at- tempting to push along a sack of corn with both knees, both feet being on the ground, and the heels raised, while the upper part of the sack was held in the arms. The only artery of importance in this region is the anterior tibial. It commences from the trunk of the popliteal nearly at right angles, traverses the opening in the upper part of the interosseous ligament, close to the neck of the fibula, and below the head of the tibia. The angular curve which the artery makes at this part of its course, according to M. Ribes, ac- counts for the great retraction of it after ampu- tation of the leg.* It descends upon the inter- osseous ligament, in the direction of a line drawn from the middle of the space between the head of the fibula and the crest of the tibia, to the middle of the instep. Through the upper part of its course it lies upon the in- terosseous ligament; as it descends it gradually advances upon the tibia, and runs upon the anterior surface of this bone through its lower third. It is found at the upper third of the leg, between the tibialis anticus and extensor communis digitorum ; in the middle third, its course is between the tibialis anticus and the extensor longus pollicis, and about four inches above the ankle-joint it passes obliquely under the tendon of this last muscle, and then is found between its tendon and that of the ex- tensor communis. It runs between two veins through its whole course. The nerve is on its outer side above ; in front in the middle; and internal below. An extensible but resistant cellular sheath unites the whole. It is evident, that in the upper part of its course the artery will be found much deeper than at the lower, when it is lying among the tendons, but in the living subject the natural state of tension of the muscles keeps these tendons more elevated than after death, and we shall consequently find the artery, even in this situation, deeper than from dissection we might have been led to an- ticipate. The surgeon will find little difficulty in discovering this artery when it is required to be tied. The marks for his guidance are clear, and the situation of the vessel on the whole pretty uniform ; but owing to the depth of its situation above, and to the immediate vicinity of the veins and nerve, some difficulty will be experienced in excluding these from the liga- ture. The only branch from it of any surgical importance is the recurrent tibial. This arises just after the trunk has passed through the in- terosseous ligament, and passes upwaids in nu- merous branches to the parts below and to the outer side of the knee-joint, anastomosing freely with the inferior external articular artery. These * See Velpeau's Anatomy of Regions, p. 47.'?. 132 REGIONS OF THE LEG. anastomoses form an important part of that system of collateral circulation by which the stream of blood is continued to the leg and foot, after the obliteration of the popliteal artery. The anterior tibial artery may require to be tied in case of wound or aneurism. In wounds of the dorsal artery of the foot, it may be advi- sable to put a ligature at the lower third of the leg, when the anterior tibial is running between the tendons. Its course may be here ascer- tained by feeling its pulsation, or by observing the line of the tendon of the extensor proprius pollicis, on the fibular side of which it here lies. When about to tie it higher up, the incision in the integuments and fascia must be the more free in proportion as it is nearer the knee ; and it may sometimes be advisable even to divide some of the fibres of the fascia transversely, to permit more freely the retraction of the muscu- lar sides of the cut. In dissection, we so easily separate the muscles and expose the artery, that we may underrate the difficulty attending the operation of tying it. The depth at which it lies in this part, the constant contraction of the muscles, and the difficulty of retracting the sides of the incision, occasioned by the strong aponeuroses, all constitute considerable obsta- cles to the operation. This artery was subcu- taneous in a case related by Pelietan, and is occasionally very small indeed, or even abso- lutely wanting. The first anomaly we have se- veral times seen in dissection, and an instance of the latter is related by Huguier* In these cases a large branch of the peroneal, which had passed through the interosseous ligament a little above the ankle-joint, supplied the place of the lower part of the artery. In a case which was met witli by Velpeau, he found this artery not perforating the interosseous ligament at all, but winding round the fibula just below the head of this bone, and in company with the musculo-cutaneous nerve.-f The artery is accompanied by two veins, one placed on each side, throughout its course. The anterior tibial nerve, which is a branch from the peroneal, runs on the fibular side of the artery first, and then obliquely crosses it, sometimes again passing outwards, towards the lower part of the leg. The deep-seated lym- phatics following the course of the vessels, deep-seated disease of the front of the leg may produce alteration of the glands of the ham. A lymphatic gland is found in front of the an- terior tibial vessels, a little below the opening of the interosseous ligament through which the vessels pass. In the posterior region of the leg the mus- cles are arranged in two distinct layers, the superficial, composed of the gastrocnemius, soleus, andplantaris; the deep, of the popli- teus, the tibialis posticus, the flexor communis digitorum, and flexor longus pollicis. The gastrocnemius becomes tendinous, considerably higher in the calf than the soleus, sending off * See Vclpeau's "Anatomy of Regions, p. 474. t See Velpeau's Medecine Operatoirc, torn. iii. 137. its broad thin tendon about the middle of the leg, to unite with that of the soleus, about the junction of its middle and lower thirds. The soleus, beginning its origin lower than the last muscle, from the bones of the leg, con- tinues its muscular fibres lower in proportion, in this respect varying considerably in different subjects. These two muscles, arising above by their distinct heads, and having but one insertion below, form in fact but one muscle, which Meckel has named the triceps sura. Their common tendon is of a strength proportioned to that of the muscles themselves, and is therefore exceedingly powerful. Notwithstand- ing, the combined action of the muscles is occa- sionally too much for the tendon, and in leap- ing, dancing, or other similar movements, it is sometimes ruptured. After this accident, the difficulty of cure results, not so much from the injury done to the tendon itself, as from the difficulty of bringing the two ends into apposi- tion. In fact, complete union never occurs, the utmost extension of the foot never bringing the lower portion so high as the upper is re- tracted by the muscles. The union, however, which is of a cellular structure, becomes suffi- ciently strong to be perfectly serviceable. Boyer speaks of a partial rupture of the tendo Achillis, and describes with precision the symp- toms, but we apprehend this form of the acci- dent is very rare.* The pathology of club- foot, which has only of late years been clearly understood, shows that permanent retraction of the muscles of the calf, either primary or se- condary, is its most frequent cause, and the division of the tendo Achillis and the other tendons of this part has in consequence been resorted to with great success.f The plan of operating which our experience leads us to prefer, is to insert a sharp-pointed bistoury through the skin, and pass it behind the tendon with its flat side towards it, till having reached its farther side, the edge is turned, and the tendon is divided in the withdrawal, without more division of the skin than the mere punc- ture. If the tendon is kept tense during the operation by the forcible flexion of the foot, and is not quite divided at one stroke, the undivided tendinous fibres are pulled and stretched, and partially torn from their lateral attachments, which occasions a sort of hissing noise, which is not heard when the force is not applied, till after the entire division of the tendon. The union here takes place in the same manner as in rupture of the tendon, but the treatment proceeds upon a somewhat diffe- rent principle, since it is in this latter case the intention to keep the divided ends apart, and the foot is therefore placed at right angles, while, in the ruptured tendon, the foot is ex- tended, in order to approximate the ends as much as possible. The extreme contraction of the muscle, in club-foot, leaves no possibility of further retraction of the upper part of the * See Boyer's Maladies Chirurgicales, torn. ii. p. 95. t See Liston's Practical Surgery, p. 154. REGIONS OF TOE LEG. 133 tendon, therefore tlie whole separation, after the division, is performed by the moving of the lower part. The powerful muscles, now described, are never known to be ruptured themselves, the tendon, as we have seen, yielding first, but a partial rupture of their fibres is not very uncommon, and is indicated by the same pain- ful symptoms as were alluded to in speaking of the anterior muscles. It is worth remarking, on the great power of these muscles, that, great as is the force required, to elevate the whole body, by acting upon the heel, yet the muscles of the calf are not nearly so soon fatigued in walking as those on the front of the leg, whose labour is merely the elevation of the foot and toes, and of this every one must be sensible after unusually long exercise on foot. Between the gastrocnemius and the soleus is the plantaris tendon, a long slender slip, which, after crossing between the muscles, runs on the inner side of the tendo Achillis, to its insertion. The belly of this little muscle is under the outer head of the gastrocnemius, close to the origin of which it arises. Authors describe the symptoms attendant upon rupture of this tendon, but the diagnosis of injury to so small and deep-seated an organ must be so uncertain, that we should be much more in- clined to refer them to an injury of some of the fibres of the great muscles of the calf, es- pecially when we compare the power of the plantaris with that of its tendon, the passive strength of the latter appearing greatly superior to the active force of the former.* Between the lower part of the tendo Achillis and the tendons of the deep layer of muscles, there is a considerable layer of cellular tissue, con- taining fat, and this is often the seat of trouble- some chronic inflammation ; and if suppuration follows, the abscess is often very difficult of healing, from the constant movement of the tendon, and the result is a troublesome sinuous ulcer, which can only be healed by keeping the foot entirely at rest. The deep muscles, bound down in the pos- terior interosseal space, by the inter-muscular layer of the aponeurosis, are found lying in this order; the flexor digitorum communis, placed innermost, upon the back of the tibia; the flexor longus pollicis, on the fibula, and the tibialis posticus between them, and partly con- cealed by them. Upon this last muscle are situated the posterior tibial vessels and nerves. As they all of them have to pass nearly behind the inner ankle, the two outermost are gradu- ally approaching to the flexor communis, as tliey descend, till they are nearly in contact one with the other. As all these tendons, either primarily or secondarily, act upon the ankle- joint, their action is retained after rupture or division of the tendo Achillis, so that the power of extension of the foot still remains, though in a feeble degree. The arteries of this region are the posterior tibial and peroneal, and are given olf from the termination of the popliteal. The anterior ti- * See Dictionnairc ties Sciences Medicalcs, ar- ticle Jambc. bial also has here a course of a few lines, from its origin, till it perforates the interosseous liga- ment. The posterior tibial maybe considered as the continuation of the trunk of the popliteal. It commences about an inch below the origin of the anterior tibial, and where the popliteal divides into this artery and the peroneal. The course of the posterior tibial may be defined by a line drawn from the middle of the ham, to a spot half an inch behind the inner mal- leolus. In this course it is accompanied by two veins, one on either side, also by the poste- rior tibial nerve; in the upper part of the leg, this nerve lies to the inner or tibial side of the artery ; it soon, however, passes over it, and inferiorly it lies to its outer or fibular side. The posterior tibial artery is covered, in the upper and middle thirds of the leg, by the gas- trocnemius and soleus muscles, but in the lower third only by the integuments, and by the su- perficial and deep fasciae of the leg. In the upper third of its course, this artery rests upon the tibialis posticus muscle, in the middle third upon the flexor digitorum communis, and in the inferior third some fat and cellular membrane separate it from the tibia, and from the internal lateral ligament of the ankle-joint. In the inferior third of the leg, the posterior tibial artery runs nearly parallel to the inner edge of the tendo Achillis ; between the os calcis and malleolus internus, it lies nearly in contact with the sheath of the flexor digitorum communis.* The only branch of surgical in- terest given off by this artery in the leg is the nutritious artery of the tibia, which comes off about its upper third, and in amputation at this part sometimes bleeds freely. In putting a ligature upon this artery, the difficulties attendant upon the operation vary according to the situation at which we seek for it. It is favourably circumstanced for opera- tion in the inferior third of its course, being covered in the two upper thirds by the muscles of the calf. It may require to be lied for a wound in the sole of the foot, or for one behind the inner ankle. In either of these cases the artery may be found and tied with facility be- hind the inner malleolus. (See Ankle-Joint, Region of.) When, however, it is deemed de- sirable to tie it at the lower third of the leg, it will be readily found by an incision of from two to three inches in length, performed mid- way between the inner border of the tibia and the tendo Achillis. After the division of the integuments, the superficial fascia, and the deep fascia, the artery will be met with di- rectly under the incision. Its accompanying- veins sometimes completely conceal it ; the nerve is here on the fibular side of it. In case of secondary haemorrhage after this operation, or in case of aneurism of the pos- terior tibial artery, forming in consequence of a wound of the artery in this situation, it may be necessary either to tie this vessel higher up in the leg, or to tie the popliteal femoral artery itself; it has been deemed prudent to give the patient the chance of success from the former ' Sec article Ankle-Joint, Region of. 134 REGIONS OF THE LEG. operation, before having recourse to so severe and hazardous a measure as that of tying the femoral or popliteal artery. The operation of tying the posterior tibial artery in the middle of the leg will be found much more difficult than either of the other situations mentioned, as this vessel here lies at such a depth from the surface, and is covered by the gastrocnemius and internal head of the soleus, which in this situation is attached to the tibia. To expose the artery here, the leg should be bent, the foot extended, and both laid on the outer side. The incision must be of considerable length, not less than four inches, along the inner edge of the tibia. The integuments and fascia being divided, (care being at the same time taken to avoid the saphena vein,) the edge of the gastrocnemius muscle will be exposed; this will be easily raised and drawn to one side. The soleus must next be divided from its attachment to the tibia, and at the bottom of this incision will be discovered some dense aponeurotic fibres, which are part of the deep fascia of the leg. The muscular fibres in the incision must now be held wide apart, and carefully sepa- rated from this deep fascia preparatory to its division, and immediately underneath this fascia lies the artery, with its accompanying veins, one on each side, with the nerve on its inner or tibial side, and here situated about an inch from the edge of the tibia. On the dead subject this operation is not attended with much difficulty ; in the living, however, the case is very different ; the mus- cles are then rigid and unyielding, and when the fascia which covers them is divided, they leave their natural situation, and become much elevated, so as to make the situation of the artery appear as a deep cavity, at the bottom of which the vessel is placed. The contraction of the muscles has been found in some cases so great an impediment to the operation, as to require the transverse division of part of the muscle. The operation of cutting directly from behind, through the fibres of the gas- trocnemius, is obviously still more objection- able, from the cause just mentioned. The second terminating branch of the pop- liteal artery is the peroneal. This is situated deeply, along the posterior part of the leg, taking the direction of the fibula ; hence it is sometimes called fibular. It commences about an inch or two below the lower border of the popliteus muscle, after perforating the tibialis posticus at the commencement of its course, and descends, almost perpendicularly, towards the outer ankle. In this course, it lies close upon the fibula, between the flexor proprius pollicis and flexor digitorum communis. On reaching the lower extremity of the interos- seous ligament, it divides into two branches, the anterior and posterior peroneal, the first of which passes through the aperture at this part of the interosseous ligament, and both of these run to the outer side of the foot. This artery is so small and so deeply seated, that its wounds are rare and unimportant. Hence but little has been said of its ligature, which would be very difficult, and could only be per- formed at the middle of the external side of the leg. We should then divide the same parts as for the tibial, but on the opposite side, and as it is enveloped in the fibres of the flexor longus pollicis, we must also detach this muscle from the fibula. Each of these arteries of the posterior region is accompanied by two veins, which fre- quently overlap the artery so as to conceal it from view, in the operation of securing it; they are also so adherent to its coats as to occa- sion some difficulty in separating them, so as to avoid including them in the ligature, parti- cularly where the artery, as in the present in- stance, is deep-seated. The best mode of accomplishing this is to insinuate the aneu- rismal needle first on one side, and then upon the other, not attempting to bring it out on the opposite side of the artery, till, by this means, the lateral attachments are separated. The deep nerve which accompanies the posterior tibial artery is the tibial, and is of considerable size, being the continuation of the trunk of the popliteal. It is situated, at first, to the outer side of the artery, and lower down it runs nearly behind it, and so close to it, that without care it may be injured, included in the same ligature, or even tied for that vessel. It may not be amiss here to observe on the distinctive marks by which the nerve may be recognized, when passing the ligature under the artery, that besides the most essential, the absence of pulsation, which may occur even to the artery itself from accidental causes, the inexperienced operator will find considerable assistance from the following, viz. the firm, round, cord-like feel of the nerve, while the artery has a flattened yielding feel when pressed between the finger and thumb, and the whitish, somewhat glistening, and promi- nent round appearance of the nerve, the artery having a somewhat reddish colour, and a flat- tened, thick, and riband-like appearance, as it is raised upon the aneurism needle. When the cut extremities of the two are seen toge- ther, after an amputation, of course the round open mouth of the one, and the prominent stump of the other, like a tight packet of thread cut across, are readily recognizable. The lymphatics of these deep parts accom- pany the bloodvessels, and pass to the glands of the ham ; hence diseases occurring in the parts beneath the aponeurosis of the leg exert their influence on the glands of the popliteal space. The two bones of the leg united by the interosseous ligament form an elongated fossa in front which is closed in by the aponeurosis, and is larger at the union of its two superior thirds than at its extremities. The muscles being imbedded here are difficult to cut in circular amputations, at the same time that its depth prevents the formation of a good flap. Posteriorly, they form a gutter, or fossa, larger than the preceding, but also much more shal- low, excepting at the lower part. Hence the deep muscles are easily comprehended in the REGIONS OF THE LEG. 135 flap in amputation. In the circular operation the section of the flesh, which can only be effected by passing the point of the knife transversely over the bottom of the interosseous fossae, is equally difficult in the flap method, in making the anterior flap, in consequence of the depth of the space in which the muscles are lodged. The difference of size of the two bones and the posterior relative situation of the fibula renders some precaution necessary in dividing them with the saw. The foot must be turned in, so as to bring the fibula a little forward, and care must be taken to commence the section upon the tibia as being the longest and strongest, but to finish the section of the fibula first, since it is too thin and mobile to support the movements of the saw without breaking at the termination. In amputation above the tubercle of the tibia, it has been field advisable to remove the head of the fibula from its joint, since this small portion of the bone is of no advantage to the stump and by its mobility may be some hindrance in the after treatment. (See Knee-Joint.) The small size and moveable nature of the fibula constitutes some difficulty in the treat- ment of fractures of the leg, since the appli- cation of the ordinary bandages, &ic., would have a tendency to press the bone inwards against the tibia, and we not unfrequently see, in old united fractures of these bones, this deformity to have been produced, in all proba- bility, from want of due precaution in the ap- plication of bandages. The defect may be obviated by proper care, that neither the splints nor the cushions should take any bearing upon the fibula itself except at its two extremities, and great assistance may be derived from proper pressure, before and behind, upon the muscles, gently forcing them against the inter- osseous ligament and bearing outwards the bone attached to it. After amputation of the leg, the tibia pre- sents a triangular surface, having the apex for- wards. As the skin covering it is hereby in- vested with the subcutaneous layer, it may, by pressure against this projection, ulcerate, or slough, and thus expose the bone. The great means for obviating this accident is to have a good supply of integument in the flap, so thai, in bringing the parts together afterwards, they may not be drawn too tight over the bone. While this rule is attended to all will go on well, whereas when the integument is left scanty, nothing can prevent unpleasant consequences. It may often, however, be advisable to remove with the saw the projecting angle of bone, and as a matter of precaution we generally do this, though not attaching much importance to it.* In amputating above the tuberosity of the tibia, we run the risk of opening into the knee- joint, as the synovial membrane is sometimes prolonged thus far. According to M. Lenoir the synovial cavity of the knee is continuous with that of the superior tibio-fibular articu- lation, once in four times. f There are always . Sec Bell's Operative Surgery, vol. ii. p. 22. t Sec Vclpcau's Anatomy of Regions, p. 484. three principal vessels to be tied in this ope- ration : first, the anterior tibial, which is found, with its collateral nerve, close upon the inter- osseous ligament; secondly, the posterior ti- bial, in contact with the deep layer of the aponeurosis, and having its nerve to its outer side; and, thirdly, the peroneal, which is found imbedded in the flexor longus pollicis muscle, and may be readily tied without fear of injuring any nerve. These three arteries sometimes retract so far into the flesh after amputation, that to secure the anterior tibial it is necessary to cut through the interosseous ligament to the extent of some lines. This probably arises principally from the attachment of the muscles to the whole parietes of the interosseous fossa, while the vessels, enveloped by elastic cellular tissue, retract considerably. It must be borne in mind, that in whatever situation the amputation may be performed, if it be the flap operation the arteries of the flap are much more difficult to be found and se- cured, owing to the oblique nature of the sec- tion, than where, as in the circular operation, the muscles and vessels are cut transversely through. When the amputation is just below the tu- berosity of the tibia, the nutritious artery has here sometimes a volume sufficient to require a ligature. With the exception of this last, the arteries to be tied will be nearly the same, in whatever part of the length of the leg the amputation is performed. The muscular branches seldom occasion much inconvenience from hemorrhage. It may not be out of place here to remark on the subject of amputations of the leg, that the division of the bones high up may often save the knee, and thus give a good bearing for a wooden leg, but that we are too often apt to act upon the principle that, in amputations below the knee, this joint must necessarily be the bearing point ; whereas we are convinced that a much more useful stump is gained by saving as much as possible of the leg, at least as far as half of its length, with the view of applying the wooden leg to the stump itself, and so preserving entirely the use of the knee- joint. We have now adopted this plan, with the most perfect success, in several instances, and always to the great comfort and satisfaction of the patient. Indeed, the loss of the limb, which is thus remedied, is really little felt, when compared with the great inconvenience of making the knee the bearing point, and thus taking away all the benefit of it as a joint. The reason why this mode of operating has not been more gem rally adopted, appears to us to consist in the fear that the cicatrix of the slump is ill able to bear the weight of the body in walking, when pressed between the ends of the two bones and the artificial leg. But be- sides that by the flap amputation in the middle of the leg, (the best possible situation for this operation, when practicable,) a soft cushion of muscle can be added to the integumental covering to obviate the effects of pressure, the fact is that in the application of the artificial leg to this stump, the bearing is not entirely 136 REGIONS OF THE LEG. upon the stump itself, but it is divided between this and some part of the anterior surface of the leg, generally falling most powerfully about the tubercle of the tibia. The bearing on the anterior part of the leg is so strong, that unless the precaution is taken of well padding that part of the wooden box, the pain occasioned by the pressure entirely pre- vents the use of the wooden leg ; but by the use of this precaution all inconvenience is ob- viated, and by this support to the weight of the body a valuable help is found for the pre- vention of injury to the cicatrix of the stump. The French surgeons used to recommend this mode of applying the artificial leg, but only in cases of conical stump, or at least where the integuments were from excess of inflammation after the amputation closely ad- herent to the bones.* But we have found it applicable to every case of amputation below the knee. The superiority which this wooden leg gives to amputations below the knee over all those at the ankle and through the joints of the foot is obvious. Besides saving the extra pain and risk of inflammation, it affords a much better point of support than the muti. lated foot can form. The anterior surface of the tibia being sub- cutaneous, and not covered by any artery of importance, indicates the region which should be chosen for exposing, when we would re- move a portion, trephine, extract sequestra, balls, &c. Superiorly, as its external region is only covered by the origin of the tibialis amicus muscle, it is favourable to the same operation. This consideration is the more important since the publication of the very valuable observa- tions of Sir B. Brodie on abscess in the can- cellated structure of the tibia, a disease which till then was little understood and scarcely at all described, and which, from our own expe- rience, we are inclined to think has not unfre- quently cost the patient a limb, which by a more correct knowledge of the disease might have been saved .-\ The periosteum of this anterior surface is the subject of troublesome inflammation more fre- quently than that of the other parts of the bone, in consequence of its greater exposure. Com- mon inflammation of it is often productive of abscess, necrosis, &c, or in a scrofulous dia- thesis, of caries ; while syphilitic inflammation is here showing itself in the form of nodes, occasioning great trouble to the surgeon and suffering to the patient, and generally leaving some permanent thickening. These nodes, which, as we have said, generally occur on the anterior surface of the bone, are sometimes thrown out upon the external and posterior parts, and when they do thus occur are doubly embarrassing to the surgeon from their deep situation among the muscles, and from the general similarity of the symptoms to mus- cular rheumatism; the extreme tenderness of * See Dictionnaire des Sciences Medicales, Art. Jambe. t See also some excellent practical observations on the subject in Liston's Elements of Practical Surgery, p. 95. the periosteal inflammation, much more acute than that of rheumatism, and the more circum- scribed nature of this tenderness, are signs which will facilitate the diagnosis, a subject, however, upon which it is not here the place to dilate. In the foetus, the tibia presents merely a slight curve anteriorly, which appears to be augmented in the adult by the weight of the body. The posterior muscles, stronger and more numerous, acting on the flexible bones, concur to the same end. Thus, in fractures, particularly from indirect causes, the angle formed by the fragments of the tibia is almost always in front, and the limb bends in the situation of the fracture. Experience proves that the two bones of the leg are more frequently broken together than singly, a fact ascribed by Boyer to the strength of the knee and ankle-joints. The direction of an oblique fracture of the tibia is generally from below upwards and from within out- wards, a circumstance due to the form of the bone. The end of the upper fragment then presents itself under the skin, at the front and main part of the leg. The most frequent situa- tion of fracture of either of the bones of the leg is at the lower third ; this, in the tibia, is readily accounted for by its being here more exposed to injury and being smaller and weaker than elsewhere ; in the fibula, on the contrary, this part is not weaker, but is here placed more superficial, the upper part being completely covered and much defended by a cushion of muscle. Fractures of the tibia at its upper part are less liable to displacement than lower down on account of the greater thickness of the bone, but the vicinity to the knee-joint here increases the danger of a fracture consi- derably. In consequence of the thickness of the bone at this point, fractures here are ordi- narily transverse, while the abundance of spongy tissue causes them to unite quickly and easily. The tibia is more frequently ^broken by itself than the fibula because it alone sus- tains the whole weight of the body, while the fibula has nothing to support. In fact if the fibula is generally broken at the same time with the tibia, the injury to the fibula is but subsequent to the other, and takes place be- cause this slender bone is not capable of bear- ing the weight of the body, the impulse of ex- ternal violence, or even the action of the mus- cles, after the tibia has given way.* There is rarely much displacement, as re- gards the length of the bones, at whatever point their fractures may have occurred, unless the cause has continued to act after the solu- tion of continuity. This appears to result from the muscles being inserted over the whole of the bony surfaces. When the fibula alone has been broken, there is very little deformity resulting, as the principal support of the limb still remains, particularly if the injury has resulted from external violence. When however the cause * See Cooper's Surgical Dictionary, article Frac- ture, MUSCLES OF THE LEG. 137 of the fracture is found in a violent twist of the ankle with dislocation, the deformity occa- sioned by this state of the joint is more or less considerable, according to the degree of this displacement. (A.T.S. Dodd.J MUSCLES OF THE LEG. — The muscles lying on the bones of the leg, both before and behind, are, with the exception of one, pro- perly muscles of the ankle-joint and foot, since their primary action i5 exclusively upon these parts. (See article Foot, Muscles of.) For the convenience, however, of description they will here be demonstrated according to their si- tuation. The muscles of the leg may be classed into anterior, external, and posterior. The anterior lying in the space between the tibia and fi- bula are four in number, consisting of tibialis anticus, extensor proprius pollicis, extensor longus digitorum, and peroneus tertius. The tibialis anticus and extensor longus alone are seen at the upper part of the leg on removing the deep fascia; the extensor proprius pol- licis emerging from between these muscles about one-third down the leg, and the peroneus tertius shewing itself as a separate slip of the extensor longus, about the same height, and at its fibular side. 1. Tibialis anticus lies upon the fibular and anterior surface of the tibia; arises, principally muscular, from the fibular side of the tibia, through its two upper thirds, from its tuber- osity and spine, and from a small portion of the interosseous ligament, from the fascia of the leg, and from an aponeurotic septum placed between it and the extensor digitorunri longus. The muscle is larger above than below ; its fleshy fibres converge to a strong tendon which crosses from the outside to the fore part of the tibia, passes through a distinct ring of the annular ligament near the ankle, runs over the astragalus and os naviculare, and is inserted into the upper part of the os cuneiforme in- ternum, and base of the metatarsal bone of the great toe. The insertion of the tendon is con- cealed in part by the adductor and flexor brevis of the great, toe. Between the tendon of this muscle and the os cuneiforme we find a small bursa mucosa. This muscle is covered in front by the fascia of the leg, to which it adheres superiorly ; behind it is in contact with the tibia and interosseous ligament, on the fibular side with the extensor digitorum communis, and extensor proprius pollicis. Its action is to flex the foot upon the leg by elevating the an- terior part of the foot. 2. Extensor longus digitorum.- — This mus- cle occupies the fibular side of the tibio-fi- bular fossa, as the last filled the inner side. This is a tapering muscle also; it arises ten- dinous and muscular from the fibular or outer part of the head of the tibia, from the head of the fibula, and from the anterior angle of that bone almost its whole length, and from part of the tibial side of it also ; it also takes origin from the interosseous ligament, from the fascia of the leg, and from the aponeurotic septum situated between this muscle and the last. Below the middle of the leg it splits into four tendons. These pass under the ante- rior annular ligament in one common sheath with the peroneus tertius. They then run along the dorsum of the foot, spreading as they go, and are inserted into the root of the first pha- lanx of each of the four smaller toes. To- wards their termination each of the tendons ex- pands into an aponeurosis, covering the upper surface of the phalanges, and this is strengthened by the tendons of the extensor brevis and gives attachment to the lumbricales and interossei. This muscle is covered in front by the fascia of the leg, the annular ligament and the in- tegument; posteriorly it rests upon the fibula, the interosseous ligament, and the tibia; exter- nally it is in relation with the peronei muscles, internally with the tibialis anticus, and extensor proprius pollicis; along its lower and fibular border lies the peroneus tertius. On the dor- sum of the foot its four tendons cross obliquely over those of the flexor brevis digitorum. Action. To extend all the joints of the four smaller toes, and to bend the ankle-joint. 3. Extensor proprius pollicis lies between the two last muscles. Its origin is hidden by them. It commences about one-third down the leg, from the smooth surface of the fibula, between the anterior and tibial angles of that bone, of which surface it occupies part, through the middle third of its length, also from the lower two-thirds of the interosseous ligament. The fleshy fibres run obliquely forward into ft tendon placed at the anterior border of the muscle, which after passing beneath the an- terior annular ligament, and along the dorsum of the foot, is inserted into the bases of the first and second phalanges of the great toe. Action. To extend the great toe, and to bend the ankle. By its fibular side this muscle is in relation with the extensor digitorum communis; by its inner side with the tibialis anticus and anterior tibial vessels. The anterior border is covered by these two muscles, as low as about the middle of the leg, and inferiorly by the anterior annular ligament, under which it passes in a separate groove, and by the integuments. The posterior border rests upon the fibula and in- terosseous ligament, and it crosses in its course over the lower end of the tibia the ankle-joint, the anterior tibial vessels, and dorsum of the foot. 4. Peroneus tertius.— This, which is in fact a mere slip of the extensor digitorum com- munis, and is situated on its fibular side, is so closely connected with it at its origin that it can with difficulty be separated. It arises from the lower third of the fibula, being at- tached to the anterior border and inner surface of the bone ; also from the interosseous liga- ment, and from an aponeurosis which connects it on the outer side with the peroneus brevis. It is inserted by a flat tendon into the fibular side of the base of the metatarsal bone of the little toe. Its action is to assist in flexing the foot upon the leg. It is in contact with the fascia of the leg 138 MUSCLES OF THE LEG. nteriorly, with the fibula and interosseous ligament posteriorly, with the peroneus brevis on the fibular side, and with the extensor com- munis on the tibial side. Its tendon passes in the same sheath with that of the common ex- tensor, under the annular ligament. A very slight effort of the extensor com- munis and extensor proprius pollicis extends the digital phalanges, and, if their action be continued, they will be made to bend the foot upon the leg. This they are enabled to do by the manner in which their line of direction is altered by the annular ligament of the ankle- joint, as it gives them all the mechanical ad- vantage of a pulley. The tibialis anticus and the peroneus tertius are the direct flexors of the foot on the leg, and if either act separately, it will give a slight inclination towards the cor- responding side, and thus the last-named muscle forms one of that important set whose action is, by elevating the outer side of the foot, to throw the weight of the body on the inner side.* In the erect position these muscles take their fixed point below, and, by drawing on the bones of the leg, keep them perpen- dicular on the foot. The external muscles of the leg are two, the peroneus longus and brevis. They occupy the whole length of the outer side of the fibula, and are placed between the extensors and flexors. 1. Peroneus longus is a long powerful muscle, arising from a small portion of the fibular side of the head of the tibia, from the upper third of the outer side of the fibula, and from the fascia of the leg and its intermuscular pro- cesses. Proceeding obliquely downwards, the fibres are attached to a strong tendon, which passes, in contact with the peroneus brevis, along a groove at the back of the outer mal- leolus, enclosed in a synovial sheath. The tendon then passes through a deep sulcus in the cuboid bone, behind the base of the meta- tarsal bone of the little toe, winding obliquely across the sole of the foot, covered by the muscles of this part, till it is inserted into the internal cuneiform bone and base of the meta- tarsal bone of the great toe. In the tendon opposite the cuboid bone, is usually found a sesamoid bone. A bursal sheath encloses it in its passage across the foot. The action of this important muscle is to assist in extending the foot upon the leg, but principally to elevate the outer side of the foot, and thus regulate the bearing of the leg so as to throw the prin- cipal part of the weight upon the great toe.f This muscle is in contact on its outer side with the fascia of the leg. Indeed this apo- neurosis almost invests it, dipping between it and the flexor behind and extensors before. The peroneus is in contact with the fibula on its inner side above, lower down it rests upon the peroneus brevis. When passing across the foot it lies close to the bones, and conse- quently is covered by all the muscles of the sole. 2. Peroneus brevis is situated at the outer * For further observations upon the action of the peronei muscles, see article Foot, muscles of. f See also Quain's Manual of Anatomy. side of the leg, but lower down as to its at- tachments than the preceding muscle. It arises fleshy from the lower half of the outer side of the fibula to near the outer malleolus. It sends offa roundish strong tendon, which passes in the same groove behind the outer malleo- lus, and in the same synovial sheath as the pre- ceding muscle, but after passing the malleolus it has a sheath proper to itself. It is inserted into the base of the metatarsal bone of the little toe. Connected on its outer side to the peroneus longus, on the inner side to the fibula, anteriorly to the common extensor and pero- neus tertius, and posteriorly to the flexor longus pollicis. The action of these two muscles is peculiar. By the change in their direction, after turning behind the outer ankle, they are enabled to draw the foot back, and so extend it on the If o- The penoneus tertius is on the contrary a flexor ; it lies before the fibula, and combines in this action with the tibialis anticus to assist the flexor. When, however, the three peronei act together, and without the other flexors, their combined action is to evert the sole of the foot, and thus counterbalance the effect of the feeble- ness of the outer side of the foot by trans- ferring the superincumbent weight to the inner side. This action is particularly exemplified in skaiting, but it is essential to every move- ment of ordinary progression. (See article Foot, Muscles of.) When the foot is the fixed point, the peronei act by keeping the fibula and the whole leg steady, and thus, as in the act of standing on one foot, counter- acting the tendency of the body to fall in- wards. The posterior region of the leg comprises seven muscles, six of which are acting on the foot and toes, and one is proper to the knee- joint. We shall examine them as they are met with in dissection, and shall therefore describe them as forming two layers, superficial and deep. The first contains three muscles : 1. gas- trocnemius; 2. soleus ; 3. plantaris. 1. Gastrocnemius. — This is situated imme- diately under the aponeurosis, and is a power- ful muscle, broad and flat anteriorly, and con- vex posteriorly, and forming the greater part of what is called the calf. It arises by two distinct heads from the back and upper part of the two condyles of the femur, of which the inner is the longer, and somewhat larger. These heads have between them a broad sulcus, which forms the lower part of the pop- liteal space. They unite a little below the knee-joint, in a middle tendinous line, and below the middle of the tibia send off a flat tendon which unites with the tendon of the soleus, a little above the ankle. The posterior surface is covered by the fascia of the leg ; anteriorly it rests upon the popli- teus, soleus, and plantaris, and popliteal vessels. When its heads pass over the con- dyles of the femur, they are guarded by synovial bursa?. 2. Soleus. — This is the second portion of that great muscle of the leg which has been MUSCLES OF THE LEG. 139 named by Meckel the triceps surte. It is seen immediately on raising the last muscle. It arises from two distinct situations ; first, from the upper and back part of the head of the fibula, and from the posterior surface and outer edge of that bone for some way down. Se- cond, from the oblique ridge on the posterior surface of the tibia, just below the popliteus, and from the inner edge of that bone during the middle third of its length. From these two attachments the muscle almost imme- diately forms a thick fleshy belly, which de- scends lower than the gastrocnemius before it sends off its tendon. This, which is flat and strong, soon unites to the tendon of the gastro- cnemius to form the tendo Achillis, and is then passing to be inserted into the upper and back part of the projecting portion of the os calcis. At its insertion there is a small bursa between the upper part of the bone and the tendon. The soleus is in contact with the gastro- cnemius posteriorly ; below its fleshy fibres ap- pear on each side of the tendon of that muscle. -Between its two origins the posterior tibial vessels and nerve are passing, defended from pressure by the tendinous expansion which is on the under side of the muscle, and which spreads across from tibia to fibula. This muscle is also in contact with the plantaris, the tendon of which crosses it obliquely from without to within. In front it rests upon the deep layer of muscles and upon the posterior tibial vessels. The tendo Achillis is the thickest and strongest tendon in the body ; it tapers down- wards nearly to the heel, and before its attachment expands again a little. It lies immediately under the skin, and between it and the bones is a considerable layer of cel- lular tissue containing fat. The action of the two last described muscles is to elevate the os calcis, and thereby to lift up the whole body. When this is done on one foot in the act of progression, the other is capable of being carried forward unimpeded by the irregularities of the surface. When the foot is the fixed point, the soleus by acting on the tibia and fibula fixes the leg, while the gastrocnemius fixes the femur, or by acting further, draws it backward so as to bend the knee and lower the body. 3. Plantaris. — This little muscle is entirely covered by the outer head of the gastro- cnemius. It arises from the upper part of the external condyle of the femur, and from the posterior ligament of the knee-joint. Its mus- cular structure is only about two inches in length, and it sends its long slender tendon downwards and inwards, between the two great muscles of the calf, emerging from between them just where their two tendons unite; it then passes down in contact with the edge of the tendo Achillis, to be inserted into the heel at the inner side of that tendon. The action of the plantaris is to assist the great extensors of the foot, and to draw upon the capsule of the knee-joint, so as to prevent any ill effects upon that ligament from the motions of the knee-joint. It is occasionally deficient. The deep layer of muscles consists of four: 1. popliteus; 2. flexor longus digitorum ; 3. flexor longus pollicis; 4. tibialis posticus. They lie in close contact with the bones, and the last three of them are covered by the deep fascia of the leg. This membrane is a thin expansion, dense in structure, connected on each side with the borders of the bones, and towards the ankles with the sheaths of the tendons ; and if traced along the interval between the inner ankle and the heel, it will be found to cover the vessels and to terminate at the internal annular liga- ment. Immediately underneath it we find the deep layer of muscles now under consi- deration. 1. Popliteus is situated below and behind the knee-joint, is flat and somewhat triangular, being broader below than above. Arises within the capsular ligament of the knee-joint, by a round tendon, from the under and back part of the outer condyle of the femur; ad- heres to the posterior and outer surface of the external semilunar cartilage; perforates the back part of the capsular ligament, and forms a fleshy belly which runs obliquely downwards and inwards. It is covered by a thin tendi- nous fascia from the tendon of the semi-membra- nosus ; inserted broad, thin, and fleshy into an oblique ridge on the posterior surface of the tibia, a little below its head, and into the trian- gular space above that ridge. Action, to bend the knee-joint, and when bent, to roll it so as to turn the toes inwards. 2. Flexor longus digitorum is thin and pointed at its commencement, but gradually increases, and then diminishes again as its fibres end in a tendon. Arises fleshy from the posterior flattened surface of the tibia, be- tween its internal and external angles, be- low the attachment of the soleus, and con- tinues to arise from the bone to within two or three inches of the ankle. The fibres run obliquely into a tendon, which is situated on the posterior edge of the muscle. This tendon runs in a groove of the tibia, behind the inner ankle, and then passing obliquely forwards into the sole of the foot, receives in its passage a strong slip from the tendon of the flexor longus pollicis. It then divides into four tendons, which pass through the slits in the tendons of the flexor brevis digitorum, and as they run along the under surface of the toes they are bound down by strong fibrous sheaths, within which there are also little accessory ligaments assist- ing in fixing them. They are inserted into the bases of the extreme phalanges of the four lesser toes. The action of this muscle is to flex all the four smaller toes, and to assist in elevating the foot upon the toes. Previously to its division, the tendon of the flexor longus gives insertion to an accessory muscle of considerable power (flexor acces- sorius ), which connects it to the calcaneum, and materially modifies the direction of its action upon the toes. Close to the point of division, the tendons give origin to four small 140 MUSCLES OF THE LEG. muscles (lumbricales), which may also be con- sidered as accessories to the flexor longus. When passing behind the inner malleolus, this tendon is in contact with that of the tibialis posticus, which lies close to the bone. They are inclosed in separate sheaths of synovial mem- brane. In the leg this muscle is bound down by the deep fascia, and covered partly by the posterior tibial vessels which separate it from the soleus; its anterior surface rests against the tibia, and overlaps the tibialis posticus muscle; in the foot, its tendon lies between those of the flexor longus pollicis which are above it, and the flexor brevis digitorum which l.es beneath it. 3. Flexor longus pollicis is shorter but stronger than the former muscle. It is si- tuated the outermost of the three deep muscles of the leg, in contact with the fibula. It arises tendinous and fleshy from the lower half of the posterior surface and outer edge of the fibula, with the exception of the undermost portion. The fleshy fibres terminate in a tendon which passes behind the inner ankle, through a groove in the tibia ; next through a groove in the astragalus ; crosses in the sole of the foot the tendon of the flexor longus digi- torum, to which it gives a slip of tendon ; passes between the two heads of the flexor brevis pollicis, and then runs in a sheath of tendinous structure which binds it to the under surface of the phalanx, and is inserted into the base of the last phalanx of the great toe. The relations of this muscle in the leg are, pos- teriorly it is covered by the deep fascia, which separates it from the soleus; anteriorly it is in contact with the fibula, and overlaps the tibialis posticus muscle and the peroneal ar- terv. Its connections in the foot have been explained above. The action of the flexor longus pollicis is not confined to the great toe; by means of the slip of tendon, which it gives to the flexor longus digitorum, it acts also upon all the toes, and secondarily upon the foot itself, assisting powerfully in the elevation of the heel in progression. But the mode of action of this muscle, and its complicated rela- tions with the other muscles of the foot, are too curious to be passed over with a slight ex- amination ; in fact, we think it may clearly be ( shewn that there is here one of the most curious and beautiful arrangements and successions of muscular action to be met with in the whole system. We have elsewhere shewn that, from the peculiar form of the foot, the action of the peroneus longus is essential to transmit the burden of progression from the weaker to the stronger side of the foot. (See article Foot, muscles of,) Let us now follow on the pro- gress of the foot in the act of walking, and we shall readily perceive the succession of action of its different parts, and the functions which each muscle performs. It is evident that the smaller toes being shorter than the large one, and nearer to the heel, they will, in the act of elevating the heel and propelling forward the body, come to their bearing on the ground somewhat before the great toe, their action being, in fact, by the breadth of base which they give to steady the onward progress of the body, and to deliver over accurately and se- curely the weight to the great toe, the main organ of propulsion of the body. In order to accomplish this to the best effect, it is neces- sary that the succession of actions should be accurate and complete, and that the muscles of the smaller toes should exert themselves be- fore that of the great toe. To this end the flexor longus pollicis gives a slip to the flexor of the toes, and by the commencement of its action, which merely firmly plants the great toe against the ground, rouses the muscles of the other toes, assisting them to complete their part of the process, while its own labour continues and is at its height when theirs is necessarily accomplished and at an end. Thus, by a beautiful combination and series of actions, the powerful effort of the great extensors of the foot is controlled and guided to its proper end, first by the peronei, next by the flexors of the smaller toes, assisted by the long flexor of the great toe ; and the body propelled onwards and balanced on this toe, the action is com- pleted by the further effort of this one power- ful muscle. The economy of muscular power is here not less striking than the combination of action, for the flexor longus pollicis being inserted into the last phalanx of the great toe, its own proper action is not called for till after the muscles of the other toes have performed their part; this muscle, therefore, considerably the most powerful of all this deep layer, were it not for the simple expedient of the slip of communication to the other flexors, would be comparatively useless until the last moment of the propulsion onwards of the body. But now it lends its powerful assistance to the weaker musc'es previous to its own peculiar effort, and when all its power is called for, the collateral demand has ceased. 4. Tibialis posticus is situated on the back of the leg between the last-named muscles. It arises fleshy from the posterior surface both of the tibia and fibula, immediately below the upper articulations of these bones with each other. Between the two portions of this at- tachment is an angular opening through which the anterior tibial vessels are transmitted. The muscle also arises from the whole interosseous ligament ; from the angles of the bones to which that ligament is attached, and from two- thirds of the flat posterior surface of the fi- bula. The fibres run obliquely towards a round tendon, which passes behind the inner ankle, through a groove in the tibia. It is here situated close to the bone enclosed in a sepa- rate synovial sheath. It is inserted into the tubercle on the plantar surface of the os navi- culare, sending tendinous filaments to most of the other bones of the tarsus, and to the meta- tarsal bones of the second and middle toes. This muscle is covered at the lower part of its origin by the flexor longus digitorum and flexor longus pollicis, and cannot be seen till those muscles are separated. But superiorly it is covered by the soleus only, and here the poste- rior tibial vessels rest upon it. Its anterior surface is in contact with the interosseous liga- LIFE. 141 ment, the tibia and fibula. Its tendon runs close to the inner ankle and tarsal bones, and where it slides under the astragalus, is thick- ened by a cartilaginous or bony deposit within its fibres, analogous in force and use to the sesamoid bones in other situations. Its action is to extend the foot upon the leg, and to turn the sole of the foot inwards. (A. T. S. Dodd.) LIFE. — Few abstract terms have been em- ployed in a greater variety of significations, or more frequently without any definite meaning at all, than the one now to be considered. And there is none regarding which it is more essential to possess correct ideas, in order to attain the fundamental truths of physiological science. The prevalence of what we deem very erroneous notions on this subject, will oblige us to follow a different plan in its treat- ment, from that which we should have adopted if our duty had been merely to give an expo- sition of the present state of our knowledge respecting it. We shall commence by offering a short statement of our own views, in order that we may, in the brief historical summary which it will be proper to include in this ar- ticle, more concisely indicate what we regard as the errors and inconsistencies of the prin- cipal theories which have obtained credit at various times. We shall subsequently con- sider more in detail some of the questions which require fuller discussion. I. General views. — We shall define Life to be the stale of action peculiar to an or- ganised body or organism. This state com- mences with the first production of the germ ; it is manifested in the phenomena of growth and reproduction ; and it terminates in the death of the organised structure, when its component parts are disintegrated, more or less completely, by the operation of the com- mon laws of matter. This definition differs but little from that given in many physiological works — " Life is the sum of the actions of an organised being;" and we apprehend that we are more in accordance with the common usage of the term, in employing it to designate rather the state or condition of the being exhibiting those actions, than the actions themselves. In this sense alone it is properly contrary to Death, the condition of an organised body in which not only have its peculiar actions ceased, but its distinguishing properties been abolished (see Death); and it is then also contradistin- guished from dormant vitality, a state fre- quently observed, in which living actions are suspended, but the vital properties of the or- ganism retained, so as to be capable of again exhibiting them when the requisite conditions are supplied. Life or vital activity, then, manifests itself to us in a great variety of ways, — in all those phe- nomena, in short, which it is the province of the physiologist to consider. The changes ex- hibited by any one living being, in its normal condition at least, have one manifest tendency, the preservation of its existence as a perfect structure ; by these it is enabled to counteract the ever-operating influence of chemical and physical laws, and to resist, to a greater or less extent, the injurious effects of external agen- cies. The first inquiiy, then, which we have to make, in the inductive study of physiology, is into the conditions of these phenomena ; and as in this process we follow precisely the same track as that over which the physical philo- sopher has already passed, we may advantage- ously avail ourselves of his guidance in it. In seeking to establish the laws by which the universe is governed, or, in other words, to obtain general expressions of the conditions under which its changes take place, the en- quirer first collects, by observation or expe- riment,* a sufficient number of instances having an obvious relation to one another, with the view of determining the circumstances com- mon to all. The facility with which this pro- cess is performed will obviously depend upon the simplicity of the phenomena, and the rea- diness with which they admit of comparison. Where their antecedents are uniformly the same, they only need to be associated a suf- ficient number of times, for the mind to be satisfied of the constancy of the relation ; and the general law of the effects is easily deduced. Thus, the law of gravitation is ascertained by the comparison of a number of corresponding but not identical phenomena; and the nume- rical ratio is established which governs the attracting force. To extend the application of this law, however, to phenomena that seemed beyond its pale, required the almost super- human genius of a Newton ; but the idea, once conceived, was easily carried out when the re- quisite data were attained. But what is the nature of the law of which we have just spo- ken as regulating the attractive force ? It is simply an expression of the property with which the Creator has endowed all forms of matter, that its masses shall attract or tend to approach each other in a degree which varies in a certain ratio to their mass and distance. This property, it must be recollected, is only assumed to exist, as the common cause of the actions constantly occurring under our notice. If none of these actions were witnessed by man, — if, for example, but one mass of matter existed in the universe, — it might be endowed with this and every other property which we are accustomed to regard as essential to matter; and yet, from gravitation never being called into action, the mind would remain ignorant of the attribute. Such a common cause, the conditions of whose action are so simple and uniform that we can account for, and even predict, by a process of deduction, all the phenomena which it can operate to produce, may be regarded for a time as an ultimate fact. It may still, how- ever, be capable of union with other facts of a * For the, proper distinction between these modes of research, and their respective applications to physiology, see Brit, and For. Med. Review, April 1838, pp. 320 et seq. 142 LIFE. similar order, under a still more comprehen- sive expression.* But it is not in every de- partment of science that the same facility in the attainment of general laws exists. Where the phenomena are of such a complex nature that the operation of the real cause is, as it were, masked by the influence of concurrent conditions, or where (as often happens in phy- siology) the effects of the same apparent cause are totally different according to the instru- ments through which it operates, it is obvious that there will be great difficulty in the first stage of the inductive process — that of the clas- sification of phenomena, — so great, indeed, that it may be regarded as one of the principal obstacles to the advancement of those branches of science in which it presents itself. Of all the branches of physical science, that of me- teorology is the most obscure and apparently uncertain, and bears most resemblance to phy- siology. The changes which it concerns are daily and hourly occurring under our observation ; and the general laws which govern them are tolerably well ascertained ; yet the mode in which their actions are com- bined is so peculiar, as hitherto to have baffled the most persevering and penetrating enquirers, in their attempts to explain or predict their operation. But no one thence feels justified in assuming the existence of any new or un- known cause, capable of controlling or sub- verting the influence of the rest ; and such a proceeding would not be justifiable, until all their possible modes of action have been ascer- tained and put aside, leaving certain residual phenomena not otherwise to be accounted for. The peculiar difficulties which beset the in- vestigation of the laws of vital action have greatly retarded our acquaintance with them, and have even led to the belief that the induc- tive process is not applicable to them. These difficulties have arisen, in the first place, from the obstacles in the way of the collection of phenomena; secondly, from the peculiarly com- plex nature of these phenomena; and, thirdly, from the vague hypotheses which have pre- vented them from being Massed as ?'.tiple facts on which generalisations are to be erected, or effects whose sources are to be ascertained, but which have clothed them in the delusive aspect of laws or causes. Until, therefore, the prin- ciples of philosophical induction are thoroughly understood, the peculiar combinations in which vital phenomena present themselves to our notice, their apparent dissimilarity from the changes which we witness in the world around, and their obvious adaptation to particular ends, might lead us astray into the labyrinth of un- profitable speculation with regard to the pre- siding agencies by which they are governed ; and the retrospective view which we shall pre- sently take will afford many examples of this error, even in recent times, and will in fact show that the legitimate objects of investiga- * Such would seem to be the tendency of certain recent speculations in regard to gravitation, mole- cular and electrical attraction, and chemical affinity. tion, and the true mode of pursuing them, are only now beginning to be understood. When we observe the circumstances under which vital actions occur, we perceive that at least two conditions are required for their pro- duction. The first is a structure in that pecu- liar state which is termed organised (see Or- ganisation); the second is a stimulus of some kind fitted to act upon it. Now this is no more than what we observe in the world around, where every action involves two con- ditions of a corresponding character. When water is changed into steam, for example, it is by the stimulus of heat. When a stone falls to the ground, it is by the attraction which the mass of the earth exercises over its own. The difference consists in the peculiarity of the actions exhibited by living beings, which are not identical with those elsewhere presented to us, and which we cannot imitate by any phy- sical or chemical operations. Whilst the me- chanical philosopher, then, refers to the pro- perty of gravitation as the cause of the effect just mentioned, the physiologist refers to the capability of exhibiting vital actions, when excited by certain stimuli, as the property of the tissue which manifests them. Thus, when he witnesses the contraction of a muscle, under the stimulus of innervation or of galvanism, &.C. he regards the effect as due to a property of contractility inherent in the muscle, and standing in precisely the same relation to its organic structure, as gravity to matter in ge- neral. So far, however, the advance in our in- quiry is more apparent than real ; since it may fairly be said that, to speak of contractility as the character of a body exhibiting contractions, is merely a change in words without absolute gain. But, having done this, we are led to inquire the conditions under which this con- tractility operates ; and to analyse a number of phenomena apparently dissimilar, so as to at- tain the general law of its action. In this man- ner we proceed in regard to other classes of phenomena; and we shall thus acquire (when our data are sufficiently precise and extensive) a knowledge of the properties of all the tissues or organised structures which compose the living body, and of the phenomena which their single or combined operation will pro- duce, under the influence of their respective stimuli. But the physiologist will not stop here. He will seek to inquire to what these properties are due, which are so different from anything exhibited by the same matter before it had be- come a part of the organised system. And, if he consider the matter in all its bearings, with a total dismissal of prejudice, he will be unable, we think, to arrive at any other conclu- sion than that they are due to the act of organi- sation, which, in combining the inorganic ele- ments into new compounds, and giving them a peculiar structure, calls out or developes in them properties which had previously existed in a dormant state, but required these circum- stances for their manifestation. To this ques- tion, however, we shall presently return, when considering other views which have been en- tertained respecting it. We shall now take a retrospective glance at the II. Histoey of opinions. — In the earlier ages of the world, before the true method of philosophising on any subject was under- stood, it was considered as a sufficient ex- planation of any phenomenon to apply to it some abstract term, expressing a vague idea of a property inherent in the body which ex- hibited it, without attempting to ascertain the conditions of its operation* Thus, all the phenomena of the movements of the heavenly bodies were attributed to the agency of a " principle of motion," the laws of which were scarcely even sought for. In like manner, the simple optical fact — that, when the sun's light passes through a hole, the bright image, if formed at a considerable distance from it, is always round, instead of imitating the figure of the aperture, — was attributed by Aristotle to the " circular nature" of the sun's light; whilst the mere consideration that the rays of light travel in straight lines, would, if properly applied, have explained this pheno- menon, not only as regards the sun, but in the case of any other round luminous body placed at a sufficient distance. It is not wonderful, then, that the still more intricate nature of the phenomena exhibited by living beings, the obvious tendency of those presented by each individual towards the same end, and the se- ductive simplicity of the hypothesis, should have induced the philosophers of that age to regard all vital actions as the immediate results of one common cause ; but that such a belief should have maintained its ground, with but little alteration, to the present day, can only be regarded as a proof of the lamentable de- ficiency in truly philosophical views among the cultivators of physiology. To the supposed cause of vital phenomena the term Life was applied by the older philo- * This mode of philosophising has been very happily ridiculed by Fontenelle. " Let us ima- gine," he says, " all the sages collected at an opera — the Py thagorases, Platos, Aristotles, and all those great names which now-a-days make such a noise in our ears — let us suppose that they see the flight of Phaeton as he is represented carried off by the Winds ; that they cannot perceive the cords to which he is attached, and that they are quite ignorant of everything behind the scenes. It is a secret virtue, says one of them, that carries off Phaeton. — Phaeton, says another, is composed of certain numbers which cause him to ascend. A third says, Phaeton has a certain affection for the top of the stage ; he does not feel at his ease when he is not there — Phaeton, says a fourth, is not formed to fly ; but he likes better to fly than to leave the stage empty; and a hundred other ab- surdities of this kind, that would have ruined the reputation of antiquity, if the reputation of anti- quity for wisdom could have been ruined. At last come Descartes and some other moderns, who say, Phaeton ascends because he is drawn by cords, and because a weight more heavy than he is descending as a counterpoise. Thus to see nature as it really is, is to see the back of the stage at the opera." — Quoted in Brown's Lectures on Mental Philosophy, Lect. v. LIFE. 143 sophers, who regarded it as a distinct entity or substance, material or immaterial, residing in certain forms of matter; and the cause, both of their organisation, and of the peculiar actions exhibited by them.* Every sect had its own notion of the origin and nature of this entity; some regarding it as a kind of fire ; others as a kind of air, ether, or spirit; and others, again, merely as a kind of water. The fable of Pro- metheus embodies this doctrine in a mytho- logical form, the artist being described as vivi- fying his clay statues by fire stolen from the chariot of the sun. Whatever was the idea entertained as to the character of this agent, all regarded it as universally pervading the world, and as actuating all its operations in the capacity of a life or soul ; whilst a special division of it — a divince particula aura — regu- lated the concerns of each individual organism. The opinions of Aristotle on this subject are very interesting, as presenting evidence of the tendency of his powerful mind to elevate itself above the level of his age, and as showing how completely even lie was bound down by the prevalent tendency to hypothetical specu- lation, which seemed to offer so easy a solu- tion to all the mysteries of Nature. " In con- sidering what holds the fabric of the universe together, and forms out of the discordant ele- ments a harmonious whole, he infers from analogy that it must be something similar in kind to that which forms and holds together an organised body, namely, a principle of life; and that this principle, from the appearance of order and design displayed in the universe, must also have intelligence." " Besides this supreme animating principle (. cyrrhoses en masses; 2°. en plaques; 3°. en kystes. Lorsqu'il existe, dit-il, des cyrrhoses dans le foie, elles forment ordinaire- nient de petites masses dont le volume ne surpasse jamais celui d'un noyau de cerise, et quelquefois egale a peine celui d'un gros grain de millet. Ces masses sont toujours extreme- ment nombreuses, et tout le tissu du foie en est pariseme. Leur petitesse fait que lorsqu'on incise un foie dans lequel il en existe un grand nombre, son tissu parait au premier coup d'ceil homo"cne et d'une couleur jaune fauve. Mais si on examine plus attentivernent le tissu hepa- tique, on s'aperpoit facilement qu'il est rempli * Dictionnaire de Medecine, Art. Foie. d'une innombrable quantity de corpuscules assez semblables, pour l'aspect a ces lobules de graisse durcie et rousseatre que Ton trouve communcment dans le tissu cellulaire sous- cutanc de la cuisse et de la jambe des sujets attaqu6s d'anasarque. Ces petites masses sont quelquefois unies tres-intimement au tissu du foie ; mais assex souvent elles en sont separees par une couche mince de tissu cellulaire qui leur forme une enveloppe tenue, et alors ils se detachent assez facilement. La surface exte- rieuredu foiedevientfletrie,rugueuse,et ratatinee a-peu-pres de la meme maniere qu'une pomme fletrie." Bouillaud* considers this condition of the liver a dissociation of the two natural elements of the organ : " les masses jaunes fauves con- stituant le tissu accidentel, appele cirrhose, ne sont autres chose que les granulations secre- toires se desorganisant graduellement par Terlet de l'obliteration du lacis vasculaire, et de l'obstacle a la circulation hepatique qui en resulte." We have already combatted the ex- istence of two substances, and further remark upon this subject must be quite unnecessary. Andral f sees, in the cirrhosis, atrophy of the red substance and hypertrophy of the yellow substance. Of all modern authors, Cruveilhier approaches nearest to the true condition of the organ, but from his misapprehension of the exact nature of the lobules, even his opinion cannot be accepted without limitation. Cirrho- sis, says this author,J is " atrophie du plus grand nombre des grains glanduleux, et hyper- trophic avec coloration jaune des grains glandu- leux restans." Now cirrhosis is undoubtedly a partial atrophy of the liver with hypertrophy of the cellular structure ; complete atrophy of some of the lobules, partial atrophy of others, and biliary congestion without atrophy or hy- pertrophy of the rest. Those small yellow grains varying in size from a millet-seed to a pea or to a hazel-nut, are not distinct lobules in a variable state of hypertrophy, but small uncongesled patches composed of parts of several adjoining lobules, and having a single or several interlobular spaces for a centre. Hence it is, as we have before shown, thatCru- veilhier§ has observed the " partie centrale de chaque granulation repond au radicule biliare, et consequeminent est souvent teinte en jaune et que la partie excentrique repond a l'element vasculaire et conseqi emment est plus rouge que la partie centrale." d. Softening of the liver may accompany any of the changes resulting from acute inflamma- tion. The degree of softening is very variable, the organ having at one time a simple abnormal degree of friability when pressed by the hand, and at others constituting a pulpy mass scarcely re- tained in its form by the cellular framework of its vessels andGlisson's capsule. Softening may be unaccompanied by any marked change in the bulk of the organ, but is always associated with a variable intensity of venous congestion. Biliary * iYIemoire de la Societe Mtdicale d'Emulation. f Anatomic Patliologiquc, vol. ii. p. 585. % Anatomie Descriptive, vol. ii. p. 568. § Anatomie Pathologique, livraison 12. ABNORMAL ANATOMY OP THE LIVER. congestion is also frequently present, and tinges the substance of the organ with a variable hue of yellow, green, &c. Portal observes that the liver of patients who have died of scurvy is often so much softened that it appears in a state of decomposition, has a reddish brown colour, and resembles the lees of red wine. Baillie remarks that softening of the liver is not uncommon in old persons, that it ap- proaches in consistence to the texture of the spleen, and is of a brownish red colour. e. Induration of the liver is occasionally attendant upon hypertrophy or atrophy of the organ, but it may also exist with a normal size of the liver without other apparent change than the brownish red tint which it receives from venous congestion, or the various shades of yellow, green, or brown induced by biliary congestion. The density and hardness acquired by the liver in a state of atrophy are sometimes truly astonishing. 1 n a case detailed by Mor- gagni the organ resisted the knife, and several such instances are to be met with among the writings of the older pathologists. ./'. Fatty degeneration of the liver. — Upon referring to the section upon the chemical analysis of the liver, it will be observed that a certain proportion of oily matter is one of its natural constituents. Under the influence of diseased action this quantity is greatly aug- mented, and increases to such an extent as completely to take the place of the normal structures. Vauquelin has published an analy- sis of a fatty liver, from which the quantity of oily matter present may be fairly estimated thus; in 100 parts he found, on 45 Parenchyma 19 Water 36 100 The fatty matter is usually distributed equally through the organ, being apparently infiltrated into the cellular texture of the parenchyma. At other times it is deposited in a mass or forms se- veral collections in different parts of theliver. The fatty liver is greasy upon the surface, and when cut into has the appearance of a section of yellow soap. The vessels seem pressed upon and are scarcely perceptible, while the greasy deposition is divided into angular masses by a coarse and compressed cellular tissue. Fatty liver is generally consistent and solid in its texture, but sometimes the fat exists almost in a fluid state. Portal has observed the liver quite white and softened almost to the fluidity of melted fat, where no hepatic sym- ptoms existed during life; and he particularly records the case of a woman suffering under a severe form of syphilis in which this condition of the liver existed. From the name which has been given to this disease by pathologists, fatty degeneration, we might be led to infer that the texture of the organ was actually converted into this oily sub- stance. This, however, is quite inconsistent with our knowledge of pathological phenomena. The fatty deposition is obviously an undue secretion of a normal constituent, but whether resulting from irritation from whatever cause, or from absence of vital energy, is a question upon which I am unwilling, without further investigation, to hazard an opinion. With regard to the causes of fatty liver Andral observes, " Les causes sous l'influence des quelles le foie devient le siege d'une secretion de matiere grasse sont encore inconnues. On n'a emis qu'une hypothese lorsq'on a dit que la degeneration graisseuse du foie etait le produit d'une irritation de cet organe. Car on pourrait tout aussi bien soutenir que cette degeneration graisseuse, loin d'avoir ete piecedee par un etat d'irritation du foie, est survenue parceque la nutrition de cet organe est devenue moins active; et cette derniere hypothese serait d'au- tant plus soutenable, qu'elle se deduirait d'une grande loi de l'cconomie en vertu de laquelle, toutes les fois qu'un organe tend a s'atrophier, une matiere grasse vient a se secreter autour de cet organe ou a la place meme de ses mole- cules."* Fatty liver is most frequently observed in persons who have died from scrofulous tubercles in the lungs; in those, says Andral, in whom the blood has not been efficiently arterialised, and in whom the pulmonary exhalation is greatly diminished. Can it be, he inquires, from the absence of the due separation of hydrogen from the lungs that this compound of hydrogen, fat, becomes deposited in the paren- chyma of the liver? This question is well deserving the attention of pathologists, and its solution might lead to important information. The disease has also been observed in some cancerous disorders and in dartrous diseases of of the skin. g. Pus. Abscess in the liver occurs in two principal forms, either as a single abscess of large size inclosed in a cyst, or as numerous small collections of matter, bounded by the substance of the liver or diffused amongst its lobules. In the first form it constitutes idio- pathic abscess of the liver, a disease of tropical countries, and rare in our temperate climates. Abscess is generally preceded by acute inflam- mation and more rarely by chronic inflamma- tion, and attains an enormous size, engrossing the whole of the right lobe and sometimes con- verting the entire organ into one huge cyst. The cyst may be thin or thick, and more or less organised. Andral and Louis conceive that its internal surface is analogous to a mucous membrane. The quantity of pus contained in one of these abscesses varies from a few ounces to several pints. My friend Dr. Macnaught, who has seen much practice in the West Indies during a residence of twenty-two years in Jamaica, has observed that abscess in the liver occurs more rarely in the West than in the East, and, moreover, that this disease affects the Euro- peans and not the Negroes. During the whole of his experience he never saw a single case of abscess in the liver in the Negro, and among the white population of his district only four well- marked instances. * Anatomie Pathologiquc, vol. ii. p. 597. ABNORMAL ANATOMY OF THE LIVER. 191 The irritation of abscess causes the effusion of lymph and adhesion to the abdominal pa- rietesor to the adjoining viscera ; ulceration fol- lows, and the contents of the cyst are discharged through the artificial opening. The situations in which the matter escapes from the cavity of the abscess are various. 1. It may burst externally, making its way either between the ribs or up- wards towards the axilla. In a case observed by Dr. Macnaught the abscess pointed at the epigastrium and was opened by the surgeon in attendance. 2. It may become adherent to the diaphragm and burst into the pleura. 3. It may cause adhesion between the serous membrane of the liver and of the diaphragm, and between the latter and the pleura pulmonalis, and the matter may escape into the lung and be coughed up, as in the case already detailed, which occurred to Dr. Munro. 4. In rare cases the pus has been effused into the cavity of the peritoneum. 5. The abscess may become adhe- rent to the stomach, duodenum, or colon, and the matter be discharged into the alimentary canal. A well-marked case of abscess dis- charging its contents into the stomach occurred to myself in the case of a woman who has since perfectly recovered. About two pints of matter were vomited by the patient. In a simi- lar case observed by Dr. Macnaught the patient recovered. In two other cases, where the matter was poured into the intestines, the patients died. 6. Abscess has been seen to open into the gall-bladder, and the pus to be conveyed thence through the ductus communis choledochus into the duodenum. 7. In one case the matter was discharged into the vena cava ; and in another, 8, described by Dr. Smith, into the pericardium ; and in a case detailed by Dr. Graves,* the abscess opened both into the stomach and pericardium. Besides the preceding form of abscess, which is idiopathic in its origin, abscess may occur in the liver from external injury, as from a blow. The inflammation attending upon this injury is much slighter than that which gives rise to idiopathic abscess ; the collection of matter is generally smaller, and terminates either by dis- charging its contents or by absorption. The second variety of abscess in the liver, that in whicli numerous purulent collections exist, depends for its cause upon the occurrence of wounds or of surgical operations. The suc- cession of abscesses in the liver from wounds, particularly of the head, has long since been admitted as a well-established fact, for the explanation of which numerous theories have been invented. Theory, however, has now yielded before facts,- — facts, too, of the most interesting and satisfactory kind, for which pathology is indebted to the genius and indus- try of Cruveilhier. The experimental re- searchesf of this. excellent author, published in 1826, enabled hiin to establish a law of the utmost importance in the consideration of the phenomena of disease, viz. that " tout corps * Dublin Medical Journal, January 1839. f Recherches sur la siege immcd, dc 1 'inflamma- tion. Nouv. Bibl, Med. vol. iv. etranger introduit en nature dans le systeme veineux determine lorsque son elimination par les emonctoires est impossible des absces visce- raux entitlement semblables a ceux qui suc- cedent aux plaieset aux operations chirurgicales, et ces absces sont le resultat d'une phlebite capillaire de ces mimes visceres."* These experiments consisted in the introduction of metallic mercury into the veins of an animal, say of the lower extremity. In the course of twelve, eighteen, or twenty-four hours the animal experienced much difficulty of breathing, and soon expired. Upon inspection globules of the mercury were found in the lungs. If a smaller quantity of mercury were introduced the animal would live for several days or weeks, and upon examining the lungs at different periods the globules were at first seen to be surrounded by a red induration and afterwards by pus. This experiment was varied by pouring the mercury into the medullary cavity of a bone with pre- cisely the same results ; in one instance he placed a single globule in the medullary cavity and found it again at the end of a month in the lungs, divided into several minute globules, each of which formed the centre of a small tuberculous abscess. Cruveilhier then injected a small quantity of mercury into one of the omental veins of a dog — the subject of umbili- cal hernia; the dog was killed in the third month after the operation, being reduced to a state of marasmus. Upon inspection the liver was found filled with small abscesses, each surrounding a small globule of mercury. Having by means of these experiments satisfied himself that the lungs were the barrier to all foreign matters introduced into the general circulation, as was the liver of those admitted into the abdominal circulation, he proceeded to another series of experiments. Opening a vein in the hinder extremity of a dog he introduced into it a long piece of stick, which gave rise to phlebitis and the secretion of pus. The pus thus produced being carried into the circulation excited, in the first instance, abscesses in the lungs, and, secondly, in the liver. Upon these facts and upon a multitude of excellent observations Cruveilhier founds his opinion that abscess in the liver from wounds and surgical operations is always preceded or accompanied by purulent collections in the lungs, and always results from the same cause, viz. from capillary phlebitis, consecutive upon phlebitis in the neighbourhood of the wound, and im- mediately produced by the irritative action of globules of pus brought from the diseased veins to the capillaries of the structures in which the secondary suppuration is developed. In every case of secondary abscess in the liver, following wounds of the head, or after amputation or operations upon bones, Cruveil- hier has found phlebitis of the vessels situated in the structure of the bones. Hence he esta- blishes an important general proposition, that " le phlebite des os est une des causes les plus ficquentes des absces visceraux suite des plaies et des operations chirurgicales dans * Anatomic Pathologiquc, liv. xi. ABNORMAL ANATOMY OF THE LIVER. lesquelles ces os ont ete interesses.'' The re- moval of haemorrhoids and operations upon the uterus are sometimes followed by abscess of the liver, a circumstance which is easily expli- cable upon the principles so clearly demon- strated by this author. An excellent instance of secondary abscess of larger size than usual has been kindly fur- nished to me by my friend and colleague Mr. Rutherford Alcock, who, from his official posi- tion in Spain and Portugal during the recent struggles, has had much experience in injuries to the head. A man received a bayonet wound in the scalp, and died upon the fourteenth day after his admission into the hospital. Upon inspection there was observed thickening of the dura mater and a small quantity of matter upon the pia mater. No pus was discovered in the lungs, but a large abscess was found occupying the greater part of the right lobe. A statistical report from a work upon gun-shot wounds by the same author is also interesting. * Of scalp wounds, with and without abrasion, there were sixty-one; two only died, and one only presented disease of the liver; the other died from an attack of erysipelas." The pathological changes which take place in the liver in these cases are, in the first instance, effusion of blood and lymph and induration around the inflamed vein ; secondly, a secretion of a yellow concrete pus into the ninute veins and among the lobules, giving to the liver, as Cruveilhier remarks, a granite-like appearance. In the next place the pus collects into small abscesses lodged in irregular cells, which increase in size by continued secretion and by communication with other cells. All these collections of matter are surrounded by a congested circle, which gives them a peculiar and characteristic appearance. After having existed for some time Cruveilhier has observed that the pus becomes converted into a concrete mass, very closely resembling the matter of scrofulous tubercle. h. Tubercle in the liver is a disease of rare occurrence, and has seldom been observed independently of the existence of similar depo- sitions in the lungs and other organs of the body, and of general indications of a scrofulous diathesis. When present, it exists in the form of small rounded tubercles, generally numerous, and varying in size from that of a millet-seed to a hazel-nut. They are composed of the soft cheesy or curdy deposit which is characteristic of this disease, and have a tendency to a brownish colour. The tuberculous matter is deposited in the tissue of the lobules by infil- tration, and the lobules immediately surround- ing the tumours are compressed and congested. The obstruction to the circulation in the organ being general on account of the number of the tubercles, the entire liver is more or less con- gested. i. Scirrhus. — Carcinoma affects the liver under a variety of forms, but appears most frequently as tubercles of different size and consistence. These tubercles are more fre- quent than those of scrofulous origin, and are generally accompanied by symptoms denoting a cancerous diathesis, and by the existence at the same time of similar tumours in other parts of the body. In their earliest development in the liver nearly all carcinomatous tumours pre- sent the same characters, resembling small, whitish, semi-opaque patches, occupying the tissue of one or of several of the lobules. As they increase in size they put on certain peculiar appearances, which have gained for them a subdivision into species and varieties. I do not intend in this place to enter into the ar- rangements proposed by authors, but will briefly describe the most striking varieties that have fallen beneath my own examination. The sim- plest of these tumours has been termed scir- rhous tubercle, a name which appears particu- larly applicable from its resemblance in cha- racters and structure to the same form of tu- mour occurring in other parts of the body. Commencing like the carcinomatous tumour generally in a semi-opaque patch, the outline of the lobules is for some time distinctly percep- tible through its area, but at a later period the centre of the patch becomes quite opaque, and presents a cartilaginous hardness and creaking sound when divided with the knife, The cir- cumference is gradually diffused in the sur- rounding textures, and the progressive increase of the tumour seems to take place by the se- cretion of a milky albuminous fluid into the meshes of the lobular venous plexuses. The circulation in these plexuses is at first unim- peded, but by the increase and induration of the secretion it is gradually arrested, and the vessels obliterated. The obliterated vessels give rise to the appearance of small cells, in which the carcinomatous matter is deposited, and the larger area are produced by the tissue of the capsules of the lobules variously dis- torted from their original form by the increased deposition. As the tumours become more and more large, white lines, formed by compressed cellular tissue, are observed radiating from the centre towards the circumference. When seeu upon the surface of the liver, the scirrhous tubercle appears flat, or very slightly depressed towards the centre. In a preparation of this form of tubercle now before me, the whole tumour is slightly raised above the surface ; it presents no central depression, is cartilaginous in appearance, and has an irregular outline. Its section is dense and hard like cartilage, with no appearance of vessels, and of that pearly and semitransparent whiteness which is generally observed in scirrhous tubercle, particularly in the variety which this prepara- tion illustrates. Sometimes these tubera are small and very numerous, of a yellowish or brownish colour, and have a great activity of increase ; the cells in which they are contained are thick and of larger size, and the albumi- nous secretion less firm than in the preceding variety. Occasionally they are reddened in the centre by the effusion of blood, from the con- gestion of unobliterated vessels, and some- times by the continuation, through the tumours, of dilated vessels, which supply them with nutrition. In their enlarged state they fre- quently coalesce and give rise to an irregular ABNORMAL ANATOMY OF THE LIVER. 193 compound mass, which assumes the form of the particular part of the organ in which it is placed, and is divided into compartments, marking its original multiple form by septa of condensed Glisson's capsule supporting dilated vessels. It would appear to be this form of tumour which has been described by Farre as the first variety of his tubera diffusa; he gives them the following character. " Tubera, ele- vated at the surface of the organ, but not uni- form in their figure, some rising with a regular swell into a round form, others acquiring a margin by being gradually depressed towards the centre, forming tumours without cysts, almost pulpy in their consistence, cellular in their structure, and containing an opaque white fluid." Another form of the albuminous carcinoma- tous tumour is the large white tubercle" of Baillie, the tubera circumscripta of Farre, by whom they are thus admirably described : " Their colour inclines to a yellowish white, and their projecting surfaces, slightly variegated with red vessels, deviate from a regular swell by a peculiar indentation at or near their cen- tres, which are perfectly white and opaque. They vary much in size, which depends on the duration of each tuber, for at its first appear- ance it is very minute, but during its growth it assumes the character above described, and at its maturity exceeds an inch in its diameter. They adhere intimately to the liver, and their figure is well defined. They commonly remain distinct at the surface of the liver, but inter- nally they ultimately coalesce and form im- mense morbid masses which pervade its sub- stance. They possess so close a cellular struc- ture that the section of them at first view appears solid and inorganic ; but on the edt;e of the knife, by which they have been disse- vered, an opaque white fluid of the consistence of cream is left, and a fresh portion of this fluid is gathered on it at each time that it is repassed over the surface of the section. Their cellular structure becomes more apparent after long maceration." The depression in the centre of carcinoma- tous tumours, although generally met with, is not a necessary character of cancer. Its mode of formation has been ably pointed out by Dr. Carswell, in his beautiful work on pathological anatomy : " The depression is not observed unless when the tumour is divided or is situ- ated on the surface of an organ, as the liver, where tumours of this kind are generally met with. In the former case the depression arises from the softer substance, after the division of the tumour raising itself by its elasticity above the unyielding nucleus ; in the latter it is pro- duced by the peritoneum adhering to the sur- face of the tumour when small, and preventing its development in that direction. If the tu- mour does not come in contact with the peri- toneum until it has acquired a considerable size, it presents no such depression, or only a very small one. Hence the reason why, in carci- noma of the liver, we meet with some tumours having a smooth globular surface, and others with a central depression of greater or less extent." vol, nr. Another variety of carcinomatous tumour is named the gelatiniform cancer, from the exis- tence of a firm and jelly-like deposit which oc- cupies the cells of the tumour m place of the albuminous secretion common to the preceding forms. 1 have before me an interesting speci- men of gelatiniform tubercle. The liver con- tains a considerable number of these tumours of variable size, and dispersed through every part of its structure. The smallest resemble the small patches described above as the inci- pient stage of carcinomatous tumour generally; the largest are equal in size to a walnut. They are distinctly circumscribed, and the lobules immediately surrounding them are flattened and compressed. In the smaller tubercles the form of the lobules is quite distinct, but in the larger the lobules have yielded to the peculiar characters of the disease. On the surface the centre of the tubercle presents an oval or cir- cularly indented ring, around which the tumour swells suddenly and then subsides to the cir- cumference. On making a section of one of these tumours, 1 found a central area of about two lines in diameter, transparent, dense, and apparently gelatinous, and distinctly bounded by a white marginal line; the marginal portion of the section forming the bulk of the tumour was elastic, and rose above the central area to subside gradually in the marginal line of the circumference. The whole section bore a stri- king resemblance to the conjunctiva affected with chemosis, only that it was paler in its colour, or to a beautiful flower with a single large and expanded circle of petals. On exa- mining a thin section with a lens of low power a number of minute parallel injected capillaries were seen traversing the marginal portion of the tubercle towards the boundary line of the area, but no vessels could be traced beyond that line into the central portion. The resem- blance to the petals of a flower was produced by white lines which radiated from the boun- dary line of the area to the circumference, and divided the marginal portion of the tumour into six or eight compartments. From careful examination it appeared to me that the central area was a single lobule expanded by the gela- tinous deposition with which its tissue was in- filtrated, and the marginal compartments pre- sented a similar character. k. Medullary sarcoma. — Another form of tu- bercle, associated with the cancerous diathesis and belonging to the carcinomatous family, is medullary sarcoma, or encephalosis. The tu- mours produced by this disease are larger than scrofulous tubercles, and more regular in form and fewer in number than scirrhous tumours. Developed originally in the same way with scirrhus, by infiltration into the tissue of the lobules, or into the vessels themselves, of the peculiar greyish white and opaque substance of which they are composed, they increase in size and obstruct the circulation in the surrounding lobules. Their internal structure is a loose cellular base, filled with a soft and brain-like matter, frequently coloured with blood, or containing coagula in various stages of soften- ing, resulting from heEmoriliagic extravasation. o ABNORMAL ANATOMY OF THE LIVER. Sometimes these tumours present a certain de- gree of consistence, but as they increase in size they become more and more softened and pulpy. Baillie describes a large tumour in the liver which he considers scrofulous from being softened in the centre, and containing a fluid resembling pus; this is most probably a tumour of the kind I am now describing. Another tumour, of which he expresses himself at a loss to understand the nature, soft, of a brownish colour, and of about the size of a nut, appears to be also referable to the same species. The second and third varieties of the tubera diffusa of Fane present characters resembling this disease. V. 2. " Tubera, elevated at the surfaces of the affected organ, encysted, or having dis- tinct cells, formed by the growth of a fungus, which separates in flakes, and is composed of a fine reticular texture, containing an opaque white fluid." V. 3. " Tumours rising with a regular swell from the surfaces of the affected parts and yielding to the touch, composed of a very delicate reticular texture, pulpy in its consistence, varying in its colour even in the same subject, charged with an opaque fluid, and growing from cysts or cells." Cruveilhier considers the venous capillary system as the seat of origin of carcinoma, par- ticularly of the form which I am now consi- dering ; hence he observes, " Ayant exprime d'une coupe faite a un foie cancereux une ma- tiere d'un blanc-rougeatre, encephaloide qui se moulait a la maniere du vermicelle, et qui pouvait acquerir en se tordant une grande lon- gueur, j'apercus sur cette coupe un orifice plus considerable que les autres ; j'incisai cet orifice et je parvins dans un vaisseau tres volumineux qui me parut etre une des ramifications de la veine porte. Alois je dissequai avec beaucoup d'attention cette veine, et je ne fus pas peu etonne de voir que cette veine, depuis les plus grandes jusq'aux plus petites divisions, etait remplie par cette matiere encephaloide, adhe- rente aux parois et tout-a-fait semblable a celle qu'on exprimait par les coupes faites au foie. II me fut facile de suivre les ramifications ex- tremement dilatees de la veine j usque dans Fareoles des coupes. L'alteration etait bornee a la veine porte, les veines hepatiques et leurs ramifications etaient parfaitement saines."* I. Fungus hamutodes is the term applied to all carcinomatous tumours which have a ten- dency to the unnatural development of new vessels and to effusions of blood into their tissue. In the same organ, hard and cartilaginous scirrhous tumours may exist with those of a softer texture, and of a medullary form, and both of these may be mingled together in the soft, elastic, and bleeding mass which consti- tutes fungus hasmatodes. The tumours of fungus hasmatodes are often of very large size, and by their frequent hemorrhagies give rise to extreme symptoms and the speedy death of the patient. Farre arranges this form of carcinoma among his tubera diffusa, of which it forms the fourth variety, which he thus defines : " Tu- mours elevated at the surfaces of the liver and inclining to a round figure ; pulpy in their con- sistence, being charged with a thick and opaque fluid, variegated in their colour, chiefly white mingled with red, the former prevailing in their incipient, the latter in their advanced stages, composed of a very vascular and reticular tex- ture, attached either to distinct pouches or to the substance of the liver, and so unlimited and rapid in its growth as to burst or destroy the peritoneal tunic of this organ and to pro- trude in the form of a bleeding fungus." m. Melanosis. — Melanosis exists in the liver, as in other structures of the body, 1st, as a melanic secretion infiltrating the cellular struc- ture of the organ, and giving a diffused general blackness to the substance of the lobules; 2d, as a morbid tissue composed of an areolar cel- lular network, in which the black carbonaceous matter is deposited ; or 3dly, as a melanic pigment accompanying carcinoma or tubercle, and imbuing the abnormal tissue with its pe- culiar colour. The colour of melanosis in the liver varies from a deep chocolate-brown to a rich black. Sometimes it is diffused in patches through the substance of the organ, at other times it exists in the form of rounded circum- scribed tubercles of variable size and number. Laennec considers melanosis as an accidental tissue without analogue among the animal tis- sues ; he classes it with cancerous degenera- tions, and describes it as existing in his two favourite conditions of crudity and softening. But the researches of Cruveilhier have shewn that in many instances melanosis is to be re- ceived as a mere pigment, resembling the pig- mentum nigrum of the choroid, which impresses its peculiar colour upon natural and morbid tissues, and he has also proved, in opposition to the view entertained by Laennec, that the softened state or state of infiltration very fre- quently precedes the more dense and encysted form. Melanosis rarely exists in the liver with- out being at the same time found in various other structures of the body, as in the brain, eye, lungs, heart, spleen, kidney, mucous mem- brane, muscles, skin, &c. 6. Disorders of function. — The principal function of the liver bein; the secretion of bile, we shall have to consider under this head the changes which may occur in the secretion of this fluid and in the fluid itself, in consequence of derangement of function in the organ. These disorders may be divided into three kinds: — a. Suppression of the bile. b. Alterations in the physical properties of the bile. c. Alterations in the chemical qualities of the bile. a, Suppression of secretion of the bile, like suppression of urine, occasionally occurs in the liver. This disease appears to have been known to Darwin,* who calls it " paralysis of the secretory vessels" of the liver; the patients, he says, " lose their appetite, then their flesh and strength diminish in consequence, there appears no bile in their stools nor in their urine, * Anatomie Pathologique, liv. 12. * Zoonomia, vol. ii, p. 5. ABNORMAL ANATOMY OF THE LIVER. 195 nor is any hardness or swelling perceptible in the region of the liver." Kiernan, who has observed several cases of this disease, informs me that the symptoms are sudden jaundice, depression of the powers of the system, and speedy dissolution ; upon dissection he found complete absence of bile in the biliary ducts, the mucous membrane of which appeared bleached. b. Alterations in the physical properties of the bile. — The changes to which the bile is l.able are in no wise referable to any particular alteration in the liver. In cases where this organ has been considerably diseased, the se- cretion of the bile has been found natural and healthy; and in other cases, where a slight de- gree of congestion was all the apparent patho- logical derangement, the secretion has assumed a morbid appearance, or has been deficient or superabundant in quantity. Gall-stones are sometimes found in the gall-bladder without any admonitory symptoms during life, and icterus may be a frequent and even a fatal malady without any obstruction appearing in the course of the biliary tubes after death, or without any satisfactory indications of diseased action in the liver. " I have been sometimes astonished," says Andral, " on seeing the enormous quantity of bile which distended the alimentary canal in cases where the slightest degree of congestion existed in its coats, and when the liver appeared in no wise altered." Nay, it has been proved both by observation and experiment that the bile is materially changed in appearance, quantity, and consist- ence by the mere alteration of diet. Experi- ments made upon living animals have long since shewn that bile taken from different indi- viduals is capable of producing very different effects upon the animals into whose bodies it has been introduced; thus some will give rise to a trifling irritation, while others will occasion more or less serious symptoms and even rapid death. Some bile may be touched and even tasted without inconvenience, while other bile, precisely similar in appearance, will produce pustular eruptions and ulcerations upon the tongue and upon the lips. " Here then," says Andral, " are serious changes in the bile which are wholly imperceptible to the investigation of anatomy." The colour of the bile differs very consi- derably, being sometimes hardly distinguish- able from serum, and at other times presenting a variable tint of amber, orange, green, brown, olive, and even black. In consistence it is equally various, being one while limpid and diffluent, and another while black, viscous, and grumous. b. Alterations in the chemical properties of the bile. — In chemical composition, the altera- tions in the bile are not less numerous than in its physical properties. In fatty liver the bile has been found composed almost wholly of albumen and water. Under other circum- stances the natural constituents are greatly altered in their relative proportion. The formation of biliary calculi may be re- ferred to disproportionate secretion of the na- tural elements of the bile, the increased quantity of certain of its constituents giving rise to the deposition and accretion of these substances in a form corresponding with the cavities in which they are produced. Gall-stones have been found in the smaller biliary ducts in the sub- stance of the liver, in the excretory ducts both within and external to the organ, and in the gall-bladder. They have also been met with inclosed in a cyst, formed most probably by the obliteration of one of the hepatic ducts, and adherent to the organ or suspended from it by a pedicle. Malpighi found gall-stones in the small biliary ducts and considered them as petrified lobules. The size of biliary concre- tions is very various, being sometimes exceed- ingly small, and at other times of considerable bulk. When small they are generally numerous ; I have counted upwards of a hundred, and in- stances are recorded where more than a thousand were found in the gall-bladder. When they are large they are few in number, and frequently single. I have seen the gall-bladder filled with three, two, and even one large calculus. A large oval gall-stone now before me equal in size to a pigeon's egg I removed from the ductus choledochus. Their form is equally various with their size and other physical cha- racters. I have now before me gall-stones with a flattened shape, triangular, and tuberculated on the angles and on the surface ; others have three equal facettes with sharp or flattened or rounded angles ; others again are irregular in their outline and would seem to be moulded to the canals and cavities from which they have been withdrawn. Being stained by the colour- ing matter of the bile, their colour varies with the predominant tint of the secretion in which they have been formed, hence some are reddish brown or black ; others are yellow, and others again white; some are mottled yellow and black, or white and black with various shades of green. In chemical composition there are, according to Andral, five principal varieties of biliary concretions; they are, 1. of yellow colouring matter; 2. of resin; 3. of cholesterine ; 4. of picromel ; 5. of phosphate of lime. The fir.^t kind appears very ill founded, for yellow is a prevailing tint among gall-stones, and is the mere pigment by which cholesterine and the other substances are coloured. By far the largest proportion of gall-stones are formed of cholesterine, either pure, when it presents a white semitransparent mass beautifully cystal- lized in its interior, or variously tinted with brown, yellow, or orange, and radiating from the centre towards the circumference or from a small central nucleus. The smaller calculi also exhibit upon fracture the same radiated appearance. The gall-stones of resin and picromel may be classed together and consi- dered as biliary concretions formed of inspis- sated bile probably accreted through the agency of cholesterine. The calculi of salts of lime are less frequent ; they are found in the gall- bladder or in the ductus communis choledochus. I have observed them to present two varieties, firstly, incrustations of phosphate of lime upon o 2 196 ABNORMAL ANATOMY OF THE LIVER. the surface of calculi of cholesterine ; and secondly, laminated calculi composed of con- centric layers of phosphate and carbonate of lime variously coloured and having a central nucleus. The latter form is, I believe, rare ; I possess but one specimen ; it is of large size, and rough and irregular upon the surface.* 7. Entozou. — The Entozoa met with in the human liver are hydatids or acephalocysts ; they are inclosed in a fibrous cyst and are con- tained in a single parent hydatid vesicle. The internal surface of the vesicle is soft and often pulpy, and covered by minute hydatids which are adherent to its sides. Besides these the parent vesicle is usually filled with a great number of smaller vesicles of variable size. The hydatid cyst generally occupies the right lobe of the liver and increases to a prodigious size, producing absorption of the structure of the organ, and forming adhesions with the neighbouring viscera. The existence of ace- phalocysts may sometimes be detected during life by the presence of a large tumour in the region of the liver, which forms a projection of the abdominal parietes, is soft and yielding to examination by the hand, and unaccompanied with symptoms denoting cancerous disease. Occasionally the cyst is hardened by deposits of cartilaginous or bony plates. Contracting adhesions with surrounding parts, the hydatid cyst has discharged its contents externally through the abdominal parietes ; more fre- quently, however, it opens into the alimentary canal, as into the stomach or colon. Occa- sionally it bursts into the cavity of the abdo- men, and in one case opened into the lungs, and many of the smaller hydatid sacs were ejected by coughing. Some small cysts have sometimes been ob- served in the liver containing a calcareous deposit, mingled with membranous substance resembling fragments of hydatid sacs. These cysts are supposed to result from the spon- taneous cure of acephalocysts. Small intestinal worms have now and then been found in the biliary ducts; these are imagined to have gained admission into those tubes from the duodenum through the ductus communis choledochus. Bibliography. — Normal anatomy. — Bianchi, Historia hepatica, Taurin. 1616, 4to. 1710, 8vo. Cortesius, De hepate, 1630. Rolfinhius, Dissertalio de hepate, &c. Jena, 1653. Glisson, Anatomia hepatis, London, 1654. Sylvius de la Boe, De bile et hepatis usu, Lugd. Bat. 1660. Malpighi, De viscerum structure, Bologna, 1666, Lond. 1699. Bidloo, Anatomia corp. humani, Amstel. 1685. Hoffmann, De vena portae, Altnorf, 1687. Revcr- horst, De motu bilis circular!, Lugd. Bat. 1692. Stahl, De vena portae, porta malorum, Halle, 1698. 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Utendorfer, Experimenta nonnulla et ob- servations de bile, Argentorat. 1774. Ambodick, De hepate, Strasbourg, 1775. Lobstein, Reply to Ambodick's diss, de hepate, Argentorat, 1775. Walter, Observationes anatomicae, 1775. Sabatier, Traite d'anatomie, Paris, 1781. Van der Leuw, De bilis indole ejusque in chyliticatione utilitate, Groning. 1783. Goldwitz, Neue versuche zu einer wahren physiologie der Galle, Bamberg, 1785. Walter, De structure hepatis et vesicula; felleae, Annot. Acad. Berlin, 1786. De polyp, uteri et hepate, Berlin, 1787. Richter, Expl. circa bilis naturam, Erlangen, 1788. Bleuland, Icon hepatis foetus octimestris, 1789. Thilow, De vasis bilem ex receptaculo ad renes ferentibus. Ploucquet, Reply to Bolley, exp. circa vim bilis chylific. Tubingen, 1792. Saunders, A treatise on the struc- ture, &c. of the liver, bile, and biliary ooncretions, Lond. 1793. Soemmering, De corporis humani fa- brica, vol. vi. 1794. Niemeyer, Comment, de cora- mercio inter animi patheinat. hepar bilemque, &c. Gottingen, 1795. Murray, Reply to Froelich, de- lineatio sciagraphica venae portae, Upsal, 1796. Metzger, Anatomia hepat. comparatae specimen, Regiom. 1796. Domling, 1st die Leber Reinigungs- organ ? Vienna, 1798. Bichat, Anatomie descrip- tive, Paris, 1801. Portal, Cours d'anatomie me- dicate, Paris, 1803. Huculieu, Descript. anat. syst. ven. port. &c. Francfort, 1810. Schumann, Diss, de hepatis in foetu magnitud. caus. ejusd. functioni, Vretisl. 1817. Mappes, Dissert, de peni- tiori hepatis humani structure, Tubingen, 1817. Bermann, Diss, de struct, hepatis ven. port. 1818. Felici, Osservaz. fisiologich. sopra le funzioni della milza, vena portae, del fegato, &c. Milan, 1818. Walther, Diss, de psychica hepatis dignitate, Halle, 1818. Bichat, Anatomie generale, Paris, 1818. Mascagni, Prodromo della grande anatomia, Firenze, 1819. Beltz, Quasdam de hepatis digni- tate, Berlin, 1822. J. F. Meckel, Manuel d'ana- tomie, generale, descriptive, et pathologique. Translation by Jourdain and Breschet, 1825. Dic- tionnaire de Medecine, art. Foie, 1828. Autenrieth, Ueber die Rindsubstanz der Leber. In Reil's Archiv. vol. vii. Roose, Physiol, untersuch. 1st Galle im Blute ? Wolf, De vesiculae pellea? hu- manae ductus, &c. In Act. Acad. Petrop. vol. iii. Plainer, Super vtilgari doct. de funct, hepat. &c. Quaestiones Physiol, vol. ii. Mutter, De glandularum secernent, struct, penit. Berlin, 1830. Voisin, Nouvel aper9u sur la physiologie du foie et ANIMAL LUMINOUSNESS. 197 sur l'usage dela bile, Paris, 1833. Kiernan, Phi- losophical Trans. 1833. Cruveilhier, Anatomie de- scriptive, Paris, 1834. Burdach, Physiologie ; translation by Jourdan, Paris, 1838. Morbid anatomy. — Fernelius, Medicina anatomia pathology. &c.Paris,1554. Kulbel,Diss.de hepatitide, Erford, 1718. Fischer, Reply to Kulbel in Halleri disp. patholog. vol. v. Kaltschmied, De vulnere hepatis curato cum disquisitione de lethalit. vul- nerum hepatis, Jena, 1735, et Haller, Disp. chi- rurg. vol. v. Wainwright, Anatomical treatise on the liver, with diseases, &c. Lond. 1737. Jacconi, De quibusdam hepatis, &c. affect. Bonon. 1740. Teichmeyer, De calculis biliariis, Jena, 1742. Hal- ler, Disp. patholog. vol. iii. White, Essay on dis- eases of the bile, York, 1771. Lysons, Practical essays upon intermitting fevers, dropsies, diseases of the liver, &c. Bath, 1772. Crawford, On the nature, cause, and cure of a disease incident to the liver, &c. Lond. 1772. Thienillier, Ergo dubio hepatis in abscessu permittanda incidendi loci per- forate, Paris, 1744. Haller, Disp. Chir. vol. iv. Coe, A treatise on biliary concretions, &c. Lond. 1757. Conradi, Experimenta cum calc. vesic. fell, human. Jena, 1775. Haase, Reply to J. S. Lie- berkiihn, de abscessibus hepatis, Lips. 1776. Schroeter, Commentatio de phthisi hepatica, Got- tingen, 1783. Mathews, Observations on hepatic diseases incidental to Europeans in the Eastlndies, Lond. 1783. Frank, De Iarvis morborum biliosis, Gottingen, 1784. Weissenborn, Von den Eiter- geschwuren der leber durch einen merkwurdigen Fall erlautet, Erfurt, 1786. Andree, On bilious dis- eases, &c. Lond. 1788. Goldwitz, Neue Versuche ueber die pathologic der Galle, Bamberg, 1789. Leake, A practical essay on diseases of the viscera, Lond. 1792. Saunders, A treatise on the structure of the liver, bile, and biliary concretions, Lond. 1793. Soemmering, De concromentis biliariis cor- poris humani, Francfort, 1795. Baillie, Morbid anatomy of the human body, Lond. 1797. Gibson, A treatise on bilious diseases, indigestion, &c. Lond. 1799. Powel, Observations on the bile and its diseases, Lond. 1801. Schwarze, Diss, de sym- path. inter cerebrum et hepate, Lips. 1811. Farre, Morbid anatomy of the liver, Lond. 1812. Portal, Observations stir la nature et le traitement des maladies du foie, Paris, 1813. Ballingall, Pract. obs. on fever, dysentery, and liver complaints as they occur amongst European troops in India, Edinburg, 1818. Mahlendorf, De ictero, Berlin, 1818. Mills, Enquiry into the effects produced on the brain, lungs, &c. by diseases of the liver, Lond. 1819. Thilenius, Ueber Leberentzundung und ibre Behandlung, &c. Hufeland's Journal, vol. xviii. Ackermann, Von Entzundung der Leber und deren Endigung in Vcreiterung, Ackermann's Bemerkungen, vol. vi. Vater, Reply to Schimmer, De calculi in vesicula fellea generatione ; in Haller Disp. Path. vol. vii. Betxold, De cholelitho ; in Haller Disp. Path. vol. iii. Haller, De calculis felleis, Opusc. Path. Morgagni, De calculis felleis, in Opusc. Misc. Percimil, On a new means of de- composing gall-stones. Beitrag, Zur Geschicte der Gallensteine vonEisfeld ; in Isenflamms und Rosen- m'ullers Beytrag, vol. i. Pemberton, A practical treatise on the diseases of the abdominal viscera, Lond. Chestons, Pathological enquiries; abscess in the liver. Poutcau, Des ulceres de la foie a la suite de blessures de la tete, CEuvres, vol. ii. L'offlcr, Ueber die Leberentzundung bei Schwangern und Wochnerinnen. Bichat, Anatomie patho- logique, par Beclard, Paris, 1825. Hope, Princi- ples and illustrations of morbid anatomy, &c. Lond. 1834. Mayo, Outlines of human pathology, 1836. Carswell, Pathological Anatomy. Cruveil- hier, Anatomie pathologique du corps humain.* ( W. J. Erasmus Wilson.) * [See also Dr. Bright's admirable paper on Abdominal Tumours and Intumescence, in Guy's Hosp. Reports, No, xi. — liD.] LUMINOUSNESS, ANIMAL. (Phos- phorescence.) An evolution of light from the bodies of living animals, independent of the re- flection of incident light. The animals which possess the property of thus emitting light are almost entirely inverte- brate, and chiefly marine. We have accounts from several naturalists of certain fishes having been seen to give out light while in their native element, and some have conjectured, — but on insufficient grounds, — that all fishes do so. The turtle and a species of toad inhabiting Surinam have been reported to have the same property ; and the eyes of some carnivorous mammals appear to emit flashes of light. But we find this function constantly and distinctly mani- fested only by certain mollusca, insects, crabs, annelida, acalephae, and zoophytes. These are the following : — Mollusca Pholas dactylus Sulpa zonaria telcsii, fyc. Pyrosoma atlanticum giganteum, 4'c- Crustacea Cyclops brevicornis Gummarus pulex Cancer J'u/gens, fyc. Scyllurus ? Insecta Lampyvis noctiluca splendidula italica ignita phosphorea nitidula lucida hemiptera japonica Eluter noctilucus Ignitus phosphoreus lampadion retrospiciens lacidulus lucernula speculator janus pyrophanus luminosus lucens extinct us cucujus lucifer Jiupcstris oceltata Chiroscelis bifencstratu Scarabtcus phosphoricus Pausus sphoerocerus Fulgora laternaria* serrutti * Doubtshave beenexpressed by several observers with regard to the luminousncss of this insect. In travelling in the countries of South America where it occurs, they have never seen it shine •, but the testimony of other naturalists is so decided in favour of it being luminous, that we are constrained to suppose that the animal may give out light in certain seasons of the year and not in others. There can be no doubt, at least, that its congeners above- named are truly luminous. 198 ANIMAL LUMINOUSNESS. Fulgora pyrrhor-hyncus candeluria Pyralis minor Acheta gryllotalpa ? Mvri A POD A Scolopendra electrica phosphorea morsitans J ul us ? Annelida Nei'eis phosphorous noctiluca cirrigera mucronata Planaria retusa Ecll 1 NODEUM ATA Aster ias ? Ophiura telactes phosphorea Ac a lephm. Almost all the species of Medusa, Beroe, Physalia, Rhizophora, Stephanomia, and Physophora. Zoophyta Pennatula phosphorea grisea rubra urgentia Infusoria. Many species belonging to the genera Cercaria, Volvox, Vibrio, Trichoda, Lincophaa. With regard to fishes, the statements of naturalists are so contradictory that we still hesitate to admit any of them on the list of truly luminous animals. The sharks, more fre- quently than other fishes, are reported as lumi- nous. The light given out by them is said to proceed from their abdominal surface. When large shoals of fishes are swimming rapidly, flashes of light, broad and deep, are sometimes seen about them and are supposed to be emitted by the fishes themselves. These appear occasionally at very great depths. They have been traced in the British seas to shoals of herrings and the coal-fish ; and Dr. M'Culloch enumerates also the pollack, the pilchard, the sardine, the whiting, the mackarel, and the gar, as being sometimes accompanied by these lights* The common earth-worm is not included in the above list, although several observers have reported it as luminous, because the fact of its being so is not sufficiently determined. It is said to give out light only during the period of propagation. Some voyagers, as Peron, have stated that they have seen sertularia, gorgonice, alcyonia, and sponges give out light immediately after being dredged from the bottom of the sea ; but we sus- pect that in most of these instances the light proceeded not from the zoophytes, but from some li£;ht-givingannelidsparasiticalupon them. This is frequently met with in the British seas. II. Characters and properties of animal light. — It is only in its most obvious qualities that animal light has hitherto been the object of scientific research. In colour and intensity it varies very much at different times in the same animal, and still more in different animals. * Edin. Encycl. art. Phuxjpliorescen.ee. With regard to colour the following varieties occur. In pholas dactylus the light is bluish- white ; in lumpyris noctiluca it is greenish with a shade of blue ; in I. italica, bright blue; in Plater noctilucus, brilliant green, with spots of " the most beautiful golden blue ;" in Fulgora pyrrhorynchus, deep purple and scarlet; in marine animals generally it is white with various shades of blue. Doubtless these differences depend chiefly upon the various colours of the integuments through which the light is seen. In lumpyris italica, there are alternate emis- sions and extinctions of the light, which take place with some degree of regularity and seem to be synchronous with the pulses of the cir- culating current, visible in the wing-cases of this beetle.* The fire-fly ( Plater ) shews two kinds of light; one constant, like that of the glow-worm, but more feeble ; the other a vivid white light suddenly intermitted. Its illuminating power seems to be greater than that possessed by any other animal ; the light emitted from its two thoracic tubercles is so great that the smallest print may be read with it ; and in the West Indies, (particularly in St. Domingo, where they are abundant,) the natives use them in- stead of candles in their houses. They also tie them to their feet and heads in travelling at night to give light to their path through the forest. The intermitting of the light in this insect is such as to give an observer the idea of a membranous veil being suddenly drawn over the source of light, and then as suddenly with- drawn. In a species of cancer seen by Smith in the Gulf of Guinea, the light (which seemed to be emitted by the brain) was of a deep blue colour when the animal was at rest ; but when it moved, bright coruscations of silvery light were darted from it in all directions. The light of some centipedes inhabiting the islands of the Pacific is of a beautiful emerald-green colour. It is connected with a mucous matter covering the animal, which may be rubbed off by the fingers, and communicates to them a smell not unlike that of muriatic acid. Sometimes the light proceeding from the sea is so white and dull as to give the effect of a sea of milk. This is frequently seen in the Gulf of Guinea, and seems to be caused some- times by the presence of numerous Salpa and Scyllari, at other times by the admixture of the debris of fishes and other marine animals re- cently dead. An extraordinary series of phenomena con- nected with a particular display of the luini- nousness of the sea, is reported by Mr. Hen- derson as having occurred in the Atlantic, (lat. 2° long. 21° 20' W.) on the 5th March, 1821. About 9 p.m. the sea appeared unusu- ally luminous. Every person who kept his eye fixed upon it for but a short time was immedi- ately affected with giddiness, headache, pain in the eyeballs, and slight sickness. Although these symptoms varied in intensity amongst the * A species of lumpyris lately found in New Hol- land is said also to slime in rhythmical pulses. Isis, vol. ii. p. 245. ANIMAL LUMINOUSNESS. 199 spectators, yet there was not one on board who did not feel some degree of them ; and all im- puted them to the effect of the light proceeding from the surface of the ocean. Mr. Henderson remarks : " For my own part, the headach, &c. which followed immediately my looking at the water, was particularly severe, nor did it go off until morning. The effects I experienced were like those produced by smoking too much tobacco."* There have been recorded some accounts of very intense light produced over a great extent of the ocean's surface by luminous animals, but it does not appear that any other voyagers have experienced physical effects from the light such as are described by Mr. Henderson. The great intensity with which it is occasionally produced by marine animals, however, is well illustrated by the descriptions that are given of the moral emotions with which it inspires the beholders. Witness, for instance, Mr. Bonnycastle's descrip- tion of a scene which he met with in the Gulf of St. Lawrence, (7th Sept. 1826.) While it was very dark, a brilliant light, like that of the Aurora, was seen to shoot suddenly from the sea, in a particular quarter. It spread thence over the whole surface of the water between the two shores of the Gulf; and shortly there was pre- sented " one blazing sheet of awful and most brilliant light." " Long tortuous lines of light showed many large fishes darting about as if in consternation at the scene." The light was suf- ficient to enable one to see the most minute objects on the ship's deck. On drawing up a bucketful of the water, and stirring it with the hand, it presented " one mass of light, not in sparkles as usual, but in actual coruscations."t Messrs. Quoy and Gaimard state that in handling luminous marine animals while alive, they have always been sensible of an odour pro- ceeding from them similar to that which is per- ceived around a highly charged electrical appa- ratus. The only observation with which we are ac- quainted that seems to indicate the evolution of heat in connexion with the light of animals, is that reported by Macartney, who states that he found the thermometer raised by two or three degrees when placed in contact with a group of living glow-worms shining, or even with their light-giving sacs cut off. The repetition of this experiment, however, has not produced the same result in the hands of others : they saw no rise of the thermometer. III. Circumstances in which light is given out, and by which its intensity is affected. — It is not known whether there be any lumi- nous animals that give out light in all circum- stances, and at every period of their existence, in their natural situations. So far as observa- tion extends, certain mollusca, and some of the species of elater appear to shine without inter- mission. But most of the other light-giving animals with which we are acquainted use their peculiar function only occasionally, and that, for the most part, under some kind of excite- ment or irritation, natural or artificial. In the absence of more direct means of investigation, we may, perhaps, attain to some measure of acquaintance with the nature and analogies of animal light by inquiring into those sources of irritation under which it is given out. Here, however, we are met by the difficulty of finding contradictory statements of facts made by dif- ferent observers. So that our exact knowledge on the subject is still insufficient to admit of any satisfactory conclusions being drawn. What is known on this point may be conveni- ently considered under the two following heads. I. Circumstances essentially connected with the state of nature in which the animals are placed when they give out light. II. Circumstances artificially produced af- fecting the emission of light. I. Natural circumstances in which light is emitted by living animals. The luminousness of animals in their natural state is affected by, 1. Changes in the state of the medium in which they live, whether air or water, in regard to its temperature and electricity. 2. By solar light. 3. By abrupt collision with other bodies. 4. By loud noises. 5. By the internal move- ments of the animals themselves, amongst which may be included the exercise of the ani- mal's will. 1. Temperature, &,c. — By far the greater number of luminous animals with which we are acquainted are natives of warm climates ; but those inhabiting the ocean are seen in almost all latitudes, even in the coldest ; al- though in these they are not so numerous, and give less light. No aerial insects give out light, in ordinary circumstances, excepting at a temperature of about 50° Fahr. and upwards ; and the higher the natural temperature, the blighter is the light emitted. In temperate climates the Lampyrida shine only in summer and autumn. L. noctiluca appears in this country between June and Sep- tember; L. splendidula, in Germany, is lumi- nous in May ; and L. hemiptera so early as in the end of April. The light of pholas dactylus is strongest in summer; and that of marine animals in ge- neral is increased before storms. 2. Solur light. — Tt is said that Scolopendra does not shine at night excepting it has been exposed during the day to solar light. A short time of exposure to the sun's rays seems to be sufficient to refresh its luminous power, as (like all other light-giving animals) it secretes itself as much as possible during the day. It is stated by Burmeister,* with regard to the Lam- pyris Italica, that if it be kept some days in the dark it entirely loses its luminousness, but regains it on being again placed in the sunshine. 3. Lunar light. — Macartney remarked that luminous medusa generally retreat from the surface of the water at moon-rise. 4. Abrupt collision with other bodies. — Marine luminous animals very readily emi their light on being struck by any moving body; so that one of the most commonly observed phenomena connected with this subject is the * Trans. Med. and Thys. Soc. of Calcutta, i. 107. * Manual of Entomology, transl. by Shuckhard, t Trans, of Lit. and Hist. Soc. of Quebec. p. 494. 200 ANIMAL LUMINOUSNESS. sparkling of the minute medusa and other animals, swimming on the surface of the sea, when they are dashed against the sides of a ship, struck by an oar, or tossed on the foamy crests of the waves ; and this even while no other light is seen excepting just at the points where the water is agitated. In experimenting with Medusa', Macartney found that, when kept in a glass vessel in a state of perfect rest, they gave out no light, but that, on the slightest movement of the vessel, a brilliant flash was emitted, which was brightest when the animals swam near the surface. Macculloch remarks, " Very often we have found the water crowded, even with the largest medusa, yet scarcely be- traying themselves by an occasional twinkle, when the dash of an oar or any accidental agi- tation was sufficient to involve the whole water in a blaze of light." 5. Loud noises. — When any loud noise is made near a luminous insect while shining, it frequently ceases to give out its light. 6. Internal movements of the animals them- selves—will, &,x. — With regard to insects, we have many concurrent testimonies to the fact that more light is emitted during the season of procreation by most of the species than at other times. So strikingly is this the case in the Lam- pyrides, that the light given out by the female has been generally regarded, (although without sufficient reasons,) as destined only to attract the attention of her mate. After the eggs are deposited, the light gradually decreases in in- tensity. W hile it is obvious that, for the most part, the emission of light is altogether independent of any voluntary effort on the part of the animal itself, yet it appears probable that, through some means or other, the animal has the power of varying the intensity of the light at pleasure. We cannot, for instance, imagine that sound can have any direct effect on the light-giving organs themselves, so as to cause them to shine less brightly when loud noises are made near them. Such effect must be communicated through the animal's sensorium. It is sup- posed by some physiologists that variations in the intensity of the light given out by insects depend on the quantities of air admitted through the trachea? in respiration, over which quantities the animal's will seems to exercise some con- trol. In observing the luminousness of the elater, Spix concluded that this control is so pei feet, as to admit of the light being wholly extinguished by the animal's preventing the ad- mission of air ; and this view is adopted also by Treviranus. These changes, however, are explained by others, (as by Miiller and Mur- ray,) by supposing that, when the light seems to fi de, the organs are merely withdrawn be- hind opaque parts, or, as it were, veiled by a curtain. In general the light is increased when the animal is in motion; and in insects, parti- cularly during flight. Macartney observed of the beroe, that when it swam slowly near the surface of the water, its whole body became occasionally illuminated in a slight degree ; but that, during its contractions, a stronger light issued from the ribs, and that when a sudden shock was communicated to the water in which it was swimming, a vivid flash was given out. That the luminous function is in many ani- mals directly under the control of their will, seems to be proved by the fact, that while - under any sudden irritation calculated to alarm them, they, at first, emit light strongly, yet on the frequent repetition or continuance of the same kind of irritation, they extinguish their light, and cannot be excited to shew it again for a considerable time. II. Artificial circumstances in which light is emitted by living animals, or by which the emission of it is affected. Light-giving animals being removed from their natural situations, and subjected to arti- ficial processes and agents, are found to have their luminousness affected by being exposed to, 1. the effects of accumulated electricity and electrical currents ; 2. immersion in va- rious fluid and gaseous media; 3. pressure of their bodies; 4. removal of their luminous organs, and mutilation of these and of other organs ; 5. exposure to various degrees of heat and moisture; 6. immersion in vacuo ; 7. re- moval from all foreign sources of light. 1 . The effects of accumulated electricity and electrical currents. In experimenting on ma- rine luminous animals, Macartney passed a shock through water in which they were swim- ming; immediately their light was extinguished for an instant, but afterwards became brighter than before. In reporting the result of a si- milar experiment, Humboldt merely says that the luminousness of the animals was increased after the shock. Macaire subjected glow- worms to the action of galvanism, and found that when one wire was forced through the body of the insect as far as the luminous organs, while the other was applied to the sur- face slightly moistened, the light became bril- liant. One galvanic pole prod uced no effect ; but when insects not shining at the time were placed in a galvanic circle they always began to give out light. This result was not ob- tained in vacuo, but whenever the air was admitted, the light reappeared. No effect what- ever seemed to be produced by common elec- tricity, howsoever applied. 2. Immersion in various fluid and gaseous media. — Luminous marine animals, when re- moved from their native element, and plunged into fresh water, give out their light for a time more vividly and more steadily, but afterwards it gradually fades and becomes extinct. Mineral and vegetable acids, alcohol, potassa, and solu- tions of corrosive sublimate, and the salts, all produce nearly the same effect ; only that by these the light-giving property is more speedily destroyed. Observers differ in their accounts of the effects produced by immersion in va- rious gases. Most of those who have experi- mented in this way have seen the light of the glow-worm very rapidly extinguished in hy- drogen gas; also in sulphuretted and car- buretted hydrogen, carbonic acid, chlorine and nitrogen gases; but Sir II. Davy found that hydrogen gas produced little or no change in the state of the light; the same was the result of Murray's experiments, who also found ANIMAL LUMINOUSNESS. 201 the glow-worm continue to shine in carbonic acid gas. Immersion in oils of all kinds de- stroys the light-giving property in most of the insects endowed with it ; but in Lampyris italica, Carradori found that the light conti- nued to be emitted when the luminous part of the body was plunged into oil. 3. Pressure of their bodies. — It has been observed that shortly after the death of the in- sect, the light-giving organs of elater emit light freely when the body is bruised, and in general mechanical irritations of all kinds cause a cer- tain degree of increase in the intensity of the light given out. Some animals, as pennatula, seem to emit their light rarely, excepting in such circumstances. 4. Removal of the luminous organs, and mu- tilation of these and of other organs. — The luminous organs may be cut out from the bodies of glow-worms and fire-flies without the peculiar property of the organs being imme- diately destroyed. The emission of light can for some time be re-excited by slight me- chanical irritations ; as by touching the organs with the point of a pin. Those of the glow- worm have been seen to shine for two or three days after excision, when slightly moistened with water, heated or electrified. In experi- menting on the same insect, Todd found that the light was extinguished within six minutes after the head was cut off ; as also when the luminous rings were cut into, but was renew- able by the application of heat. Sheppard removed the luminous matter from a glow- worm ; the wounds healed within two days, and the body became again filled with new light-giving substance.* 5. Exposure to various degrees of heat and moisture. — Light-giving insects in general do not shine at any temperature below that of 53° Fahr. Macaire took some glow-worms that had been kept for some time at a tem- perature of 50° Fahr., plunged them into water at 5.5°, and gradually raised the temperature. Light was emitted for the first time at 77°, and increased in intensity until the water was at 105°. At this temperature the animals died, but the light continued until the temperature had reached 134° .5, when it wholly disap- peared. When glow-worms are thrown alive into water heated to 110° and upwards, they die instantly, but at the moment emit a brilliant light. When they are exposed to an artificial cold suddenly, they perish at any degree below the freezing point of water; but the light may be partially restored by a temperature of 70 , although the animals shew no other sign of vitality. When the insects are dried artificially, the light is extinguished, but it may be restored by their being again moistened. 6. Immersion in vacuo. — When glow-worms are placed in vacuo, their light fades, but re- appears on admission of air. 7. Removal from all foreign sources of light. — If luminous insects be confined in a dark place, they shine little in the early part of the day, but long before night they begin to do so ; * Kirby and Spence's Entomology, ii. 426. although generally, in their native situations, they do not emit light until the twilight. If the confinement in a dark place be protracted, they do not shine so brightly as after having seen the sun during the day. IV. Seat of luminousness in different animals. — In most of the luminous animals that inhabit the ocean, a great part of their surface seems to be endowed with the property of forming, and pouring out, a mucous fluid, which contains the luminous matter, and is frequently mis- cible with water and other fluids. This some- times so entirely covers the whole animal as to cause it to emit light from every point of its surface ; but more generally when the animal is swimming, the light is seen to proceed only from certain regions. Some of the medusa, even of the largest size, emit light from a very small point, particularly when the luminous organ is placed in the central parts of the body. When the light is vivid, it seems to be larger than it really is, from the refracting power of the gelatinous tissues through which it passes. Occasionally the luminous point has not a diameter equal to the l-200th of that of the animal itself. In cydippe pileus and Oceania pileata of the Baltic, Ehrenberg finds that the light issues solely from the vicinity of the ovaries, and in Oceania hemispherica, from the bases of the cirri. Pholas dactylus gives out light most strongly from the internal surface of its respiratory tubes. The luminous mucus is sometimes poured out even by very small animals in such quantity as to leave a lumi- nous wake behind them, as in an instance mentioned by Quoy and Gaimard. These ob- servers saw such luminous lines formed in the paths of certain extremely small creatures, so transparent that their forms could not be dis- tinctly made out. The positions of their bodies were marked in the water by bright spots, which were followed in their course by lumi- nous wakes, at first about an inch In breadth, but afterwards by the movements of the water spread out to the breadth of two or three inches. This luminous mucus is supposed to be the seat also of the remarkable stinging property possessed by many of the acalepha. It retains its luminousness in some instances for a day or two after being emitted by the animal, but loses it whenever putrefaction commences. But although this luminous mucus be so ge- nerally secreted and emitted by marine ani- mals, it is evident that the light given out by many of them has its seat in certain organs more or less internal, whence it proceeds in gleams and momentary flashes that seem to depend only on the movements of some im- ponderable agent. The exact position and re- lations of these organs can seldom be satis- factorily discovered, but in some crabs and mi- nute crustaceous animals that emit light, it is observed to proceed from the central organs of the nervous system. In other Crustacea the whole body seems to be full of light, which is emitted, as at so many windows, through the translucent membranes interposed between the segments of the crust. Dr. Macculloch con- 202 ANIMAL LUMINOUSNESS. eludes from his numerous observations on this subject, that, in marine animals generally, the coats of the stomach and intestines are the light-giving organs. In insects the seat of luminousness is more satisfactorily ascertained, and is found to vary very much in different species and tribes. The eggs of the Uimpyrides are said to be fre- quently seen luminous, and to continue so for several days after being deposited. In the states of larva and chrysalis also, the same in- sects emit light most vividly when touched, chiefly from the posterior segments of the body. On being much irritated, the whole of the chrysalis seems to shine in a slight degree, and for a short time. In the perfect female glow-worm of this country, the light is emitted chiefly from the inferior and lateral surfaces of the two or three last segments of the abdomen. The male of the same species presents only two small luminous points on the sides of one of the segments. When the light-giving surfaces of the female lampyris noctiluca are narrowly examined, it may be seen that, on the penul- timate and antepenultimate segments, they pre- sent bands of a bright greenish-yellow light, which are abruptly terminated towards the trunk by an irregularly waved line ; and that from the rest of the same segments there issues a fainter light of a pale green colour. There is also a little light given out by the posterior extremity of the dorsal line. In L. italica, the two last segments are wholly and nearly equally luminous. Most of the glow-worms in displaying their light recurve their tails upon their backs, so as to bring their luminous surfaces into view. E/ater noctilucus gives out light principally from two points of the thorax, which are some- what raised, and of an oval shape; but it has also two light-giving organs situated beneath the wing-cases, which are not seen except when the insect is flying. Light is also emitted from the internal parts through the interstices between the abdominal segments. In bupestris octllata, the light is emitted from certain yellow spots upon the elytra : in scarabaus phosphoricus from the belly : in c/iiroscelis bifenestrata, (a New Holland insect) from two oval, hairy, reddish spots on its second ventral segment; while, in pausus spha- rococcus, a dim phosphoric light issues from its singular hollow globular antennae. Macartney says that he always observed the shining of scolopendra electrica to be accom- panied by the appearance of an effusion of a luminous fluid upon the surface of the animal, paticularly about the head. On touching this, his fingei and other bodies received on their surface a phosphoric light, which continued to shine for a few seconds, and then died away; and yet he could not see any actual moisture, even upon smooth glass, although examined immediately and attentively. The researches of Treviranus have led him to conclude that there is no special luminous organ in insects; but that the generally dif- fused fatty matter is the seat of the function, by which the luminousness is produced. He concludes, therefore, that, when the air has free access to the interior of the body through the respiratory tubes, the whole of the internal organs give out light; and that this is not seen, excepting at certain points of the surface, merely because the integuments are not trans- lucent. V. Anatomy of light-giving organs. — The accounts of examinations of these organs that have hitherto been published are rather imper- fect. This appears to be owing chiefly to the fact that the organs themselves are of very simple structure and furnish no materials for lengthened description. So much so are they in insects, that one would be inclined readily to conclude with Treviranus, that they are nothing but the common fatty or interstitial substance which fills up the bodies of insects, slightly modified by the presence of some phosphoric matter, were it not for the fact, particularly observed by Macartney, that, in the glow-worm, the luciferous organs are ab- sorbed after the season for their use is past, and their places supplied by the fatty sub- stance. The following are the results obtained by this naturalist and by Spix from their dis- sections of the glow-worm, the fire-fly, and the lantern-fly. In the glow-worm, there is spread over the internal surface of the segments of the abdo- men a yellowish substance of the consistence of paste, which is thickest in the middle of each segment, and terminates near each margin by a wavy outline. It is of a closer texture than the fatty matter, but otherwise resembles it. Besides this substance, the last segment is furnished internally, just beneath the most transparent part of its integument, with two small round bodies, lodged in depressions, which contain yellow matter of more close and homogeneous texture. Miiller and Murray describe these round bodies as " two small ovate sacs, composed of thready membranes, and filled with a soft yellow pasty matter." Under the microscope, they appeared to Macaire to be composed of numerous branching fila- ments, with minute granules adhering to them. It is from points of the surface corresponding to the situation of these round bodies that the light is most constantly and most brightly emitted. When dry, these luminous organs have somewhat of the appearance of gum. The dried matter is translucent and yellowish, becomes darker on being kept, and appears to be granular in its structure. Its specific gra- vity is a little greater than that of water. In the fire-fly, the internal concavities of the yellow spots of the corselet, whence the light proceeds, are filled with a soft yellow sub- stance, oval in shape, and of very uniform consistence and density. This, under the mi- croscope, appears to be formed of a large number of very minute parts or lobules, closely pressed together. Around these oval bodies, the fatty matter of the corselet is arranged in a radiated manner. Spix describes the same organs as " yellowish glandular masses, into which many branches of the trachea enter." ANIMAL LUMINOUSNESS. 203 In elater ignitus the masses of luminous sub- stance are extremely ii regular in their figure; they are situated close to the posterior angles of the corselet, and are more loose in their structure than the same parts in clator noctilucus. The luminous proboscis or snout of the Julgora is hollow, and has a free communica- tion with the external air by a narrow slit situated near the base of the organ. Its cavity is lined with a fine membrane, between which and the outer translucent corneous crust, there is interposed a soft tissue of a pale reddish colour, arranged in lines longitudinally, which is supposed to be the seat of luminousness in this insect. In several instances it has been found that the light-giving substance has continued to sh ine for a considerable time after being re- moved from the body of the insect. In such cases it has been observed that there appeared to be no diminution either in the weight or the bulk of the luminous organs, excepting what was obviously produced by evaporation of the fluids. VI. Geographical distribution of luminous animals. — In almost all seas, in every latitude from 60° S. to 80° N., have light-giving ani- mals been seen ; but they are more abundant, and shine with greater brilliancy, in the tropical than in the colder climates. In general, it is observed by voyagers, the luminous mollusca and acalepha? occur in greatest numbers not far from land ; and that they are particularly plen- tiful in the seas surrounding groups of small islands within the tropics. The luminous insects are met with chiefly in the warmer climates of the temperate zones and within the tropics. We are not aware of any having been met with beyond the latitude of 58°. VII. Theories of animal luminousness. — Very numerous have been the theories formed by philosophers with regard to the nature of the luminous matter which produces the phe- nomena now under review. From the facts stated above, it appears that we are not yet in a position to determine with certainty whether or not animal luminousness has its source in the operations of any agent already known. At least it appears to us that facts enough have been accumulated to set aside the assumption of most of the theories hitherto promulgated. The following are some of these. 1. That light is imbibed from the sun's rays by luminous animals and given out in the dark. (Beccaria, Mayer, &c.) 2. That the light is owing to a kind of com- bustion maintained by the oxygen of the air. (Spallanzani.) 3. That light is swallowed with the food, and disengaged by peculiar organs. (Brugna- telli.) 4. That the light-giving matter is composed of phosphorus and albumen ; and that the variations in the intensity of the light depend on the more or less complete coagulation of the albumen, by some internal means placed under the control of the animal's will. (Macaire.) 5. That a fluid containing phosphorus is secreted by the luminous organs, and shines on its being exposed to the oxygen of the air introduced by respiration. (Darwin, H. Davy, Heinrich, Treviranus, and Burmeister.) 6. That the luminous organs concentrate and modify the nervous influence so as to form it into light; so that, according to this theory, animal luminousness is an effect solely of vital power. (Macartney and Todd.) 7. Tiedemann thus expresses his opinion : " Animal luminousness would seem to depend on a matter, the product of the changes of composition accompanying life, and, to all ap- pearance, secreted from the mass of humours by particular organs. This liquid probably contains phosphorus or an analogous combus- tible substance, which combines with the oxy- gen of the air or of aerated water at a medium temperature, and thus produces the disengage- ment of light. The preparation and secretion of this substance are acts of life, which change, augment, or decrease by the influence of ex- ternal stimulants, whose action on the animals modifies their manifestations of life. But the phosphorescence itself depends on the com- position of the secreted matter and cannot be regarded as a vital act ; because, on certain occasions, it continues for whole days and even after the death of the animal." * This opinion seems to coincide pretty nearly with that of Darwin, Heinrich, and others, stated above (5) ; and we must admit that it ap- pears toharmonize the facts better than any of the other theories that have been propounded. But, while it seems satisfactorily to assimilate many of the phenomena to others more familiar to us, and more within the reach of our investigations, and thus appears to furnish future inquirers with a key to the elucidation of what yet re- mains obscure, it is obvious that it leaves some of the phenomena unexplained, and that se- veral of these seem to be quite irreconcilable with the theory of the phosphorescence being essentially dependent on the composition of secreted fluids. In some of the extremely delicate acalephtv, for instance, from which the brightest radiance is so frequently emitted in momentary fitful flashes, it is difficult to con- ceive why, if the light mainly depended on the nature of some matter poured out by cer- tain organs at the instant of the flash, the light should not continue for at least a few seconds. The circumstance of its doing so in some in- stances, and even mixing gradually with the surrounding sea-water, certainly proves that there is such a fluid as this theory supposes in certain animals ; but does not remove the dif- ficulty presented by the facts we have al- luded to. We feel ourselves constrained by these and other such facts to believe (with Macartney and Todd) that in many, perhaps in all, lumi- nous animals, both terrestrial and marine, the light emitted is the consequence of an evolu- * Comparative Physiology, translated by Drs. Gully and Lane, i. 2'70. 204 ANIMAL LUMINOUSNESS. tion of an imponderable agent by the nervous systems of the animals, just as the electrical fishes give their shock without the interposition of any visible or ponderable secretion. In this view we may regard the luminous organs as playing the same part in relation to the evo- lution of light as the electrical organs of the torpedo do to the production of the shock. The single fact of luminousness continuing in the organs or in their effused fluids, after they have been removed from the body of the ani- mal, seems to point to a great difference ex- isting between the two classes of phenomena which we have just compared, in certain ani- mals ; but it may be that the difference is more apparent than real ; for this fact may be explained by supposing that a phosphoric sub- stance really does enter into the composition of the light-giving organs; and yet we may with great probability conjecture that it is not the chief' agent in causing the phenomena of luminousness. It remains, then, for future in- quirers to determine the chemical composition of the luminous organs, and the fluids emitted by the animals, the phenomena of whose lu- minousness seem to be irreconcileable with the idea of their being dependent on the nature of these fluids ; if they be found to contain phosphoric matter, it may be concluded that, as this does not appear to be essential in them to the production of the phenomena of lu- minousness, so neither may it be in other ani- mals, in which it is believed to be the chief agent in the manifestation of their light-giving function. To this theory, (which is only a combination of the two most generally received in modern times,) we do not, in the facts which have come under our notice, see any serious objec- tion. The only argument adduced against Macartney's theory by Tiedemann and other physiologists, who have carefully considered the facts of the case, is founded on the circum- stance of the light continuing, in a certain degree, for some time after the death of the animals, which, of course, cannot be supposed to be owing to the continued operations of the nervous system. This posthumous light, how- ever, may depend on the phosphorescence of the luminous organs or their effused fluids in virtue of their composition, while the full evo- lution of light during life may be produced chiefly by the play of imponderable agents in and from the nervous system, independently, in some cases, of the chemistry of the fluids ; iu other cases, aided and modified by the nature of these and by the structure of peculiar organs. It is scarcely necessary to take particular notice of the various other theories that have been suggested, as the facts stated in the pre- ceding part of the article are sufficient to set them aside. VIII. Uses of animal luminousness. — We know nothing certainly with regard to the uses of the light-giving function ; but as almost all observers have remarked that male insects seem to be attracted towards their mates by the brilliancy of the light emitted by the latter, it has been generally supposed that the luminous- ness is subservient to the generative function. Although it may be so to a certain extent, it is obviously not essentially connected with it, even in the glow-worm ; for the light endures long after the season of love is past. Some have conjectured that the light may sometimes be the means of preserving its possessors from the destructive attacks of enemies. Thus Shep- pard observed a large beetle running round a shining scolopendra, as if wishing to attack it, but seeming to be scared by the light. We may imagine, also, that the light enables its possessors to see surrounding objects at night, and so to thread their way in safety through the darkest places. Considering that, in the ocean, there is abso- lute darkness at the depth of 800 or 1000 feet, at least that, at such depths, the light of the sun ceases to be transmitted, Macculloch has suggested* that, in marine animals, their lumi- nousness may be " a substitute for the light of the sun," and may be the means of enabling them to discover one another, as well as their prey. He remarks, " It seems to be parti- cularly brilliant in those inferior animals which, from their astonishing powers of reproduction, and from a state of feeling apparently little superior to that of vegetables, appear to have been in a great measure created for the supply and food of the more perfect kinds." IX. Luminousness of animals not innate, and other allied phenomena. — We have ac- counts of the surface of the human body ap- pearing luminous in consequence of phos- phoric matter being largely mixed with the sweat in the course of various diseases. The urine also both of men and several of the lower animals is occasionally luminous under similar circumstances. It is said that the urine of Viverra mephitis and V. putorius is al- ways so.f The eyes of human albinoes, almost all the mammalia which possess a tapetum lucidum, as also those of some birds of prey, serpents, and insects, seem to shine in a feeble light from the reflexion and concentration of the rays falling upon them from external objects. Pallas thought that this light was developed in the retina, and regarded it as an electrical phe- nomenon. But it has been plainly proved by Prevost, Gruithuisen, and Esser,! that the shining of the eye depends, in most cases, on reflexion of light. They found that there was no appearance of luminousness in absolute darkness; and that the eyes of dead animals gave the same effect as those of the living, when placed in similar circumstances.§ It would appear, however, from some obser- vations made by Rengger on the eyes of a certain South American ape, ( Nyctipithecus trivirgatus,) that there is reason to believe in * Edin. Encycl. art. " Phosphorescence." f Langsdorff, Reise. ii. 184. t Edin. New Phil. Jour. ii. 164. 6 See also Hessenstein, de Luce ex quortindam animal, oculis prodeunte, atque de Tapeto lucido. Jenas, 1836. LYMPHATIC AND LACTEAL SYSTEM. 205 the emission of light from the eyes of some animals, independently of the reflexion of in- cident light. The ape in question is nocturnal. The luminousness of the eye was seen by Rengger only when there was total darkness ; and then the light was so brilliant that objects at the distance of a foot and a half from the eye were distinctly seen.* In commenting on this statement by Rengger, Treviranus remarks,-!- "that the intensity of light may be increased by the brilliant tupetum of the eye, while it is concentrated as in a concave mirror, cannot be doubted. But it is impossible that a feeble light so concentrated should illuminate objects placed at the distance of a foot and a half from the eye of this ape, in a dark place." The same physiologist seems to be satisfied that some dogs also have a similar power of gene- rating light within their eyes. In these, he states, the light is seen only when an impres- sion on the sight or hearing arouses the ani- mal's attention, or when he is excited by the operation of some instinct or passion. We are, therefore, constrained to conclude that this subject is still open for elucidation by future inquirers. If it should be proved that some of the higher animals really do emit light from their eyes, independently of the in- cidence and reflexion of that from without, it will go far to render it probable that, in lumi- nous animals generally, the development of light depends more upon the movements of some imponderable agent in and from their nervous system, than upon the nature of the composition of the fluids poured out by the luminous organs. Another series of phenomena, intimately connected with, and illustrative of, those previ- ously considered, demands notice here, namely, the shining of fishes, and other animal bodies shortly after death. The luminousness of dead fishes is a very common subject of observation, but not on that account the less worthy of par- ticular attention. It has been ascertained that the light is given out from every part of the body, external and internal, that is exposed to the air ; and that on the surface of the luminous parts there is a slight moisture, or solution of the tissues of the animal, which can be scraped off, or diffused in water, and continues lumi- nous for a short time after being so removed. When pieces of the skin or muscle of a fish are placed in a little water, the luminousness appears only on the surface when the water is at rest; but whenever it is agitated the light is diffused through the whole body of water. In some fishes, as the whiting, this lumi- nousness appears within a very short time after death ; in others, not for some days ; but in all it ceases before the truly putrefactive process has commenced. It is observed that those fishes which most quickly putrefy, are also those which give out light the soonest. From the circumstance mentioned above, that this luminous fluid formed on the bodies of dead fishes is miscible with water, and re- * Rengger's Naturgesch. der Saugthiere von Paraguay, s. 383. t Biologie, i. 439. tains its luminousness for a short time after being so mixed, it has been concluded that the beautiful phenomenon of the phosphorescence of the sea may be frequently owing to the pre- sence, in great quantity, of the remains of fishes recently dead. It is certain that the most careful observers sometimes fail to detect any entire living animals in sea water taken up from a brilliantly luminous sea; and find only abundance of small fibres and shreds of what seem to be broken-down animal tissues. Pro- fessor Smith* concluded from his own obser- vations made in the Atlantic, that, while the bright sparkling light of the surface of the ocean is always emitted by living animals, that duller diffused luminousness, which is fre- quently seen over a vast extent of the sea, giving it the appearance of milk, is given out by "a dissolved slimy matter, which spreads its light like that proceeding from phosphorus.'' Under the most powerful microscope, Smith saw nothing in such water but " the most mi- nute glittering particles, having the appearance of solid spherules." Humboldt saw a great extent of the surface of the sea rendered almost gelatinous by the admixture of numbers of dead dagysa and medusa. It may, therefore, be regarded as probable, at least, that the luminousness of the ocean is sometimes caused by dead matter ; but it is certain that, in the great majority of instances, it is entirely owing to the presence of living animals, possessed of the light-giving property .-f In attempting to examine these, so as to deter- mine their forms and habits, it is important to keep in mind that they are sometimes ex- tremely small, so as to be distinguished with considerable difficulty, even with the aid of the best microscopes. And when they are larger, they are frequently so transparent as to elude notice. Bibliography.— Canton, Phil. Trans. 1769. 446. Macartney, Phil. Trans. 1810. 2. Spallah- xani, Mem. della Soc. Ital. vii. 271. Macaire, Mem. sur les Lampyres, in Jour, de Physique, xciii. 46. Humboldt, Reise i. 109. Todd, Jour- nal of Science, 1826. 241. Murray, Experimental researches, 1826. Kirby and Spence, Introd. to pii- tomol. ii. 256. Quoy and Gaimard, Ann. des Sc. Nat. iv. 1. Tiedenutnn, Comp. physiol. i. 257. Macculloch, Phosphorescence, in Edin. Encycl. xvi. 1823. Burmc'ister, Manual of entornol by Sltuch- hard, 494. Midler, Physiology, by Baly, vol. i. ed. 1, 1839. LUNG. — See Pulmonary Organs. LYMPHATIC AND LACTEAL SYS- TEM.— (Fr. Si/slime lymphatique ; Germ. Saugadersystem oder Lymphgef'dsssystem. * Tuckey's Voyage, 258. t Martin, Canton, Hulme, and others supposed the luminousness of the sea to be caused by a phos- phorescent oil, generated during the putrefaction of animals. Silberschlag regarded it as phosphoric. Mayer, Beccaria, Monti, Brugnatelli, and others, believed it to be owing to the giving out of light imbibed from the sun's rays. Bajon, Delaperriere, and Gentil imputed it to electrical agency, because it is excited by friction. Foster supposed it to be sometimes electric, and sometimes putrefactive. 206 • LYMPHATIC AND LACTEAL SYSTEM. Syn. Absorbent system.) — The lymphatic sys- tem is composed, in the first place, of the vessels which collect and convey the lymph from all parts of the body and the chyle from the intestines, and ultimately deposit them in the veins. Secondly, of the small fleshy bo- dies called conglobate, lymphatic, or absorbent glands, which are found connected with this system of vessels in various parts of their course. The lymphatic system is confined to the class Vertebrata. It is the least complicated in Fishes, and consists in them simply of pel- lucid valveless vessels. In Reptiles, also, it is composed of these vessels only, but which are armed with more or less perfect valves. In the two higher orders of Vertebrata, Birds and Mammalia, to the vessels containing very nu- merous and perfect valves, the conglobate glands are superadded : in all, however, the ter- mination of the system is in the veins, and its origin and general arrangements are probably in all essentially the same. The different parts of the lymphatic system had escaped the notice of anatomists until the middle of the sixteenth century, and the entire system was not discovered till the middle of the seventeenth. I must here except the lym- phatic glands, which from their large size must have been observed by the earliest anatomists, and we accordingly find them alluded to by Hippocrates, who classed them with the other glandular organs. The first isolated discovery in the vascular part of this system was made by Eustachiusin 1563, who saw and described accurately the thoracic duct in a horse. He called it the vena alba thoracis, and traced it downwards from the left subclavian vein to the lumbar ver- tebra3, where he noticed the dilatation now called the receptaculum chyli ; he however had no conception that it formed the trunk of a se- parate system of vessels, but conceived it. to be a vein of a peculiar kind. Fifty-nine years af- terwards, in the year 1622, Asellius was fortu- nate enough to discover the lacteal vessels on the mesentery of a dog ; and although on the following day he was much disappointed in not being able to see them in another dog in- spected for the purpose, by continuing his re- searches he soon convinced himself of their ex- istence in most animals. He also attributed to them their proper function, having remarked that whenever there was chyle in the intestines, these vessels also contained a white fluid, and could then only be seen. He failed, however, to connect the vena alba thoracis, the discovery of Eustachius, which had probably been for- gotten, with his own, and mistaking the lym- phatics of the under surface of the liver for the continuation of his vessels, was led into the error of supposing them to terminate in the liver. Asellius, who died in 1626, had not seen the lacteals in man, but inferred and as- serted their existence. According to Haller, Veslingius was the first who saw these vessels in the human subject, in the year 1634; but Breschet informs us, in his Systeme Lympha- tique, page 4, that, "en 1628, les lympha- tiques du m£sentere furent aperc, us pour la pre- miere fois chez l'homme. Peiresc, Senateur dAix, informe par Gassendi de la decouverte qu'avait faite Aselli, distribua plusieurs exem- plaires de l'ouvrage de ce proffesseur aux tne- decins de sa connoissance, et leurabandonna un criminel condamne a mort, pour verifier le fait sur son cadavre. On fit bien manger cet homme avant de le conduire au supplice, et une heure et demie apres sa mort, l'ouverture du bas ventre montra le mesentere tout cou- vert de vaisseaux lact, lymphatics laid open longitudinally to shea' the arrangement of the valves in their interiors. ( After Breschet.) The valves of the lymphatics resemble in their mode of formation and in their appear- ance the same structures in the veins ; they are however more frequent and more universal in the lymphatic system ; indeed, in the more per- fect animals they are found every where except in the incipient networks of this system. It has already been stated that in fishes and in some amphibious animals the lymphatic system is either entirely deficient in valves, or is only supplied with them in a partially developed state. The valve is composed of two semi- lunar flaps, so arranged that the reflux of the fluid within, forces them away from the sides of the vessel towards its centre, where the two flaps meet and completely close it, while the fluid passing in its proper direction * Professor Weber has described one of these hearts in a large serpent, the pithpn bivitatus. It measured nine lines in length, and four in breadth ; it had an external cellular, a middle muscular, and an internal serous tunic. See Phil. Trans 1833, Muller's Archiv. for 1835, and Valentin's Reper- torium, I5d. 1, p. 294. [Muller has subsequently described similar lymphatic hearts in the Chclonkm Reptiles. Archiv. 1840, p. 1-4.— Ed.] I> 210 LYMPHATIC AND LACTEAL SYSTEM. simply presses the flaps back against the sides of the vessel, and thus no obstruction is offered to its onward course. The flap of a valve con- sists of a fold of the inner coat of the vessel, which, where a valve is to be formed, ceases to Fig. 48. i a, b, and c, lymphatic vessels inverted, giving three different views of the valves formed by the lining membrane. (After Bresehet.) line the vessel, and is reflected towards its inte- rior ; having reached half-way across, it is doubled upon itself, and returns to the side of the vessel, which it continues to line as if it had never been interrupted. The two layers of this fold adhere very firmly togethei so as to form a very delicate transparent semilunar flap. It presents a convex attached, and a straight or slightly concave unattached edge; the former corresponds to a semilunar line on the interior of the vessel, the horns of which look towards the trunks of the system, where the lining mem- brane was reflected from and returned to the side of the vessel ; the latter to the line of doubling Fig. 49. a, a front view of a valvular flap, b, a profile view of a lymphatic vessel and valvular flap ; the lower half of the flap, or that nearest the base, is represented thicker than the rest. According to Lauth and Bresehet, this thicker portion is formed of all the coats of the vessels j the thinner portion, of the lining membrane only. ( From Bresehet.) of the membrane upon itself; thus a little pouch is formed between the flap and the side of the vessel, which can only be filled by the fluid passing in one direction ; and as a valve is constituted of two such pouches, when they are filled the vessel is completely closed. Some anatomists conceive that a lamina of fibrous tissue intervenes between the layers of the fold. Bresehet, in his " Systeme Lymphatique," adopts Lauth's view of the structure of the valve. He describes the flap of a valve as composed of two parts, one thicker and situated at the base of the fold, the other forming the rest of the flap more thin and delicate. It is this latter part which he conceives is formed by a doubling of the lining membrane only, while the thicker part, near the base, he has assured himself is produced by a prolongation which the fibrous coat sends inwards between the folds of the inner tunic. I have not been able to verify this description of the structure of the valve, but I have distinctly observed circular constrictions in the more bead-like lymphatics seen in the neighbourhood of some of the lymphatic glands, into the formation of which the fibrous coat does appear to enter. On laying open one of these vessels previously distended with quicksilver and dried, opposite the external constrictions, which were numerous, and not more than a line apart, valvular folds, differing from those hitherto described, were seen to project into the interior of the vessel ; they did not completely close its cavity, but left a circular or oval opening, through which the contents of the vessel might pass in either direction. These valvular constrictions re- sembled much the dried pyloric valve (fig. 50, B) ; and I am inclined to believe, from their thickness, that they contain circular fibres de- rived from the middle coat, by which during life they may be able to close their vessels as perfectly as the pyloric valve closes the com- munication between the stomach and duode- num. In very many places there occur two semilunar folds (Jig. 50, A), apparently formed of the lining membrane only, like the flaps of the ordinary valves, from which they differ, how- ever, in having their attached and unattached edges, as well as the flaps themselves, on the same plane, consequently not forming pouches, but a transverse though incomplete septum across the vessel. Each of these flaps extends only one-third across the vessel, and terminates by a crescentic edge, by which arrangement an elliptical opening is left in the central third of the vessel, between the two folds. This form of valve would appear to offer a partial obstruc- tion to the passage of the lymph in either direc- tion, as no provision is manifest by which these flaps would be made to fall against the sides of the vessel, either by the onward or retrograde course of its contents. I have frequently no- ticed a combination of the circular constriction with the semilunar flaps here described (fig. 50, C) , by which mechanism, supposing the former to be endowed with a vital contractility, the latter might be brought in contact, so as com- pletely to close the elliptical opening that would otherwise be left in the centre of the vessel. At the entrance of the lateral branches into the thoracic duct, or of one lymphatic into ano- ther, a valve will be found, of a somewhat diffe- rent form to those already described. It is com- posed oftwo semilunar flaps, seldom of equal size, arranged somewhat like the ilio-coecal valve. One flap is occasionally so slightly developed that there appears but one large semilunar fold at the entrance of the vessel. At the union of some of these vessels with others, especially of those which lie nearly parallel with each other, no valve will be found, but simply a defined curved line, marking the orifice of communica- tion. The valves in the lymphatic system are very closely set together. The distance be- tween them varies much. In vessels of a line LYMPHATIC AND LACTEAL SYSTEM. 211 Fig. 50. Exhibits three forms of valves of very frequent occur- rence in the lymphatics, especially in the neighbour- hood of glands, and which are not described in works on Anatomy. ( Taken from specimens pre- pared for the microscope.) Magnified ten diameters. A. a, the interior of the vessel. b, b, the valvular flaps composed of the lining membrane only. The attached, the unattached edges, as well as the surface of these flaps, are on the same plane ; they do not perfectly close the vessel. B. a, the interior of the vessel. 6, the valvu- lar flap of a circular form, resembling the dried pyloric valve of the stomach ; apparently com- posed of the fibrous as well as the inner tunic. C represents a combination of the two former. a, the interior of the vessel. 6. valvular flaps re- sembling those of A. c, a third fold resembling the circular fold of B. in diameter they are frequently not more tlian a line apart, while in others of half that magni- tude there may be an interval of an inch between them. It has been observed that they are more frequent and closer together in the larger lym- phatics than in the smaller; this is not always the case ; for instance, the lymphatics of the upper extremity, which are much smaller than those of the lower, have less intervals between their valves ; and in the neck, where the vessels are still smaller, the valves are less distant apart. It appears to me that the valves are much more approximated to each other in the neighbour- hood of the glands, and this observation applies to the vasa afferentia as well as to the vasa effe- rentia, but especially to the latter; from which circumstance the notion may have arisen, that the valves are more frequent the larger the vessel. The valves recur less frequently in the thoracic duct than in any other part of the system. It is not uncommon to find in this vessel an interval of two or three inches in extent without a valvular fold. Mode of origin of the lymphatics. — The plan I have hitherto adopted in describing the lymphatic vessels has been to present to the reader, first, that which is most readily understood, because easily recognizable by our senses, and about which there could be little difference of opinion ; but I have now to direct attention to a part of our subject which has hitherto baffled the efforts of all inquirers, viz. the mode of origin of the lymphatic vessels, concerning which the sight, aided by the most powerful glasses, has failed to supply us with satisfactory and demonstrable information. The numerous opinions and conjectures on this sub- ject, only present us with so many instances, of the vain struggles of the human mind, to ad- vance in a strict science of observation, beyond the limits assigned to our senses, and of the unwillingness, even in the philosopher and man of science, to acknowledge the weakness and limited range of his faculties. When we consider the transparency of the coats of the lymphatic vessels, as well as of their contents, the small size of their secondary branches, and the numerous valves they every where present, we cannot feel surprised that their precise origin should be involved in much obscurity. From the opaque natuie of the chyle, it might be imagined that while the vessels were distended with this fluid, the anatomist would be enabled to trace them to their commencing branches, but unfortunately, it is almost impossible to prevent the onward motion of the chyle in the vessels first re- ceiving it, while the valves offer a complete barrier to any retrograde movement. Added to which, the opacity of the coats of the intestine renders it extremely difficult to follow these vessels from the peritoneal surface of the outer, to the villous surface of the inner tunic, even when distended with chyle. Transparency of the coats of the intestine may be obtained by drying, but the chyle becomes transparent at the same time. Various modes of investigation have been adopted by anatomists to overcome these difficulties, the principal of which it may be necessary here to mention. Injections of quicksilver or coloured fluids have been thrown into the arteries, by which means the injection has occasionally made its appearance in the lymphatic vessels : this result occurs, accord- ing to Panizza, in a particular organ in an animal of one species, while in another the experiment will succeed, not in the same, but in some other organ. Thus he succeeded in filling the lymphatics from the arteries, in the intestines of the dog and pig; in the liver of man, the horse, and dog ; in the testicle of the dog and bull; in the penis and spleen of the horse. He was unsuccessful in the intestine? of man, the horse, birds, the salamander, and the tortoise ; in the liver of reptiles ; in the spleen of man, the dog, and the pig ; in the kidneys of mammalia and birds; in the penis of man and the dog. Breschet is of opinion that injections by the veins pass more readily into the lymphatic sys- tem. I have now in my possession two prepa- rations where the lymphatics have been acci- dentally injected from the veins ; one in the mesentery of the turtle, the other in the kidney of man ; and I have undoubtedly observed this occurrence much more frequently after in- p 2 212 LYMPHATIC AND LACTEAL SYSTEM. jections by the veins than by the arteries. Every anatomist who has had much experience in injecting the lymphatic vessels has been in- commoded by the injection passing unex- pectedly into some large vein, and on looking for the communication, he has found the veins from a lymphatic gland conveying the injection into one of the nearest large venous trunks. This has occurred to me frequently in the human subject, where the common iliac veins and the cava inferior have received the quick- silver from the veins of the neighbouring lymphatic glands. I have also seen the same occurrence lately in the horse, and have the specimen shewing the fact now in my museum. It was these veins conveying the injection from the lymphatics into the venous trunks, which Lippi mistook for the vasa efferentia of the glands, and which induced him to publish his work describing many terminations to the lymphatic system in mammalia, hitherto un- known to anatomists. This error was the more excusable, inasmuch as his opinion appeared to be confirmed on the investigation being pursued by himself and others in the remain- ing classes of vertebrate animals, where various communications do actually take place between the lymphatic trunks and the veins. Coloured fluids have been thrown into the ca- vity of the pleura and peritoneum in living ani- mals for the purpose of bringing the lymphatic vessels into view, and of tracing if possible their extreme branches after absorption had taken place. In this way it is said that minute vessels anastomosing with each other, and forming a delicate net-work, may be made apparent on the surface of the serous membrane, and that the trunks of the neighbouring lymphatics may be seen filled with the coloured fluid. In post- mortem examinations also, the absorbent vessels have been observed distended with a fluid of a yellow or red colour, where effusions of pus or blood had taken place during life. In all these instances we probably first notice the injection in the larger lymphatic vessels which are easily recognized by their numerous valves, and on tracing these back to their commencing branches we only discover an intricate net-work of mi- nute vessels apparently continuous with each other. It is exceedingly difficult to distin- guish these from equally small branches of artery and vein, filled probably with the same coloured injection. You look in vain for the channel by which the injection has entered these vessels ; no continuity of lymphatic with the minute twigs of the other sets of vessels can be detected ; no open orifice belonging to either can be distinguished. Many anatom- ists have endeavoured to fill the commencing branches of the lymphatic system by forcing the injection, thrown into them, in a retrograde direction, and in fishes where there are no valves, with the effect of shewing very nume- rous lymphatic vessels destitute of orifices, but not so universally distributed as has been imagined. Fohmann, Breschet, and others have simply made a puncture in the tissues, and by forcing quicksilver into the wound, have occasionally succeeded in fillingaminutenet-work of lympha- tics. Cruickshank and Hewson employed liga- tures to the thoracic duct, to the larger lympha- tics, or simply round the limb immediately pre- vious or subsequent to the death of the animal, for the purpose of distending the radicles of the system. Lastly, the microscope has been had recourse to by most observers. But the pre- vailing physiological opinions of the day have had more influence than all our anatomical in- vestigations in determining our notions of the mode of origin of the lymphatic vessels. In- deed, so much has this been the case, that I shall find it convenient, in treating the subject of the origin of these vessels, to refer to the physio- logical views of the periods during which the successive opinions have been broached. The only other observation I shall make on entering upon this difficult and still obscure subject is, that the chyle seen on the coats of the in- testine, contained in its proper vessels, so near to the villous tunic, has tempted anatomists to confine their observations perhaps too much to this one-absorbing surface, with the fixed intention of applying the information thus gained, to the whole system ; whereas the fluid contained in the chyliferous vessels differs so much from that of the rest of the system, that it is not very improbable that the former which admit particles of matter should possess ori- fices, while the latter should receive its con- tents by imbibition without perceptible orifices, which, in fact, is the opinion held by two emi- nent physiologists, who have paid considerable attention to the subject, Magendieand Cruveil- hier. The first opinion with respect to the mode of origin of the lymphatic, vessels which I shall consider is that by open orifices. Many investigators at various periods have attributed open orifices to the radicles of the lymphatic vessels; indeed, this has been the prevailing opinion till within the last few years. Asellius, the discoverer of that part of the system which is connected with the intes- tines, imagined that his " vasa lactea" com- menced by open mouths from the interior of the intestine. His words are, " ad intestina instar hiant spongiosis capitulis." The first dis- coverers of the rest of the system, the " vasa lymphatica," did not attribute to them the func- tion of absorption, but regarded them as destined to assist the veins in returning the circulating fluids to the heart. They supposed them, there- fore, to be continuous with those arteries whicli admitted a colourless fluid only, while the veins in a similar way received their contents from the arteries conveying the red blood. The lymphatics properly so called were not consi- dered to possess open orifices at their origin, until they were generally recognized as sharing with the lacteals, the important office of absorb- ing fluids, as well as conveying them towards the heart. It was not fairly established until the time of the Hunters, that these vessels formed part of the absorbent system, although Glisson and Hoffmann had expressed their opinion to this effect, a few years after the dis- covery of the lymphatic vessels. But to do justice to this part of our subject, it will be LYMPHATIC AND LACTEAL SYSTEM. 213 necessary to enter more fully into the Hun- terian theory of absorption. The Hunters, Monro, and their followers Cruickshank, Hewson, and Sheldon, conceived that the lacteals and lymphatics formed one great system of vessels by which alone absorp- tion was effecled in the living body, either for the purpose of collecting new materials, or for the removal of the old ; consequently, that these vessels were essential agents in the growth and habitual nutrition of the structures ; — that whenever any of the solid or fluid components of the body, whether of a healthy or morbid character, disappeared, their removal was effected by the lymphatic vessels ; this in- cluded the ulcerative process, which they considered as exclusively carried on by these vessels. Many ingenious experiments were performed to disprove absorption by the veins. Fluids of various colours impregnated with musk and other odours were thrown into the intestines of living animals, and were after- wards detected in the lacteals, but not in the veins, and imbibition was considered impos- sible in the living structures. These views were generally received throughout Europe, and have been acquiesced in almost to the present day. Our phraseology, written or oral, whether in reference to Pathology, Physiology, or Anatomy, is evidently still imbued with them. This theory of the func- tions of the lymphatic system necessitated a corresponding anatomical disposition in the mode of origin, as well as in the general ar- rangement of these vessels. They were re- quired to be universal for the purposes of growth and nutrition ; wherever there was the artery to deposit, there must be lymphatic to absorb ; and as imbibition was inadmissible, they were endowed, as a matter of necessity, with open mouths, by which they were said to commence from all serous and from all mucous surfaces, including the interior of all the visceral cavities, the serous linings of the arteries, veins, and even of the lymphatics themselves, the synovial surfaces of the joints ; the surface of the skin, the mucous linings of the alimentary canal, of the aerial, urinary, and other pas- sages, of the excretory ducts, and from the in- terstitial cellular tissue of the whole organism. It was admitted that the orifices of the lymph- atic vessels could not be shewn ; that they eluded our senses by their transparency and extreme minuteness ; but on the villi of the in- testine, the commencing lacteals were supposed to be detected, turgid with chyle, and their mode of origin by patent orifices was described by more than one anatomist. An analogous arrangement at their commencement was ad- judged to the lymphatics, without any further investigation directed specially to these vessels. Cruickshank thus describes the appearance of the supposed lacteal orifices on the villi, seen in a female who died suddenly seven or eight hours after a full meal. " In some hun- dred villi, I saw a trunk of a lacteal forming or beginning by radiated branches. The ori- fices of these radii were very distinct on the surface of the villus, as well as the radii them- selves, seen through the external surface pass- ing into the trunk of the lacteal ; they were full of a white fluid. There was but one of these trunks in each villus." He states also that Dr. Hunter examined them under the microscope, and counted as many as fifteen to twenty orifices to each villus. According to Lieberkuhn, the lacteal commences on the apex of each villus by one or more orifices leading to an ampullula situated near the apex of the villus, from whence one lacteal branch proceeds through the centre to the base of the villus. The ampullula, he states, is lined by a spongy cellular tissue, which he conceives is subservient to absorption. With respect to the orifices, his words are : " Quod autem unum saltern adsit foraminulum in cujusvis ampul- lulae apice, certo examine mihi constat : in- terduin tamen, licet rarissime, plura ut in pa- pillis mammarum, vidisse memini." Sheldon admits Lieberkuhn's description of the orifice of the lacteal vessel, and of the ampullated ap- pearance of its commencement from the villus ; but it appears to me, on looking at Shel- don's plates, and reading his description of the ampullula', that he as well as Lieberkuhn, whose plates he has copied, have mistaken the mucous follicles of the intestines for the am pullated villi. Speaking of the ampullula?, Shel- don says, " I have seen them of different forms, most commonly bulbous, as represented by Lieberkuhn. I have also seen a number of ampullula1 filled with chyle, sometimes form- ing clusters, as represented in plate I., while in other parts of the small intestines I have found them solitary, and projecting beyond the villi, as may be seen in several of the figure? in plate I." Hewson has seen a net-work 01 lacteals as well as of bloodvessels on the villus, but no ampullulas; he states that the orifices of the lacteals can only be discerned when the villus is rendered turgid and erect by the fullness of the bloodvessels. In refer- ence to these orifices, he says : " It might be here objected that these were only lacerations of the villi, but I am persuaded they were not, from having, on repeatedly examining them, observed the pores or orifices very distinct and empty ; whereas, were they lacerations, I think I should have seen the injection in them, as the villi were so much injected by it.'' These are the data upon which has been founded the opinion that the lacteals and lymphatics arise every where by open mouths. I have myself examined under the microscope the villi of various animals destroyed at different periods after a meal, for the purpose of detecting the mode of origin of the lacteal vessels. I have looked at them for hours together before and after the bloodvessels had been filled to great minuteness, but have never been enabled to discover orifices on the apices, or on any other part of the villus, and I can adduce the names of a host of modern observers of consi- derable celebrity, Rudolphi, Panizza, Haasse, Lauth, Fohmann, Breschet, Miiller, Treviranus, and others, who deny the existence of any such orifices. Magendie and Cruveilhier conceive that the chyle must enter the lacteals by ori- 214 LYMPHATIC AND LACTEAL SYSTEM. fices on account of the material particles of which this fluid is composed; the lymph they suppose enters the vessels by imbibition through their coats. Before alluding to the other opinions on the subject of the origin of the lymphatic vessels, it may be as well to premise the changes which have taken place in our physiological notions with respect to the function of ab- sorption since the time of the Hunters and their immediate successors. Magendie has proved by numerous convincing experiments, that imbibition does take place in the living as well as in the dead body, not only through the coats of the lymphatics and bloodvessels, but through all the tissues. It has been equally well established by Magendie, Delille, Segalas, Mayer, Emmert, and other physiologists, that we can no longer exclude the veins from parti- cipation in the important function of admitting new and foreign matters into the animal sys- tem. With respect to imbibition, I will select one of many experiments instituted by M. Magendie. He exposed the external jugular vein in a dog, and having separated it from its cellular attachments, placed a piece of card underneath the vessel so as to isolate it from the surrounding parts. He now applied to the centre of the vein a watery solution of the spirituous extract of nux vomica. In four mi- nutes the symptoms of poisoning made their appearance. If then it be admitted that imbibi- tion takes place in the living textures, there can be no longer an absolute necessity for open mouths to the origins of the absorbing vessels, and it follows that the lymphatics cannot be the sole agents in the process of absorption. I will now adduce some experiments con- ducted by different physiologists, proving theen- tranceof varioussubstancesinto the livinganimal system by other channels than the lymphatics. Magendie divided all the structures of the hind leg of a living dog, with the exception of the femoral artery and vein, through which the circulation was carried ou. He then inserted the upas tieute poison into the foot of the mutilated limb. The animal was poisoned in the usual space of time required for this sub- stance to take effect. He repeated the same experiment with the additional precaution of placing inert tubes into the artery and vein, and afterwards dividing these vessels, leaving the limb connected to the trunk by the tubes only, through which the blood passed to and from the limb ; the same effect followed on the introduction of the poison. Mayer injected a solution of prussiateof pot- ash into the lungs of an animal : in from two to five minutes after the injection, the serum of the blood, tested by a salt of iron, gave evidence of the presence of the prussiate of potash by the usual green or blue precipitate. It was detected in the blood long before it could be perceived in the contents of the tho- racic duct, and in the left side of the heart be- fore it appeared in the right. It was therefore evident that the pulmonary veins and not the lymphatics had first received the prussiate of potash and conveyed it to the heart. Segalas included a piece of intestine between two liga- tures in a living animal, and tied all the blood- vessels leading to it excepting one artery ; the lacteals were left uninjured and pervious ; an aqueous solution of nux vomica was now in- jected into the piece of intestine and there secured for an hour without producing any symptoms, but on removing the ligature from one of the veins, the poison took effect in six minutes. The converse of this experiment was performed by Magendie and Delille. A por- tion of intestine of a living animal was in- cluded between two ligatures ; the lacteals pro- ceeding from it were ligatured and divided, the bloodvessels being left pervious. A so- lution of nux vomica thrown into this piece of intestine destroyed the animal in six minutes. Emmert applied a ligature to the abdominal aorta in a dog, and afterwards inserted prussic acid into the foot of one of the hind legs; no ill effects followed in seventy hours ; the liga- ture was then removed, and in half an hour symptoms of poisoning appeared. In addition to simple imbibition, Dr. Dutro- chet has shewn that fluids situated in contact with animal membranes permeate them in obedience to certain laws. When two fluids of different densities are in contact with the opposite sides of a membranous septum, they both permeate it, but with different degrees of rapidity. The more rapid current takes place from the rarer to the denser fluid ; to this he applies the term of Endosmosis : the slower current from the denser to the rarer fluid he calls Exosmosis. These remarkable powers must be continually in action in the animal machine, composed as it is of solids and fluids, and cannot for the future be lost sight of in considering the sub- ject of the absorption and deposition of fluids in a living animal, or the arrangement of the structures by which these important functions are accomplished. Taking these facts into con- sideration, and bearing in mind the experi- ments above detailed, we are led to the con- clusion, that the capillary bloodvessels and even other tissues imbibe indiscriminately fluids brought in contact with them, and appa- rently in obedience to the physical or mecha- nical laws regulating imbibition, rather than in virtue of any new and essential agency with which they may be endowed as living struc- tures ; while the lymphatic system is left in possession of a higher grade of absorption ac- companied with an elective power (especially manifest in the lacteals) existing only with life, and if not entirely independent of mechanical or physical laws, at any rate frequently at variance with them ; by this elective power they are enabled, to a great extent, to refuse materials injurious to the economy of the animal, and to select those alone which may be made subservient to the nutrition of the system. These physiological considerations will pre- pare us better for the examination of the re- maining theories on the mode of commence- ment of the lymphatic vessels. We shall next enter upon that which ascribes to them an origin from the cellular tissue. Fohmaiin has LYMPHATIC AND LACTEAL SYSTEM. 215 injected the lymphatic vessels from the cellular tissue, and most anatomists have remarked that when an injection thrown into the bloodvessels has extravasated into the cellular membrane, it has occasionally entered the lymphatic vessels. I have several times injected Fohmann's so called lymphatic cells of the umbilical cord, and have preserved a specimen shewing them, but cannot acquiesce in the opinion that they form a part of the lymphatic system. These cells, which readily receive the quicksilver in- troduced into a puncture made in the cord, vary in diameter from l-100th to l-250th of an inch, and communicate freely with each other ; they have a very regular and organized appearance, but can only be injected after putrefaction has commenced. Fohmann describes them as situated between the lym- phatics of the placenta, which terminate in them, and those of the foetus, which commence from them. I have never succeeded in pressing the injection from the cells of the cord into the lymphatics of the foetus or of the placenta. Treviranus conceives that the lymphatics every- where commence by elementary cylinders of cellular tissue, and that in the villi of the intes- tines these elementary cylinders are so arranged as to have one of their extremities terminating in a lacteal vessel situated in the centre of each villus, while the other reaches the periphery of the villus, on the surface of which they present little vesicular projections, in whose centre he thinks he perceives a minute orifice. Arnold also observed a similar arrangement of the cel- lular tissue of the orbit into minute cylinders, which he supposed to be an incipient net-work of lymphatic vessels. Cruveilhier considers it probable that the cellular tissue and the serous membranes are formed of lymphatic vessels ; and Mascagni makes a more sweeping assertion that all the white textures and the whole cel- lular web of the body is composed of these vessels. The opinion that the lymphatic system com- mences by a plexus or net-work of vessels larger than the capillary bloodvessels, and which can always be seen by the unassisled eye when injected, appears to be the best supported by evidence, and to be that more generally received by modern investigators. These incipient plexuses are considered to be destitute of orifices either on the villi or elsewhere, and in this respect to resemble ■ the peripheral branches of the arteries, veins, and excretory ducts, which, according to the more recent views in minute anatomy, no where present open mouths. The splendid injections of Mascagni, Fohmann, Lauth, and Panizza, shewing these vessels in various parts of the body, on the interior of mucous mem- branes, on the surface of particular portions of the skin, on the serous membranes, especially that part covering the solid viscera, on the lining membrane of the heart and blood- vessels, and of the excretory ducts of the glandular viscera, offer a body of evidence which can scarcely be resisted. In none of these situations can open orifices be discovered by the aid of the microscope or by means of urging on the injection. On the surface of the liver, where the lymphatics may be injected with great facility, by pressing in a retrograde direction the injection may be forced beyond the valves, and by continuing the force some extremely minute globules of mercury may be made apparently to pass through the coats of the vessels. Haase has also, by the same pro- cedure, forced the mercury through a net-work of lymphatics on the surface of the skin; but these circumstances can hardly warrant the supposition of lateral organized pores. These primary networks of lymphatic vessels are said to be deficient in valves in some situations. The meshes of the networks are of various forms and sizes : sometimes they are nearly equal-sided, at others oblong or irregular ; in some places the vessels are so . closely set that the spaces between them can scarcely be seen ; in others they are larger and very distinct. The plan adopted by Fohmann to display these vessels, though liable to some objections, ap- Fig. 51. Shewn an incipient plexus of lymphatic vessels. ( From Breschet. ) a, the more superficial plexus formed of very minute valveless vessels., b, a deeper plexus formed of larger valveless vessels, which receive the contents of the former, and which terminate in lymphatic vessels armed with valves. pears to be the most successful. He pierces the part to be injected with a sharp-pointed lancet, held nearly horizontally, so as to pro- duce a very superficial wound, the lymphatic net-work being generally nearer the surface than the capillary bloodvessels ; into the wound thus effected the pipe of the mercurial injecting tube is inserted, and the quicksilver is made to enter some of the vessels opened in the in- cision, either by the weight of the column of the mercury or by urging it on with the handle of a scalpel. On the glans penis this method scarcely ever fails to fill the lymphatics, which are of large size. In the skin of the scrotum, and in the neighbourhood of the nipple, success will occasionally attend the attempt to shew these vessels ; but in other parts of the integument, the endeavour has with me always been fruit- less, so much so that I cannot help doubting their universal existence on the surface of the true skin. Breschet's description of a net- work of lymphatics brought it to view by piercing the cuticle only, with a ( apillary tube of glass connected with a columi of mercury, lam convinced is deceptive : hi; words are — 216 LYMPHATIC AND LACTEAL SYSTEM. ' II consiste (ceproccde) apercer superficielle- ment le tissu cutane avec 1'extremite d'un tube capillaire en verre ou en acier, de facon a n'interesser que l'epiderme, pour arriver au reseau vasculaire situe entre cet epiderme et le chorion. On obtient ainsi l'injection de reseaux admirables de vaisseaux lymphatiques." I have frequently produced the appearance here alluded to in all parts of the body : a fetus answers best for the purpose, but the proper lymphatics are never filled from these supposed net-works of lymphatic vessels. They are clearly nothing more than the spaces around the bases of the papilla? of the skin, from which, as putrefaction commences, the cuticle sepa- rates more readily than from their apices, con- sequently little canals are left around the pa- pilla5, which communicate with each other and form a pretty exact resemblance to vessels fill- ing rapidly as the mercury runs around the bases of the papillae. The appearance can only be produced at a certain stage of putrefaction when the cuticle is about to separate. On removing the cuticle, the pretended vessels im- mediately disappear; but on the glans penis, on the scrotum, and on the skin of the nipple the removal of the cuticle will not disturb the net-works of vessels which may be there in- jected ; moreover from these the lymphatic trunks can always be filled. I am also dis- posed to think, contrary to the received opinion, that the serous membranes do not universally present this superficial network of lymphatics; there are at any rate parts of these membranes where I have never seen these vessels injected, while there are others in which anatomists in- variably succeed in shewing them ; and for the mere purpose of absorbing the fluid secreted by the serous sacs, there appears to me nothing extraordinary in the supposition, that those por- tions of the membrane only which are most conveniently situated for the purpose should be endowed with the proper organization to effect it. The mode of procedure, however, adopted by Fohmann and others to display the incipient lymphatic net-works is open to serious objec- tions, and calculated without great circumspec- tion to lead into error. The capillary blood- vessels will often be implicated in the wound required to pierce the lymphatic net-work, con- sequently the injection may be found in the arterial and venous as well as in the larger lymphatic branches leading from the part. To succeed to any extent many punctures may be required, and in all probability some of these will conduct the injection into the three sets of vessels; but I have several times by the first puncture succeeded in injecting a net-work of vessels on the glans penis, which has conveyed the injection at once into the lymphatic branches on the body of the penis, and into these vessels only. The cellular tissue will also readily receive the injection, and where the cells are very small and uniform, as is the case with the umbilical cord, they resemble very much a net-work of vessels distended with quicksilver; and although Fohmann ad- mits these to be cells, yet fiom their regularity he has been led to consider them a part of the lymphatic system. In the same category may be classed the supposed lymphatic cells of the cornea observed by Arnold and by Miiller. The submucous cellular tissue also is fre- quently arranged in little cylindrical cells which communicate with each other, and these cells on receiving the mercury put on the appearance pretty exactly of a net-work of vessels, but lymphatic vessels are not found conveying the injection away from them to the nearest lym- phatic glands, which I imagine should be the proof required before we admit any vessels or cells to belong to the lymphatic system, how- ever beautifully displayed by our injections. The subserous tissue is open to the same re- mark, and I can hardly offer a better instance of what appears to me to be an error arising from this source, than by quoting Fohmann's own words in reference to what he describes as the lymphatics of the brain. " Les vaisseaux lymphatiques des enveloppes des masses cen- trales du systeme nerveux sont ties faciles a demontrer, surtout au cerveau et au cervelet. Lorsqu'on enfonce une lancette entre la pie- mere et l'arachnoide, et qu'on insuffle le canal que Ton vient de pratiquer, on voit paraitre un reseau lymphatique interpose entre ses deux tuniques, reseau forme de rameaux d'un calibre plus considerable que dans les autres tissus du corps; cependant leurs parois sont si foibles qu'elles se dechirent presque aussitot qu'on y introduit le mercure." With respect to the universal net-work of lymphatics attributed to the lining membrane of the heart, and to that of the arteries and veins, I cannot admit, that the injections of a few minute canals with quicksilver on the lining membrane of the heart in the horse, by Lauth, and similar in- jections by Cruveilhier and Bonamy, can be received as demonstrative : the injection was not traced from them to a distinct lymphatic vessel, armed with valves_and pursuing its course towards a lymphatic gland ; these mi- nute canals might have been capillary blood- vessels, or, as Breschet observes in his expla- nation of the plate which he gives from Lauth of these supposed vessels, " Nous pensons qu'ils sont uniquement constitues par des la- cunes du tissu cellulaire." In concluding what I had to say of the origin of the lymphatic vessels, a subject so inextricably mixed up with our preconceived physiological notions, I ought, perhaps, to offer some apology for advancing in an article of this nature any opinion peculiar to myself ; I mean in reference to curtailing the extent to which the lymphatic system will be found to exist in the organism. My own mind has been forced to this conclusion after some years of attention to the subject, both from anatomical and physiological considerations. It has appeared to me in the first place, that anatomists who have especially devoted their time to this interesting subject of late years, have not yet fairly freed themselves from the influence of the Hunterian views with respect to the part performed by the lymphatic vessels, as well as by the arterial capillaries, in effect- ing the growth and habitual nutrition of the LYMPHATIC AND LACTEAL SYSTEM. 217 structures. To support the Hunterian theory the lymphatic was required to be present with every molecule of the organization, there with open mouth (for imbibition in the living body was not admitted as possible) to remove the old material in order to make room for the new, which was supposed to be deposited by the open mouths of capillary arteries. Now, although physiologists no longer admit that the arteries any where terminate by open mouths, but consider all nutrition to take place by the transudation of the liquor sanguinis through the delicate tunics of the capillary blood- vessels, and although venous absorption, as well as lymphatic, is acknowledged to take place, consequently that the ubiquity of the lym- phatic ceases to be a matter of necessity, still it appears to me that physiologists have not yet shaken off the old impression, that every particle of the organization must have its lym- phatic vessel, and I cannot help thinking that the continuance of this impression is mislead- ing us in our notions of the arrangement of the system. There are also some additional anatomical considerations which have had their weight in leading me to the opinion that the lymphatic system is less extensive than is generally sup- posed. It is not, I believe, known to anato- mists that the lymphatic vessels admit readily of dissection in their uninjected state; these vessels do not easily give way under traction, and by using the forceps to hold them, and a blunt but pointed instrument to detach them from the surrounding cellular membrane, to which they are but loosely attached, they may be dissected with equal facility as the cuta- neous nerves, for which they are not unfre- quently mistaken by the young dissector. I have in this way several times dissected the lymphatics of the upper extremity, from the glands in the axilla to the fingers, and in the lower, from the inguinal glands to the toes. In proceeding thus to trace these vessels, scarcely a single lateral branch can be detected in the leg and thigh, by which the supposed universal net-work of the surface of the skin could have been connected with the rest of the system. When the subcutaneous lymphatic vessels are injected with quicksilver, every anatomist must hav e remarked the absence of lateral branches ; this has always been accounted for by sup- posing a valve at the termination of each late- ral branch into the larger longitudinal vessels; but in dissecting these vessels in their unin- jected state, the lateral branches if present ought to be met with, which is not the case. I am fully aware that Haase, and other inves- tigators, have succeeded in getting the injection to pass in a retrograde direction from the sub- cutaneous lymphatics of the lower extremity into a net-woik of vessels of small extent situ- ated close to the surface of the skin : this has occurred to myself on two occasions, in the skin over the tibia, and in the inguinal region, but in both these instances it was in a portion of skin presenting a cicatrix ; the net-work was circumscribed, and left the impression on my mind of an abnormal rather than of a normal condition of these vessels. The entire pro- fession have adopted the notion that the pro- cess of ulceration is effected by the lymphatic vessels, consequently that, as every structure may ulcerate, so it must have its lymphatic vessel. But I may be permitted to ask patho- logists to consider, whether they are not still influenced by the Hunterian theory, viz. that the countless open mouths of the lymphatics (which modern anatomists do not allow them to possess) effect the removal of the textures disappearing by ulceration, rather than by the few facts and observations bearing upon this important question. I would ask whether the occasional instances, of inflamed lymphatics containing pus, being found leading from an ulcerated surface, are sufficient to establish the opinion, that the whole process is effected by this set of vessels ; or whether the occurrence is not more satisfactorily accounted for, by the supposition that the ulcerative process has im- plicated a lymphatic vessel, and that the pus has entered the vessel by an opening thus effected in its paries, or that the pus has been formed in the lymphatic itself, as the result of inflammation affecting its interior; more par- ticularly when it is borne in mind, that the pus globule is much too large to have entered these vessels by imbibition, and that open mouths are denied to them. The parts of the body in which I have seen pus in the lymphatics, have been on the surface of the lung, on the mu- cous membrane of the intestines, on the penis when ulcers had occurred in these organs, also in the subcutaneous lymphatics after suppura- tion and sloughing of the cellular tissue, — situ- ations in which every anatomist has seen lym- phatics, and where the ulcerative or sloughing processes might readily have effected an open- ing into them. The lymphatic or absorbent glands, called also conglobate glands by Sylvius, and lym- phatic ganglia by Chaussier, are small fleshy bodies of a flattened form, rounded or oval in outline, varying from the size of a millet-seed to that of an almond ; so situated in various parts of the body as to intercept the lymphatic vessels in their course towards the trunks of the system. They are generally clustered together, but occasionally are found single or isolated. The isolated glands are usually very small ; the large ones clustered together. The lym- phatic glands are well protected from pressure. In the limbs they are principally situated in the cellular spaces at the flexures of the joints, and enjoy the same protection as the main bloodvessels, close to which they are generally located. The loose cellular tissue in which they are for the most part imbedded, allows them great freedom of motion, by which they are enabled to elude pressure. The lymphatic glands are most developed in childhood, least so in old age, and are interme- diate in this respect in adult life. They are not found in Amphibia and Fishes, and in Birds only in the cervical region : intricate plexuses of large lymphatic vessels occur fre- quently in those animals which are destitute of lymphatic glands. 218 LYMPHATIC AND LACTEAL SYSTEM. The colour of the lymphatic gland, depending apparently on the contents of its bloodvessels, is of a pale rose pink, resembling in this re- spect the colour of the salivary glands or of the cineritious matter of the brain ; the exceptions to this observation will be found in the mesen- teric glands while the chyle is passing through them, when they assume a whitish colour ; the lymphatic glands in the neighbourhood of the liver and gall-bladder have been observed to possess a slight yellow tinge, but this is tobe con- sidered a post-mortem appearance. The black coloui of the bronchial glands is remarkable and not easily accounted for ; the lymph passing from the lung to them being always perfectly transparent and colourless. The lymphatic gland has a capsule of con- densed cellular tissue, which surrounds it and firmly adheres to it, appearing to send cellular prolongations into its substance; the outer sur- face of this capsule is connected to the surround- ing textures by a loose cellular tissue. The capsule appears to serve the purposes of convey- ing the bloodvessels to the interior of the gland, of isolating it from the surrounding parts, and of preventing its over-distension by the lymph conveyed to it. The bloodvessels of the lymphatic glands are large and distinct; frequently more than one artery is traced to a gland ; the returning veins do not generally correspond either in direction or number with the arteries. The veins are much larger, but have appeared to me fewer in number than the arteries. Nerves of considerable size pass to the lym- phatic glands and can generally be traced through them, from which circumstance it has been doubted whether any filaments are left in the gland; but if acute sensibility to pain from undue pressure or from disease be admitted as dependent upon a proper supply of nerve, un- doubtedly they possess it. The exact mode of arrangement of the bloodvessels in the interior of the gland is not well known. After a success- ful injection of these vessels the gland assumes the same colour as the injection itself. Our knowledge of the structure of the ab- sorbent glands rests mainly upon the informa- tion obtained by throwing injections of mercury or coloured wax into the lymphatic vessels. In this mode of investigating their texture, the walls of the canals or cavities containing the injection, which appear, as in the kidney and testicle, to form the parenchyma of the organ, are com- pressed, and when dry become transparent. The arrangement of the minute bloodvessels on the lining membrane of these canals has not been sufficiently investigated, and until this has been effected, our knowledge of the structure and function of the lymphatic gland must be considered very unsatisfactory, and as consist- ing of little more than conjecture. The great point of controversy has been, whether the in- jection thrown into the gland by the afferent lymphatic vessels was contained in cells or in convoluted vessels, which if decided would throw but little light upon the office performed by the gland — a desideratum in physiology of considerable importance, and without which we are left in the dark at the very threshold of our investigations with respect to the first changes effected in the lymph and chyle, in advance towards sanguification. On examining Fig. 52. Lytnpliatic glands injected with mercury. ( A fter Mascagni. ) A, gland injected and dried, a, a, vasa affe- rentia. b, vasa efferentia. B, gland injected and laid open to show the appa- rent cells, i, apparent cells ; e, vas efferens ; a, vasa affetentia. the glands thus distended with injections, the vasa inferentia are seen reaching the gland from various sources, and on their approach to it they may be observed to subdivide into ex- tremely minute branches, which disappear by plunging into its substance : equally minute vessels may be observed emerging from its opposite side or surface, which soon unite to form the vasa efferentia of the gland ; the gland itself, which is intermediate in position between these vessels, when injected, presents a gra- nular surface, and at first sight an observer would generally conclude that he was look- ing upon minute cells filled by the injection ; in making a section also into the substance of the gland and allowing the mercury to escape, the appearance on a superficial in- spection is still that of cells ; proceeding, however, with more attention to examine these supposed cells, especially after making a section as close to the surface of the gland as possible, by the aid of the microscope it will be evident that tubes closely set together and adherent to each other, have been laid open, passing in various directions, and in their interior many valvular constrictions and thread-like intersec- tions may be seen ; in fact the gland appears to be entirely composed of a convoluted vessel, the sides of which as they come in contact are firmly held together by cellular membrane derived from the capsule. This convoluted tube forming the gland is not always cylindrical, but is occasionally dilated, and looks flattened near the surface where pressed by the capsule ; the size of this tube LYMPHATIC AND LACTEAL SYSTEM. 219 is much larger than that of the branches of the vasa afferentia and efferentia, a fact that has been too much overlooked by anatomists, and which leads me to conjecture that these vessels enter and arise from its convolutions by open mouths; be this as it may, we know that the injection conveyed into the gland by the vasa afferentia readily passes from it by the vasa efferentia. I should not here omit to mention a circumstance already adverted to of consi- derable interest, viz. that the injection conveyed to a gland by an afferent vessel is occasionally received by the veins of that gland, and to all appearance without rupture or extravasation. The occurrence itself is admitted by all ; but physiologists differ much in their explanations of the channel by which the injection has en- tered the vein. Some explain it by an extrava- sation into the cellular tissue from an injury by which both sets of vessels have been opened ; others, who conceive that a minute net-work of lymphatics exists on the interior of the veins and arteries, will have no difficulty in ima- gining a rupture of this net-work ; the vasa vasorum of the lymphatics, which may be dis- tinctly seen on their interior after a minute in- jection, may be supposed to have given way and to have admitted the injection from the interior of the lymphatics. But these opinions will not explain why this communication should take place within the gland only, and invariably with the vein, never with the artery. The general opinion is that this communi- cation takes place accidentally, and not by any real continuity of canal. Fohmann stands almost alone in asserting that a natural commu- nication does exist between the lymphatics and veins within the glands, especially in those situations where in birds, reptiles, and fishes, the lymphatics have been proved to terminate directly in the veins. Fohmann even ventures an opinion as to the mode in which the lym- phatic joins the vein ; not, he conceives, by con- tinuity of peripheral branches, but by an effer- ent lymphatic opening into the side of a vein before the latter emerges from the gland. Without committing myself to the exact mode of union, I must confess I agree with Fohmann that a natural communication does exist in some of the glands between the lymphatics and the veins. It has been observed hundreds of times. It has occurred to every anatomist who has engaged himself with the injection of these vessels ; I have met with at least twenty such instances myself, while a similar communica- tion between a lymphatic and artery within a gland has never been observed. I am entirely at a loss, therefore, to account for these occur- rences without admitting a natural channel to exist between the one set of vessels and the other. I have before observed that the exact arrange- ment of the bloodvessels in the interior of the canals of which the glands are constituted, is not known ; but we are equally in the dark with respect to the vascular supply received by other minute tubes, such as the seminiferous, urini- ferous, and lactiferous tubes, from the capilla- ries of whose lining membranes, however, we admit that their appropriate secretions are de- rived. As far, then, as organisation is con- cerned, there is nothing to forbid our ascribing a secreting function to the interior of the canals of the lymphatic glands, or of the lym- phatic vessels generally. There can be little doubt but that the lymph and chyle undergo modifications in their passage through the ab- sorbent glands, although we are not at present prepared to state the nature of that modification. It lias been observed that the chyle included between two ligatures in its own vessel before it has reached a gland will not coagulate, although after it has passed the gland coagula- tion readily takes place. Muller remarks from this circumstance that the glands of the mesentery appear to have the power of changing part of the albumen of the chyle into fibrin. At any rate we are warranted, from the little we do know of the structure of the absorbent gland, in asserting, that the chyle and lymph collected from various sources must be mingled together in the glands, that they must be divided into extremely minute streams on their entrance into or exit from a gland, that they must be submitted to a great extent of surface of their containing vessels, and subjected to considera- ble delay in their passage through the gland. Mr. Gulliver's observations on the fluid con- tained in the absorbent glands would almost lead us to conclude that their proper office was to fabricate the peculiar globule of the lymph and chyle; my own observations on these fluids before and after reaching the glands would not bear out this opinion ; but as I have next to consider the characters, physical, microsco- pical, and chemical, of these fluids, I shall shortly enter more fully into this subject. Lymph is a transparent fluid, slightly opa- line, of a light straw colour ; its specific gravity is 1022-28, water being 100000; its odour, which is slight, varies, and is peculiar to each animal ; it is alkaline, and has a saline taste. I collected in an ounce-phial about three drachms of lymph from a large lymphatic in the axilla of a horse, by inserting a small silver tube into it. In about ten minutes the whole had coa- gulated into a jelly-like mass ; in half an hour a separation had taken place into a fluid and solid part : the latter formed a soft tremulous clot modelled to the form of the phial. A drop of this lymph placed on a piece of glass, and covered by talc, was submitted to inspec- tion under the microscope, immediately after its removal from the vessel. A number of colourless spherical globules were observed in it having a granular surface, and precisely resembling those described by Mr. Gulliver as belonging to the mesenteric, lymphatic, and thymus glands. I am not aware whether Mr. Gulliver considers these globules as belonging exclusively to the glands, or whether he thinks them distinct from or identical with the lymph and chyle globule. My own observations lead me to state that they are found in the lymph or chyle before and after passing the glands, as well as in their transit through them. I am also dis- posed to assert that these globules remain co- lourless, and that whenever the lymph possesses a slightly red tint, it obtains that tint from the 220 LYMPHATIC AND LACTEAL SYSTEM. presence of blood corpuscules which have ac- cidentally entered it. After coagulation had taken place, the lymph was again examined under the microscope, the globules were all found entangled in the clot ; scarcely one re- mained in the transparent fluid. The clot, when disturbed, torn, and pressed, contracted to less than one-twentieth of its original bulk, and the few blood corpuscules it contained, being now approximated closely together in the contracted clot, gave it a slightly red tint. On examining the serum of this lymph under the micro- scope a week afterwards, when putrefaction had commenced, numerous exceedingly minute animalcules were seen diffused through it in active motion. Muller gives an account of a fluid which makes its appearance after a portion of the skin of a frog is removed from the muscles ; this fluid he considers to be pure lymph ; he de- scribes it as perfectly transparent and colourless, having a saline taste, but void of smell. Under the microscope he detected in it a number of colourless and spherical globules, about one- fourth of the magnitude of the elliptical blood corpuscule of the same animal, a few of which were unavoidably mixed with this lymph. Muller also describes what he considers to be human lymph, obtained from a small fistulous opening on a man's foot, the remains of a wound received on the instep ; by pressure from the great toe towards the opening a transparent fluid could be made to transude; this fluid also contained colourless spherical globules, much smaller than the blood corpuscules. It, as well as that obtained from the frog, coagulated spontaneously, and appeared to possess the other properties of lymph. After coagulation had taken place in the fluid obtained from the man's foot, he observed that the globules were partly found in the clot, while some remained in the fluid surrounding the clot. In the horse's lymph examined by myself, all the globules were entangled in the clot. The red colour of the contents of the tho- racic duct, especially in the horse, has been remarked by most observers, but the cause of this redness has not been well ascer- tained. Breschet says, in his Systeme Lym- phatique, page 160 : " Ce qu'il eut 6te in- teressant surtout de determiner, c'est si la ma- tiere colorante qui teint quelquefois le chyle, et meme la lymphe, y est dissoute, ou si elle afl'ecte soit toujours, soit au moins quelque- fois, la meme disposition que celledes globules du sang." I have frequently examined micro- scopically this reddish fluid of the thoracic duct, and have invariably found it to depend upon the presence of red corpuscules of precisely the form and size of those of the blood. I believe that these red corpuscules are extraneous to the lymph, that their presence is accidental, and should be considered as a post-mortem occur- rence. I would attribute their existence in the contents of the thoracic duct to the circum- stance that very many lymphatics must be di- vided with the other structures, before the tho- racic duct or indeed any large lymphatic can be exposed; these divided lymphatics must necessarily have blood applied to their cut extremities ; the vessels being open receive the blood corpuscules, and convey them from all parts to the thoracic duct. This is not mere conjecture. I have seen the blood enter the divided vessels in the following experiment made for the purpose. On the under surface of the liver of a horse recently killed I ob- served some large lymphatics filled with a beautifully transparent fluid. I made an inci- sion into the liver over these vessels, of course di- viding them, and in a few seconds saw them con- veying a reddish fluid towards the thoracic duct. The lymph bears great resemblance to the liquor sanguinis both in its physical and che- mical characters. Muller, who had observed that the blood of frogs will not coagulate when they are kept out of water in summer for eight or ten days, mentions the coincidence that when this is the case, the transparent fluid which he obtained by removing a piece of skin from a living frog, and which he conceived to be the lymph of the animal, was also incapable of spontaneous coagulation. Leuret and Lassaigne give the following analysis of lymph obtained from the lympha- tics of the neck in a horse : — Water 925 Albumen 57-36 Fibrine 3-30 Chloride of sodium ~\ Chloride of potassium . . . f 1A Phosphate of lime 100000 Salivary matter, ozmazome, carbonates, sul- phates, muriates, and acetates of soda and potash, with phosphate of potash, have in addi- tion been detected in the lymph by Tiedemann and Gmelin. Chevreul analysed some lymph procured by Magendie from the thoracic duct of a horse after five days' abstinence. Its composition. was as follows : — Water 926-4 Fibrine 4-2 Albumen 6 10 Muriate of soda 61 Carbonate of soda T8 Phosphate of lime 1 Carbonate of magnesia . . . . £ 5 Carbonate of lime j 10000 M. Magendie and M. Collard de Martigny have examined the lymph in animals, after de- priving them altogether of sustenance ; up to the tenth or twelfth day the lymph was found in greater abundance, appeared to have more of the red tinge, and to be more consistent ; but after this period it diminished in quantity, be- came more watery and had less of the rose tint. The latter physiologist rejects altogether the opinion entertained by some, that the lymph would assume a redder colour the longer the animal fasted. LYMPHATIC AND LACTEAL SYSTEM. 221 The lymph is said to coagulate more readily after passing through the lymphatic glands, and the nearer it approaches the thoracic duct. I have not found this to be the case in so marked a degree as has been stated. I have collected lymph from the lymphatics of the intestines before they reached the glands, and from va- rious parts of the body in which no glands are situated, and have invariably found the fluid to coagulate spontaneously, although if in small quantity it may shortly return to the liquid state. The fluid contained in the lacteal vessels in Mammalia is of a white colour like milk, and is called chyle ; it has a marked saline taste, is slightly alkaline, and has no perceptible odour. I have now before me several specimens of recent chyle collected carefully from the lacteal vessels, before they reach the glands, from the glands themselves, from the vasa efferentia of the glands, and from the thoracic duct. These specimens were taken from a donkey killed for the purpose, seven hours after a full meal of oats and beans. About half a drachm was obtained from the vasa inferentia, and a drachm from the mesenteric glands themselves in watch-glasses; from the vasa efferentia about three drachms were procured in a test-tube, and from the thoracic duct in a phial nearly an ounce. All were of a pure milk-white colour except that from the thoracic duct, which had a slight pink tint. They all jellied spontaneously in from five to ten minutes; that from the vasa infe- rentia again liquified in about half an hour, and remained in this state ; on other occasions I have known it retain its solidity. I have also seen the chyle from the glands, and from the vasa efferentia, return to the liquid state after having been coagulated for a short period. I have observed the same occurrence in lymph before and after it had traversed a gland. In about half an hour, with the exception already noticed, these specimens of chyle separated into a kind of serum and clot, the latter form- ing by far the greater portion, at least four-fifths of the whole. This clot, however, on being broken up and pressed, contracted to one- twentieth part of its former bulk; both the serum and the clot retaining their white colour. In the specimen obtained from the thoracic duct the pink tint was confined to the clot, and the serum was whitish or whey-coloured. It ought here to be stated that chyle, before it has reached the receptaculum, will not always se- parate into a fluid and solid portion, but will remain of the consistency of a soft white jelly, from which, however, by breaking it up, a white fluid may be obtained. I find great error and confusion in the descriptions hitherto given of the microsco- pical appearances of the chyle. Miiller and Breschet both state, that the white colour of the chyle depends upon its globules, which they then proceed to describe; they both quote Prevost and Dumas as estimating the diameter of the chyle globule at l-7199th of an inch, or about half that of the blood glo- bule in man. Miiller says that in the cat he finds them of the same size as the blood cor- puscules, and in the rabbit some of them were larger ; in the calf, the dog, and the goat he found them much smaller than the blood cor- puscules of the same animal. Breschet, in his work on the lymphatic system, published in 1836, acknowledges the unsatisfactory state of our knowledge with respect to the globules of the chyle and lymph. Tiedemann and Gmelin, in their elaborate work on digestion, distinctly state they consider the white colour of the chyle to depend upon fatty particles, which form a sort of emulsion with the serous portion of the chyle. Mr. Gulliver has given by far the most correct description of the microscopical appear- ances of the chyle that I have met with ; he is the first who has noticed the extremely minute particles which constitute the characteristic microscopical appearance of the chyle, for the larger globules, noticed by most observers, are found also in the lymph. Mr. Gulliver has not, however, corrected the statement of Miiller, Bre- schet, and others that the white colour of the chyle depends upon these larger globules; but I doubt not he would acquiesce with me in opinion that the white colour depends alto- gether upon the more minute particles. With these preliminary remarks I shall proceed to describe the microscopic characters of the chyle from my own obervations. Every one is aware that the lacteals, when not conveying chyle, contain a transparent fluid not to be distinguished by the eye from the lymph of other parts of the system ; to this fluid is added, during the digestion of a meal, myriads of extremely minute parti- cles, twenty or thirty times less in size than the lymph or blood globules of the same animal, and which can scarcely be distin- guished by a glass of less power than one- eighth of an inch focus, upon which un- doubtedly the white colour of the chyle de- pends; when these particles are very numerous, the chyle is perfectly white and opaque ; when less so, it will be whey-coloured or semitrans- parent. These particles are peculiar to the chyle, and I have been in the habit, for the last two years, of calling them the chyle gra- nules, in contradistinction to the globules of different kinds which are also found in this fluid. The chyle granules, when allowed to dry on a piece of glass, measure from l-20,000th to l-10,000th of an inch in diameter, and are larger and more distinct in carnivorous than in graminivorous animals. The most remarkable peculiarity, which I believe I am the first to notice, of these chyle granules, is their con- tinual vibratory or oscillatory motions. On viewing under the microscope a drop of chyle taken from the lacteal of a carnivorous animal, and placed between a piece of glass and' talc, the motions of the chyle granules will be seen to be so constant and ceaseless that the observer would at first sight be led to consider the chyle as a moving mass of restless animalcules; but on noticing the limited range, as well as the sameness, and apparent want of object, in these to and fro movements, he will probably feel inclined to attribute them to some unknown attraction and repulsion, influ- 222 LYMPHATIC AND LACTEAL SYSTEM. encing inert and unorganized particles. It is assuredly a striking fact, and one fraught with great interest, that the new molecules on their first introduction into the living system, should possess one of the most conspicuous attributes of vitality, viz. motion.* Mr. Ancell, who has paid great attention to the animal fluids, has frequently examined these moveable granules with me, and is inclined to consider their mo- tions, as indicating the first obvious impress of vitality which the new material has received from its association with living matter. Be- sides the granules, there exist in the chyle numerous spherical globules colourless and granular on the surface, averaging l-5000th, but ranging between l-3000th and l-7000th of an inch in diameter, resembling in every par- ticular the lymph globule, with which they are probably identical. These globules I conceive are not derived from the interior of the intes- tine as some have supposed, nor from the glands, as I presume is Mr. Gulliver's opinion, but I would rather say are formed in the chyle and lymph by the aggregation of similar par- ticles, probably fibrinous. Globules of oily or fatty matter are also found in the chyle; these may be readily distinguished by their circular and even outline, by their smooth and apparently flat surfaces, and by the great variety of their size, some being as small as the chyle granule, while others exceed the globule in diameter ; in many respects they resemble the milk globule in appearance. Blood corpuscules will of course be frequently seen mixed with the chyle, as it is exceedingly difficult to collect it free from them. In the chyle the blood cor- puscule loses its circular outline, its ordinary flattened form, its concave or cupped surface, and assumes a corrugated or wrinkled appear- ance, a spiked or serrated edge ; the blood corpuscules, when thus corrugated, are less in diameter than the surrounding chyle globules, and have frequently been mistaken for them. On examining the blood taken from a living animal after a recent flow of chyle into it, this appearance of the blood corpuscule will also be readily distinguished. The corrugations alluded to on the blood corpuscule may be mistaken for spots on it ; and when the corpus- cule is revolving or vibrating, they may even appear like particles moving within it. I was for a short time misled by this deceptive ap- pearance into the belief that the chyle granule, when received into the blood, entered the envelope of the blood corpuscule to form its nucleus. This erroneous notion, however, was soon corrected on finding that other fluids pro- duced the same appearance in the blood cor- puscules. It will be observed then, that I am induced to think that the chyle is never per- fectly free from lymph ; that in fact the lymph is termed chyle when it is rendered white by the addition of the moveable chyle granules from the interior of the intestine, to which are * [Wagner has depicted in his Icones Physiolo- gies minute granules, which he designates " Mole- cular minores, cujusmodi in liquore chyli natant, procul dubio chyli granula futura." Tab. xiii. fig. 11.— Ed.] added from the same source the oily or fatty particles. If the clot and serum of the chyle be exa- mined separately under the microscope, they will both be found to contain the chyle granule in sufficient quantity to render them white ; the chyle globule, or any blood corpuscule that the specimen may have contained, will be entangled in the clot, while the oily particles will be principally found in the serum. If the coagulation has been incomplete, or the spe- cimen has been agitated, some chyle globules and blood corpuscules will of course be mixed with the serum. The chyle has been analyzed by Reuss and Emmert, by Vauquelin, by Marcet, Prout, and Brande, by Leuret and Lassaigne and by Tiedemann and Gmelin, but in a science so ra- pidly progressive as chemistry it is desirable to adduce the most recent information bearing on the subject. I shall therefore select the ana- lysis given by Berzelius, (taken from the trans- lation of his treatise on Chemistry by Me. Es- linger, published at Paris in 1833,) who adopts some of the opinions of Tiedemann and Gme- lin, and with whose analysis of the chyle his pretty exactly agrees. In 100 parts of chyle, taken from the tho- racic duct of a horse during the digestion of a meal of oats, he obtained, after breaking up and pressing the clot, 96 99 parts by weight of serum and 301 of clot: the former was re- duced by desiccation to 7-39 parts and the latter to 0-78 ; consequently, after evaporation, the proportions in 100 parts stood thus — Desiccated clot 0-78 Desiccated serum 7-39 Water 91-83 100-00 The dry clot softened when digested in dis- tilled vinegar, but without being dissolved by it to any perceptible extent. A small quantity of a brownish-yellow oil was obtained from it by the action of boiling alcohol. One hundred parts of the desiccated serum contained — Brown fatty matter 15-47 Yellow fatty matter 6-35 Osmazome, lactate of soda, and chlo- ) jq-q2 ride of sodium $ Extractive matter soluble in water, in- soluble in alcohol, with carbonate > 2-76 and a little phosphate of soda .... * Albumen 55-25 Carbonate with traces of phosphate of lime 98-61 It has been generally stated and believed that a sufficient quantity of chyle for chemical analysis could not be obtained from the lacteals before they reached the thoracic duct, conse- quently, that which has hitherto been submitted to chemical examination has been taken from the trunk of the system, where it must of ne- cessity have been mixed with a greater or less LYMPHATIC AND LACTEAL SYSTEM. 223 quantity of lymph; the comparison therefore between chyle and lymph has never been fairly instituted. Regretting with others the defici- ency in our knowledge of the relative compo- sitions of these important fluids, which, though derived from such different sources, enter in combination the already circulating blood, I performed some experiments, which need not here be described in detail, for the purpose of ascertaining the quantity of chyle that might be procured from the vasa efferentia of the mesenteric glands, and found that by a little care and contrivance as much as half an ounce of perfectly pure chyle might be procured from a horse after a full meal. I now applied to Dr. G. O. Rees, well known to me as an able and zealous investigator of the too much neglected science of animal chemistry, and re- quested him to undertake the analysis of the unmixed chyle and lymph, and to institute the desired comparison between them. Dr. Rees kindly acquiesced in my proposal, and has published the result of his inquiry in one of the late numbers of the London Medical Gazette, from which I transcribe his analysis with some of his observations, the whole of which are well worthy of perusal. The fluids in question were procured from a donkey, killed seven hours after a full meal of oats and beans. Analysis of chyle and lymph before reaching the thoracic duct, by Dr. G. O. Rees — Chyle. Lymph. Water 90-237 . . 96-536 Albuminous matter 3-516 . . 1 200 Fibrinous matter 0-370 .. 0-120 Animal extractive matter so- ^ (3.332 0-240 luble in water and alcohol S Animal extractive matter so- ) 1.333 1-319 luble in water only . . . . S Fatty matter 3-601 .. a trace. f Alkaline chloride,"! ] sulphate and carbo- ] SaltsV nate, with traces of >0-711 .. 0 585 J alkaline phosphate, I L oxide of iron .... J 100-000 100-00 Dr. Rees describes the albuminous matter of chyle as possessing a dead-white colour, which he attributes to the admixture of a substance of a peculiar character, and upon which he conceives it probable that the white colour of the chyle depends. Will further investigation prove this peculiar substance to be derived from the chyle granule ? or is the chyle granule formed of a combination of this substance with fatty matter ? This peculiar matter, Dr. Rees states, is readily obtained by agitating chyle with aether, when the mixture speedily separates into three distinct strata, the centre stratum being the substance in question ; a similar matter, he observes, may be obtained from saliva by treating it in the same way. He found it to react as follows : — " It was insoluble in alcohol, both hot and cold — insoluble in aether — miscible with water, and soluble in liquor potassae. When it had been dried on platinum foil, the addition of water made it pulpy, and it was found still to be miscible with that fluid, from which, how- ever, it separated in flakes on the addition of diacetate of lead." I have now examined each part of the lym- phatic system in detail, and on reviewing it as a whole, with the mind fully emancipated from the old erroneous views in physiology, and with a full conviction of the truth of the modern discoveries with respect to imbibition, endosmosis, and exosmosis, including venous absorption, as established by Magendie, Du- trochet, Segalas, Delille, and others, and ad- mitted by Miiller, Panizza, Fohmann, Lauth, Breschet, and all the modern investigators in this interesting and intricate field of inquiry, in which 1 regret not to be able to mention the name of one of our own countrymen since the time of Cruickshank, Hewson, and Sheldon — in bringing, I say, with our present improved state of knowledge in physics and physiology, the mind to bear upon the subject of the lym- phatic system, it appears to me that we are justified in materially modifying our opinions, both with respect to the functions exercised by this system of vessels, as well as with regard to its anatomical arrangement, which has been made to depend so much upon the precon- ceived physiological notions respecting it. I venture then to suggest that we are going too far in attributing to the lymphatic (since the veins also absorb) the important and universal function of interstitial absorption of the old material, previous to the deposition of the new, in the process of growth and nutrition; that it is without sufficient proof that we admit the ulcerative process to be carried on solely through the agency of the lymphatic system, or that the removal of all morbid growths or depositions is effected by the one order of ab- sorbent vessels unassisted by the other ; and indeed that there would be nothing repugnant to sound reasoning, or at variance with the pre- sent improved state of our knowledge, were we to confine the functions of the lymphatic system more within the bounds ascribed to the lacteal vessels during the process of digestion, viz. to select and prepare nutritious materials for the purpose of sanguification, and to deposit them in the already circulating current. Descriptive anatomy. — I novv proceed to describe the exact course which the lymphatic vessels take in the different parts of the body, the position and number of the absorbent glands which they traverse, and the precise direction, mode of commencement, and termi- nation of the two principal trunks, into which they pour their contents. This part of our subject, the descriptive anatomy, neither requires nor admits of that rigid exactness which is absolutely necessary in tracing out the ramifications of the blood- vessels. In the first place, the surgeon, in the performance of his operations and in the treat- ment of wounds, scarcely finds it necessary to take the lymphatic vessels into consideration. To relieve the stricture in strangulated femoral 224 LYMPHATIC AND LACTEAL SYSTEM. hernia, he unsparingly divides the principal lymphatics and glands in the inguinal region. In the next place these vessels vary so much in number, and consequently in position in different individuals, while there exist so many parts, where their presence is rather presumed than demonstrated, that a general outline of their course is all that can be re- quired or depended upon. In the distribution of these vessels two principal objects are spe- cially provided for ; the conveyance of the lymph to its appropriate glands, and after- wards from them to the two trunks of the sys- tem. We, consequently, first notice an evident tendency of the vessels from the structures in which they take origin towards the glands which intervene between them and the trunks of the system ; secondly, their necessary course From these glands to the trunks themselves. With this key to the distribution of these vessels, I propose to describe, first, the posi- tion of the glands, then to treat of the trunks of the system ; and, lastly, having these two fixed points, to trace the vessels throughout their course. In the lower extremities the conglobate glands are chiefly found in the inguinal region, where they are divided into a superficial and deeper seated cluster; a few small glands are situated in the popliteal space surrounding the bloodves- sels. We rarely meet with one between the popliteal space and the inguinal region, and they are only occasionally met with below the knee, and then isolated and extremely small. In the upper extremity the large and clustered lym- phatic glands are only found in the axillary space; a single gland is generally located just above the internal condyle of the humerus ; below this point a distinct gland is rarely met with. In the cervical region the principal lympha- tic glands are situated in two cellular intervals, found at the upper part between the omo-byoid and sterno-cleido-mastoid muscles, and below between the latter muscle and the trapezius. The glands in these positions are ranged in a line so as to form a sort of chain of glands, hence the term glandula? concatenate as applied to them. On the head and face the glands are few, small, and isolated. One may be pretty con- stantly met with behind the ear over the mas- toid process of the temporal bone, another in front of the ear in the neighbourhood of the parotid gland. One or two will be found under the margin of the lower jaw, both in the median line and also more laterally situated. A small lymphatic gland will usually be distin- guished amonst the numerous but small buccal and labial glands. In the cavity of the cranium no lymphatic glands have been discovered, but in the abdo- minal and thoracic cavities they are very nume- rous. In the abdomen they are chiefly situated in the neighbourhood of the larger bloodvessels. In the pelvic region they form clusters, or rather chains of glands accompanying the external, in- ternal, and common iliac vessels, and in the lumbar region they are similarly arranged on either side of the aorta, as high as the point of origin of the superior mesenteric artery. The absorbent glands which intercept the lacteals in their course towards the receptaculum chyli are large and numerous; they are situ- ated between the folds of the mesentery, and accompany the trunk and some of the branches of the superior mesenteric artery ; they are usually termed mesenteric glands. The remain- ing lymphatic glands of the abdominal viscera, though numerous, are smaller and more isolated ; they will generally be found close to the arteries of the viscera to which they belong, and conse- quently between the folds of the peritoneum. Of this description may be considered those accompanying the hepatic and splenic vessels : the coronary and gastro-epiploic arteries of the stomach, the small glands of the mesocolon or epiploon, those associated with the renal or spermatic arteries. The largest absorbent glands of the thoracic cavity are those which receive the lymphatics from the lungs; they are situated at the roots of the lungs, pretty closely attached to the bronchi ; they are generally of a dark colour and are called bronchial glands. Those asso- ciated with the lymphatic vessels of the heart are few and small ; two or three may generally be noticed of the size of millet-seeds on the aorta and pulmonary artery, where these vessels are invested by the pericardium. In the poste- rior mediastinum close to the thoracic duct three or four large lymphatic glands are usually met with, as well as several smaller ones in the intercostal spaces, not far from the thoracic duct. In the anterior mediastinum also some small glands may be observed imbedded in loose cellular tissue in the neighbourhood of the internal mammary vessels. Occasionally a small gland may be seen on the convex sur- face of the diaphragm. In the substance or parenchyma of the dif- ferent organs no lymphatic glands have been detected. They have never been seen in the brain, spinal marrow, in the lungs, liver, spleen, kidney, or testicles, in nerve, muscle, or bone. Having given this general outline of the position of the lymphatic glands, I shall now proceed to describe the trunks of the system. The thoracic duct, (Jig. 53,) or principal trunk of the lymphatic system, generally com- mences on the body of the second lumbar vertebra pretty exactly in the median line, concealed behind the root of the right emul- gent artery, bounded on the right by the right crus of the diaphragm, and to the left by the aorta, to which it is connected by cellular tissue. It may be said to be formed by the union of the lymphatics of the lower extremities with the trunks of the lacteals proceeding from the intestines. At the conflux of the principal vessels from these three sources, — and there may be more than one from each, — a dilatation is sometimes found, which has been called the receptaculum chyli. From the body of the se- cond lumbar vertebra the thoracic duct ascends into the thorax between the aorta and vena azygos. In the thorax it is situated behind the right pleural fold of the posterior medias- LYMPHATIC AND LACTEAL SYSTEM. 225 Fig. 53. The thoracic duct and right lymphatic trunk. ( After Mascagni. ) a, Thoracic duct. b, The right lymphatic trunk. c, The trunk of the cervical lymphatics entering separately the internal jugular vein. s, Subclavian vein. Internal jugular vein. », Vena azygos. tinum, having; the aorta to its left, the vena azygos to its right, and the oesophagus in front. In this position it ascends as high as the fourth or third dorsal vertebra, at which level, con- tinuing its course upwards, it turns from right to left, passing behind the descending portion of the arch of the aorta, above which it ap- pears a little external to the root of the left subclavian artery, from whence continuing to ascend it passes between the latter and the left common carotid artery, lying on the longus colli muscle; it now mounts into the cervical region in front of the vertebral artery and vein to the level of the seventh cervical vertebra, opposite to which it begins to form a curve, first forwards and outwards, then down- wards and inwards, striding over the subclavian artery to reach the angle of union between the subclavian and internal jugular veins, at which point it empties itself into the venous system either by one or more branches. The thoracic duct is not uniform in diameter throughout its course ; besides the occasional dilatation at its commencement, it generally presents another on the fourth dorsal vertebra just below its passage behind the descending thoracic aorta. Its narrowest part usually cor- responds to the sixth or seventh dorsal vertebra. The duct is frequently tortuous and rarely single throughout. It often splits into two or more branches, which after a longer or shorter course reunite ; this division and reunion may be two or three times repeated, and it may ul- timately terminate by two or three branches instead of one, VOL. III. The principal irregularities in the arrange- ment of the thoracic duct, which have been recorded by anatomists, are — a double duct, one terminating in the left, the other in the right side of the neck ; a bifurcation of the duct at a higher or lower level, one branch terminating in the angle of union of the subclavian and internal jugular veins of the left side, the other emptying itself either into the corresponding point on the right side or joining the right lymphatic trunk, close to its termination ; a single trunk terminating altogether on the right side of the conflux of the internal jugular and subclavian veins, in which case a short lym- phatic trunk is found on the left side similar to that which usually exists on the right, con- stituting a partial lateral inversion or trans- position confined to the trunks of the lymphatic system. Besides the lymphatics of the lower extre- mities and the lacteals, the thoracic duct re- ceives directly or indirectly the lymphatics of the remaining abdominal viscera (except a few from the right lobe of the liver), those from the exterior and interior of the lower half of the trunk ; also the lymphatics of the left upper extremity, and left side of the head and neck, those from the left lung, the left side of the heart, and from the exterior and interior of the left upper half of the body. The right lymphatic trunk nearly equals the thoracic duct in diameter; it is, however, not more than half an inch in length. Its situation is in the neck at the level of the lower edge of the seventh cervical vertebra, where it will be found lying upon of the subclavian vessels close to the inner edge of the scalenus anticus muscle, and opposite to the union of the subclavian and internal jugular veins, at which point it termi- nates in the venous system. The right lymphatic trunk receives the lym- phatics of the right upper extremity and of the right side of the head ar d neck, those from the right lung and right side of the heart, some few from the right lobe of the liver, and from the exterior and interior of the right upper half of the body. Some of the principal branches which ordi- narily empty themselves into the right lym- phatic Irunk occasionally terminate separately in the internal jugular or subclavian veins close to their junction. When these vessels all enter the veins separately, then the right lymphatic trunk is said to be deficient. Having described the position of the trunks of the lymphatic system as well as the situa- tions of the conglobate glands in the various parts of the body, I now proceed to trace the vessels themselves. I shall commence with the description of the lymphatics of the lower extremities, as being the most remote from the trunks of the system. They are divided, as in all other parts of the body, into a superficial and deep-seated set, which latter accompany the principal bloodves- sels. They are associated successively with the digital arteries, the internal, external plantar, and dorsal arteries of the foot ; in the leg with the anterior, posterior tibial, and fibular vessels. 226 LYMPHATIC AND LACTEAL SYSTEM. Fig. 54. Superficial lymphatics of tlie lower extremity. ( After Muscagni.) a, Saphena major vein. b, Inguinal glands. c, Commencing branches. d> e, f, ' 3—3' 1— 1 1 molars, - - ; molars, - — - : - - 46. 3—3 4—4 Al! the teeth are of small size ; the canines resemble the spurious molars in size and shape, and these are separated by intervals, as in Myr- mecobius. The marsupium opens downwards in the Chatropus, as in the true Bandicoots. The species described has no tail. The genus would seem by its dentition to rank between Myrmecobius and Perameles. Its digital cha- racters are anomalous and unique among the Marsupialia, but are evidently a degeneration from the Saltatorial or Bandicoot type. y. Scansoria. Genus DIDELPHYS, (Opossums,7?g. 85.) These Marsupials are now exclusively con- fined to the American Continents, although the fossil remains of a small species attest their former existence in Europe contemporaneously with the Palaothere, Anoplothere, and other extinct Pachyderms, whose fossil remains cha- racterize the Eocene strata of the Paris Basin. The dental formula of the Genus Didelphys is, — r • 5—5 1—1 Incisors, ; canines, ; pra- 4—4 1 — 1 1 molars, - — - ; molars, . '. ^ : = 50. 3—3 4—4 The Opossums resemble in their dentition the Fig. 85. Didelphys Virginiana. Bandicoots more than the Dasyures : but they closely resemble the latter in the tuberculous structure of the molars. The two middle in- cisors of the upper jaw are more produced than the others, from which they are also separated by a short interspace. The canines are well de- veloped ; the upper being always stronger than the lower. The false molars are simply conical, but are more compressed than in the Carnivo- rous Marsupials. The posterior false molar is the largest in the upper jaw ; the middle one is the largest in the lower jaw ; the anterior one is the smallest in both jaws. The true molars are beset with sharp cusps which wear down into tubercles as the animal advances in age. The crowns of the upper molars present a triangular horizontal section : the base of the triangle is turned forward in the posterior mo- lar ; and obliquely inwards and outwards in the rest. In the lower jaw the true molars are narrower and of more equal size than in the upper jaw: there are five tubercles on each, four placed in two transverse pairs, the anterior being the highest, and a fifth forming the anterior and internal angle of the tooth : the anterior and external angle seems as if it were vertically cut off'. The smaller species of Didelphis, which are the most numerous, fulfil in South America the office of the insectivorous Shrews of the old Continent. Their external resemblance is so close that some have been described as spe- cies of Sorex, but. no true representative of this placental genus has hitherto been disco- vered in South America. The larger Opossums resemble in their habits, as in their dentition, the Carnivorous Dasyures, and prey upon the smaller quadrupeds and birds, but they have a more omnivorous diet, feeding on reptiles and insects and even fruit. One large species, ( Did. cancrivora ) prowls about the sea- shore and lives, as its name implies, on crabs and other crustaceous animals. Another spe- cies, the Yapock, frequents the fresh waters, and preys almost exclusively on fish. It has all the habits of an Otter; and, in consequence of the modifications of its feet, forms the type of the sub-genus Cheironectes, 111. Besides being web-footed the anterior extremities pre- sent an unusual development of the pisiform bone, which supports a fold of the skin, like a sixth digit; it has indeed been described, as such, by M. Temminck : this process lias not, of course, any nail. The dentition of the Vapock resembles that of the ordinary Didelphis. All the Opossums have the inner digit of the hind foot converted by its position and development 262 MARSUPIALIA. into a thumb, but without a claw. The hinder hand is associated in almost all the species with a scaly prehensile tail. In some of the smaller Opossums the sub- abdominal tegumentary folds are rudimental, or merely serve to conceal the nipples, and are not developed into a pouch : the young in these species adhere to the mother by entwining their little prehensile tails around her's ; and they cling to the fur of the back, hence the term dorsigera applied to one of these Opos- sums.* Tribe III. CARPOPHAGA. Stomach simple ; ccecum very long. In this family the teeth, especially those at the anterior part of the mouth, present consider- able deviations from the previously described formula; ; the chief of which is a predomi- nating size of the two anterior incisors, both in the upper and lower jaws. Hitherto we have seen that the dentition in every marsupial genus has participated more or less in a carni- vorous character ; henceforth it will manifest a tendency to the Rodent type. Genus PHALANGISTA. The Phalangers, so called from the phalanges of the second and third digits of the hinder ex- tremity being inclosed in a common sheath of integument, have the innermost digit modi- fied to answer the purposes of a thumb; and this hinder hand being associated in many of the species with a prehensile tail, they evidently, of all Frugivora, come nearest to the arboreal species of the preceding section. In a system framed on locomotive characters they would rank in the same section with the Opossums. We shall see, however, that they differ from those Entomophagous Marsupials in the con- dition of the intestinal tube. Let us examine to what extent the dental characters deviate from those of the Opossums. Fig. 86. Phalangista Cookii. In the skull of a Phalangista Cookii, of which the dental formula is accurately given in Jig. 86, there are both in the upper and lower jaws four true molars on each side, each * Few facts would be more interesting in the present branch of zoology than the condition of the new-born young, and their degree and mode of uterine development in these Opossums. Since the marsupial bones serve, not as is usually de- scribed to support a pouch, but to aid in the func- tion of the mammary glands and testes, they of course are present in the skeleton of these small pouchless Opossums as in the more typical Mar- supials. beset with four three-sided pyramidal sharp- pointed cusps ; thus these essential and most constant teeth correspond in number with those of the Opossum : but in the upper jaw they differ in the absence of the internal cusp, which gives a triangular figure to the grinding surface of the molars in the Opossum ; and the an- terior single cusp is wanting in the true molars of the lower jaw. Anterior to the upper grinders in this Phalanger there are two pre- molars of similar shape and proportions to those in the Opossum ; then a third premolar, too small to be of much functional importance, separated also, like the corresponding anterior premolar in the Opossum, by a short interval from those behind. The canine tooth but slightly exceeds in size the above false molar, and consequently here occurs the first great difference between the Phalangers and Opossums ; it is, however, but a difference in degree of development ; and in the Ursine and other Phalangers, as well as in the Petaurists, the corresponding tooth pre- sents more of the proportions and form of a true canine. The incisors, which we have seen to be most variable in number in the Carnivorous section, are here three instead of five on each side of the upper jaw, but their size, especially that of the first, compensates for their fewness. In the lower jaw there is the same number of molars and functional premolars as in the Opossums ; the two very minute and function- less molars, which form part of the same con- tinuous series, represent the small premolar and canine of the upper jaw; and anterior to these there is one very small and one very large and procumbent incisor on each side. Now if this comparison be just and natural, the difference in the number of teeth between the Phalanger and the Opossum will resolve itself into the former being minus certain incisors in the up- per and lower jaws : in the latter, the great development of the middle incisors seems to produce an atrophy of all the rest. The interspace between the functionally de- veloped incisors and molars in both jaws always contains in the Phalangers teeth of small size and little functional importance, and variable not only in their proportions but their number. The constant teeth in the Phalangers are the ^ ^ true molars, and the - — - incisors. 4—4 1—1 Fig. 87. PJuilangista Vulpina. MAHSUPIALIA. 263 The canines ( c.fig. 86 and 87,) are constant in regard to their presence, but variable in size ; they are always very small in the lower jaw. With respect to the functional premolars | — 1, these are always in contact with the molars, and their crowns reach to the same grinding level ; sometimes a second premolar is similarly developed in the upper jaw, as in the Phal. Coukii, and as in the great flying Phalangers, (Petaurus Taguanoides, Jig. 88) but it is commonly absent, or re- placed by a very minute tooth, shaped like a canine ; so that in the upper jaw, between the posterior or functional premolar and the in- cisors, we may find three teeth, of which the posterior is the largest, as in Phal. Cookii, or the smallest as in Phal. cavifrons ; or there may be only two teeth as in Phal. ursina and Phal. vulpina, and the species, whatever that may be, which M. Fr. Cuvier has selected as the type of the dentition of the Genus. In the lower jaw similar varieties occur in these small and unimportant teeth; e.g. there may be between the procumbent incisors and the posterior premolar, either three teeth as in Phal. Cookii and Phal. cavifrons, or two, as in Phal. ursina, Phal. maculata, Phal. chry- sorrhoos ; or finally one, as in Phal. vulpina and Phut, fuliginosa. The most important modification is presented by the little Phal. gliriformis of Bell, which has only three true molars on each side of each jaw. As these modifications of the teeth are unaccompanied by any change of general structure or of habit, whilst those teeth which most influence the diet are constant, it is obvious that these differences of dentition are unimportant, and afford no just grounds for subgeneric distinctions. The Phalangers, being provided with hinder hands and prehensile tails, are strictly arboreal animals, and have a close external resemblance to the Opossums, by which name they are generally known in Australia and the Islands of the Indian Archipelago, where alone they have hitherto been found. They differ from the Opossums chiefly in their dentition; and in accordance with this difference their diet is more decidedly of a vegetable kind.* The Australian Phalangers feed chiefly on the ten- der buds and the leaves of Eucalypti : but according to Temminck,f the Indian Phalan- gers are omnivorous, and combine insects with fruits and leaves. Mr. OgilbyJ states that both " the Phalangers and Petaurists display so decided a preference for live birds, as to make it probable tint these constitute a main portion of their food in a state of nature." I find, however, that the intestinal canal, and especially the coecum, offers so great an addi- tional development in length, as, with the cor- responding predominance of the incisors, and atrophy of the canines, to indicate clearly a * In the stomach and intestines of specimens sent to me in spirits from Australia, I have never found any other alimentary substances but those of a vegetable nature. t ^tonographies de Mammalojiic, p, 3. I Mag. Hist. Nat. 1837, p. 458. natural and constant tendency in the Phalangers to a vegetable diet. Guided therefore by the totality of their organization, I am led to place them in a distinct section from that which con- tains the Opossums, but, in that section, they come the nearest to the true Opossums. The Phalangers of the Indian Isles have short ears and the greater part of the tail naked. To this group have been applied the names Cconyx, discus, and Balantia ; the Australasian Pha- langers have moderately long ears, and the greater part, or else the whole of the tail is covered with hair. All the species possess considerable freedom of lateral movement in the anterior digits, and in some small species, as Phal. gliriformis, Bell, they appear to be naturally divided into two groups, the two outer being opposed to the three inner fingers. To the hairy-tailed Phalangers exhibiting this character, Mr. Ogilby gives the subgeneric name Pseudocheirus, restricting the term Phalan- gista to the remaining species. With reference to the subgenera Cuseus, Balantia, Pseudo- chcirus, &.c. I heartily concur in the opinion of the experienced and judicious Temminck,* that these numerous sections are perfectly use- less, and a burthensome charge to the memory. Genus PETAURUS. There are many species of Marsupialia limi- ted to Australia and closely resembling, or identical with, the true Phalangers in their den- tal characters and the structure of the feet. 1 allude to the Petaurists or Flying Opossums : these, however, present an external character so easily recognizable, and influencing so ma- terially the locomotive faculties, as to claim for it more consideration than the modifica- tions of the digits or spurious molars which we have just been considering in the Pha- langers. A fold of the skin is extended on each side of the body between the fore and hind legs, which, when outstretched, forms a lateral wing or parachute ; but which, when the legs are in the position for ordinary support or progression, is drawn close to the side of the animal by the elasticity of the subcutaneous cellular membrane, and there forms a mere te- gumentary ridge. These delicate and beautiful Marsupials have been separated generically from the Phalangers under the name of Petaurus: they further differ from the Phalangers in want- ing the prehensile character of the tail, which, in some species of Petaurus, has a general clothing of long and soft hairs, whilst in others the hairs are arranged in two lateral series. Now in the Petaurists there is as little con- stancy in the exact formula of the dentition as among the Phalangers. The largest species of Petaurus (Pet. Taguanoides) for example, is almost identical in this respect with the Pha- langisla Cookii, which M. Fr. Cuvier has therefore classed with the Pelauri. Those teeth of Pet. Taguanoides which are sufficiently developed, and so equal in length, as to exer- cise the function of grinders, or in other words, the functional series of molars, includes six teeth on each side of the upper jaw, and five * Loc. cit. p. 10. 264 MAIISUPIALIA. teetli on each side of the lower jaw. The four posterior molars in each row are true, and bear four pyramidal cusps, excepting the last tooth in the upper jaw, which, as in Ph. Cookii, has only three cusps. In the upper jaw the space between the functional false molars and the in- cisors is occupied by two simple rudimentary teeth, the anterior representing the canine ; but being relatively smaller than in Ph. Cookii, the crowns of the two anterior incisors are rela- tively larger. In the lower jaw the sloping alveolar surface between the functional molars and large procumbent incisors is occupied, ac- cording to M. Fr. Cuvier, by two rudimentary minute teeth, as represented in the figure (fig. 88). I have not found any trace of these Fig. 88. Petaurus Taguanoides. in the two skulls of Pet. Taguanoides examined by me. In Ph. Cookii we have seen that there are three minute teeth in the correspond- ing space ; but these differences would not be sufficient ground to separate generically the two species if they were unaccompanied by modifications of other parts of the body. In Petaurus sciurcus and Petaurusjiaviveuter the dentition more nearly resembles that of Phalangista vulpina. In the upper jaw the functional molar series consists of five teeth on each side; the four hinder ones being, as in Pet. Taguanoides, true tuberculate molars, but diminishing more rapidly in size as they are placed further back in the jaw; the hinder tooth has three tubercles, the rest four ; the apices seem to be naturally blunter than in Pet. Taguanoides. Between the functional premolar and the incisors there are three teeth, of which the Fig. 89. Petaurus flaviventer. representative of the canine is relatively much larger than in the Pet. Taguanoides; the first false molar is also larger and has two roots ; the second, which is functional in Pet. Taguanoides, is here very small. The canine is more deve- loped ; the first incisor is also relatively larger and more produced. In the lower jaw the functional series of grinders consists of the four true tuberculate molars only, of which the last is relatively smaller, and the first of a more triangular form than in Pet. Taguanoides. The space between the tuberculate molars and the procumbent incisor is occupied by four small teeth, of which the one immediately anterior to the molars is large, compressed, pointed, and has two roots; the remaining three are rudi- mentary and have a single fang; the anterior of these corresponds to the one regarded as canine in the upper jaw. Among the species exhibiting this dental formula, viz. 3—3 1—1 canines Incisors 1—1 1—1 premo- lars 40, 3—3 , 4—4 ; molars 3—3 4—4 are Pet. sciureus, Pet. flaviventer, and Pet. mucrurus. The Pigmy Petaurist differs from the pre- ceding and larger species, in having the hairs of the tail distichous, or arranged in two regular lateral series like the barbs of a feather, and in having the spurious molars large and sharp-pointed ; and the true molars bristled each with four acute cusps. This tendency in the dentition to the insectivorous character, with the modification of the tail, induced M. Desmarest to separate the Pigmy Petaurist from the rest of the species, and constitute a new sub-genus for its reception under the name of Acrobates.* To Mr. Waterhouse, however, is due the credit of having first pointed out that the Pigmy Petaurist had but three true molars on each side of each jaw instead of four. There seems, there- fore, to be better reason for accepting this sub- generic section, although we evidently perceive a transition to this condition in the small size of the hinder or fourth molars in the Sciurine Petaurist and its congeners. The description of the dentition of the Pigmy Petaurist in the Regne Animal, besides being defective in this remarkable particular, is not quite exact in other respects. In four adult specimens, two of which were males, and two females with young in the pouch, I find the fol- lowing dental formula to be constant (fig. 90). Incisors : canines . ; premo. 3—3 1 — 1 1 lars ?Z±; molars 3— : 36. 5—3 3—3 Fig. 90. Petaurus pigmceus, twice the natural size. The three quadricuspidategrinders of theupper jaw are preceded by three large premolars, each of which has two fangs, and a compressed triangular sharp-pointed crown, slightly but pro- * Axpoj, summits, @aivai, gradior, as frequenting the summits of trees. MARSUPIALIA. 265 gressively increasing in length as they are placed forward. An interspace occurs between these and the canine, which is long, slender, sharp-pointed, and recurved. The first incisor is longer than the two behind, but is much shorter than the canine. In the lower jaw the true molars are preceded by two functional false ones, similar in size and shape to the three above the anterior false molar, and the canine are represented by minute rudimental simple teeth; the single incisor is long and procumbent as in the other Petaurists. With these differences of dentition approach- ing more or less to one or other of the modifi- cations of the dentition in the group of Phalan- gers, the Petaurists may nevertheless be readily discriminated from those Phalangers which they most resemble ; for example, the Petuurus Tuguunoides may be distinguished from the Phulungista Cookii by the greater relative length in the latter of the nasal and maxillary portion of the skull; while in most of the other species of Petuurus, the facial part of the skull is relatively shorter than in the Pet. Tuguu- noides. Genus PIIASCOLARCTUS. The absence of anomalous or functionless premolars and of inferior canines appears to be constant in the only known species of this genus. The dental formula in three examples of this species ( Phusc.J'uscus, Desm.) is T . 3—3 ■ 1 — 1 Incisors : canines ; premo- 1—1 0—0 lars — 1 ; molars 4~4 : = 30. (Fig. 95.1 1—1 4—4 1 ° J The true molars are larger in proportion than in the Phalangers ; each is beset with four three-sided pyramids, the cusps of which wear down in age, the outer series in the upper teeth being the first to give way ; those of the lower jaw are narrower than those of the upper. The spurious molars are compressed and terminate in a cutting edge ; in those of the upper jaw there is a small parallel ridge along the inner side of the base. The canines slightly exceed in size the posterior incisors; they terminate in an oblique cutting edge rather than a point ; their fang is closed at the extremity : they are situated as in the Phalangers close to the inter- maxillary suture. The lateral incisors of the upper jaw are small and obtuse ; the two ante- rior or middle incisors are twice as long, broad, and thick as the posterior incisors ; they are conical, slightly curved, sub-compressed, be- velled off obliquely to an anterior cutting edge, but differing essentially from the dentes scul- prurii of the Rodentia in being closed at the extremity of the fang. The two incisors of the lower jaw resemble those of the upper, but are larger and more compressed ; they are also formed by a temporary pulp, and its absorption is accompanied by a closure of the aperture of the pulp cavity, as in the upper incisors. The Koala, therefore, in regard to the number, kind, and conformation of its teeth, closely resembles the Phalangers, with which it also agrees in its long coecum and the general conformation of its digestive organs. It has also the extremities similarly organised for prehension ; each is ter- minated by five digits; the hind feet are provided with a large thumb, and have the two contiguous digits enveloped in the same tegumentary fold ; the anterior digits are divided into two groups ; the thumb and index being opposed to the other three fingers. We have already noticed a structure approaching to this in some of the small Phalangers. The Koala, however, differs from the Phalangers and Petaurists in the ex- treme shortness of its tail, and in its more com- pact and heavy general form. It is only known to feed on the buds and leaves of the trees in which it habitually resides. Tribe IV. POEPHAGA: The present tribe includes the most strictly vegetable feeders; all the species have a com- plex sacculated stomach, and a long simple ccecum. Genus HYPSIP11YMNUS. Potoroos. Guided by the modifications of the teeth we pass from the Koala to the Potoroos and Kangaroos — animals of widely different general form. The Potoroos, however, present Fig. 91. Hypnprymnua murinus. absolutely the same dentition as does the Koala, some slight modifications in the form of certain teeth excepted. The premolars in their longi- tudinal extent, compressed form, and cutting edge, would chiefly distinguish the dentition of the Pvtoroo; but the Koala evidently offers the transitional structure between the Phalangers and Potoroos in the condition of these teeth, of which one only is retained on each side of each jaw in the Potoroos as in the Koala. The dental formula of Hypsiprymnus, the generic name of the Potoroos, is Incisors ■ canines llll • premo- 1 — 1 0—0 1 lars iZL? ; molars 1~4 : = 30. 1—1 4—4 The two anterior incisors are longer and more curved, the lateral incisors relatively smaller than in the Koala. The pulps of the anterior incisors are persistent. The canines are larger than in the Koala ; they always project from the line of the intermaxillary suture ; and while the fang is lodged in the maxillary bone' the crown projects almost wholly from the in- termaxillary. In the large Ht/psipn/mnus ursi- nus the canines are relatively smaller than in the other Potoroos, a structure which indicates the transition from the Potorooto the Kangaroo genus. In the skeleton of this species in the 266 MARSUPIALIA. Leyden Museum, the canines have a longitu- dinal groove on the outer side. The characteristic form of the trenchant pre- molar has just been alluded to : its maximum of development is attained in the arboreal Po- toroos of New Guinea ( Hypsiprymnus ursinus and Hyps, dorcocephalus ), in the latter of which its antero-posterior extent nearly equals that of the three succeeding molar teeth. In all the Potoroos the trenchant spurious molar is sculp- tured, especially on the outer side, and in young teeth, by many small vertical grooves. The true molars each present four three-sided pyramidal cusps ; but the internal angles of the two opposite cusps are continued into each other across the tooth, forming two angular or concave transverse ridges. In the old animal these cusps and ridges disappear, and the grind- ing surface is worn quite flat, as in Jig. 91, which represents the dentition of the original Potoroo, described in White's Voyage. Genus MACROPUS. Kangaroos. In the genus Mucropus (fig. 92) the normal condition of the permanent teeth may be ex- pressed as follows : — t 3 — 3 0 — 0 Incisors, . ; canines, lars, molars, 0 — 0 = 28. premo- 1 — 1 '4 — 4 The main difference, as compared with Hyp- siprymnus, lies in the absence of the upper canines as functional teeth ; the germs, how- ever, of these teeth are always to be found in the young mammary feetus of the Macropits major, and I have seen them present, but of very small size, and concealed by the gum, in the adults of some small species of kangaroos, Fig. 92. Macropits major, one-third nat. size. as Macropus rujiventcr, Ogilby, and Macr. psilopus, Gould. This, however, is a rare ex- ception ; while the constant presence and con- spicuous size of the canines will always serve to distinguish the Potoroo from the Kangaroo. But there are also other differences in the form and proportions of certain teeth. The upper incisors of the Macropi have their cutting margins in the same line, the anterior ones not being produced beyond that line, as in the Hyp- siprymni : the third or external incisor is also broader in the kangaroos, and is grooved and complicated by one or two folds of the enamel, continued from the outer side of the tooth ob- liquely forward and inward. In most species the anterior fold is represented by a simple groove : the relative size of the outer incisor, the extent and position of the posterior fold of enamel, and consequently the proportions of the part of the tooth in front or behind it, vary more or less in every species of Macropus : there are two folds of enamel near the anterior part of the tooth in Macr. major, and the pos- terior portion is of the greatest extent, and the entire crown of the tooth is relatively broadest in this species. The middle incisor is here also complicated by a posterior notch and an external groove. These modifications of the external incisors of the kangaroos were first no^ ticed by Mr. Jourdan, and subgeneric distinc- tions, with names often sufficiently unmeaning, if not absurd,* have been subsequently based upon them ; but such dental characters possess neither sufficient constancy nor physiological importance to justify such an application. M. Fr. Cuvier has proposed a binary divi- sion of the genus Mucropus, as here defined, founded on the absence of permanent spurious molars, and a supposed difference in the mode of succession of the true molars in certain spe- cies of Kangaroo, combined with modifications of the muzzle or upper lip, and of the tail. The dental formula which I have assigned to the genus Macropus is restricted in its ap- plication by that naturalist to some small spe- cies of Kangaroo, grouped together under the term Halmaturus, originally applied by Illiger to the Kangaroos generally .f The rest of the Kangaroos, under the generic term Macro- pus, are characterised by the following dental formula: — Incisors, -: molars, 1 = 24. 2 4 — 4 The truth, however, is, that both the Halmaturi and Macropi of M. Fr. Cuvier have their teeth developed in precisely the same num- ber and manner : they only differ in the length of time during which certain of these teeth are retained.! 1° the great Kangaroo, for exam- ple, the permanent premolar which suceeeds the corres- ponding deciduous one in the vertical direction, is pushed out of place and shed by the time the last * E. g. Bettongia, Gray, Petrogale, Gray, which signifies * rock weasel.' t Prodromus Systematis Mammalium et Avium, 8vo. 1811. The dental character which this ex- cellent naturalist gives, accurately expresses the condition of the canine or laniary teeth, " La- niarii aut nulli, aut superiores 2 ambigui, minuti, in medio inter primorcs et molares collocati,'' p. 80 ; but there are never more than five molars in place on each side of each jaw in the Kangaroo. X M. Fr. Cuvier was aware that a deciduous spu- rious molar existed in the great Kangaroo and other species of his subgenus Macropus, but he believed that it was peculiar to an early period of life, and then existed only in a rudimental state, or " en germe," and that instead of being displaced and MARSUPIALIA. 267 true molar has cut the gum : the succeeding true molar is soon afterwards extruded ; and I have seen a skull of an old Macropus major in the Museum at Leyden, in which the grinders were reduced to two on each side of each jaw by this yielding of the anterior ones to the vis a tergo of their successors. The general form of the body in the Ma- cropodidts is that of an elongated cone, the broad and stout haunches forming the base, and the produced tapering muzzle the apex. The proportions of the body are, however, re- duced by so elegant a gradation that they are justly considered as among the most picturesque of quadrupeds. The hinder extremities are al- ways longer and stronger than the fore ones, but in various proportions ; the difference being least in the arboreal Potoroos, and in that section of the genus represented by the Hypsiprymnus myosurus of Van Dieman's Land. The tail is very long in all the species, but is strongest in the great kangaroos, which make use of it as a kind of crutch or fifth extremity in their slower modes of progression. In the Potoroos the tail is more slender, and in these and some of the smaller species of kangaroo it is bent be- neath the body when the animal reposes. Tribe V . R HIZO PHAGA. In this tribe, the stomach is simple in out- ward form, but complicated within by a large cardiac gland ; and the ccecum, which is short and wide, with a vermiform appendage. Genus PHASCOLOMYS, (fig. 93.) In its heavy shapeless figure, large trunk, and short equably developed legs, the Wom- bat offers as great a contrast to the Kangaroos as Fig. 93. Phascolomysfusca, Geoff, one-half nut. size. does the Koala, which it most nearly resembles in its general outward form and want of tail. But in the more important characters afforded by the teeth and intestinal canal, the Wombat succeeded in the vertical direction by a permanent spurious molar, as in the Halmaluri, it was dis- placed by the true molars, which are developed from behind forwards. 1 have however detected the crown of the permanent spurious molar in the jaws of the Macropus major in a concealed alveolus, and have observed it completely formed and in place in an individual which had nearly attained its full size. — See F. Cuvier's account of the Halmaturus Thetis in the " Histoirc des Mammiferes," folio. differs more from the Koala than the latter does from either the Phalangers or Kangaroos. The dental system presents the extreme de- gree of that degradation of the teeth, interme- diate between the front incisors and true molars, which we have been tracing from the Opossum to the Kangaroos : not only have the function- less premolars and canines now totally disap- peared, but also the posterior incisors of the upper jaw, which we have seen in the Potoroos to exhibit a feeble degree of development as compared with the anterior pair; these in fact are alone retained in the dentition of the present group, the representative of which possesses the fewest teeth of any Marsupial animal. The dental formula of the Wombat is thus reduced both in number and kind to that of the true Rodentia.* t • 2 0 , 1 — 1 Incisors, _ ; canines, - ; premolars, • 2 0 1 — 1 ' 4 4 molars, = 24. 4 — 4 The incisors moreover are Irue dentes sculpra- rii, with persistent pulps, but are inferior, espe- cially in the lower jaw, in their relative length and curvature to those of the placental Glires; they presentasubtriedral figure, and aretraversed by a shallow groove on their mesial surfaces. The spurious molars present no trace of that compressed structure which characterizes them in the Koala and Kangaroos, but have a wide oval transverse section; those of the upper jaw being transversed on the inner side with a slight longitudinal groove. The true molars are double the size of the premolars : the su- perior ones are also traversed by an internal longitudinal groove, but this is so deep and wide that it divides the whole tooth into two prismatic portions, with one of the angles directed inwards. The inferior molars are in like manner divided into two triedral portions, but the intervening groove is here external, and one of the facets of each prism is turned inwards. All the grinders are curved, and describe about a quarter of a circle: in the upper jaw the con- cavity of the curve is directed outwards ; in the lower jaw, inwards. The false and true molars, like the incisors, have per- sistent pulps, and are consequently devoid V of true fangs, in which respect the Wom- bat differs from all other Marsupials, and resembles the extinct Toxodon, the denti- gerous Bruta, and herbivorous Rodentia. I may add that the Wombat deviates from the other Marsupials in the number of its ribs; as these are very constant in the rest of the order, the difference in the Wombat, which has 15 pairs, instead of 13 or 12, is the more deserving * In all the placental Rodents, which have more than three molars in each lateral series, the addi- tional ones are placi d at the anterior part of the row, and are subject to displacement by a perma- nent successor in the vertical direction, and conse- quently arc essentially " premolars," or spurious molars; the Wombat strikingly manifests its mar- supial character in having four true molars on each side of both jaws. 268 MARSUriALIA. of notice. The Koala, like the Phalangers and Kangaroos, has 13 pairs of ribs ; but this class of characters will form the subject of the fol- lowing section. Osteology of the Marsupialia. Of the Skull.— The form of the skull varies much in different Marsupial animals, but it may be said, in general terms, to re- semble an elongated cone, being terminated by a vertical plane surface behind, and in most of the species converging towards a point ante- riorly : it is also generally more depressed or flattened than in the placental Mammalia. The skull is also remarkable in all the Marsupial genera for the small proportion which is de- voted to the protection of the brain, and for the great expansion of the nasal cavity immediately anterior to the cranial cavity. In the stronger carnivorous Marsupials the exterior of the cranium is characterized by bony ridges and muscular impressions, but in the smaller herbivorous and insectivorous species, as the Petaurists, Potoroos, and Myrmecobius, the cranium presents a smooth convex surface as in Birds, corresponding with the smooth un- convoluted surface of the simple brain con- tained within. The breadth of the skull in relation to its length is greatest in the Wombat,* Ursine Da- syuref and Petaurists, in which it equals three- fourths of the length, and is least in the Pera- melcs lagotis, in which it is less than one-half. The occipital region, which is generally plane, and vertical in position, forms a right angle with the upper surface of the skull, from which it is separated by an occipital or lambdoidal crista. This crista is least developed in the Myrmecobius, Petaurists, and Kangaroos, and most so in the Thylacine and larger Opossums, in which, as also in the Koala, the crest curves slightly backwards, and thus changes the occipi- tal plane into a concavity for the firm implanta- tion of the strong muscles from the neck and back. The upper surface of the skull presents great diversity of character, which relates to the dif- ferent development of the temporal muscles, and the varieties of dentition in the different genera. In the Wombat the coronal surface offers an almost flattened tract bounded by two slightly elevated temporal ridges, which are upwards of an inch apart posteriorly, and slightly diverge, as they extend forwards to the anterior part of the orbit. The skull of the Virginian Opossum pre- sents the greatest contrast to that condition, for the sides of the cranium meet aboveat an acute angle, and send upwards from the line of their union a remarkably elevated sagittal crest, which, in mature skulls, is proportionally more deve- loped than in any of the placental Carnivora, not even excepting the strong-jawed Hveena. The Thylacine and Dasyures, especially the Ursine Dasyure, exhibit the sagittal crest in a somewhat less degree of development. It is again smaller, but yet well marked in the Koala and Perameles. The temporal ridges meet at * As 15 lo 20. t As 10 to 14. the lambdoidal suture in the larger Phalangitis and in the Hypsiprymni, but the size of the muscles in these does not require the deve- lopment of a bony crest. In the Kangaroo, the temporal ridges, which are very slightly raised, are separated by an interspace of the third of an inch. They are separated for a proportionally greater extent in the Petaurists, especially P etaurus ftaviventer ; and in the smooth and convex upper surface of the skull of Petaurus sciureus, Pet. pigmaus, Myrmecobius, the im- pressions of the feeble temporal muscles almost cease to be discernible. The zygomatic arches are, however, complete in these as in all the other genera: they are usually, indeed, strongly developed ; but their variations do not indicate the nature of the food so clearly, or correspond with the diffe- rences of animal and vegetable diet in the same degree as in the placental Mammalia. And this is not surprising when we recollect that no Marsupial animal is devoid of incisors in the upper jaw, like the ordinary Ruminants of the placental series : accordingly the more com- plete dental system with which the herbivorous Kan garoos, Potoroos, Phalangers, &c. are pro- vided, and which appears to be in relation to the scantier pasturage and the dry and rigid character of the herbage or foliage on which they browse, requires a stronger apparatus of bone and muscle for the action of the jaws, and especially for the working of the terminal teeth. There are, however, well marked diffe- rences in this part of the Marsupial skull ; and the weakest zygomatic arches are those of the Insectivorous Perameles and Acrobates, in which structure we may discern a correspon- dence with the Edentate Anteaters of the pla- cental series. Still the difference in the deve- lopment of the zygomata is greatly in favour of the Marsupial Insectivora. The Hypsiprymni come next in the order of development of the zygomatic arches ; which again are proportionally much stronger in the true Kangaroos. The length of the zygomata in relation to the entire skull is greatest in the Koala and Wombat. In the former animal they are remarkable for their depth and straight and parallel course, as well as for their longi- tudinal extent. In the Wombat they have a considerable curve outwards, so as greatly to diminish the resemblance which otherwise ex- ists in the form of the skull between this Mar- supial and the Herbivorous Rodentia of the placental series, as, e. g. the Viscaccia. In the carnivorous Marsupials the outward sweep of the zygomatic arch, which is greatest in the Thylacine und Ursine Dasyure, is also accompanied by a slight curve upwards, but this curvature is chiefly expressed by the con- cavity of the lower margin of the zygoma, and is by no means so well marked as in the placental Carnivora. It is remarkable that this upward curvature is greater in the slender zygomata of the Perameles than in the stronger zygomata of the Dasyures and Opossums. In the Koala and Phalangers there is also a slight tendency to the upward curvature ; in the MARSU PI ALIA. 209 Wombat the outwardly expanded arch is per- fectly horizontal. In the Kangaroo the lower margin of the zygoma describes a slightly undu- lating curve, the middle part of which is con- vex downwards. In many of the Marsupials, as the Kangaroo, the Koala, some of the Phalangers, Petaurists, and Opossums, the superior margin of the zygoma begins immediately to rise above the posterior origin of the arch. In the Wombat an external ridge of bone commences at the middle of the lower margin of the zygoma, and gradually extends outwards as it advances for- wards, and being joined by the upper margin of the zygoma, forms the lower boundary of the orbit, and ultimately curves downwards in front of the ant-orbital foramen, below which it bifurcates and is lost. This ridge results, as it were, from the flattening of the anterior part of the zygoma, which thus forms a smooth and slightly concave horizontal platform for the eye to rest upon. The same structure obtains, but in a slighter degree, in the Koala. In the Kangaroo the anterior and inferior part of the zygoma is extended downwards in the form of a conical process, which reaches below the level of the grinding-teeth. A much shorter and more obtuse process is observable in the corresponding situation in the Phalangers and Opossums. The relative length of the facial part of the skull anterior to the zygomatic arches varies re- markably in the different Marsupial genera. In the Wombat it is as six to nineteen ; in the Koala as five to fourteen ; in the Pe- taurus sciureus and Petaurus Henrietta it forms about one-fourth of the entire skull ; in the Phalangers about one-third ; in the carnivorous Dasyures and Opossums more than one-third ; in the Thylacine nearly one-half ; in Perameles, Macropus, and Hypsiprymnus murium, III. the length of the skull anterior to the orbit is equal to the remaining posterior part ; but in a species of Hypsiprymnus from Van Dieman's Land ( Hypsiprymnus myosurus, Ogilb.), the facial part of the skull anterior to the orbit exceeds that of the remainder, and the arboreal Hypsi- prymni from New Guinea present a still greater length of muzzle. In most Marsupials the skull gradually converges towards the anterior extremity ; the convergence is more sudden in the Petavrists, especially Pet. Bennettii; but in the Perameles lagotis the skull is re- markable for the sudden narrowing of the face anterior to the orbits, and the prolongation of the attenuated snout, preserving the same diameter for upwards of an inch before it finally tapers to the extremity of the nose. In the Koala the corresponding part of the skull is as remarkable for its shortness, as it is in the Per. Ingutis for its length, but it is bounded laterally by parallel lines through its whole extent. Before concluding this account of the general form of the skull, I may observe that in nearly all the Marsupials two long processes project downwards from the inferior angles of the occipital region ; they correspond in func- tion with, and have been described as the mastoids, but they are developed from the ex-occipital bones. These processes are longest in the Kangaroos and Koala ; in the Wombat they co-exist with the true mastoid pro- cesses, which are of larger size. In the Opos- sums and Dasyures the exoccipital processes are short and obtuse; in Acrobates they cease to exist, but they are present in the larger Petaurists. Of the coinposition of the cranium. — The occipital bone is developed, as in the placental Mammalia, from four centres or elements, — the basilar below, the supra-occipital above, and the ex-occipitals at the sides; but these ele- ments remain longer separate, and in some genera do not become at any period of life united by continuous ossification. In the skull of an aged Virginian Opossum, I found the supra-occipital still distinct from the ex-occipitals, and these not joined together, though anchylosed to the basilar element. I say not joined together, because in this Mar- supial animal they meet above the foramen occipitale and complete its boundaries, as the corresponding superior vertebral laminae com- plete the medullary canal in the region of the spine. I find the same structure and condition of the occipital bone of an adult Dasyurus Ursinus, and it is exhibited in the plate of the cranium of this species given by M. Temminck.* In the skull of the mature Wombat, of which a reduced representation is given at fig. 94, the ex-occipitals were still unanchylosed ; the left is figured separate at a. In the skull of a Perameles nasuta the ex- occipitals are separated by an interspace, so that a fissure is continued from the upper part of the foramen magnum to the supra-occipital element. The same structure may be observed in the great Kangaroo, and it is very re- markable in the young skulls of this species ; I found this superior notch wide and well marked in Macropus Bennettii. In the Wombat the corresponding fissure is very wide, and the lower margin of the supra-occipital is notched, so that the shape of the foramen magnum somewhat resembles that of the trefoil leaf. In the Koala, the Pha'anger, Petaurists, Hyps'i- prymni, and Dasyurus Maugei, the elements of the occipital bone present the usual state of bony confluence. The temporal bone generally presents a per- manent separation of the squamous, petrous, and tympanic elements. I have observed this reptilian-like condition of the bone in the ma- ture skulls of an Ursine Dasyure, a Virginian Opossum, a Perameles, in different species of Potoroo and Kangaroo, in the Wombat, and in the Koala. The petrous and mastoid elements are commonly anchylosed together. So loose indeed is the connexion of the tympanic bone, that without due care it is very liable to be lost in preparing the skulls of the Marsupials. In the Kangaroo and Wombat (jig. 94, b) it * JVIonographies de Mammalogie, pi. viii. 270 MARSUPIALIA. Fig. 94. Pltascolomys. forms a complete bony tube, about half an inch in length, with an irregular exterior ; it is wedged in between the mastoid and articular processes of the temporal bone. In the Potoroo the bony circle is incomplete at the upper part; in the Perameles and Da- syures the tympanic bone forms a semicircle, the posterior part being deficient, and the tym- panic membrane being there attached to a des- cending process of the squamous element of the temporal bone. Here we have a near ap- proach to the form of tympanic bone in Birds, but we have a still closer resemblance to its condition both in Birds and Reptiles, in its want of union with and relations to the petrous element of the temporal bone. In the Rodent quadrupeds the tympanic, petrous, and mas- toid elements of the temporal bone are always anchylosed together; this condition is well shown in the skull of the Porcupine and Beaver, in which the mastoid element sends down a thin obtuse process behind the petro- tympanic portion. It is to the expansion of the petro-tympanic, and not of the mastoid portion of the temporal bone, that the enlarge- ment of the tympanic cavity is due in the Rodentia, and this expansion forms in that order, as is well known, a large bulla ossea, which is situated anterior and internal to the mastoid process. In many of the Marsupials, as the Dasyures, Petaurists, Perameles, Po- toroos, and Koala, there is also a large bulla ossea for the purpose of increasing the extent of the auditory cavity ; but, with one single ex- ception, the Wombat, this bulla is not formed by the tympanic or any other element of the temporal bone, but by the expansion of the base of the great ala of the sphenoid bone. In Acrobutes and Perameles lagotis, in addition to the preceding bulla there is also an external dilatation of the petrous element of the tem- poral bone, which thus forms a second and smaller bulla on each side, behind the large bulla ossea formed by the sphenoid. In other Marsupials the petrousbone is of smallsize,gene- rally limited to the office of protecting the parts of the internal ear, and sometimes, as in the Koala, is barely visible at the exterior of the base of the skull. The petrous and mastoid elements are usually anchylosed together in the Marsu- pials, and the mastoid portion appears in the occipital region of the skull of the Koala, between the ex-occipital bones and squamous portion of the temporal. The petrous element of the temporal bone appears externally in the corresponding part of the skull of a young Emeu. In the Kangaroos and Wombat the petro-mastoid bone presents a larger size, and is visible in two situations on the outside of the skull, viz. at the usual place at the basis, where the petrous portion is wedged in be- tween the basilar bone, ex-occipital and sphe- noid, and again at the side of the cranium, where the mastoid portion appears between the squamous, ex-occipital, and supra-occipital bones. In the Wombat it sends outwards the strong compressed process which terminates the lateral boundaries of the occipital plane of the cranium ; but this process is entirely due to the ex-occipitals in the Koala and other Marsupials. The auditory chamber of the ear is aug- mented in the Phalangers, the Koala, the Kan- garoos, and Potoroo, by a continuation of air- cells into the base or origin of the zygomatic process ; but the extent of the bony air-cham- bers communicating with the tympanum is proportionally greatest in the Flying Opossums, where, besides the sphenoid bulla, the mastoid element and the whole of the zygomatic pro- cess of the temporal bone are expanded to form air-cells with very thin and smooth walls, thus presenting an interesting analogy in the structure of the cranium to the class of birds. The direction of the bony canal of the organ of hearing corresponds, as in the placental Mammalia, with the habits of the species. The meatus is directed outwards and a little forwards in the carnivorous Dasyures ; out- wards and a little backwards in the Perameles and Phalangers ; outwards, backwards, and upright in the Kangaroos, and directly out- wards in the Petaurists and Wombat; but the differences of direction are but slightly marked. The squamous element of the temporal bone MARSUPIALIA. 271 generally reaches half-way from the root of the zygoma to the sagittal ridge or suture ; it is most developed in the Wombat, in which its superior margin describes a remarkably straight line. The zygomatic process of the temporal bone is generally compressed and much ex- tended in the vertical direction in the Opossum, Dasyure, Phalanger, Koala, and Kangaroo. In the Wombat it curves outwards from the side of the head in the form of a compressed and almost horizontal plate; it is then sud- denly twisted into the vertical position, to be received into the notch of the malar portion of the arch. The cavity corresponding to the sphenoidal bulla ossea in other Marsupials is in this species excavated in the lower part of the squamous element of the temporal bone at the inner side of the articular surface for the lower jaw. This articular surface, situated at the base of the zygomatic process, presents in the marsupial, as in the placental Mammalia, various forms, each manifesting a physiological relation to the structure of the teeth and adapted to the required movement of the jaws in the various genera. In the herbivorous Kangaroo the glenoid cavity forms a broad and slightly convex surface, as in the Ruminants, affording freedom of rotation to the lower jaw in every direction. In the Phalangers and Potoroos the articular surface is quite plane. In the Perameles it is slightly convex from side to side, and concave from behind forwards. In the Wombat it is formed by a narrow convex ridge considerably extended, and slightly con- cave, in the transverse direction. This ridge is not bounded by any descending process pos- teriorly, so that the jaw is left free for the movements of protraction and retraction. But this structure is widely different from that which facilitates similar movements in the Ro- dentia. In these there is a longitudinal groove on each side, in which the condyle of the lower jaw plays backwards and forwards, but is im- peded in its lateral movements ; these, on the contrary, are freely allowed to the Wombat, and the oblique disposition of the lines of enamel upon the molar teeth correspond with the various movements of which the lower jaw of the Wombat is thus susceptible. In the Koala the glenoid cavity is a transversely ob- long depression with a slight convex rising at the bottom, indicating rotatory movements of the jaw. In the carnivorous Dasyures it forms a concavity still more elongated transversely, less deep than in the placental Carnivoia, but adapted, as in them, to a gitiglymoid motion of the lower jaw. In all the genera, save in the Wombat, retraction of the lower jaw is opposed by a descending process of the temporal bone immediately anterior to the meatus auditorius and tympanic bone. The glenoid cavity presents a characteristic structure in most of the Marsupialia in not being exclusively formed by the temporal bone. With the exception of the Petaurists, the malar bone forms the outer part of the articular sur- face for the lower jaw, and in the Tliylucinus, Dmyurus Mavgei, Dasyurus ursinitSg Pera- meles, Hypsiprymnus, and Macropus the sphe- noid ala forms the inner boundary of the same surface ; but this ala does not extend so far out- wards and backwards in the Wombat or Koala. The sphenoid bone has the same general form and relative position as in the ordinary Mammalia, but in many Marsupials it presents a similarity to that in the Ovipara in the per- sistence of the pterygoid processes as separate bones, as shown in the Wombat (Jig. 94, c). It is only in the Koala that I have observed a complete obliteration of the suture joining the basilar element of the sphenoid with that of the occipital bone. In the Thylacine a narrow straight bridge of bone is continued from the auditory sphenoidal bulla forwards to the base of the pterygoid process, resembling the condition of the pterygoids in Birds. The chief peculiarity in the sphenoid bone is the dilatation of the root of the great ala already alluded to. This dilatation communi- cates and is filled with air from the tympanum. It forms the hemispherical bulla ossea on each side of the basis cranii in the Dasyures and Phascogales, and the large semi-ovate bulla' in the Myrmecobius, Cook's Phalanger, &c. ; but in the Koala the bullae (b, fig. 95,) are stil! Fig. 95. Phascolarctus. more developed, and are produced downwards to an extent equal with the ex-occipital pro- cesses (a, Jig. 95) ; they are somewhat com- pressed laterally, and instead of the smooth and polished surface which characterizes them in the preceding genera, terminate here in a rough ridge. The dilated air-chambers or bullae of the sphenoid are very small in the Thylacine ; in the Phalangers and Potoroos they are relatively smaller than in the Dasyures, and they are incomplete posteriorly in the Kan- garoos and Wombat. In the Brush-Kangaroo the above process from the sphenoid joins the base of the large descending process of the ex-occipital. The pterygoid processes are relatively largest in the Kangaroo, Wombat, and Koala, and present in each of these species distinct hamular processes. In the Potoroo, Kangaroo, and Wombat the sphenoid ala com- bines with the pterygoid process to form a large and deep depression opening externally. In the Kangaroo, Dasyures, Koala, and Wom- bat the great ate of the sphenoid articulate with the parietal bones, but by a very small portion in the two latter species : in the Pera- 272 MARSUPIALIA. meles and Potoroos the sphenoid aire do not reach the parietals. There is little to notice in the parietal bones except the obliteration of the sagittal suture in those species in which a bony crista is deve- loped in the corresponding place. They pre- sent a singularly flattened form in the Wombat, in an aged skull of which, and in a similar one in the Kangaroo, I observe a like obliteration of the sagittal suture. In the Kangaroo, Potoroo, Petaurus, Phalanger, and Myrme- cobius there is a triangular inter-parietal bone. The corresponding bone I find in three pieces in the skull of a Wombat. The frontal bones are chiefly remarkable for their anterior expansion and the great share which they take in the formation of the nasal cavity. In the Thylacine the part of the cranium occupied by the frontal sinuses exceeds in breadth the cerebral cavity, from which it is divided by a constriction. The coronal suture presents in most of the Marsupials an irregular angular course, forming a notch in the frontals on each side which receives a corresponding triangular process of each parietal bone : this form of the suture is least pronounced in the Acrobates and Myrmecobius. A process cor- responding to the posterior frontal augments the bony boundary of the orbit in the Thylacine, the Ursine Dasyure, and in a slighter degree in the Virginian Opossum ; it is relatively most developed in the skull of the Myrmecobius J'asciatus, where the orbit is large ; but the bony boundary of the orbit is not complete in any of the Marsupials. In the Myrmecobius there is a deep notch at the middle of the supra-orbital ridge. A corresponding but shallower notch is present in the skull of Petaurus sciureus. 1 have found the frontal suture obliterated in old specimens of the Thylacine, the Virginian Opossum, Cook's Pha- langer, the taguanoid, and yellow-bellied Pe- taurists; but the frontal suture exists in Petaurus Sciur.eiis, Acrobales, and other Marsupials. The inter-orbital space is concave in the Pha- langers and in the Petaurus Taguanoides, but is quite flat in the other Petaurists. The lachrymal bones vary in their relative size in different Marsupialia. In the Koala they extend upon the face about a line beyond the anterior boundary of the orbit, and at this part they present a groove with one large and two or three small perforations. In the Wom- bat their extent upon the face is slightly in- creased ; it is proportionally greater in the Kangaroos, Potoroos, Phalangers, Petaurists, and Dasyures, in which this part of the lachrymal bone presents two perforations close to the orbit. In the Thylacine, besides the two external holes there is a large perforation within the orbital margin. This carnivorous Marsupial, as compared with the Wolf, pre- sents a greater extent of the facial portion of the lachrymal hone, and thus indicates its inferior type. In the Myrmecobius the lachry- mal bone exhibits its greatest relative develop- ment. The malar bones are very strong and of great extent in almost all the Marsupialia. They are least developed in Acrobates, Myrme- cobius, and Pcrameles lagotis. In the latter the malar bone presents a singular form, being bifurcate at both extremities: the processus zygomaticus maxillte superioris is wedged into the cleft of the anterior fork ; the correspond- ing process of the temporal bone fills up the posterior notch ; the lower division of this bifurcation is the longest, and in all the Mar- supialia enters into the composition of the articular surface for the lower jaw, except in the Petaurists, where it just falls short of this part. The anterior bifurcation of the malar bone is not present in the Marsupials generally; the external malo-maxillary suture forms an oblique and almost straight line in the Wombat, Phalanger, Opossum, Dasyures, and Kangaroo. Owing to the inferior development of the zygo- matic process of the superior maxillary in the Wombat, the malar bone is not suspended in the zygomatic arch in this Marsupial as in the placental Rodentia. It is also of relatively much larger size and of a prismatic form, arising from the development of the oblique external ridge above described. In the Kan- garoos, Potoroos, Great Petaurus, and Pha- langers it is traversed externally by a ridge showing the extent of attachment of the masseter ; in the Koala the ridge extends along the malar bone near the upper margin, and the surface below presents a well-marked excava- tion. The nasal bones vary in their form and rela- tive size in the different genera; they are longest and narrowest in the Perameles, shortest and broadest in the Koala. Their most charac- teristic structure is the expansion of their upper and posterior extremity, which is well marked in the Wombat, Myrmecobius, Petaurists, Phalangers, Opossums and Dasyures. In the Potoroos the anterior extremities of the nasal bones converge to a point which pro- jects beyond the inter-maxillaries. In some Petaurists and Perameles the corresponding- points reach as far as the inter-maxillaries, and in a skull of the Perameles lagotis I have found the bony case of the nasal passages to be further increased by the presence of two small rostral bones, resulting, as in the Hog, from ossification of the nasal cartilage. The inter-maxillary bones always contain teeth, and the ratio of the development of these bones corresponds with the bulk of the dental apparatus which they support. They are con- sequently largest in the Wombat, where they extend far upon the side of the face and are articulated to a considerable proportion of the nasal bones, but do not, as in the placental Rodentia, reach the frontal or divide the maxillary bone from the nasal. They pre- sent a somewhat lower degree of development in the Koala, but both in this species and in the Wombat they bulge outwards and thus remarkably increase the transverse diameter of the osseous cavity of the nose. Neither in Hypsiprymnus nor Macropus do I find the incisive palatal foramina entirely in the intermaxillary bones, as is described by the author of the text in Pander and D'Alton's MARSUPIALIA. Skelete der Beutelthiere ; a small proportion of their bony circumference is due to the anterior- extremity of the palatal process of the maxil- lary : the same structure obtains in the Wom- bat, Koala, and Opossums. In the Dasyures and Phalangers a greater proportion of the posterior boundary of the incisive or anterior palatal foramina is formed by the maxillaries; in the Petaurists they are entirely surrounded by the maxillary bones, while in the Perameles they are, on the contrary, entirely included in the intermaxillaries. They always present the form of two longitudinal fissures : the Myrme- cobius agrees with the other Marsupials in this structure. The superior maxillary bone in the Wom- bat sends upwards a long, narrow, irregular nasal process, which joins the frontal and nasal bones, separating them from the inter- maxillaries; the part of the maxillary bone which projects into the temporal fossa behind the orbit presents two or three smooth tuberosi- ties, formed by the thin plate of bone covering the pulps of the large curved posterior grinders. The corresponding part in the Perameles lagotis is perforated by numerous minute apertures like a cribriform plate, and this structure is presented in a slighter degree in the Potoroos and Ursine Dasyure. The antorbital foramen does not present any marked variety of size, which is generally moderate. It is much closer to the orbit in the carnivorous Marsu- pialia than in the corresponding placental quadrupeds. It is relatively largest in the Ursine Dasyure. It presents the form of a vertical oblique fissure in the Wombat. I have observed it double in the Kangaroo. The chief differences in the maxillary bones, indepen- dently of the teeth and their alveoli, are pre- sented by the palatal processes, the modifica- tions of which we shall consider in conjunction with those presented by the palatal processes of the palatal bones. The perforations and vacuities of the bony palate deserve, indeed, particular attention, as they are often specific and of consequence in the determination both of recent and fossil species. In Phahmgista Cookii, in Petaurus Jlaviven- ter, and Ptlaurus sciureus, in Macropits major, and some other great Kangaroos the bony palate is of great extent and presents a smooth surface, concave in every direction towards the mouth ; it is pierced by the two posterior palatine foramina at the anterior external angles of the palatine bones, either within or close to the transverse palato-maxillary sutures. Behind these foramina, in the Kangaroo, there are a few small irregular perforations. The bony palate is similarly entire in the Hypsiprymnus ursinus. In Macropus Benneltii there are four orifices at the posterior part of the bony palate. The two anterior ones are situated upon the palato-maxillary suture, and are of an ovate form with the small end forwards. The two posterior foramina are of a less regular form and smaller size. In the Brush Kangaroo (Macropus Brunii, Cuv.) the posterior palatal foramina present the form of two large fissures placed obliquely and converging posteriorly. vol. nr. They encroach upon the posterior borders of the maxillary plate. Anterior to these vacancies there are two smaller foramina, and posterior to them are one or two similar foramina. In the Australian Potoroos, Wombat, and Koala, the posterior palatal openings are large, and oval, and situated entirely in the palatal bones. In Hyps, setosus they extend as far for- wards as the interspace between the first and second true molars; in Hyps, murinus they reach to that between the second and third true molars. Posterior and external to these large vacuities there are two small perforations. In the Phalangers, with the exception of Ph. Cookii, the palatal openings are proportionally larger ; they extend into the palatal process of the maxillaries, and the thin bridge of bone which divides the openings in the Potoroo, &c, is wanting ; the two perforations at the pos- terior external angles of the palatine bones are also present. In the Virginian Opossum the bony palate presents eight distinct perforations, besides the incisive foramina ; the palatal pro- cesses of the palatine bone extend as far for- wards in the median line as the third molars : a long and narrow fissure extends for an equal distance (three lines) into the palatal processes both of the palatines and maxillaries : behind these fissures and nearer the median line are two smaller oblong fissures ; external and a little posterior to these are two similar fissures, situated in the palato-maxillary suture ; lastly, there are two round perforations close to the posterior margin of the bony palate. In the Ursine Dasyure a large transversely oblong aperture is situated at the posterior part of the palatal processes of the maxillary bones, and encroaches a little upon the palatines ; this aperture is partly,* perhaps in young skulls wholly, bisected by a narrow longitu- dinal osseous bridge. In Mauge's Dasyure there are two large ovate apertures crossing the palato- maxillary sutures separated from each other by a broad plate of bone ; posterior to these are two apertures of similar size and form, which, being situated nearer the mesial line, are divided by a narrower osseous bridge ; each posterior external angle of the bony palate is also perforated by an oval aperture. In the Viverrine Dasyure the two vacancies which cross the palato-maxillary suture are in the form of longitudinal fissures, corresponding to the fourth and fifth grinders ; the posterior margin of the bony palate has four small aper- tures on the same transverse line. Now there is no carnivorous quadruped in the placental series which has a bony palate cha- racterized by perforations and vacuities of this kind. In the Dog, the Cat, and the Weasel-tribe the bony palate is only perforated by two small oblique canals which open in or near the palato-maxillary suture. The very great in- terest which is attached to the fossil remains of the Stonesfield Marsupials, the only mammi- * The large aperture in the skull of the Da- si/ums ursinus figured by Temminck is the result of accidental injury to the bony palate. Mono- graphics de Mammalogie, pi. viii. T 274 MARSUPIAL1A. ferous remains hitherto discovered in the se- condary formations, will justify the minuteness, perhaps tediousness, with which I have dwelt on characters that, inclusive of the teeth, serve to distinguish the cranium of the Marsupial from that of any Placental quadruped. The structure of the bony palate in the Marsupials is interesting in other respects. Since the de- fective condition of this part of the cranium is one of the characteristics of the skull of the Bird, it might be expected that some approx- imation would be made to that structure in the animals which form the transition between the Placental and Oviparous Classes. We have already noticed the large vacuities which occur in the bony palate of nearly all the Marsupials ; but this imperfectly ossified condition is most remarkable in the great Perameles lagotis and Acrobulcs. In the former ( fig. 96) the bony Fig. 96. Perameles lagotis. roof of the mouth is perforated by a wide oval space extending from the second pre- molars to the penultimate molars, exposing to view the vomer and the convolutions of the inferior spongy bones in the nasal cavity. Be- hind this space there are six small perforations, two in a transverse line midway between the great vacancy and the posterior margin of the bony palate, and four in a transverse line close to that margin. In Acrobutes a still larger pro- portion of the posterior part of the palate is formed by membrane. Cavity of- the cranium. — The pariefes of the cranial cavity are remarkable for their thickness in some of the Marsupial genera. In the Wombat the two tables of the parietal bones are separated posteriorly for the extent of more than half an inch, the insterspace being filled with a coarse cellular diploe ; the frontal bones are about two and a half lines thick. In the Ursine Dasyure the cranial bones have a si- milar texture and relative thickness. In the Koala the texture of the cranial bones is denser, and their thickness varies from two lines to half a line. In the Kangaroo the thickness varies considerably in different parts of the skull, but the parietes are generally so thin as to be dia- phanous, which is the case with the smaller Marsupials, as the Potoroos and Petaurists. The union of the body of the second with that of the third cranial vertebra takes place in the marsupial as in the placental Mammalia at the sella turcica, which is overarched by the back- ward extension of the lesser alae of the sphenoid. The optic foramina and the fissurae lacerae anteriores are all blended together, so that a wide opening leads outwards from each side of the sella. Immediately posterior and externaf to this opening are the foramina rotunda, from each of which in the Kangaroo a remarkable groove leads to the fossa Gasseriana at the com- mencement of the foramen ovale ; the same groove is indicated in a slight degree in the Dasyures and Phalangers, but is almost ob- solete in the Wombat and Koala. The carotid canals pierce the body of the sphenoid, as'in Birds, and terminate in the skull very close together behind the sella turcica, which is not bounded by a posterior clinoid process. The sphenoidal bulla, which forms the chief part of the tympanic cavity in the Perameles lagotis, forms a large convex protuberance on each side of the floor of the cranial cavity in that species. The petrous bone in the Kangaroo, Koala, and Phalangers is impressed above the meatus auditorius by a deep, smooth, round pit, which lodges the lateral appendage of the cerebellum. The corresponding pit is shallower in the Da- syuri, and is almost obsolete in the Wombat. The middle and posterior fissurae laceraa have the usual relative position, but the latter are small. The condyles are each perforated ante- riorly by two foramina in most of the Mar- supials, the Thylacinus forming the exception. Of the composition and form of the foramen magnum we have already spoken : it is of great size in relation to the capacity of the cranium ; the aspect of its plane is backward and slightly downwards. In the Kangaroo and Phalan, by simple glan- dular pouches at the sides of the fauces ; for example, they consist of an oblong glandular body on each side in the Dasyurus macrurus. The liver. — The liver is subdivided into many lobes in all the Marsupial genera. It is relatively largest in the burrowing Wombat and carnivorous Dasyure; relatively smallest in the graminivorous Kangaroo, in which it is situated, as in the placental ltuminants, en- tirely to the right of the mesial plane. The small or Spigelian lobe, which fits into the lesser curve of the stomach, is given off from the left lobe of the liver in the Kangaroos, but from the right in most other Marsupials ; the difference just noticed in the Kangaroo depends on the peculiar disposition of its remarkable stomach. In the Koala the under surface of the liver (fig. 130) is singularly sculptured and subdi- vided into thirty or forty lobules; this condition is presented in a minor degree in the liver of the Ursine Dasyure. In a long-tailed Dasyure, which weighed 3 lbs. 8J oz., the liver weighed 3J oz. avoir- dupoise. The gall-bladder is present in all the Marsu- pials, and is generally of large size and loosely lodged in a deep cleft of the cystic lobe. In the Opossum it generally perforates that lobe, and the fundus appears at a round opening on especially of the ccecum ; and it may be allowable to speculate upon the influence which difference of diet and confinement may have had in producing this difference. Mr. Martin's admeasurements of another Phal. Vulpina agree more nearly with mine. — See Zool. Proceedings, 1837. t The vermiform process measures two inches in length. MARSUPIALIA. Fig. 130. the convex surface of the liver. The coats of the ductus choledochus are thickened towards its termination, and become the seat of nu- merous mucous cysts which open into the in- terior of the duct. In the Phalangers the terminal half-inch of the ductus choledochus is similarly enlarged and glandular. The biliary and pancreatic ducts generally unite together before perforating the duodenum. In the Virginian Opossum, the long-nosed Bandicoot, and the long-tailed Dasyuie they pour their secretions into tlie gut an inch from the pylorus. In the great Kan- garoo the glandular ductus choledochus is joined by the pancreatic duct, and terminates in the duodenum five inches from the pylorus. The pancreas. — The pancreas extends as usual from the duodenum to the spleen, be- hind the stomach; it is characterized by a pro- cess sent off at right angles, or nearly so, to the main lobe at or near its left extremity. I have observed other small and thin processes branching out into the duodenal mesentery in a Phalanger; and similar but still more nu- merous processes, so as to give the organ a dendritic appearance in the Kangaroo; but the first-named process is constant. The spleen. — It is interesting to observe that the spleen corresponds in this triangular or T- VOL. III. shaped figure with the pancreas. In the great Kangaroo ( Macropus major ) I found the main body of the spleen ten inches long, and the rectangular process six inches ; both parts were narrow and thin. Absorbents. — The lacteal absorbents form, in the Dasyurus viverrinus, two thin, subelongate, dark-coloured mesenteric glands : one of these is situated near the pylorus, at the end of the pancreas. The plexiform cysterna chyli is si- tuated in the Kangaroo (Macropus Parry i was the species from which the following descrip- tion is taken) upon the crura of the diaphragm, and extends upon the right side above the dia- phragm into the thorax. Two thoracic ducts are continued from the cysterna, one along the left, the other along the right side of the bodies of the dorsal vertebrae. The right duct crosses the seventh vertebra and joins the left, which again divides and reunites, forming a slight plexus, before finally terminating at the confluence of the left subclavian and jugular veins. The double thoracic duct in the Kangaroo was first noticed by Dr. Hodgkin ; it is interesting, on account of its resemblance to the characteristic condition of the great nutrient conduit in the Bird and Crocodile ; in these, however, each division terminates in the vena innominata of its own side, which was not the case in the Kangaroo above described. Blood. — From the characteristic elliptical form of the blood-discs of Birds and Reptiles, and the rare occurrence of that form, as in the exceptional case of the Camel tribe, among the placental Mammalia, the examination of these particles of the circulating fluid in the Marsu- pial genera was attended with more than ordi- nary interest, and the results, derived from a comparison of species belonging to all the lead- ing groups, show that the different tribes of Marsupial animals correspond with the analo- gous placental Mammalia both in the circular or subcircular contour of the blood-discs, and very nearly also in their size.* Dasyurus viverrinus. — The blood-discs of this small carnivorous Marsupial were sensibly larger than those of the analogous placental Mammalia, as the Cat. The ordinary or un- broken discs had their margin rounded off. The number of the granulated discs was con- siderable; many of them presented a well- defined margin, notched like a cog-wheel. The average diameter obtained by me was 35jjth of an inch. Dasyurus ursinus. — The average diameter of the blood-discs is ^ : observed extremes of size 54, and ,3^. Perameles lagotis. — The blood of this Mar- supial, which was examined while recently drawn from the living animal, and under the same circumstances as that of the two species of Dasyi/rc, presented a still greater number of the granulated blood-discs mixed with others of the ordinary form. The descriptions of such altered blood-discs not only by Ilewson and Falconer, and in recent times by Professor * Sec Medical Gazette, November 13, 1839, and Mr. Gulliver's observations, London and Edinb. Pliilos. Magazine, February, 1840. x 306 MA11SUPIAL1A. Wagner, (Meeker's Liter'arische Annalen, Fe- bruarheft, 1834,) but also in works in our own language, as in Hodgkin's Translation of Ed- wards's Influence of Physical Agents on Life, Appendix, p. 438, 1832, have rendered the fact sufficiently familiar. But the connection of this well-known appearance with the mode of formation or multiplication of the blood par- ticles had not before attracted the attention it seemed to deserve; on this subject I have else- where remarked : " In some of the granulated blood-discs of the Perameles the subdivisions producing that appearance were fewer and larger, and were separated by deeper clefts than I had before observed ; they suggested to me the idea that the blood-disc was under- going a spontaneous subdivision into smaller vesicles, and, although my observations are not at present sufficiently numerous to warrant the hypothesis that the development of smaller ve- sicles within itself is a normal property of the ordinary coloured vesicle or blood-disc, yet the obscurity which still hangs over the origin and reproduction of the blood-discs, and the unex- pected constancy of the granulated form in a greater or less proportion of them while recent, and floating in the serum, in different species of animals examined by me, makes me unwilling to suppress any idea naturally arising out of such observations and likely to be suggestive of examination of the same appearances by other microscopical observers."* The general form of the blood-vesicles of the Perameles is the usual circular flattened disc: they presented a greater variety of size than in the Daysurus, but upon the whole a larger average diameter, viz. gjljgth of an English inch. Phalunghta Vulpina. — Average diameter of blood-disc 5755th inch. Petuurus sciurevs. — Ditto ditto 3955th inch. Macropus penicillatus. — Do. do. ^^th inch. Macropus major. — Ditto ditto ^^th inch. Phascolomi/s Vombatus. — Do. do. 3S55th inch. The results of the present observations on the blood of the Marsupial quadrupeds cor- respond generally with those obtained from the placental Mammalia, inasmuch as the blood- cliscs of the species which derives its nutriment from the greatest variety of organized substances, as the Perameles, which subsists on insects, worms, and the farinaceous and succulent ve- getables, are larger than those of the strictly carnivorous Dasyure, and of the herbivorous Kangaroo, the blood-discs of the latter, like those of the placental Ruminant, being the smallest, though not in the same proportion. In each natural group of Marsupialia there is a direct relation between the size of the blood- disc and that of the species. Heart. — The heart is inclosed in a pericar- dium, and situated in the same relation to the lungs, mediastinum, and thoracic cavity as in the Rodent and most other mammiferous quad- * Medical Gazette, 1839, 1. c. My hypothesis has received a certain degree of confirmation by the subsequently published observations on the division of the corpuscles of the blood by Mr. Quekett, ( iVTed. Gazette, January, 1840,) and by Dr. Martin Barry, Philos. Trans. 1840, p. 595. rupeds. It offers no peculiarity in its general outward form. The apex is less obtuse in some species, as the Phalanger and Wombat, than in others, as the Kangaroo. The serous layer of the pericardium is reflected upon the large vessels near to the heart. The fibrous layer of the pericardium adheres to the sternum in the Kangaroo. The appendix of the right auricle is always divided into two angular pro- cesses, (a, a, figs. 131 and 132,) one in front and the other behind the trunk of the aorta. Fig. 131. Heart of the Kangaroo. Besides this characteristic modification of its external form, the right auricle presents some still more essentially marsupial conditions in its interior. There is no trace, for example, of a ' fossa ovalis' or an ' annulus ovalis in any marsupial animal;* and the absence of these structures, which are present in the heart of all the placental Mammalia, doubtless re- lates to the very brief period during which the auricles intercommunicate in the Marsupials, and to the minute size, and in other respects incompletely developed state, at which the young marsupial animal respires air by the lungs, and has the mature condition of the pulmonary circulation established. The right and left auricles intercommunicate by an oblique fissure in the uterine embryo of the Kangaroo, when two-thirds of the period of gestation is past, but every trace of this foetal structure is obliterated in the subsequent growth of the heart; so that in the mature animal the wide terminal orifice of the posterior cava is * Physiological Catalogue, Mus. Royal College of Surgeons, 4to. vol. ii. p. 52. MARSUPIALIA. 307 separated from that of the anterior cava by a simple crescentic ridge ( e, figs. 131 and 132), which forms a salient angle of the parietes of the auricle between these apertures. The an- terior cava (b ) returns the blood from the right side of the head and the right anterior extre- mity; the corresponding vein on the left side (c ) passes down in all the Marsupials, as in Birds and Reptiles, behind the left auricle, below the two pulmonary veins, and, after receiving the coronary vein, joins the inferior cava (d ) immediately before its expansion into the auricle. Fig. 1 32. Heart of the Wombat. "Where the posterior extremities are less or not larger than the anterior ones, as in the Ursine Dasyure and Wombat, the posterior cava is somewhat less than the left vena innominata (Jigs. 131 and 132), and they appear to terminate by separate apertures in the auricle; but in the Kangaroo (Jig. 131) the proportions of the two veins are reversed, and the posterior cava more obviously receives the left vena innominata before it terminates: these two veins meet at a very acute angle, and are separated by a crescentic ridge similar to, but thinner than, that which divides their common orifice from the orifice of the anterior cava. The right auriculo-ventricular valve is mem- branous, as in the placental Mammalia, and its free margin is attached by fine chorda; ten- dine ae to three columns: carnese ; these in the Kangaroo (fig. 131) all arise from the septum ot the ventricles, but in the Wombat (fig. 132) the base of two of the columns; is situated at the angle between the septum and the thin outer wall of the ventricle. The right ventricle extends nearly to the apex of the heart in the Wombat, but falls short of that part in the Kangaroo. The ven- tricle is continued in the form of a pyramidal process, somewhat resembling a bulbus arte- riosus, to the origin of the pulmonary artery (f, Jigs. 131 and 132), and projects beyond the general surface of the heart further than in ordinary Mammalia. The appendix of the left auricle is notched in the Kangaroo to receive the apex of this pro- cess, but not in the Wombat. Two pulmonary veins (i, figAS'A) terminate close together, or by a single trunk, at the upper and dextral angle of this auricle. The mitral valve is regulated by two short and thick columns; (k, k,Jig. 133), which send their tendinous chords to the margin and ventricular surface of the valve. Fig. 133. Heart of the Wombat. The ventricles and auricles present the usual mammalian proportions and relative thickness of their parietes. Three sigmoid valves are situated at the origin of the pulmonary artery, and the same number at that of the aorta. After the coronary arteries, the primary branches from the arch of the aorta rise in some species by three, in others by two trunks. The broad-chested Marsupials, the Koala and Wombat for instance, are those in which the left carotid (g',fig. 132) and subclavian (h! ) arise separately from the arch ; the arteria inno- minata dividing into the right subclavian and carotid (g,h, fig. 132), as in man. In most of the other Marsupials the innominata gives off both carotids ( g, g, fig. 131) as well as the right subclavian (h ); and the left subclavian x 2 cos M ARSU PI ALIA. (h ) alone has a separate origin. The common carotid in the Kangaroo gives off the thyroid artery, and afterwards divides opposite the transverse process of the atlas into the external and internal carotids. The internal carotid describes a sharp curve at its origin, and passes along the groove between the occipital condyle and the exoccipital process to the foramen ea- roticum. The vertebral arteries are given off by the subclavians, and pass to the skull, as usual, through the vertebral foramina of the cervical transverse processes. They unite be- neath the medulla oblongata to form the basilar artery, which sends off at right angles to the cerebellum two branches as large as itself : it divides opposite the anterior margin of the pons Varolii, and the diverging branches are connected by two straight transverse canals, before they anastomose with the internal caro- tids to form the circle of Willis. No pecu- liarly marsupial condition occurs in the distr i- bution of the other arteries of the head, or those of the neck, the chest, and anterior ex- tremities; but I may observe that in the Koala, Wombat, Kangaroos, Potoroos, most Phalan- gers, ( Phal. Coukii is an exception,) most Pe- taurists, (Pet. Sciweus is an exception,) the Opossums, Bandicoots, and Phascogales, the brachial artery perforates the internal condyle of the humerus; it passes over that condyle, impressing it with a more or less deep groove in the Dasyures and Thylacine. In the abdomen, the primary branches of the aorta are sent off in the same order as in most of the ordinary Mammalia, with the ex- ception of the constant absence of an inferior mesenteric artery. This modification probably relates to the simplicity of the mesenteric at- tachment of the intestines above described. A still more marked example of the oviparous affinities of the Marsupialia, as exemplified in the arterial system, occurs in the mode of origin of the great arteries of the posterior extremities. In Man and the ordinary Mam- malia these are derived, as is well known, from a single trunk on each side — the common iliac artery; in Birds from two primary branches of the aorta, one corresponding with the external iliac and femoral, the other with the internal iliac and ischiadic arteries. In the Kangaroo and Phalangista vulpina the aorta gives off, opposite the interspace of the two last lumbar vertebra1, the iliac arteries ; but these are after- wards resolved into the ordinary branches of the external iliac of the placental Mammalia, with the addition of the ilio-lumbar artery. The trunk of the aorta, much diminished in size, maintains its usual course for a very short distance, and then gives off the two internal iliacs, and is continued as the ' arteria sacra media' to the tail. The transitional cha- racter of this part of the marsupial sangui- ferous system between the oviparous and pla- cental types, is manifested in the large size of the external iliacs as compared with the internal iliacs, their greater share in the supply of blood to the hinder extiemities, and the brevity of the aortic trunk between their origins. In most Birds the femorals or external iliacs are smaller than the ischiadic or internal iliac arteries subsequently given off. At the upper part of the thigh the femoral artery divides into two equal branches ; the one which corresponds with the radial artery in the fore leg ( m, fig.\34 ) principally supplies the foot in the Kangaroos ; it passes along the back of the radius, between the gastrocnemius internus and tibialis posticus, and divides a little above the internal malleolus. The smaller division (I, Jig. 134), which follows the ordinary course of the femoral along the popli- teal space, is lost upon the inner and posterior part of the tarsus; the larger branch winds over the malleolus to the front of the tarsus, sends off the anterior tarsal artery, and is then continued along the inner and afterwards the under part of the metatarsal bone of the long and strong toe. In JigA3A, a is the trunk of the cceliac artery ; b that of the superior and inferior mesenteric arteries; c is the capsular artery of the left side; d, d, the renal arteries ; e the spermatic artery, of which the left branch is shown continued to the left ovarium q, which, with the uterus r, vagina s, and bladder t, is drawn to the right side ; the spermatic arteries arise close together but separately in the male Vulpine Phalanger: y"is the external iliac, corresponding with the com- mon iliac in placental Mammalia, and with the femoral artery in Birds, (see Vol. i. p. 337, Jigs. 170, 23 ;) below these are given off A, the arteries corresponding with the ischiadic ar- teries in Birds, (Vol. i. p. 337, fig. 170, 26,) and with the internal iliacs in Mammalia; [they are represented of too small a size in the cut] ; k is the femoral artery ; / the ex- ternal, m the internal branch ; » is the sacro- median or caudal artery, which is protected in its course along the tail by the haem- apophysial or chevron-like processes of the caudal vertebra?. This artery of course cor- responds in size with the developement and functional importance of the tail, and must be rudimentary in the tail-less or nearly tail-less Marsupials, such as the Chceropus, Koala, and Wombat. With respect to the veins of the Marsupials it may here be noticed that the iliac veins combine to form the trunk of the abdominal cava, as in the rest of the Mammalia, without conveying any part of their blood to the kid- neys : in the Kangaroo they both pass on the central aspect of the iliac arteries. The renal veins, in like manner, directly communicate with the abdominal cava, and do not contri- bute any share in the formation of the portal vein. This great secerning trunk of the hepatic organ presents the strictly mammalian condi- tion, being formed by the reunion of the gastric, intestinal, pancreatic, and splenic veins. It is in the chest that we first meet with decided traces of the oviparous type of structure in the venous system of the Marsupialia. The primi- tive veins of the animal system of organs, commonly called ' azygos,' retain their original separation and symmetry; the left 'azygos' bends over the left bronchus to communicate with the left anterior cava, and the right azy- gos over the right bronchus to join the right anterior cava. The left anterior cava commonly Brandies of ike ahdom receives also the coronary vein of the heart: the termination of this and the two other venous trunks in the right auricle has already been noticed. Respiratory organs. — In the condition and structure of the respiratory organs all the Mar- supial species adhere to the Mammalian type ; the only tendency to the Ovipara is in the entireness of the tracheal rings in certain spe- cies. In the Phalangista J'uliginosa, where I counted twenty-nine rings, the first four-and- twenty were entire ; below these they were divided posteriorly, the interspace growing ■wider to the twenty-ninth ring. In the Dasi/- iims mucrurm the rings of the trachea are twenty-three in number, and are incomplete or rather ununited behind. In the Perameles the tracheal rings are divided posteriorly by a fis- sure. In no species have I found the trachea divided near the larynx into two long bronehise, irutl aorta, Kangaroo. as in the Rodent genus Heliimys, nor convo- luted in the chest as in the Edentate Sloth, both of which modifications are more striking ap- proximations to the oviparous type of structure than the entire rings above-mentioned. The lungs present the most simple form in the Wombat, in which they consist of a single lobe on both the right and left sides, with a small lobulus azygos extending from the right lung to the interspace between the heart and diaphragm. In the Mucropus major I found the right lung with two notches on the anterior margin, and the left lung undivided. In the Macropus Parryi both lungs had one or two notches. In another Kangaroo I found the right lung divided into four lobes, the left into two. The azygos lobe is large in consequence of the length of the chest in the Kangaroos, and the distance of the heart from the diaphragm : it is 310 MARSUPIALIA. three-sided, one side convex, the second con- cave.and applied to the pericardium, the third side concave, and in contact with the dia- phragm. In the Potoroo the left lung is unilobate with a fissure on the anterior or upper edge ; the right lung has two or three deep fissures. The azygos lobe is elongated, pointed, and triedral, as in the Kangaroo. In the Petaurists and Phalangers the right lung is trilobate, the left bilobate ; there is also a lobulus azygos. The Koala has the lungs similarly divided, and not simple as in the Wombat. In the Opossums, Dasyures, and Perameles the right lung is usually trilobate, (bilobate in Didelphys brachyura,) and with the usual azygos appendage : the left lung is commonly divided into two, but is sometimes entire, as in the Perameles and Didelph. brachyura. In all the Marsupials the right lung is the largest, owing to the oblique inclination of the heart to the left side. The thyroid glands are two disunited bodies in the Dasyures ; they were each the size of a horse-bean in the Das. macrums. They were of the same size in a Phalangista fuliginosa, but were united by a filamentary strip passing between their lower extremity, across the first tracheal ring. In the Koala, the thyroid gland is situated lower down extending from the fourth to the ninth or tenth tracheal ring. In the Wombat I found the thyroid glands two elongated bodies of a dark colour reaching from the thyroid cartilage to the seventh tracheal ring on each side. The larynx of the Marsupialia consists of a cricoid, thyroid, and arytenoid cartilages and an epiglottis. The latter is always remarkable for its large size, and generally for its emar- ginate apex. There is no muscle passing from the epiglottis to the tongue; its base is con- nected in the Kangaroo by a triangular fascia to the body of the os hyoides and the greater cornua; and a small muscle passes from the middle part of the body of the os hyoides to the dorsum linguae. In the Phalangers the epiglottis is broad and short, and with a bifid apex. In the Pe- rameles and Phascogale the sides of the broad and short epiglottis are attached to the apices of the arytenoid cartilages, retaining thus much of its early condition, which will be adverted to in the account of the peculiarities of the mam- mary foetus. In the Perameles lagotis I found on the base of the tongue in front of the epiglottis a small sacculus of mucous membrane, which communicated by a regular symmetrical cre- scentic aperture, situated between the body of the os hyoides and the thyroid cartilage, and continued down in front of the thyroid cartilage : the surface of the cavity was smooth and lubri- cated, and it seemed to be for the purpose of facilitating a hinge-like motion between the thyroid cartilage and the body of the os hy- oides. The thyroid cartilage is convex externally and protuberant in the Phalangers and Koala, but offers no particular modification in other Mar- supials. The base af the arytenoid cartilages is broad in the antero-posterior direction, and the chordae vocales short and feebly developed. The Marsupials have little or no voice : the Wombat emits a guttural hissing sound : the Dasyurus ursinus a snarling growl or whine : the Thylacine is described as uttering a short guttural cry. I have never heard a vocal note of any kind from the Kangaroos, Potoroos, Pe- taurists, Phalangers, or Perameles. Renal system. — The kidneys present a simple conglobate external form in all the Marsupials, as in Jig. 134, o, o, and in their structure and po- sition in the abdomen agree with the Mamma- lian type of structure. In the Macropus Parryi the kidneys are situated six inches above the brim of the pelvis, and lying in the same transverse line: they have the same relative position in other Poephaga. In the Koala the right kidney is higher by its whole lengtli than the left. In the Dasy- uri mucrurus and viverrinus, the right kidney lies half an inch higher or in advance of the left : in this carnivorous genus a few branches of the renal veins are distributed upon the sur- face of the kidney, but not in the same pro- portion or with the beautiful arborescent dis- position characteristic of the kidneys of the Cats, Suricates, and Hyaena. In a Dasyurus macrurus weighing three pounds eight ounces, the two kidneys weighed thirteen drachms. In a Phalangista vulpina, weighing five pounds three ounces, the two kidneys weighed only ten drachms. The substance of the kidney is divided into a cortical and medullary part ; the former is generally a thin layer. The tubuli uriniferi terminate on a single mammilla which projects into the commencement of the ureter in the Opossums, but does not extend beyond the pelvis of the kidney in the Kangaroos. In the Kangaroos the medullary substance forms several lateral abutments to the base of the main mammilla. The supra-renal glands generally present the relative position and proportions to the kidneys represented in the Kangaroo, at jig. 134, p. They are, as in most of the smaller quadrupeds, less flat than in man : the right body generally adheres to the coats of the vena cava, and the left to the renal vein. In the Dasyures the ex- ternal stratum is light-coloured ; this surrounds a dark-coloured layer, and then there is a light- coloured central part, but no cavity. The ureters terminate at the back of the neck of a muscular and pendulous urinary bladder (t), which only exhibits a trace of urachus at the middle of its anterior part in the young marsupial, while in the maternal pouch. Male organs of generation. — The testes, which are still abdominal at the time of birth, descend, soon after the foetus is transferred to the pouch, into the external pedunculate pre- penial scrotum ; the canal of communica- tion between the abdominal cavity and the tu- nica vaginalis is long and narrow, but always remains pervious. MARSUPIAL! A. 311 The tubuli testis are relatively smaller than in the Rodentia, but are similarly arranged, the corpus Highmorianum being near the surface and upper part, not at the centre, of the gland. The epididymis is large, and generally loosely attached to the testis : in a small species of Kangaroo I found the connecting fold of serous membrane half an inch broad. The vasa de- ferentia pass from the globus minor along the infundibular muscular sheath formed by the cremaster as far as the abdominal ring, then bend downwards and backwards, and termi- nate below and external to the ureters, at the commencement of the urethra (a, Jig. 135), on each side a longitudinal verumontanal ridge. There are no vesiculae seminales in any Mar- supial quadruped. Fig. 135. A , Hypsiprymnus. B, Phatcolarchis. C, Phuscolomys. As the part of the urethral canal immediately succeeding the termination of the vasa defe- rentia is the analogue of the vagina, some mo- dification of this part might be anticipated in the male corresponding with the extraordinary form and developement which characterise the vagina in the female : accordingly we find that the combined prostatic and membranous or muscular tract of the urethra is proportionally longer and wider in the Marsupial than in any other Mammiferous quadrupeds (Jig. 135, b). It swells out immediately beyond the neck of the bladder, and then gradually tapers to its junction with the spongy part of the urethra : it is not, however, divided like the vagina. Its walls are thick, formed of an external thin stratum of nearly transverse muscular fibres; and a thick glandular layer, the secretion of which exudes by innumerable pores upon the lining membrane of this part of the urethra. In a male Kangaroo I found that a glairy mucus followed compression of*this musculo-prostatic tracl of the urethra: the canal itself is here slightly dilated. Three pairs of Cowper's glands ( c, c, c, fig. 135) pour their secretion into the bulbous part of the urethra : the upper or proximal pair are not half the size of the two other pairs in the Kangaroo, but are relatively larger in the Koala and other Marsupials : the two lower pairs are situated, one on each side the lateral division of the bulb of the urethra; their ducts meet and join, above this part, with the duct of the smaller gland : each gland is inclosed by a muscular capsule. The penis consists of a cavernous and a spongy portion, each of which commences by two distinct bodies. The separate origin of each late- ral half of the spongy body constitutes a double bulb of the urethra ( e, e,Jig. 135), and the ' ac- celerator urina1,' as it is termed, undergoes a similar division into two separate muscles, each of which is appropriated to compress its par- ticular bulb. The two bulbous processes of the corpus spongiosum soon unite to surround the urethra, but again bifurcate to form a dou- ble glans penis in the multiparous Marsupials, in which most of the ova are impregnated in both ovaria, as the Phalangers, Perameles, Opossums, &c. (b, b, Jig. 136). This modification of the opposite extre- mities of the corpus spongiosum, called 4 bulb' and ' glans,' was detected by Cowper in his dissection of a male Opossum ; and, in his account of the anatomy of that animal in the Philosophical Transactions for the year 1704, he says, " As the bulb of the urethra in man is framed for the use of the glans, to keep it sufficiently distended when required, so it seems it is necessary to have two of these bulbs, inclosed with their particular mus- cles in this animal, to maintain the turgescence of its double or forked glans when the penis is erected." — Vol. xxiv. p. 1585. The force of this ingenious "reasoning on the correlation of the bulb to the glans might seem to be invalidated by the fact that in the uniparous Marsupials, as the Kangaroo, the glans penis (J', Jig. 135) is single, and yet the bulb double : 312 MARSUPIALIA. but in this circumstance we may perceive an example of the retention of a typical structure at the deeper seated part of a system of organs, when not incompatible with a slight modifi- cation of a peripheral segment of the same system ; it being by no means obviously neces- sary to abrogate the division of the urethral bulb simply because the blood accumulated in each division was to be driven in a concen- trated current upon a single, instead of a dou- ble glans penis. The intermediate structures of the glans be- tween the two extremes above instanced are presented by the Ursine Dasyure, Koala, and Wombat. In the Koala (jig. 1 35, B) the glans penis terminates in two semicircular lobes, and the urethra is continued by a bifurcated groove along the mesial surface of each lobe. In the Wombatfy/g. 135, C)thereisasimilarexpansion of the urethra into two divergent terminal grooves, but the glans is larger, cylindrical, and par- tially divided into four lobes:* the chief struc- ture of interest in this part of the Wombat is the callous external membrane of the glans, and its armature of small recurved, scattered horny spines, which do not occur in any other Marsupial animal. The small retroverted pa- pillae on the infundibuliform glans of the Koala and on the bifurcate glans of the Phalan- gers and Petaurists are not horny. In the Pcrameles lagotis not only is the glans bifurcate, but each division is perforated, and the urethral canal is divided by a vertical septum for about half an inch before it reaches the forked glans. From the septum to the bladder the canal is simple, as in other Marsupials. The bifurcations of the glans in the Opossums and Phalangers are simply grooved. If the experiments of Haighton and the detection, by Drs. Bischoff and Barry, of sper- matozoa upon the ovary itself after coitus, had not rendered the question of the neces- sity of the contact of the semen with the ovarium for impregnation almost independent of the aid of Comparative Anatomy, the diffe- rences of structure above described in the urethra and glans penis of the Marsupial animals would have gone far to explode the once prevalent notion of an ' aura seminalis' fertilizing the ovum through the medium of the circulating fluid : for why, on such an hypothesis, should the impregnation of two ovaria, each communicating with a distinct oviduct, uterus, and vagina, as in the Opos- sum, require two conduits of the semen in the male, one for each vagina? — and wherefore, in the case of an uniparous Marsupial, in which the fecundating stream need ascend only to a single ovarium, as in the Kangaroos and Potoroos, is the penis terminated by a single glans ? The spermatozoa of the Perameles have a single barb at the base of the head, which is sub-elongate and compressed ; in other respects, as in size and proportion of the filamentary tail, they resemble the spermatozoa of the Ilabbit. * Cuv. Logons d'Anat, Comparee, 1805, t. v. p. 91. Neither in the Kangaroo, Phalanger, nor Da- syure did the spermatozoa present a spiral head or any noticeable deviation from the characters of the spermatozoa in the smaller placental quadrupeds : those of the Dasyure have a node at the base of the head. The corpus cavernosum penis commences by twocrura(rf, d, figs. 135, 136), neither of which have any immediate attachment to the bony pelvis. Cuvier correctly states, that in the Kangaroo the two crura of the corpus cavernosum, and the two bulbs of the corpus spongiosum, soon unite to form a single cylindrical body, having a canal which nearly follows the direction of its axis, whose parietes are equally strong and fibrous, and which contains the urethra; so that the transverse section of the corpus cavernosum resembles a ring ; but the two lateral cavities are separated by two vertical septa which ex- tend one from the central canal to the dorsum penis, the other from the central canal to the inferior wall of the penis.* In the Kangaroo and Potoroo, the erectores penis (Jig. 135 d, d ) arise by a thin fascia from near the lower part of the symphysis pubis, soon become fleshy, and increase in thickness as they pass outwards : each muscle then returns upon itself, at an acute bend, to grasp the crus penis, and terminates in a strong tendinous expansion at the junction of the cavernous with the bul- bous structure. Fig. 136. Male Organs, Opossum. ( Cuwper, I. c.) The retractor penis (figsA 35, 1 36, g, g) arises in the Kangaroo from the middle of the sa- crum, and divides into two muscles, behind the rectum, opposite the dilated commencement of the musculo-prostatic part of the urethra; each division diverges to the side of the rectum, then passes to the interspace between the rec- tum and roots of the penis, and along the . * Lemons d'Anat. Comp. 1805, t, v. p. 73. MARSUPIAL! A. 313 lateral and posterior part of the penis, until it is inserted with the opposite muscle at the base of the glans. In the Opossum and those Marsupials which, having a bifid glans, enjoy, as it were, a double coitus, there is a levator penis (f, f, fig. 136), which is not present in the Kangaroo. Each portion of this muscle takes its origin from the fascia covering the crus penis, con- verges towards its fellow above the dorsum penis, diminishing as it converges, and termi- nates in a common tendon inserted into the upper part of the base of the glans. There is another powerful muscle which, though not immediately attached to the penis, must exert, in all Marsupials, so important an influence upon its erection as to merit notice here. This is the external sphincter ani, or more properly ' sphincter cloacae : ' it is an inch and a half in breadth in the Kangaroo and half an inch in thickness; from the back of the termination of the rectum it passes over the anal glands and sides of the base of the penis, inclosing the two bulbs with Cowper's glands and their muscles, and terminates anteriorly in a strong fascia above the dorsum penis, so as to compress against that part the venae dor- sales. This adjustment and function of the great sphincter did not escape the observation of Cowper. Speaking of the erectores penis of the Opossum, he says, " the muscles of the cavernous bodies of the penis of this creature, having no connexion with the os pubis, cannot apply the dorsum penis to the last-named bone and compress the vein of the penis, whereby to retard the refluent blood and cause an erec- tion, as we have observed in other creatures ; but some large veins of the penis here take a different course, and pass through the middle parts of the bulb (crus), and are only liable to the compression made by the intumescence of the muscles (c c) that inclose them. But the chief agent in continuing the erection of the penis in this animal is the sphincter muscle of its anus, or rather cloaca; and not only the sphincter muscle of the cloaca of the male Opossum, but that of the female also, closely embraces the penis in coition, and effectually retards the refluent blood from its corpora caver- nosa, by compressing the veins of the penis."* The penis is bent upon itself in a sigmoid form when retracted ; with the glans concealed just within the cloacal aperture, from which it emerges, as in the Ovipara, when the penis is turgid and erect. Female, organs. — These consist of two ovaries, two oviducts or fallopian tubes, two uteri, two vagina?, an uro-genital canal, a clitoris, mam- mary organs, and marsupial pouch. The ovaries are small and simple in the uniparous Kangaroos ; tuberculate and rela- tively larger in the multiparous Opossums; but the largest size and most complicated form of these essential organs which I have met with in the Marsupial order were pre- sented by the Wombat (jig. 137). The * Phil. Trans, vol. xxiv. 1704, p. 1584. ovaria are represented of their natural size in fig. 138, a a', in the great Kangaroo, where they present an oval form and a smooth unbroken exterior, except after impregnation, when a large corpus luteum projects from the surface, as at a. The ovaria are not inclosed by a cap- sular duplication of the peritoneum, but are lodged within the expanded orifice of the ovi- duct, or 'pavilion,' near the upper or anterior extremities of its two principal lobes or pro- cesses. These are of considerable extent, and their internal surface, which is highly vas- cular, is beset with rugae and papillae. In the Dasyures and Petaurists the ovaries are elliptical, subcompressed, and smooth. In the Opossum the ovarium consists of a lax stroma remarkable for the number of ovisacs imbedded in it, the largest of which are the most super- ficial, and give rise to the tubercular projections on the surface of the ovary. In the Wombat (fig. 137) each ovary, be- sides being lodged in the pavilion, as in the Kangaroo, is inclosed with the pavilion in a Fig. 137. f Ovarium and pavilion, Wombat. Natural sixe. peritoneal capsule. In the unimpregnate< female examined by me, the ovaries were si', times as large as in the Kangaroo, and pre- sented a well-marked botryoidal form, resem- bling the ovarium of the bird. Numerous ovi- sacs in different stages of growth projected from the surface, the largest presenting a diameter of eight lines (fig. 137, ay, the structure of these ovisacs, the character of the stroma in which they are imbedded, and the dense albugineous tunic by which they are inclosed, bespeak the strictly mammalian type of the ovaria of the Phascolo- mys as of every other genus of Marsupial; but the affinity of the Wombat to the Rodent order, in many species of which the ovaria are tu- 314 MARSUPIALIA. Female organs, Kangaroo. MARSUPIAL! A. 315 berculate, is again manifested in this part of its structure. The expanded orifices of the fallopian tubes present a greater development than in the Kangaroo, and are still more re- markable for the number, size, and variety of the fimbriated processes and folds which aug- ment the internal vascular surface of the pavi- lion. In both the Wombat and Kangaroo the lining membrane of the contracted portion of the oviduct is similarly complicated by minute and delicate reticular plications and processes. The oviducts are shorter and less sinuous in their course in the uniparous Kangaroo, fig. 138, 6, than in the muciparous Opossums (b, fig. 139). In the above described essential parts of the female generative apparatus the mammalian type of structure is closely adhered to ; the de- viations most characteristic of the implacental group begin to manifest themselves in the re- maining parts, and here under so irregular and complicated a form as to require a brief review of the analogous structures in other groups of animals for their intelligibility. The variations of structure which the female generative organs present in the oviparous classes of Vertebrata are fewer and of less de- gree than those observable in the different orders and genera of the Mammalia. The most pre- vailing characteristic of the oviparous type of the female generative organs is the absence of union in the mesial plane of the lateral efferent tubes, which consequently continue separate to their terminations in the excretory outlet. In Birds the genital apparatus is characterised by the higher, and, in the female, as far as function is concerned, exclusive development of the left moiety ; and the uniformity in the condition of the excluded ovum in this class corresponds with the sameness which prevails in the structure of the organs concerned in its production. In Reptiles the ovaries and efferent parts of the genital system are equally developed, or nearly so, on both sides. But although a con- siderable uniformity of structure is found to pre- vail in this system throughout the different orders of the class, the widest difference obtains both in the place of development of the ovum and the condition in which it quits its mother. No one, e. g , could have predicated from a comparison of the structure of the ovaries and oviducts in poisonous and innocuous Serpents that any difference existed in the structure and development of the ovum, much less that the for- merwere ovo-viviparous but the latter oviparous; or, from a comparison of the same organs in Lacerta croceu and Lacerta agilis, that a like difference should exist in the generative eco- nomy of species so nearly allied as for a long time to have been confounded together by naturalists. In Mammalia, however, in most of the orders of which the connexion of the ovum with the uterus is so much more intimate than in the preceding classes, the variations in the structure of the female sexual organs are more numerous and remarkable; and though it be admitted that the nature of the foetal coverings and ap- pendages results from the original constitution and properties of the ovum, yet the modifica- tions of the uterus have evidently, in this class, a subordinate relation to those differences. In tracing the female generative apparatus from the human subject through the different orders of Mammalia, we find that it approxi- mates to the oviparous type of structure in two ways, viz., by an obliteration of the os tinca% which is the characteristic limit between the uterus and the vagina in this class ; and by a gradually increasing division of the uterus and vagina until they become two separate tubes throughout their entire extent. In no mammiferous genus do the female organs present that character of unity or con- centration, with distinction of parts, which is found in the human subject ; for in the lower orders, besides the more essential differences above-mentioned, there is always an elongation of the uterus, with a thinning of its parietes, and in general a blending together of the urethral and sexual passages. This latter deviation com- mences in the Simia, and in the Lemures the angles of the uterus begin to elongate and to assume the form of ccrnua. The mesial cleft increases, and the cornua preponderate in the Carnivora, the Cetacea, the Ruminantia, and the Pachydermata ; but it is in the Kodentia, which present affinities to Birds in other parts of their structure, that the uterus is first found completely divided into two lateral halves. This structure is not, indeed, uniformly met with in all the genera of the order ; but besides the Hare and Rabbit, in which the double uterus is allowed to exist by De Graaf and Cuvier, a similarly complete division of the organ obtains in the genera Sciurus, Arctomys, Spulax, Bathyergus, Echimys, Eretizon, (F. Cuvier) and Hydrocharus ; while in the genera Mas, Cavia, Calogenys, and Dasi/procta, a portion of the true uterus still remains undi- vided ; though this part, to which alone the term ' corpus uteri' can be properly applied, is ex- tremely small or rudimental. Nevertheless, although the corpus uteri exists in these genera, the true vagina is as remarkable for its length and capacity as in those in which the corpus uteri has ceased to exist. Hitherto the vagina has presented itself un- der the form of a simple undivided canal, communicating with the urethro-sexual passage, at least after impregnation by a single aperture. But it is a remarkable and interesting fact that in the Sloth, in the Mare and Ass, in the Pig, and in the Cow, the vagina in the virgin state com- municates with the urethro-sexual passage by a double aperture, in consequence of being traversed by a narrow vertical septum or chord. This septum has been described by veterinary authors as a hymen in the Mare ; the analo- gous part in the human subject also occasionally presents the same structure, and has even been observed in some cases to extend as a mesial partition inwards towards the uterus. In the MursupiaUa, where from the small size of the fcetus at birth a similar conformation is permitted to remain as a permanent structure, the vagina is in some genera wholly, and in 316 MARSUPIALIA. others partially divided ; but the divided por- tion in the latter is always that which is nearest the urethro-sexual passage. The true uterus is completely divided in all the Marsupial genera, and each division is of a simple elongated form, as in the Rodent ia. The superadded complications in the female generative organs of the Marsupials, as com- pared with other mammals, are not then rightly attributable to the uterus, but to the vagina ; and they are of such a nature as to adapt the latter to detain the foetus, after it has been ex- pelled from the uterus, for a longer period than in other Mammalia. These complications vary considerably in the different marsupial genera. On a comparison of the female organs in Didelphys dvrsigera, Petaurus pygmaus, and Petaurus taguanoides, in Dasyurus viverrinus, in Didelphys Virgi- niana, in Macropus major, and Hypsiprymnus murium, I find that the relative capacity which the uteri bear to the vaginae diminishes in the order in which the above-named species follow, while the size of the external pouch increases in the same ratio. In Didelphys dorsigera the uteri (Jig. 139, c, c,) rather exceed the unfolded vaginae in Fig. 139. Didelj)hys dorsigera. length. In most Marsupials the vaginas at first descend as if to communicate directly with the urethro-sexual passage ; but in this small Opossum, in which the abdominal pouch consists of two slight longitudinal folds, and the young, as is implied by its trivial name, are transported by the mother on her back, each vaginal tube ( e, e, fig. 139,) after em- bracing the os tincae (d), is immediately con- tinued upwards and outwards, then bends downwards and inwards, and, after a second bend upwards, descends by the side of the opposite tube to terminate parallel with the extremity of the urethra (h) in the common or uro-genital passage (J). In the Petauri, the vaginae, when unfolded, are a little longer than the uteri. ■ On examining a specimen of the Pigmy Petaurist which had two very small young in the pouch, I found both the true uteri of three times the diameter of the same in an unimpregnated specimen ; but the vaginae were unaltered in size, indi- cating that the situation in which gestation takes place in this species is the same as in the Kangaroo. The vaginae, after receiving the uteri, descend close together half-way towards the commencement of the urethro-sexual pas- sage, but do not communicate together in this part of their course. From the upper part of these culs-de-sac they are continued upwards and outwards, forming a curve, like the han- dles of a vase, then descend, converge, and terminate close together, as in the preceding example. In Dasyurus viverrinus and Didelphys Vir- giniana, the mesial culs-de-sac of the vagina descend to the urethro-sexual passage, and are connected to, but do not communicate with it. The septum dividing them from each other is complete, being composed of two layers which can be separated from each other, and which result indeed from the apposition and mutual cohesion of the vaginae at this part. In order to reach the common passage, each tube is con- tinued outwards from the upper end of the cul- de-sac, and forming the usual curve, terminates parallel to the orifice of the urethra. The vaginae in the Dasyures are smaller in propor- tion to the uteri than in the Virginian Opossum, but of a similar form. In another species, the Didelphys Opossum of Linnaeus, it would appear from the descrip- tion and figures of Daubenton,* that the septum of the mesial culs-de-sac of the vaginae was im- perfect; but it is doubtful whether this inter- communication was not the result of parturition, or of an accidental rupture in the specimen ex- amined. If it should prove to be a specific difference of structure, it is an approximation to the condition of the female organs in the Phalangers, the Wombat, and the Kangaroos. In the Macropus major the vaginae (fig. 138, e, e' ) preponderate in size greatly over the uteri (r, c) ; and, the septum (e") of the descending cul-de-sac being always more or less incom- plete, a single cavity (e) is thus formed, into which both uteri open ; but however imperfect the septum may be, it always intervenes and preserves its original relations to the uterine orifices (d, d). The foetus has been conjectured to pass into the urethro-sexual cavity by a direct aperture formed after impregnation at the lower blind end of the cul-de-sac, but I have not been able to discover any trace of such a foramen in two kangaroos which had borne young ; and be- sides, I find that this part of the vagina is not continuous by means of its proper tissue * Buffon, Hist. Nat. torn. x. p. 279. MARSUPIALIA. 317 with the urethro-sexual passage, but is con- nected with it by cellular membrane only ; as might have been anticipated from the struc- ture presented in the simpler forms of the mar- supial uterus, as in Didelphys dorsigera and the Petauri, in which the culs-de-sac do not come into contact with the urethro-sexual passage. The evidence of M. Rengger on the develop- ment of the young and the parturition of the Didelphys Azara. is also directly opposed to the theory of a temporary orifice in the mesial cul-de-sac. The last form of the marsupial female organs which may be noticed is that which is found in one species at least of the Kangaroo Rat ( Hyp- siprymnus murinus). The type of construction is, however, the same as in the great Kangaroo, but the mesial cul-de-sac of the vagina attains a still greater development ; it not only reaches downwards to the uro-genital passage, but also expands upwards and outwards, dilating into a large chamber, which extends beyond the uteri in every direction. From the sides of this chamber the separated portions of the vagina continue downwards, to terminate, as usual, in the urethro-sexual canal.* In all the preceding genera the structure of the uteri is as distinct from that of the vaginae as in the Rodentia. The fibrous or proper tunic of the uteri is thicker than that of the vagina;, and the lining membrane is soft and vascular, and disposed in numerous irregular folds, which, in section, give apparently a still greater thickness to the uterine parietes. The whole extent of the vaginas, on the contrary, is lined with a thin layer of cuticle, which is rea- dily detachable, even from the middle cul-de- sac, so generally considered as the corpus uteri in the Kangaroo. The inner surface of the culs-de-sac in the Opossum is smooth, but in the lower part of the single cavity in the Kangaroo and Potoroo it presents a reticulate structure. The lining membrane in the lateral canals in all the genera is disposed in regular longitudinal folds, a dis- position which characterizes the true vagina in most of the ordinary quadrupeds. In the Kangaroo, as in the other Marsupialia, the lateral canals communicate with the common or urethro-sexual cavity without making a pro- jection ; but at the distance of three-fourths of an inch from their termination there is a sudden con- traction, with a small valvular projection in each (fig. 138). By those who consider the cul-de- sac and lateral canals as a modification of the corpus uteri, these projections will probably be regarded as severally representing an os tincae; but as they do not exist in the Opossums and Petaurists, in which there is simply a contrac- tion of the vaginal canals at the corresponding part, and as in both these and the Kan- garoo, the true uteri open in the characteristic valvular manner, as in the Rodentia, without the slightest appearance of a gradual blending with the median cul-de-sac, the valvular struc- ture in the lateral canals cannot be regarded as * See Phiki. Trans., 1834, pi. vi. fig. 6. invalidating the view here adopted of the vaginal nature of the median cul-de-sac, which is supported both by the general tex- ture and connexions of the part in question, as well as by what is now ascertained to be its limited function. Moreover, in the large single vagina of some of the Rodentia, as the Hare, Rabbit, and Paca, there are two corresponding valvular folds of membrane near its commence- ment, a little way above the urethral aperture. In endeavouring to trace the purposes an- swered by the different forms of the female marsupial organs above described, considerable difficulty arises from the want of the necessary evidence which would be afforded by the ex- amination of the pregnant uterus in each genus, and by the absence of information as to their respective periods of gestation, and the powers of the new-born foetus. As far, however, as a conclusion can be drawn from the relative pe- riods of gestation in the Kangaroo and Opos- sum, the proportionate capacities of the vaginas to the uteri would appear to be greater as gesta- tion is shorter ; the vaginae being thus calculated to present fewer obstacles to the escape of the foetus in proportion to the duration of its uterine existence ; and, consequently, a less capacious and complete external pouch is requisite for its ultimate perfection. From Rengger's descrip- tion of the connexion of the foetal Opossum to the uterus, it might be concluded that the gene- ration in that animal approximated to the true viviparous mode more nearly than it does in the Kangaroo; but the determination of this inte- resting question will require a more exact inves- tigation into the nature of the foetal vessels and membranes in the genus Didelphys. The im- pregnated uteri of the smaller pouchless Opos- sums of South America would be objects of peculiar interest and value in the present state of the inquiry. With respect to the variations of structure in the marsupial female organs, it may also be remarked, that though they are apparently most complicated in the Kangaroos and Pha- langers, yet in reality they deviate from the type of the normal Mammalia in a minor de- gree in these Marsupialia than in the Dic/el- pludes and Petauri. For, the essential differ- ence being a division of the vagina into two canals, we find this bipartition to be most com- plete in the multiparous genera, while in the Kangaroos the division is only partial, and the complexity arises from augmented capacity and extent. It is to be observed, however, that the bipartition of the vaginal canal in the Kanga- roos is not continued from the uterus into the va- gina, leaving its distal extremity single, but com- mences at the urethro-sexual cavity, and is arrested near the uteri, the orifices of which thus open into a common canal. The situation of the rudimentary vaginal septum or hymen in the unimpregnated female organs of the placental Mammalia before men- tioned, corresponds with this formation in the Kangaroo; and in a case where this septum was preternaturally developed in the human subject, it was found to obey the same law of 318 MARSUPIALIA. formation, and at the same time to have been coincident with a completely divided uterus.* It is not unusual to find the vaginae of the Kangaroo distended with a gelatino-mucous adhesive secretion containing hard irregularly shaped fibrous masses. One of these bodies, which was found in the mesial cul-de-sac of a Kangaroo, was described and figured by Sir Everard Homef as the vertebral column and occipital bone of a foetus ; and his first theory of marsupial generation appears to have been much influenced by this belief. Professor Leuckart,} who found similar bodies in the vaginal tubes of a Kangaroo, compares them to a mola, or false conception, but observes that there was nothing in their structure that would permit him to form a conclusion that they were parts of a foetus. In the Wombat the lining membrane of the vaginal culs-de-sac is greatly increased by innumerable irregular rugae and papilla?, the urethro-sexual canal is lined by a thick epi- thelium, and its surface is broken into count- less oblique rugae and coarse papillae ; the surface immediately surrounding the urethral orifice, which in this as in other Marsupials is close to the vaginal orifices, is comparatively smooth. The clitoris is situated in a preputial recess near the outlet of the uro-genital passage : it is simple in those marsupials that have a simple glans penis, but is bifid in those which have the glans divided : and in the Opossum each division of the glans clitoridis is grooved. Development of the Mursupiulia. — Before proceeding to detail the present received doc- trine of the generation and development of the Marsupialia, it may not be unprofitable to take a rapid glance at the different opinions that have prevailed at different periods respecting this interesting and difficult part of their economy. The minute size of the young of the Ameri- can Opossum when first received in the mar- supium, their pendulous attachment to the nipples, and perhaps the mode in which the nipples themselves are developed, gave rise, among the earlier observers, to a notion that the young were originally formed by and from those parts. And this belief was not only current then, as now, among the unscientific settlers in the colo- nies where the marsupial animals are common, but was entertained likewise by the best in- formed Naturalists of those times. Thus the learned Marcgrave, in his account of the Opos- sum, says, when speaking of the marsupial pouch, " Hac bursa ipse uterus est Animulis, nam alium non habet, uti ex sectione illius com- pieri; in hue semen concipitur et catuli forman- tur." § And Piso repeats the assertion more strongly. " JEx reiteratis horum aninialium sectionibus alium non invenimus uterum prater * Dr. Purcell, Philosophical Transactions, vol. Ixiv. p. 478. t Philos. Trans, vol. lxxxv. p. 228. % Meckel's Archiv fur Physiologie, torn. viii. p. 442. $ Hist. Rerum Naturaliura, Brasil. 1648. hanc bwsam, in qua semen concipitur et catuli Jbrmantur. Quos deinde quinos velsenos simul circunrfert, mobiles, perfectos, sed depiles, udeo- que pertinaciter uberibus affixos, ut a perpetuo suctu vix aveUantur, ante.quam permittente matre ad pastum ipsi egrediantur." * The assertion that the young grow from the nipple was again repeated in regard to the Philander Opossum ( Didelphys Philander) by Valentin in his History of Amboyna, and has even been revived at a comparatively recent period. f Some glimpses of the truth were ob- tained, however, before the time of the authors who have been last quoted. Hernandez, for example, speaks of the generation of the Opossum almost in the same words in which CuvierJ sums up the then existing know- ledge of the subject in the second edition of his ' Regne Animal.' " Quaternos, quinosve parit catulos, quos utero conceptos, editosque in tucem, alvi capacitate quadam, durn adhuc par- vuli sunt, claudit ac servat."§ And Maffeius more particularly describes the attachment of the young to the nipple. " Ulud autem mirum in Cerigonibus'' (Opossums) " ex ejus alvo duae dependent veluti manticae, in iis catulos cir- cumfert, et quidem adeo pertinaciter suoquem- que uberi affixos, ut a perpetuo suctu non avellantur, antequam ad pastum ipsi per se progredi valeant."|| Nevertheless, as the uterine gestation is here simply alluded to without any detailed obser- vations in proof of it, the assertion was compara- tively of little value in a scientific point of view ; and the gemmiparous theory, supported by Marcgrave aud Piso, seems to have been pre- valent at the time when Dr. Tyson first turned his attention to this subject. The discovery of the true uterus, recorded by that learned and accurate anatomist in the 20th volume of the Philosophical Transactions, p. 105, was the first step towards a correct theory of the generation of the marsupial ani- mals. It necessarily caused him to reject the gemmiparous theory, but, as often happens in such cases, Tyson was led into the opposite or sceptical extreme; and he was also induced to doubt the really accurate statements of Her- * De Indiae utriusque Re Naturali et Medica, lib. v. c. 24, 1658. t See Geoff. St. Hilaire, in the Journal Comple- mentaire du Diet, des Sciences Medicales, torn. iii. p. 193 (1819) : " Si les animaux a bourse naissent aux tetiues de leur mere." X " La premiere de toutes leurs particularites est la production prematuree de leurs petits, qui naissent dans un etat de developpement a peine comparable a celui auquel des foetus ordinaires par- viennent quelques jours apres la conception. In- capables de mouvement, montrant a. peine des germes de membres et d'autres organes exterieures, ces petits s'attachent aux mamelles de leur mere et y restent fixes jusqu'ace qu'ils se soient developpcs au degre auquels les animaux naissent ordinaire- ment. Presque toujours la peau de 1'abdomen est disposee en forme de poche aiitoiir de ces mamelles, et ces petits si impart'aits y sont preserves, comme dans une seconde matrice." Regne Animal, 1829, vol. i. p. 172. i Hist. Mexican, lib. ix. p. 330. II Job. Petr. Maffeius, Hist. Indica. MARSUPIALIA. 319 nmtdez and Maffeius respecting the function of the marsupial pouch ; " for," says Tyson, " here I find they place the mammae or teats, and they tell very odd stories about it," &c. The female Opossum which Tyson dissected appears to have been a young one, and there- fore, for a reason which has lately been clearly explained by Mr. Morgan, he was unable to detect the nipples within the pouch, and although he confesses that he was equally unable to find them upon the outer skin, he rejected the state- ments respecting the premature birth of the young and their pendulous attachment to the nipple, and, believing the generation of the Opossum not to deviate from that of ordinary quadrupeds, he limited the function of the mai'supium to that of affording a temporary shelter to the young in time of danger. The assertions of Hernandez and Maffeius were soon, however, corroborated by other ob- servers ; and Daubenton* repeated and con- firmed the dissections of Tyson, so far as re- garded the existence and general form of the uterus; but no satisfactory explanation was offered as to the nature or precise period of the uterine development or of the passage of the young to the marsupium. The next .really important advance towards the solution of this problem was made by John Hunter, who in the dissection of some marsupial foetuses of the Kangaroo detected evidences of a deviation from the ordinary mode of mammiferous development, in the ab- sence of the usual traces of a placental organi- zation ; there being in these foetuses no per- ceptible remains either of an urachus, of umbi- lical arteries, or of an umbilical vein. The beautiful series of preparations! exhibiting these and other interesting facts in the structure of the mammary + foetus of the Kangaroo are pre- served in the Museum of the Royal College of Surgeons, and afforded the principal materials for the paper on Marsupial Generation, pub- lished by Mr. (afterwards Sir Everard) Home, in the 85th vol. of the Philosophical Transac- tions (1795). I have already shewn that one of the chief grounds of the theory of marsupial generation there proposed is untenable, the sup- posed remains of the foetus, § described as being situated in the corpus uteri, (vaginal cul-de-sac,) being nothing more than a portion of the inspis- sated secretion commonly present both in this sac and the lateral canals. The temporary ori- fice by which the foetus is stated to pass imme- diately from the so called corpus uteri into the vagina (uro-genital passage) does not exist. In the subsequent theory of marsupial gene- * Buffon, Hist, Naturelle, vol. x. t See Nos. 3758-3777, Physiol. Catal. vol. v. p. 209. t I adopt this term from M. de Blainville, in preference to the term ' marsupial ' previously pro- posed by Dr. Barton, to express the condition of the young of the Marsnpialia from the time they enter the pouch to that of quitting the nipple, or to the close of the period of their uninterrupted attach- ment to the nipple. $ No. 3460 F. Physiol. Series, Mus. R. Coll. of Surgeons. ration propounded by Sir Everard Home,* the ' cornua uteri' of Tyson are regarded as por- tions of the Fallopian tubes. These he believes to furnish the yelk of the ovum, while the lateral canals, ' uteri reduplicali ' of Tyson, secrete the albumen ; the ovum is supposed to be impreg- nated and incubated in the uterus, (middle cul- de-sac formed by the communication of the two vaginal canals,) out of which the young one is stated to pass into the vagina (uro-genital pas- sage) by a particular opening, which prior to gestation does not exist. The only observations published by John Hunter himself relative to marsupial genera- tion are contained in the ' Zoological Appendix to White's Voyage to New South Wales,' where, in the introduction to his descriptions of the quadrupeds of that country, Mr. Hunter alludes to the American Opossum, and ob- serves, " there is something in the mode of propagation in this animal that deviates from all others ; and though known in some degree to be extraordinary, yet it has never been at- tempted, where opportunity offered, to com- plete the investigation. I have often endea- voured to breed them in England; I have bought a great many, and my friends have assisted me by bringing them or sending them alive, yet never could get them to breed ; and although possessed of a great many facts re- specting them, I do not believe my information is sufficient to complete the system of propaga- tion in this class." At this period, when it was admitted on all hands that some remarkable peculiarities were connected with the marsupial generation, and yet their precise nature and signification re- mained unelucidated by any direct and accu- rate observation or experiment, it is not sur- prising that the subject should have given rise to many curious hypotheses and speculations ; those of Sir Everard Home have already been noticed. I shall next briefly allude to the writings of M. Geoffroy St. Hilaire. The fruitful and discriminating labours of this talented Naturalist in advancing the zoolo- gical history of the Marsupialia cannot be too highly esteemed, but his attempts to elucidate their generative economy have been less suc- cessful. Placing an undue reliance on the relation of Count Aboville,f he first revived the gem- miparous doctrine, J meeting the objection afforded by Tyson's discovery of an uterus, by the remark tbat the foetus of the marsupial animal has never been found there ; but that the teats are developed in the ratio of the size and according to the number of the young : that mules equally possess a generative appa- ratus, which is stricken with sterility : that some plants with a perfect system of procrea- tive organs, nevertheless propagate by gemma- * Philos. Trans. 1819, p. 234, and Lectures on Comparative Anatomy, vol. iii. t See the note at the end of the 2d volume of ' Cliastelleux Voyage a l'Amerique Septentrionale, Paris, 1786.' X Journal Complcmentaire du Diet, des Sciences Medicales, 1819. 320 MARSUPIALIA. tion, &c. This theory, however, was aban- doned, or at least considerably modified after the publication of Dr. Barton's letters relative to the breeding of the Opossum. The product of marsupial generation is then stated by M. Geoffrey to quit the uterus in the condition of a gelatinous ovulum, comparable to a Medusa, and to become organically connected with the nipple by continuity of vessels. He supposed, there- fore, that a flow of blood followed the detach- ment of the mammary foetus from the nipple,* and even speculates upon the signification of the thyroid gland, on the strength of this hypo- thetical confluence of the maternal and foetal vascular systems in the marsupial tribe. f In another essay M. Geoffroy abandons this opinion, it having been proved by repeated observation that the adhesion of the foetus to the nipple is by simple contact merely ; J and finally, he falls into the opposite extreme, and from some appearances of an urachus which were pointed out to him in a very small foetus of an American Opossum, he describes them as vestiges of a placental organization. Mr. Morgan, § in his elaborate and excellent Memoirs on the Structure and Development of the Mammary Organs of the Kangaroo, bears testimony to the simply mechanical mode of attachment between the mammary foetus and the nipple in the Kangaroo, and was the first to show that the young animal, in its blind and naked condition, prior to the act of volun- tary detachment, — the birth ' a la maniere des Marsupiaux,' as it is called by M. Geoffroy, — would bear a separation from the nipple for two hours, and voluntarily regain its hold. The mammary foetus of the Kangaroo on which Mr. Morgan experimented was nearly the size of a fully grown Norway rat. Mr. Collie, surgeon R.N. in a letter addressed from New South Wales, and published in the Zoological Journal, (No. xvin. p. 239,) obtained the same result in detaching from the nipple of a smaller species of Kangaroo ( Macropus Brunii ) a mammary foetus, not two inches in length : he says, " I gently pressed with the tip of my finger the head of the little one away from the teat of which it had hold, and continuing press- ing a little more strongly for the space of a minute altogether, when the teat which had been stretched to more than an inch came out of the young one's mouth, and showed a small circular enlargement at its tip, well adapting it for being retained by the mouth of the sucker." * Geoffroy St. Hilaire, in detailing some observa- tions on a Kangaroo in the ' Annates des Sciences,' observes, " car le sang aper(;u a la litiere est un indice qu'a ce moment le icetus s'est detache de la tetine et qu'il est ne definitivement a la maniere des marsupiaux." Vol. ix. p. 342, 1827. t " Des vaisseaux nourriciers se repandroient-ils des parties du pharynx le long et entre les lames de la trachee artere pour entrer le cceur, et (conjecture de M. Serrcs) le gland thyroide seroit-il le point de leur reunion?" Geoff. St. Hilaire, Memoires du Museum, torn. xix. p. 406, 1822. t Art. Marsupiaux, Diet, des Sciences Nat. torn, xix. 1823. § Transactions of the Linnaean Society, vol. xvi. pp. 61, 455. — " An hour afterwards the young was ob- served still unattached, but in about two hours it had hold of the teat, and was actively em- ployed sucking." Dr. Barton's very interesting observations on the American Opossum are as follows : — " The female Didelphis Woapink sometimes produces sixteen young ones at a birth. I have actually seen this number attached to the teats, but never a greater number. When they are first excluded from the uterus, they are not only very small but very obscurely shaped. The place of the future eyes is merely marked by two pale bluish specks; we see no ears; in short the animal is a mere mis-shaped embryon. Its mouth, which is afterwards to become very large, is at first a minute hole, nearly of a trian- gular form, and just of a sufficient size to receive the teat, to which the little creature adheres so firmly, that it is scarcely matter of surprise that Beverly* and other writers have asserted that the young grow fast to the teats. " It is not true that the young cannot be detached from the mother without the loss of blood ; I can assert the contrary from many ex- periments made upon embryons weighing nine grains and upwards. I have fully satisfied myself as to all the various circumstances, both in the structure and in the exertions of the minute animal, which enable it, while yet a mere speck of living matter, to cling so firmly to the fountain of its support. " The wonderful little Didelphis is by no means the inanimate or the passive being some physiologists and naturalists have repre- sented it.f " The toes of the fore-feet of the new born embryon opossum are furnished with sharp and hard nails or claws, but this is not the case with the hind-feet. The latter are for some weeks of little use to the animal; but by means of the former it is enabled to cling most firmly to the teat, and especially to the hair in the marsupium immediately around the teat. " An opossum-embryon,orfoetus, which weighed sixty-seven grains, lived upwards of thirty hours after I had detached it from the teat. Another which weighed 116 lived thirty- eight hours, at which time I killed it by putting it in spiiits. " Superfoetation (I should perhaps in strict propriety say uterine superfoetation) is wholly incompatible with the established laws of the economy of the Didelphis. But Nature, always provident, wastes no time. While, therefore, the first litter of young opossums are fast ap- proaching to their adult state, the mother ac- cepts the ardour of the male ; she is impreg- nated ; and after a gestation which is not, I think, remarkably short, if we consider the small size of the embryons when they are ex- cluded from the uterus, the marsupium is des- tined to perform the office of a second, I was going to say a more important, uterus ; just at the time when the first litter have attained such a size that they are no longer (one or two of * History of Virginia, p. 136, 1722. t Pennant, Arctic Zool. i. p. 84. MARSUPIALIA. 321 them at tlie utmost) capable of taking refuge in her pouch." * Besides the satisfactory evidence, thus afforded by different and independent observers, respect- ing the condition of the mammary foetus and its true relations to the nipple, the discovery of the uterine foetus was announced nearly at the same time by two naturalists in two different species of marsupial animals. Mr. Collie, whose experiment on the young mammary foetus of a Kangaroo has just been quoted, states in the same letter, " I have just now procured two gravid uteri, (of the Macro- pus Brunii,) in which foetuses seem to be arrived at, or very near to, the termination of the period of gestation. One of them, which is about the size of the smallest young already mentioned, which was about one-half larger than the body of the common wasp, as being in the abdominal sac, has protruded through an opening inadvertently made in the uterus, and is distinctly seen through its transparent membranes and the liquor amnii."f About the same time Dr. Kengger, a naturalist who was detained several years by the Dictator Francia in Paraguay, gave the following account of the generation of a species of Opossum ( Didelphis Azara ) in his work on the Mammalia of that province. " The foetuses are developed in the cornua uteri, and not in the lateral canals. Some days after impregnation they have the form of small round gelatinous corpuscles, which do not appear, even when examined with a lens, to have any communication with the mother, but a red line indicates the first commencement of development. Towards the end of gestation, when the foetuses have attained the length of six lines, they are seen to be en- veloped in a membrane and provided with an umbilical chord, which is united to the uterus by the medium of many filaments. The head, the four extremities, and tail are recognizable with the naked eye, but those foetuses which are nearest the Fallopian tubes are generally least advanced. " In gestation they make the circuit of the lateral canals, in which they are found to be deprived of their foetal envelopes, and to have no communication with the parent by means of the umbilical chord ; whilst one foetus was found in this situation, two others were still in the body of the uterus (vaginal cul-de-sac), from which the umbilical chords were not yet detached. At this period a slight enlargement of the cul-de-sac and lateral canals was the only change perceptible in them. "J Thus, by the various observations derived from the different sources above indicated, the following propositions are satisfactorily esta- blished, viz. that the young of the Marsu- pialia are developed, primarily, as Tyson con- jectured, in the true uteri or cornua uteri ; but that, contrary to Tyson's opinion, they are, as * Barton, • Facts, Observations, and Conjectures relative to the Generation of the Opossum.' Annals of Philosophy, vol. vi. 1823, p. 349. f Zoological Journal, vol. v. p. 240. t From the Analysis of Rengger's " Saugcthiere von Paraguay" in the Bulletin des Sciences Nat. torn. xxi. p. 469. VOL. III. compared with other Mammalia, prematurely born; and that, nevertheless, the attachment of the immature young to the nipple is essen- tially the same as in ordinary mammals, the young marsupial being nourished by the lac- teal secretion, and its blood aerated by its own independent respiratory actions. Such, therefore, being the condition of the problem of marsupial generation in the year 1830, there remained to be determined by exact experiment and observation the period of uterine gestation, the structure of the foetal envelopes and appendages, the nature of the connection, if any, between the uterine foetus and the womb, the manner of the uterine birth, and the condition and powers of the new-born young. With a view to the solution of these ques- tions, I applied for and obtained from the Council of the Zoological Society permission to perform the requisite experiments on the Kan- garoos in the menagerie in Regent's Park. A healthy female ( Macropus major, Shaw) was separated from the rest; she had a young one which measured about one foot two inches from the nose to the root of the tail, and which continued to return to the pouch for the purpose of sucking and for shelter. The right superior nipple was the one in use; it was nearly two inches long, and one-third of an inch in dia- meter ; the mammary gland formed a large swelling at its base. The other three nipples were everted, and about half-an-inch in length. A healthy full-grown male was admitted into the paddock with this female for a certain period each day, and watched, during that time, by the keeper or myself. In the course of a week the female seemed to be in a con- dition to excite the sexual ardour, and after a few days toying on the part of the male, she received his embrace on the 27th August, at 1 p.m. The female stood with her fore-paws off the ground, the male mounted, ' more canino,' embracing her neck with his fore-paws, and retained his hold during a full quarter of an hour; during this period the coitus was repeated three times, and on the second occa- sion much fluid escaped from the vulva. The male was removed from the female in the evening of the same day, and was not after- wards admitted to her. On September the 2d, six days after the coitus, I examined the pouch of the female, and this scrutiny was repeated every morning and evening until the birth of the young kangaroo had taken place. I select the following from the notes taken on those occasions : — " Sept. 6th. — 10th day of gestation. The pouch is nearly free from its peculiar brown musky secretion. The right superior nipple retains its large size, and the young one that has left the pouch returns occasionally to suck. " Sept. 11th. — 15th day of gestation. No appearance of a mammary foetus ; nipples in the same condition ; the young kangaroo con- tinues to suck and return to the pouch for shelter. " Sept. 30th.— 34th day. The nipple in use by the young kangaroo (which has died) is diminished in size, and the brown secretion Y 322 MARSUPIALIA. has begun to be formed. Qy. — Will the foetus seize the larger nipple as the readiest, or be directed to another more proportionate to the size of its mouth ? " Oct. 4th. — 38th day. The keeper has observed the female putting ber nose into the pouch, and licking the entry. She was exa- mined at six in the evening ; there was a slight increase of the brown secretion ; the nipple formerly in use has diminished one-third in size ; the other nipples indicate no appearance of approaching parturition. " Oct. 5th. — 39th day. The keeper exa- mined the pouch at seven this morning, and found there the young one attached to a nipple. On being made acquainted with this fact I re- paired to the Zoological Gardens, and examined the pouch. The new-born kangaroo (Jig. 140) was attached to the left superior nipple (Jig. 1 40, «), to the point of which it adhered pretty Fig. 140. New-born fwtus and left nipples, Macropus major. firmly. It measured one inch from the mouth to the root of the tail, was quite naked, and co- vered by a thin semitransparent vascular integu- ment; the place of attachment of the umbilical chord was obscurely indicated by a longitudinal linear cicatrix. The fore-legs were longer and stronger than the hind ones, and the digits were provided with claws ; the toes were developed on the hind legs ; the body was bent forward ; and the short tail tucked in between the hind legs. This little animal breathed strongly, but slowly ; no direct act of sucking could be perceived. Such, after a gestation of thirty- eight days, is the condition of the new-born young of a species of Kangaroo, of whicli the adult, when standing erect on his hind feet and tail, can reach to the height of seven feet. The birth having taken place in the night, the mode of transference of the young to the pouch and nipple was not observed. The hypothesis of an internal passage from the uterus to the pouch — countenanced by some imperfect anatomical observations on the course of the round ligament to the abdominal ring, and the continuation thence of the cre- master to the posterior part of the mammary gland, together with the primitive inverted condition of the nipple — is wholly refuted by more exact observations of the conditions of these parts. I was chagrined at the loss of so favourable an opportunity of determining, ex visv, this interesting part of the problem ; for it had been my intention, if the symptoms of approaching pregnancy had been more marked, to have established a night as well as day-watch over the female; but by placing perhaps too much reliance on the observations on the preg- nant kangaroo recorded in the 9th volume of the Annales des Sciences, in which the duration of four months is assigned to the uterine gesta- tion of this species, I had not anticipated so speedy a termination of that process as resulted from my experiment. In order, however, to remedy, as far as might be, this omission, it occurred to me that if the young kangaroo were detached from the nipple and deposited at the bottom of the pouch, any actions of the parent, by which its original transference from the uterus to the nipple had been aided or effected, might be instinctively repeated, and thus an insight be gained into their nature. As, therefore, the experiments of Messrs. Morgan and Collie seemed to show that this might be done without necessarily causing the death of the young one, I performed the experiment with the sanction and assistance of Mr. Bennett, then Secretary of the Zoological Society. " Oct. 9th. — I examined the pouch of the female, and found the young one, now four days old, evidently grown, and respiring vigo- rously ; it adhered more firmly to the nipple than was expected, requiring a continued gentle pressure to detach it : when that took place, a minute drop of whitish fluid, a kind of serous milk, was expressed from the nipple. No blood followed, nor anything to indicate a solution of organic continuity; the extremity of the nipple was small, not swollen as in Mr. Collie's case. The young one moved its extre- mities vigorously. It was deposited at the bot- tom of the pouch, and the mother was left and then carefully watched. Soon after this was done she seemed uneasy, was often scratching the exterior of the pouch, and every now and then dilated the cavity with her two fore- paws, grasping the sides of the aperture, and pulling them in contrary directions, just as in drawing open a bag; she then inserted her muzzle pretty deeply into the pouch, moving her head about as if to lick off something from the interior, or perhaps to move the little one. She kept her nose in the pouch sometimes for half-a-minute. I never observed her to put her fore-legs, or either of them, in the pouch ; they were always occupied in keeping open the mouth of the pouch, while she was at work with her mouth within it. She generally con- cluded by licking the mouth of the pouch, and occasionally she stooped down to lick the cloaca, which she could reach with ease. When she scratched the outside of the pouch it seemed as if to push up something that was in- side towards the aperture. These actions she repeated at short intervals for about an hour ; she then lay down and appeared quiet. She had also lain down in the intervals of the above operation, but during that time never meddled with the pouch ; when stimulated to do so by some uneasy sensation, she always rose upon her hind feet, and then inserted her muzzle alternately into the pouch and vulva. Observing the freedom with which she could reach both these parts, I was led to believe that the mode of removal of the young from the vulva to the MARSUPIALIA. pouch was by the mouth of the mother. Her fore-paws, in this case, would be used, not for the transport of the young, but for keeping the mouth of the pouch open for its reception, it being deposited therein by the mouth, and so held over a nipple until the mother had felt it grasping the sensitive extremity of the nipple. This means of removal is consistent with analogy ; dogs, cats, mice, all transport their young from place to place with the mouth. In the case of the kangaroo, it may be supposed that the foetus would be held by the lips only, not the teeth, on account of its delicate con- sistence. Whether this theory, suggested by witnessing the actions of the mother after an artificial separation of the Marsupial foetus, be correct, must be confirmed by actual obser- vation. There is no internal passage from the uterus to the pouch : — the mouth of the vagina cannot be brought into contact with that of the pouch, either by muscular contraction in the living or by any force of stretching in the dead kangaroo : — as the young was proved by the result of this experiment not to have the power of itself to regain the nipple, a fortiori we may conclude that it could not transfer itself from the vulva to the interior of the pouch and to the apex of the nipple : — the fore-paws of the Kangaroo would not so effectually protect the tender embryo from the external air as the mouth, nor so safely ensure its passage to the pouch, notwithstanding that they are adroitly used in grasping objects, being similar, in respect of the extent and freedom of motion of the digits, to the fore-paws of the Rodents. After the mother had rested quietly for a short time, we again examined her, but found the young one still detached, moving more vigorously than before. On an examination two days afterwards the marsupium was found empty : the young one had died and had pro- bably been removed by the mother. Thus the period of uterine gestation, the condition of the new-born young, and the pro- bable mode of its transference to the nipple being determined in the genus Macropus, it next remained to be determined how the embryo was nourished in utero. The means of giving the required solution were shortly after afforded by specimens of the impregnated uterus, trans- mitted to me by Mr. George Bennett, Captain Grey, and Dr. Sweatman. The first was of the Macropus major, nearly two-thirds of uterine gestation having been completed ; the second was of the Macropus penicillatus, at about the same or somewhat earlier period of gestation; the third exhibited the uterine foetus at nearly the completion of that period of its existence. Before, however, giving the summary of what I have elsewhere* recorded respecting the uterine development of the Marsupialia, a de- scription of the ovarian ovum must be pre- mised. In the Kangaroo this part agrees in all essen- tial points with the observed ovarian ova of placental Mammalia: the main modification * Proceedings of the Zool. Society, 1833. Philos. Trans. 1834. is the greater proportion of vitelline fluid and globules, and the smaller proportion of fluid between the external membrane of the ovum (vitelline membrane) and the ovarian vesicle, or lining membrane of the ovisac. In a female Macropus Parrt/i, the ovum from the largest ovisac of the left ovarium measured •j'gth of a line in diameter, the germinal vesicle fjjth of a line in diameter. We are at present ignorant of the changes that take place in the development of the ovum between the period of impregnation until about the twentieth day of uterine gestation. At this time, in the great Kangaroo ( Macropus major ), the uterine foetus (fig. 138) measures eight lines from the mouth to the root of the tail ; the mouth is widely open (fig. 141); the tongue large and protruded; the nostrils are small round apertures; the eyeball not yet wholly defended by the palpebral folds; the meatus auditoriusexternus is not provided with an auricle ; the fore-extremities are the largest and strongest; they are each terminated by five well-marked digits ; those of the hind legs are not yet developed ; the cervical fold of the mucous layer or the branchial fissure is still unenclosed by the integument. The tail is two lines long, thick and strong at the com- mencement; impressions of the ribs are visi- ble at the sides of the body ; the membranous tube of the spinal marrow may be traced along the back between the ununited elements of the vertebral arches ; posterior to the um- bilical chord there is a small projecting penis, and behind that, on the same prominence, is the anus. This foetus and its appen- dages were enveloped in a large chorion, puckered up into numerous folds, some of which were insinuated between folds of the vascular lining membrane of the uterus, but the greater portion was collected into a wrinkled mass. The entire ovum was re- moved without any opposition from a placental or villous adhesion to the uterus. The chorion (a, a, fig. 141) was extremely thin and lacera- ble; and upon carefully examining its whole outer surface, no trace of villi or of vessels could be perceived. Detached portions were then placed in the field of a microscope, but without the slightest evidence of vascularity being discernible. The next membrane, whose nature and limits will be presently described, was seen extending from the umbilicus to the inner surface of the chorion, and was highly vascular. The foetus was immediately enve- loped in a transparent amnios. On turning the chorion away from the foetus, it was found to adhere to the- vascular m|cm- brane above-mentioned, into which the um- bilical stem suddenly expanded. With a slight effort, however, the two membranes could be separated from each other, without laceration, for the extent of an inch ; but at this distance from the umbilicus the chorion gave way on every attempt to detach it from the internal vascular membrane, which here was plainly seen to terminate in a well-defined ridge, formed by the trunk of a bloodvessel. When the whole of the vascular membrane y 2 324 MARSUPIALIA. Fig. 141. Uterine foetus with chorion and foetal appendages, Maeropus major. The foetus is magnified twice the natural size. (b, fig. 141) was spread out, its figure ap- peared to have been that of a cone, of which the apex was the umbilical chord, ~and the base the terminal vessel above-mentioned. Three vessels could be distinguished diverging from the umbilical chord and ramifying over it. Two of these trunks contained coagulated blood, and were the immediate continuations of the terminal or marginal vessel : the third was smaller, empty, and evidently the arterial trunk. Besides the extremely numerous rami- fications dispersed over this membrane, it dif- fered from the chorion in being of a yellowish tint. The amnios (c, 141) was reflected from the umbilical chord, and formed, as usual, the immediate investment of the foetus. The umbilical chord measured two lines in length and one in diameter. It was found to contain the three vessels above-mentioned, with a small loop of intestine; and from the ex- tremity of the latter a filamentary process was continued to the vascular membrane. The margins of the umbilicus or abdominal open- ing were very strong, offering much resistance to their division. On tracing the contents of the chord into the abdomen, the two larger vessels with coagulated blood were found to unite; the common trunk then passed back- wards beneath the duodenum, and after being joined by the mesenteric vein, went to the under surface of the liver, where it penetrated that viscus: this was consequently an omphalo- mesenteric or vitelline vein. The artery was a branch of the mesenteric. The membrane, therefore, upon which they ramified, answered to the vitellicle, i. e. the vascular and mu- cous layers of the germinal membrane, which spreads over the yolk in oviparous animals, and which constitutes the umbilical vesicle of the embryo of ordinary Mammalia. The fila- mentary pedicle which connected this mem- brane to the intestine was given off near the end of the ileum, and not continued from the coscum, the rudiment of which was very evi- MARSUPIALIA. 325 dent half a line below the origin of the pedicle. (See the fcetus in Jig. 141.) The small intestine above the pedicle was disposed in five folds. The first from the stomach or duodenum curved over the vitel- line vein, and the remaining folds were dis- posed around both the vitelline vessels. From the ccecum, which was given off from the re- turning portion of the umbilical loop of the intestine, the large intestine passed backwards to the spine, and was then bent, at a right angle, to go straight down to the anus. The stomach did not present any appearance of the sacculated structure so remarkable in the adult, but had the simple form of a carnivorous stomach. The liver consisted^of two equal and symme- trically disposed lobes. The vena portae was formed by the union of the vitelline with the mesenteric, and doubtless the other usual veins, which were, however, too small to be distinctly perceived. The diaphragm was perfectly formed. The vena cava inferior was joined, above the diaphragm, by the left superior cava, just at its termination in a large right auricle. The ventricles of the heart were completely joined together, and bore the same proportions to each other as in the adult, — a perfection of structure which is not observed in the embryos of ordi- nary Mammalia at a corresponding period of development. The pulmonary artery and aorta were of nearly the same proportionate size as in the adult: the divisions of the pul- monary artery to the lungs were at least double the size of those observable in the embryo of a sheep three inches in length. The ductus arteriosus, on the contrary, was remarkably small. The aorta, prior to forming the de- scending trunk, dilated into a bulb, from which the carotid and subclavian arteries were given off. The lungs were of equal size with the heart, being about a line in length, and nearly the satne in breadth : they were of a spongy tex- ture and of a red colour, like the veins, from the quantity of blood they contained. This precocious development of the thoracic viscera is an evident provision for the early or prema- ture exercise of the lungs as respiratory organs in this animal : and on account of the simple condition of the alimentary canal, the chest at this period exceeds the abdomen in size. The kidneys had the same form and situ- ation as in the adult. The supra-renal glands were half the size of the kidneys. The testes were situated below the kidneys, and were one-half larger than those glands, the superiority of size depending on their large epididymis, with the adherent remains of the Wolffian body. They continue within the ab- domen for six weeks after uterine birth. At a later period of uterine development, when the fetus, measured in a straight line from the mouth to the root of the tail, is ten lines in length, the urachus expands into a small allantois ( d, Jig. 141), of a flattened pyriform figure, and finely wrinkled external surface. This bag insinuates itself between the amnios and chorion, carrying along with it two small hypo- gastric arteries and an umbilical vein, but not establishing by their means an organized and vascular surface of the chorion by which a placental attachment is formed between the ovum and the womb. The allantois depends freely from the end of the umbilical chord, and has no connexion at any part of its cir- cumference with the adjoining membrane. Its office is apparently that of a receptacle of urine. The vitellicle or umbilical sac presented the same large proportionate size and vascular structure as in the first described fcetus. The chorion which enveloped this fcetus and its appended sacs was adapted to the cavity of the uterus by being disposed in innumerable folds and wrinkles. It did not adhere at any part of its surface to the uterus, but presented a modification not present in the chorion of the earlier fetus, in being partially organized by the extension of the omphalo-mesenteric vessels upon it from the adherent vitellicle. The di- gits of the hind legs were distinctly formed in this embryo. The new-born fetus of the great Kangaroo does not exceed, as we have already shown, one inch in length ; its external characters have been already described. Dr. Barton has given the following account of the Opossum (Didel- p/n/s Yhginiuna ) at an analogous period. " I have been so fortunate as to ascertain the size and weight of several embryos imme- diately after their exclusion from the uterus. One of them weighed only one grain ! The weight of each of the six other young ones was but little more than this. The young opossums, unformed and perfectly sightless as they are at this period, Jind their way to the teats by the power of an invariable, a deter- minate instinct" (qu.?). " In this new domi- cilium they continue for about fifty days, that is, until they attain the size of a common mouse ( Mus musculus ), when they begin to leave the teats occasionally, but return to them again until they are nearly the size of rats. " At the end of about fifty or fifty-two days from its first reception in the pouch the eyes of the young begin to open. " I have found that the same embryon has increased in weight 531 grains in sixty days, that is, at a rate of almost 9 grains daily. The animal attains to nearly its full growth in about five months ; but never, 1 believe, (in our lati- tudes 1 mean,) procreates the first year of its existence. " On the 21st of May, upon looking into the box which contained the female Opossum, I found that she had just excluded from her uterus seven embryons ; the smallest of which scarcely weighed one grain, another barely two grains, and the remaining five (taken together) exactly seven grains." * In the Kangaroo about ten months elapse before the mammary fetus quits the pouch: it bus, prior to this period, quitted the nipple, * Barton, in Annals of Philosophy, vi. (1823), p. 349. " Facts, Observations, and Conjectures relative to the Generation of the Opossum." 326 MARSUPIALIA. and occasionally protrudes its head and changes its position in the pouch. The anatomical condition and progressive development of the mammary foetus of the Marsupialia offer a subject of highly interest- ing research, especially if compared with the same circumstances in the uterine foetus of an equal sized and analogous placental species. Much still remains to be done in this chapter of the history of Marsupial generation ; at present I have to offer the following obser- vations. By comparing the new-born Kangaroo with a similarly sized foetus of a sheep, we find that, although, in the Kangaroo, the ordinary laws of development have been adhered to in the more advanced condition of the anterior part of the body and corresponding extremities, yet that the brain does not present so dispropor- tionate a size ; and the same difference is ob- servable in the uterine foetus of the Kangaroo, even when compared with the same sized em- bryo of an animal of an inferior class, as the bird. This difference, I apprehend, is owing to the rapidity with which the heart and lungs acquire their adult structure in the Kangaroo, whereby the passage of the purer and more nutritious blood through the foramen ovale and left auricle to the primary branches of the aorta and so to the brain is impeded. The brain, however, of the mammary foetus, though exhibiting a low degree of development, yet is of a firmer texture than in a similarly sized fcetus of a sheep, and attains its ultimate pro- portion by a more gradual process of growth. In a mammary foetus, one inch and a half in length, the urinary bladder is largely deve- loped, and adheres by its apex to the perito- neum, exactly opposite that part of the abdo- minal integument where a small linear ridge indicated the previous attachment to the umbi- lical chord and appendage. There are also minute but distinct traces of umbilical arteries running up the sides of the bladder to this point of attachment. As the urinary bladder be- comes afterwards expanded in the abdomen, the peritoneum is gradually, as it were, drawn from this part of the abdominal parietes, form- ing an anterior ligament of the bladder. In a mammary fcetus of the Kangaroo about a month older than the above, there was at the superior part of this duplicature a small projecting point from the bladder, like the remains of a ura- chus; but the fundus, now developed con- siderably above this point, was covered with a perfectly smooth layer of peritoneum; and it is this modification, I apprehend, which led Hunter to suppose that there was no trace of urachus or umbilical arteries in the foetuses of the Marsupialia. In the Sloth, the Manis, and the Armadillo, the urachus is continued in the same manner from the middle of the anterior part of the bladder, and not from the fundus. In neither of the above foetuses of the Kan- garoo was there any corresponding trace of umbilical vein, although there was a distinct ligamentum suspensorium hepatis, formed by a duplicature of the peritoneum descending from the diaphragm to the notch lodging the gall-bladder, and not entering, as usual, the fissure to the left of that notch : the allantois is too small, and its function too limited for the preservation of any permanent trace of its peculiar vein. The small intestines in the mammary fcetus, one inch and a half long, when compared with those of the uterine fcetus above de- scribed, were found to have acquired several additional convolutions ; the fold to which the umbilical vesicle had been attached was still distinct, but now drawn in to the back of the abdomen. The coecum was much elongated, but the colon proportionately not more deve- loped than in the uterine fcetus ; the subse- quent modification, therefore, of the large in- testines seems evidently destined to complete the digestion of the vegetable food. The stomach was not sacculated, but the division between the cardiac and middle com- partments was more marked than in the uterine foetus. The liver had now advanced in its development beyond the oviparous form which it presented in the uterine foetus, the right lobe being subdivided into three. The supra-renal glands bore the same proportionate size to the kidneys. The testes were still larger than the kidneys, and were situated below them, not having yet passed out of the abdomen : this takes place when the mammary fcetus is about three inches long from the nose to the root of the tail. The ductus arteriosus was distinct in the small mammary foetus, but I could not perceive any trace of the thymus gland. Is this gland unnecessary on account of tlie pre- cocious development of the lungs ? or because of the small size and gradual growth of the brain ? The latter appears the more probable condition of its absence, as in the ovovivipa- rous classes with small and simple brains the thymus gland is rudimental or of doubtful existence. Notwithstanding that the new-born Kanga- roo possesses greater powers of action than the same sized embryo of a sheep, and approxi- mates more nearly in this respect to the new- born young of the rat, yet it is evidently in- ferior to the latter. For, although it is enabled by the muscular power of its lips to grasp and adhere firmly to the nipple, it seems to be unable to draw sustenance therefrom by its own unaided efforts. The mother, as Professor Geoffroy and Mr. Morgan have shown, is therefore provided with the peculiar adaptation of a muscle (analogous to the cremaster) to the mammary gland, for the evident purpose of injecting the milk from the nipple into the mouth of the adherent foetus. Now it can scarcely be supposed that the foetal efforts of suction should always be coincident with the maternal act of injection ; and if at any time this should not be the case, a fatal accident might happen from the milk being forcibly injected into the larynx, unless that aperture were guarded by some special contrivance. Professor Geoffroy first described the modi- fication by which this purpose is effected; and Mr. Hunter appears to have anticipated the ne- MAESUPIALIA. 327 cessity for such a structure, for he dissected two small mammary foetuses of the Kangaroo for the especial purpose of showing the rela- tion of the larynx to the posterior nares. The epiglottis and arytenoid cartilages are elongated and approximated, and the rima glottidis is thus situated at the apex of a cone-shaped larynx, (Jig. 142, c,) which projects, as in the Cetacea, into the posterior nares, where it is closely embraced by the muscles of the soft palate. The air-passage (0) is thus completely separated from the fauces, and the injected milk passes in a divided stream on either side the larynx to the oesophagus. Fig. 142. Nijjple, and head of Mammary Fottus, Kangaroo. Thus aided and protected by modifications of structure, both in the system of the mother and its own, designed with especial reference to each other's peculiar condition, and afford- ing, therefore, the most irrefragable evidence of creative foresight, the small offspring of the Kangaroo continues to increase, from suste- nance exclusively derived from the mother, for a period of about eight months. During this period the hind legs and tail assume a great part of their adult proportions; the muzzle elongates ; the external ears and eyelids are completed ; the hair begins to be developed at about the sixth month. At the eighth month the young Kangaroo may be seen frequently to protrude its head from the mouth of the pouch, and to crop the grass at the same time that the mother is browsing. Having thus acquired additional strength, it quits the pouch and hops at first with a feeble and vacillating gait, but continues to return to the pouch for occasional shelter and supplies of food till it has attained the weight of ten pounds. After this it will occasionally insert its head for the pur- pose of sucking, notwithstanding another foetus may have been deposited in the pouch ; for the latter, as we have seen, attaches itself to a dif- ferent nipple from the one which had been pre- viously in use. Mammary Organs. — In the young Marsu- pial, as Mr. Morgan was the first to observe in the Kangaroo, the nipples are not visible, but are indicated by the orifices of a kind of cutaneous preputial sheath in which they are concealed. M. Laurent has noticed a similar condition of the nipples in a mam- mary foetus of an Opossum and a I'erameles. I have also observed it in the mammary foetus of a Petaurist and Dasyure : it is doubtless, therefore, common to all Marsupials. Once naturally protruded and the preputial sheath everted, the nipples, in the Kangaroo at least, continue external. They are longer and more slender than in other quadrupeds, and when in use generally present a terminal expansion (fig. 142, d). This part lies in a deep longitudinal fossa on the dorsum of the tongue {a, fig. 142) ; and the originally wide mouth of the uterine foetus is changed to a long tubular cavity, with a terminal sub- circular or triangular aperture just large enough to admit the nipple, to which the young Mar- supial thus very firmly adheres. In the Phascogale, in which the nipples are relatively larger than usual, and of a subcom- pressed clavate form, the young, when grown too large to be carried in the pouch, are dragged along by the mother, if she be pursued, hanging by the nipples. The number of nipples bears relation in the marsupial, as in the placental Mammalia, to that of the young brought forth at a birth; although from the circumstance of the produce of two gestations being for a short time suckled simultaneously, the nipples are never so few. Thus the uniparous Kangaroo has four nipples ; of which the two anterior are generally those in use : the Petaurists, which bring forth two young at a birth, have also four nipples : the Thalycine has four nipples : the multiparous Virginian Opossum has thirteen nipples, six on each side and the thirteenth in the middle. In the Didelphys Opossum there are nine nipples, four on each side and one in the middle. The Didelphys dorsigera has the same number of nipples, although six is the usual number of young at a birth ( fig. 143). In the Phas- cogale pcnicillata there are eight nipples ar- ranged in a circle. The Perameles nasuta has the same number of nipples arranged in two slightly curved longitudinal rows; this Mar- supial has three or four young at a birth. The nipple in ail the Marsupials is imper- forate at the centre ; the milk exudes from six to ten minute orifices arranged round the apex. It increases in size with the growth of the mammary foetus appended to it. The mammary gland, has the same essential structure as in the ordinary Mammalia; it has no cavity or udder; its chief peculiarity arises from its being embraced by the muscle, already noticed, which has the same origin and course as the cremaster muscle in the male. Marsupial pouch. — The development of the pouch is in an inverse ratio to that of the uteri and directly as that of the complicated vagina? : thus it is rudimental in the Dorsigerous Opos- sum, which has the longest uteri and the sim- plest vagina? : we may conclude therefore that the young undergo a greater amount of deve- lopment in the womb in this and allied species.* * Is there any essential modification of the mem- branesof the ovum in these small Marsupials? The means of determining this question are most de- sirable. 328 MARSUPIAL1A. Fig. 143. Female Didelphya dvrsigera, with young and pouch. In the Kangaroos and Potoroos, which have the shortest uteri and longest vaginal tubes and cul-de-sac, the marsupial pouch is wide and deep. It is composed of a duplicature of the integument, of which the external fold is sup- ported by longitudinal fasciculi of the panni- culus carnosus converging below to be im- planted in the symphysis pubis. The mouth of the sac is closed by a strong cutaneous sphincter muscle. The interior of the pouch is almost naked : a few hairs grow around the nipple: it is lubricated by a brown sebaceous secretion. The mouth of the pouch is directed forwards in most Marsupials : the reversed position in the Perameles and Chaeropus, where the mouth is directed towards the vulva, has been already noticed. M. Laurent* has made the interesting observation of the presence of a rudimental pouch in the male mammary foetus of an Opossum : he could not discern equal traces of the nipples: that of the pouch is * Annalcs d'Anatomie et cle Physiologie, 1839, p. 237. soon obliterated, as the scrotum increases in size. In the male Thylacine the rudimental mar- supium is retained, in the form of a broad triangular depression or shallow inverted fold of the abdominal integument, from the middle of which the peduncle of the scrotum is con- tinued. In the female the orifice of the capa- cious pouch is situated nearer the posterior than the anterior boundary of that receptacle. A few observations on the claims of the Mar- supialia to be regarded as a natural group of ani- mals may not inappropriately conclude this ar- ticle. Cuvier, in 1816, first separated the mar- supial from the other unguiculate quadrupeds, to form a distinct group, which he describes as forming, with the Monotremes, a small collateral chain, all the genera of which, while they are connected together by the peculiarities of the generative system, at the same time correspond in their dentition and diet, some to the Car- nivora, others to the Rodentia, and a third tribe to the Edentata. M. de Blainville, in the tables of the Animal Kingdom which he published in the same year, 1816, constituted a distinct sub-class of Cuvier's " small col- lateral chain " of mammals, and gave to the sub-class the name of Didelphes in antithesis to that of Monudelpfies, by which he distin- guished the Placental Mammalia. The class or subclass ' Implacentalia,' of which the Marsupialia form one order, also in- cludes a second order, the Monotremata, which can only be termed ' Didelphes ' in the sense in which the word is applicable to many of M. de Blainville's ' Monodelphes,' i. e. in re- ference to their having two distinct uterine tubes. But the merit of the primary division of the Mammalia into Placentalia and Im- placentalia does not rest upon the appro- priateness of the terms, but upon the esta- blishment, by a long series of anatomical re- searches, of a primary division of the Mam- miferous class, which before was a mere hy- pothesis. Many acute and sound-thinking naturalists refused their assent to the views of Cuvier and De Blainville, which, as they were supported by a knowledge of the conformity of organiza- tion of only the generative system in the Mar- supials, were unquestionably defective in the evidence essential to enforce conviction. The best arguments for returning to the older views of classification, and for distributing the Mar- supial genera, according to the affinities appa- rently indicated by their dental and locomotive systems,amongthedifferentorders of the Placen- tal Mammalia, have been advanced by Mr. Ben- nett, the accomplished author of the Gardens and Menagerie o/ the Zoological Society de- lineated, (vol. i. p. 265); and these have been repeated with approbation, and adopted by later systematists, as by Mr. Swainson. The discovery of the true affinities of the Marsupialia could only flow from an insight into their whole organization, and the question which Mr. Bennett proposes with reference to the genus Pfiancolomi/a, " What is there of im- MARSUPIALIA. 329 portance in the structure of the Wombat, except this solitary character of the Marsupium, to separate it from the Rodent order?" — a ques- tion which he might in 1831 have asked with equal force in reference to any other Marsupial genus, — could only be answered satisfactorily by the submission of the Marsupialia in ques- tion to a thorough dissection. Although the Marsupials present modifica- tions of the dental system corresponding with the carnivorous, omnivorous, and herbivorous types, yet they agree with each other, and differ from the analogous Placental Mammalia in having four instead of three true molars, i. e. four molars which are not displaced and succeeded by others in the vertical direction. The incisor teeth, also, either exceed in number those of the analogous Placental classes, or are peculiarly arranged and opposed to each other. In the locomotive organs it is true that we see some of the Marsupials having a hinder thumb, like the Placental Quadrumana; others are digitigrade, with falculate claws, like the Placental Ferse ; a third, as the Wombat, has the feet adapted for burrowing ; a fourth, like the Cheironectes, is aquatic, and has webbed feet ; yet all these Marsupials agree with each other in having a rotatory movement of the hind foot, analogous to the pronation and su- pination which, in the placental quadrupeds, are limited when enjoyed at all to the fore feet; and they manifest moreover a peculiar modi- fication of the muscles of the hind leg and foot in relation to these rotatory movements. In those Marsupials, as the Kangaroos, Potoroos, and Perameles, in which the offices of support and locomotion are devolved exclusively or in great part upon the hind legs, these are strengthened at the expense of the loss of the rotatory movements of the feet ; but in the enormous development of the two outer toes, and the conversion of the two inner ones into unguiculate appendages, useful only in cleans- ing the fur, these Marsupials differ from all Placentals, whilst the same peculiar condition of the toes may be traced through the Pedima- nous group of Marsupials. Thus the locomo- tive organs, notwithstanding their adaptation to different kinds of progression, testify to the unity of the Marsupial group in the two remarkable peculiarities of structure above cited. The vascular system gives evidence to the same effect. We have seen that the Marsupials present the following peculiarities in the struc- ture of the heart : viz. the right auricle mani- fests no trace of either fossa uvalis or annulus ovalis, and receives the two vena cuva supe- riures by two separate inlets. This genera- lization is, however, less urgent than the pre- ceding in the present question, because the modification, as regards the separate entry of the superior vena? cavae, obtains in a few pla- cental species, as in the elephant and certain Rodents ; but as the first cited cardiac cha- racter is common and peculiar to the Mar- supial Mammalia, and as the second, while it is universal in the Marsupials, occurs only as an exceptional condition in the placental series, the arguments which they afford to the unity of the Marsupial group cannot be over- looked in a philosophical consideration of the affinities of the Mammalia. With respect to the nervous system, it has been shown that in the structure of the brain, the Marsupialia exhibit a close correspondence with the Ovipara in the rudimental state of the corpus callosum ; the difference which the most closely analogous placental species offer in this respect is broadly marked. These coincidences in the Marsupialia of important organic modifications of the dental, locomotive, vascular, cerebral, and reproductive systems, establish the fact, that they constitute, with the Monotremes, a natural group inferior on the whole in organization to the Placental Mammalia. The following is a tabular view* of the subor- dinate divisions in the Marsupialia regarded as an order of the Implacental sub-class of Mam- malia : — * Of the various forms of Marsupial animals attempted to be arranged in natural groups in the present classification, it may be asked which is the typical form ? or in other words, which genus com- bines most of the points of organization peculiarly characterizing the Marsupialia? We have seen that certain modifications of the nervous, circulating, and generative systems are common to all the genera. But the female gene- rative organs approach nearest to the Rodent type in the small dorsigerous Opossums, in which the characteristic external pouch becomes very nearly obsolete. It is not the genus Dklelphys therefore that we should select as the type of the Marsupials. It appears to me that there is both a dental and a digital character which may be re- garded as eminently marsupial ; the former, be- sides the number of true molar teeth, consists in the opposition of six vertical incisors above to a large procumbent single pair below ; the latter is exemplified in the atrophied and coadunate con- dition of the second and third digits of the hinder foot. The Phalangers, Petaurists, Koalas, Kan- garoos, and Potoroos possess, in addition to the ordi- nary Marsupial characters, both these modifications of teeth and digits. It seems, therefore, that it is from one of these genera that we should select the Marsupial type par excellence. If we say the Plta- lanysrs, it may be objected that the hinder hand and opposable prehensile thumb indicate in these a transition from the Marsupialia to the Quadru- mana. Should the Petauri be our choice, then again we perceive in the development of the lateral tegumentary folds, and their connection with the lo- comotive members, a tendency to the Plying Squir- rels. The tail-less Koala may be deemed to ex- hibit in its clumsy form and proportions a resem- blance to the tree-bears. The Kangaroos and Potoroos obviously typify the Rodent Jerboas, and they have lost the peculiar rotation of the hind leg and the muscular modification connected there- with. If, however, the type of a natural group of animals, and such I have proved the Marsupial group to be, is that which manifests the greatest number of the structural modifications peculiar to the group, and the smallest number of such as are common to other natural assemblages of Mammalia, then the Koala has the best claim to typical pre- eminence. The Marsupial bones might be readily supposed to afford a simple indication of the most peculiarly Marsupial animal, if they offered different relative magnitudes in different genera : now the range of variety in this respect is, in fact, consi- derable, and the Marsupial bones present their greatest development in the Koala. 330 MARSUPIALIA. Classification of the Marsupialia. Tribes. 1. Sarcophaga. Families. Genera. Suis -genera. Three kinds of teeth, canines long in both jaws ; a simple stomach, no in- £ Dasyuridae testmum cacum Extinct transitional forms 2. Entomophaga. Three kinds of teeth in both jaws ; a ~\ simple stomach, a moderately long > Ambulatoria . intestinum caxum. C Thylacinus. < Dasyurus. ' Phascogale. \ Phascolotherium. } Fossil ( Thylacoilierium(?) S Myrmecobius. Saltatoria . f Chasropus. ' ^ Perameles. Scansoria Didelphys 3. Carpophaga. Anterior incisors large and long in both-} jaws; canines inconstant; stomach f simple, or with a special gland ; a ' very long intestinum cxcum .... Phalangistidae Phascolarctidae . Macropodidae . . | 4. Poephaga. Anterior incisors large and long in both jaws; canines present in the upper jaw only, or wanting ; a complex stomach, a long intestinum cmcum . . 5. Rhizophaga. Two scalpriform incisors in both jaws;-\ no canines ; stomach with a special f pjias 0]om \^ gland ; cacum short, wide, with a< ^ vermiform appendage * Phalangista . . Petaurus . Phascolarctus. ( Phascolomys. i Diprotodon.. ( Didelphys. ' ( Cheironectes. C Cuscus. . < Pseudocheirus. CTapoa. C Petaurista. A Belidia. (. Acrobata. Hypsiprymnus. Macropus. r Lagocheles. J Halmaturus. } Macropus. V.Osphranter. Fossil. Bibliography. — Marcgraviut, G. Historia natu- ralis Brasilia, 1648 ; Piso, De India- utriusque re naturali, fol. 1658. Hernandez, Hist. Mexican, lib. ix. p. 330. Tyson, Philos. Trans. 1698, vol. xx. Cowper, Philos. Trans. 1704, vol. xxiv. Daubenton, Buffon, Hist. Nat. torn. x. p. 325, 1750. Aboville, Count, in Chastelleux Voyage a l'Amcrique Septentrionale, 1786. Hunter, John, Appendix to White's Journal of a Voyage to New South Wales, 1790. Home, Sir Everard, Philos. Trans. 1795, 1819 ; Lectures on Comparative Anatomy, 1814-1823. Cuvier, G. Lecons d'Anato- mie Comparee, 1799-1805 and 1836-1840 ; Annates du Museum, t. v . ; Ossemens Fossiles, 1822, t.iii. ; Regne Animal, 1816 and 1829. Geoffroy St. Hilaire, Annales du Museum, 1803; Journal Complemen- taire du Dictionnaire des Sciences Medicales, t. iii. 1819; Memoires du Museum, 1822; Anatomie Philosophique, torn. ii. 1822 ; Dictionnaire des Sciences Naturelles, art. Marsupiaux, 1823; An- nates des Sciences Naturelles, 1827. Meckel, J. F. Abhandl. aus der menschl. & vergl. Anatomie und Physiologie, 1806; System der vergl. Anatomie, 1821-1828. Blainmlle, Bulletin de la Soc. Philo- mathique, 1818; Comptes Rendus de l'Acad. des Sciences, 1838. Tiedemann, Icones cerebri simia- rum, &c. 1821 . Barton, Dr. Annals of Philosophy, vol. vi. 1823. Treviranus, Biologie, 1802-1821 ; Zeitschrift fiir Physiol. Bd. iii. 1827. Burdach, Physiologie, Bd. i. pi. iv. 1828. Laurent, Lettre sur deux sujets d' Anatomie Comparee, Bulletin des Sciences Medicales, Juin 1827 ; Voyage de la Favorite, 1839; Annales d'Anatomie et de Phy- siologie, 1839. Broderip, W.J. Zoological Journal, 1828. Grant, Dr. R. Wernerian Transactions, vol. vi., Anatomy of Perameles nasuta. Collie, Dr. Zoological Journal, No. xviii. 1828. Ritgen, Ueber einige Eigenthiimlichkeiten im Bau der Beutel- thiere, Zeitschrift fur organische Physik, Eisenach, 1828. Leuckhart, Meckel's A rchiv.fur Physiologie, t. viii. Rengger, Dr. Saugethiere von Paraguay, 8vo. 1829. Morgan, John, Trans. Linnaean Society, vol. xvi. 1829 and 1833, Mammary Organs of Kangaroo. Owen, R. Proceedings of Zoological Society — 1831, Female Organs of Kangaroo; 1833, Uterine Gestation and Foetus of Kangaroo ; 1834, Anatomy of Macropus Parryi ; 1835, Anat. of Dasyurus Macrurus ; 1836, Anat. of Wombat; 1837, Allantois of Kangaroo; 1838, Anat. of Koala, Osteology of Marsupialia; 1839, Classifi- cation of Marsupialia. Phil. Trans. — 1834, Gene- ration of Marsupialia ; 1837, Brain of Marsupialia ; Medical Gazette, 1839, Blood-discs of Marsupialia j Physiological Catalogue of Museum Royal College of Surgeons, 1834, 1840; Notes to Hunter's Animal fficonomy, ed. 1837 ; Description of Aus- tralian Fossil Marsupials, in Mitchell's Expeditions into the Interior of Eastern Australia, 1839; Geological Transactions, second series, vol. vi. Mayo, H. Outlines of Physiology, 1833, Spinal Chord of Kangaroo. Carus, Lehrbuch der Ver- gleich. Anat. 1834. Waterhouse, Zoological Tran- sactions, 1836 ; Marsupialia, vol. xi. of the Naturalist's Library, 1841. Vrolik, W. Ontleed — en Natuurkundige Aanteekeningen over den grooten Kangaroo, in Van der Hoeven's Natuur Tydschrif. 3 deel. 1837. Temminck, Monographies de Mam- malogie. Wagner, R. Lehrbuch der vergleich. Anatomie, 1835. Valenciennes, Comptes Rendus de l'Acad. des Sciences, Paris, 1838. Muller, S. Over de Zoogdieren van Indischen Archipel. 1840. Gould, Monograph on Kangaroos. (it. Owen.) MEMBRANE— MENINGES— MICROSCOPE. 331 MEMBRANE, (in Anatomy,) Gr. pvnyt ; Lat. Membrana ; Fr. Membrane ; Germ, die Hunt. This term is commonly applied to designate those textures of the body which are disposed' or arranged as laminse, destined to cover organs, to line the interior of cavities, or either singly or by their application one over the other, to constitute the walls of canals or tubes. Expansion with very slight thickness is the main morphological characteristic of mem- branes in their ordinary sense. I do not intend here to give any classifica- tion of the membranes : the term is extensively used in descriptive as well as in general ana- tomy ; and anatomists differ materially as to the degrees within which they limit its meaning. Anatomists hitherto have been content to adopt the gross anatomy of the textures as the basis of their classification, a circumstance which has given rise to much error, as well as to great variety of opinion. Now, aided as we are by excellent microscopes, and by the light which they have thrown upon the minute anatomy of the tissues, we should only admit that classifi- cation which is based on an ultimate or even proximate anatomical analysis. As these points will be all fully treated of in the article Tissue, reference is made to it for the details respecting the membranes. (R. B. Todd.) MENINGES. — This word signifies mem- branes; it is specifically applied to those mem- branous expansions which cover and more or less protect the brain and spinal cord, and in this sense is best interpreted by the German word Hirnhaut. The term is in common use on the continent, but not so frequently em- ployed by British anatomists, although always understood by them in the sense above given. It appears to have been thus applied first by Galen, who distinguished pYjnyZ •na.yyrtfn, or the dura mater, and p.riny| htirrri, or the pia mater. The description of the membranes of the brain and spinal cord will be found in the article Nervous Centres. (R. B. Todd.) MICROSCOPE, (jLux§o?, small, and c-xowiw, to look at,) an instrument for aiding the eye in the examination of minute objects. Although a description of the structure and uses of this instrument cannot be considered as strictly belonging to a work like the present, yet the knowledge of them is so closely connected with its general objects that it has been deemed ad- visable to make it an object of special attention. The applications of this instrument to the pur- poses of the anatomist and physiologist are so numerous, that a whole treatise might easily be written upon them alone. We are not aware, until we come to think on the subject, how much of our knowledge of what takes place within the living body is dependent upon its revelations. To take a familiar illustration, — the capillary circulation might be, in some degree, guessed at by tracing the ramifications of the bloodvessels as far as they could be dis- cerned with the naked eye; but we should have known extremely little of it without the micro- scope. Our whole knowledge of the early processes of development in plants and animals is gained by the same assistance. Not only is much of that, which ranks as established ana- tomical or physiological truth, founded upon microscopic researches, but similar researches, which are being prosecuted at the present time, are yielding a harvest of discovery still richer in amount, whilst not less important in its cha- racter. We propose, in the present article, to take a general view of the principles, optical and me- chanical, which are concerned in the construc- tion of the microscope ; and then to give an outline of the results of some of the most re- cent enquiries in which it has been profitably employed, — confining ourselves chiefly, how- ever, to those which concern the origin and formation of the principal organized structures. If it be thought that the former portion is too much extended, we have only to say, that we know of no single treatise to which we can refer our readers for a large part of the informa- tion which we desire to convey ; and that we have therefore judged it desirable to make the article complete in itself. I. Optical principles governing the CONSTRUCTION OF MICROSCOPES. All microscopes, except those which operate by reflection (to be hereafter noticed), depend for their operation upon the influence of convex and concave lenses on the course of the rays of light passing through them. This influence is the result of the well-known laws of refraction — that a ray passing from a rare into a dense medium is refracted towards the perpendicular, and vice versa. When, therefore, a pencil of parallel rays passing through air impinges upon a convex surface of glass, the rays will be made Fig. 144. ■ , A . If ' G A B, parallel rays of light falling upon the convex surface F, B, G ; D the centre, D B, D B, radii, which are the perpendiculars to the curved sur- face at the several points ; B C, course of the rays if uninterrupted ; B E, their course in con- sequence of the refraction they have undergone, converging to a focus at E. to converge, for they will be bent towards the centre of the circle, since the radius is the per- pendicular to each point of curvature. The central ray, as it coincides with the perpendi- cular, will undergo no refraction ; the others will be bent from their original course in an increasing degree in proportion as they fall at a distance from the centre of the lens ; and the effect upon the whole will be such, that they 332 MICROSCOPE. will be caused to meet at a point, called the focus, some distance beyond the centre of cur- vature. This effect will not be materially changed, by allowing the rays to pass into air again through a plane surface of glass, such as would be formed by a section of the glass in the vertical line ; a lens of this description is called a plano-convex lens ; and it will hereafter be shown to possess properties, which render it very useful in the construction of microscopes. But if, instead of passing through a plane sur- face, the rays re-enter the air through a convex surface, they will be made to converge still more. This may be best understood by considering the course of parallel rays, as in the adjoining Fig. 147. |1B lis--. Parallel rays falling on a plano-convex lens brought to a focus at the distance of its diameter, and vice versa. if a double convex lens will bring parallel rays to a focus in the centre of its sphere of curva- ture, it will on the other hand cause rays to assume a parallel direction, which are diverging from its focus ; so that if a luminous body were placed in that point, all its cone of rays, which fell upon the surface of the lens, would pass out in a cylindrical form. Again, if rays al- ready conveiging fall upon a convex lens, they Fie. 148. A B, parallel rays passing through glass and falling upon the convex surface FUG; B H, B H, radii prolonged, which are the perpendiculars to the curved surface at the several points ; B C, course of the rays if unrefracted ; B E, their course in consequence of refraction. figure (Jig. 145). Here the radii prolonged will be the perpendiculars to the curved surface; and, according to the law of refraction just alluded to, the rays passing from the dense into the rare medium will be bent from the perpendicular, so as to be made to converge towards a focus, as in the former instance. It is easy to see, therefore, that the effect of the second convex surface will be precisely equivalent to that of the first; for the contrary direction of the sur- face is antagonized by the contrary direction of the refraction ; so that the focus of a double convex lens will be at just half the distance from it, or (as commonly expressed) be half the length of the focus of a plano-convex lens. In fact, the focus of the former to parallel rays will be the centre of its sphere of curvature, and its focal length will therefore be the radius; whilst the focus of the latter will be in the op- posite side of the sphere, and its focal length will be the diameter. Now it is evident that Fig. 146. Rays already converging brought to a focus nearer than the centre ; and rays diverging from such a point, still diverging in a diminished degree. Fig. 149. Parallel rays falling on a double convex lens brought to a focus in its centre ; and rays diverging from such a point rendered parallel. Rays diverging from points more distant than the prin- cipal focus on either side brought to a focus be- yond it. will be brought to a focus at a point nearer to it than the focus for parallel rays (which is called its principal focus) ; and, if they be di- verging from a distant point, their focus will be more distant than the principal focus. The further be the point from which they diverge, the more nearly will the rays approach the pa- rallel direction ; until, at length, when the ob- jects are very distant, their rays in effect become parallel, and are brought to a focus in the centre of the sphere. If they diverge from the other extremity of the diameter of the sphere, they will be brought to a focus at a correspond- ing distance on the other side of the lens. On the other hand, if they be diverging from a point MICROSCOPE. 333 within the principal focus, they will neither be brought to converge nor be rendered parallel, but will diverge in a diminished degree. The same principles apply equally to a plano- convex lens, the distance of its principal focus being understood to be the diameter of the sphere. They also apply to a lens whose sur- faces have different curvatures ; the principal focus of such a lens is found by multiplying the radius of one surface by the radius of the other, and dividing this product by half the sum of the same radii. For the rules by which the foci of convex lenses may be found for rays of different degrees of convergence and divergence, we must refer to works on optics. The influence of concave lenses will evidently Fig. 150. W "l Ik Parallel rays fulling on a plano concave lens made to diverge as from its principal focus, and rays con- verging to that focus rendered parallel. be precisely the converse of that of convex. Rays which fall upon them in a parallel direc- tion will be made to diverge as if from the principal focus, which is here called the nega- tive focus. This will be, for a plano-concave Fig. 151, Hays greatly converging made to converge less, and rays slightly diverging made to diverge more. lens, at the distance of the diameter of the sphere of curvature; and for a double concave, in the centre of that sphere. In the same manner, rays which are converging to such a degree that, Fig. 153. " — - — Tttxrtai-vr sagf I w~ ~~ 1 I m ~jMu-^.\ Rays slightly converging made to diverge. if uninterrupted, they would have met in the principal focus, will be rendered parallel ; if converging more, they will still meet, but at a greater distance ; and if converging less, they will diverge as from a negative focus at a greater distance than that for parallel rays. If already diverging, they will diverge still more, as from a negative focus nearer than the principal focus; but this will approach the principal focus, in proportion as the distance of the point of di- vergence is such, that the direction of the rays approaches the parallel. If a lens be convex on one side and concave on the other, forming what is called a meniscus, its effect will depend upon the proportion be- tween the two curvatures. If they are equal, as in a watch-glass, no perceptible effect will be produced ; if the convex curvature be the greater, the effect will be that of a less powerful convex lens ; and if the concave curvature be the more considerable, it will be that of a less powerful concave lens. The focus of conver- gence for parallel rays in the first case, and of divergence in the second, may be found by dividing the product of the two radii by half their difference. Hitherto we have considered only the effects of lenses upon a pencil of rays issuing from a single luminous point, and that point situated in the line of its axis. If the point be situated above the line of its axis, the focus will be below it, and vice versa. The surface of every luminous body may be regarded as comprehend- ing an infinite number of such points, from every one of which a pencil of rays proceeds, and is refracted according to the laws already specified ; so that a perfect but inverted image or picture of the object is formed upon any surface placed in the focus, and adapted to re- ceive the rays. Fig. 154. In optical diagrams it is usual, in order to avoid confusion, to mark out the course of the rays proceeding from two or three only of such points. By an inspection of the subjoined figures, it will be evident that, if the object be placed at twice the distance of the principal focus, the image being formed at an equal dis- 334 MICROSCOPE. Fig. 155. Formation of images by convex lenses. tance on the other side of the lens, will be of the same dimensions with the object : whilst, on the other hand, if the object be nearer the lens, the image will be farther from it, and of larger dimensions ; and if the object be farther from the lens, the image will be nearer to it, and smaller than itself. Further, it is to be re- marked, that the larger the image in proportion to the object, the less bright it will be, because the same amount of light has to be spread over a greater surface ; whilst a smaller image will be much more brilliant, in the same proportion. The knowledge of these general facts will enable us readily to understand the ordinary operation of the microscope ; but the instru- ment is subject to imperfections of various kinds, the mode of remedying which cannot be comprehended without an acquaintance with their nature. One of these imperfections re- sults from the spherical aberration of the rays which have passed through lenses, whose curva- tures are equal over their whole surfaces. If the course of the rays be carefully laid down, it will be found that they do not all meet exactly Fig. 156. A B, rays falling on the periphery of the lens; F, focus of these; a, b, rays falling nearer the centre ; f, more distant focus of these. in the foci already stated, but that the focus of the rays which have passed through the peri- pheral portion of the lens is much closer to it than that of the rays which are nearer the line of its axis ; so that, if a screen be held in the former, the rays which have passed through the central portion of the lens will be stopped by it before they have come to a focus ; and if the screen be carried back into the focus of these, the rays which were most distant from the axis ■will have previously met and crossed, so that they will come to it in a state of divergence. In either case, therefore, the image will have a certain degree of indistinctness ; and there is no one point to which all the rays can be brought by a lens of spherical curvature. The difference between the focal points of the cen- tral and of the peripheral rays is termed the spherical aberration. It is obvious that, to produce the desired effect, the curvature is re- quired to be increased around the centre of the lens, so as to bring the rays which pass through it more speedily to a focus, and to be diminished towards the circumference, so as to throw the focus of the rays influenced by it to a greater distance. The requisite conditions may be exactly fulfilled by a lens one of whose surfaces, instead of being spherical, is a portion of an ellipsoid or hyperboloid of certain pro- portions ; but the difficulties in the way of the mechanical execution of lenses of this descrip- tion are such, that, for all practical purposes, they have been entirely abandoned in favour of lenses with spherical surfaces. Various means have been devised for diminishing the aber- ration of these. In microscopes of ordinary construction, the method employed is to dimi- nish the aperture or working surface of the lens, so as to employ only the rays that pass through the central part, which, if sufficiently small in proportion to the whole sphere, will bring them all to nearly the same focus. The use of this may be particularly noticed in the object-glasses of common microscopes ; where, although the lens itself be large, the greater portion of its surface is rendered inoperative by a stop, which is a plate with a circular aperture interposed between the lens and the rest of the instrument. If this aperture be gradually enlarged, it will be seen that, although the image becomes more and more illuminated, it is at the same time becoming more and more indistinct; and that, in order to gain defining power, the aperture must be reduced again. Now this reduction is attended with two great inconveniences ; in the first place, the loss of intensity of light, the de- gree of which will depend upon the quantity transmitted by the lens, and will vary therefore with its aperture ; and, secondly, the diminu- tion of the number or quantity of rays, which will prevent the surfaces of objects from being properly seen. Thus, for example, we shall suppose the observer to be looking at the scales of a butterfly's wing with a microscope fur- nished with two object-glasses of the same focal length, — one corrected, the other not so. If, with the same illumination of the object, he apply to it the uncorrected objective, the aper- ture of which is necessarily small, after having looked at it with the corrected lens, he will, in the first place, perceive that the whole field is much darker; but if, by increasing his illumi- nation, he give the image an equal brightness, and see its outline with equal distinctness, he will be completely unable to see with the un- corrected lens a series of delicate lines upon the surface of the scale, which the other makes evident. The power of exhibiting these and similar objects is termed penetration ; it de- pends upon the size of the conical pencils of light admitted by the lens, and therefore upon its aperture. The spherical aberration may be considerably diminished by making the most advantageous use of single lenses. Thus the aberration of a plano-convex lens, whose convex side is turned towards parallel rays, is only -^ths of its thickness, whilst, if the plane side be turned MICROSCOPE. 335 towards the object, the aberration is 4£ times the thickness of the lens. Hence, when a plano- convex lens is employed, its convex surface should be turned towards a distant object, when it is used to form an image by bringing to a focus parallel or slightly-diverging rays; but it should be turned towards the eye, when it is used to render parallel the rays which are diverging from a very near object. The single lens having the least spherical aberration is a double convex, whose radii are as 1 to 6. When the flattest face is turned toward parallel rays, the aberration is nearly 3§ times its thick- ness ; but when the most convex side receives or transmits them, the aberration is only ^ths of its thickness. The spherical aberration may be still further diminished, however, or even got rid of altogether, by making use of com- binations of lenses so disposed that their op- posite aberrations shall correct each other, whilst magnifying power is still gained. For it is easily seen that, as the aberration of a con- cave lens is just the opposite of that of a con- vex lens, the aberration of a convex lens placed in its most favourable position may be cor- rected by a concave lens of much less power in its most unfavourable position ; so that, although the power of the convex lens is weak- ened, all the rays which pass through this com- bination will be brought to one focus. This is the principle of the aplunutic doublet proposed by Sir J. F.W. Herschel, consist- j?j„ 157^ ing of a double-convex lens of Jf |\ the most favourable form, and a \, 1,'ja meniscus with the concave of MSmS longer focus than the convex.* Ml A doublet of this kind may be fJ I made of great use in the mi- W lilf croscope, as we shall hereafter r show. Herschel's But the spherical aberration is not doublet. the only imperfection with which the optician has to contend in the construction of micro- scopes. A difficulty equally serious arises from the unequal refrangibility of the differentcoloured rays, which together make up white or colour- less light,t so that they are not all brought to the same focus, even by a lens free from sphe- rical aberration. It is this difference in their refrangibility which causes their complete sepa- ration by the prism into a spectrum ; and it manifests itself, though in a less degree, in the image formed by a convex lens. For if pa- rallel rays of white light fall upon a convex surface, the most refrangible of its component rays, namely, the violet, will be brought to a focus at a point somewhat nearer to the lens than the principal focus, which is the mean of the whole ; and the converse will be true of the red rays, which are the least refrangible, and whose focus will therefore be more distant. * The exact curvatures to be given to these sur- faces will be found in the original memoir, Phil. Trans. 1821. t It has been deemed better to adhere to the ordinary phraseology, when speaking of this fact, as more generally intelligible than the language in which it might be more scientifically described, and at the same time leading to no practical error. fig. 158. A M A 11 B T. - r t 1} A 11 2sf~ - r Diagram illustrative of chromatic aberration. A B, rays of white light refracted by a convex lens ; C, the focus of the violet rays, which then cross and diverge towards E F ; D, the focus of the red rays which are crossed at the points E E, by the violet; the middle point of this line is the mean focus, or focus of least aber- ration. This is easily proved experimentally. If a lens be so fixed as to receive the solar rays, and to illuminate a white screen at any dis- tance between the lens and the mean focus, the luminous circle will have a red border, because the red rays will there form the exterior of the cone ; but if it be removed beyond the mean focus, the circle will have a violet border, be- cause the violet rays will then be outermost. As the spherical aberration would be mixed up with the chromatic in such an experiment, the undisguised effect of the latter will be better seen by taking a large convex lens, and co- vering up its central part, so as to allow the light to pass only through a peripheral ring ; and since the greater the alteration in the course of the rays, the greater will be the separation of the colours, (or dispersion, as it is techni- cally called,) this ring will exhibit the pheno- menon much better than would be done by the central portion of the lens. Hence, in prac- tice, the chromatic aberration is partly obviated by the same means used to diminish the sphe- rical aberration, — the contraction of the aper- ture of the lens, so that a very small portion of the whole sphere is really employed. But this contraction is attended with so much in- jury to the performance of the microscope in other respects, that it becomes extremely de- sirable to avoid it. In no single lens can any correction for chromatic aberration be effected ; and it requires a very nice adjustment of two, three, or even more, to accomplish this with perfection. The correction is accomplished by bringing into use the different dispersive powers of va- rious materials, which bear no relation to their simple refracting power. As the effects of con- cave lenses are in all respects the converse of convex, it is obvious that, if a concave lens of the same curvature be placed in apposition with the convex, in such an experiment as that just alluded to, the dispersion of the rays will be entirely prevented, but neither will any change in the course of the rays take place. If, however, we can obtain a substance of higher dispersive power in proportion to its power of refraction, it is obvious that a con- cave lens of less curvature formed of it will correct the dispersion occasioned by the convex lens, without altogether antagonising the re- fraction of the latter. This is accomplished 336 MICROSCOPE. without any essential difficulty in practice ; for the dispersive power of flint-glass is so much greater than that of crown-glass, that a convex lens of the former, the focal length of which is 7jj inches, will produce the same degree of colour with a convex lens of crown-glass whose focal length is 4J inches. Hence a concave lens of the former material and curvature will fully correct the dispersion of a convex lens of the latter, and will yet diminish its refractive powvr only to such an extent as to make its focus ten inches. The correction for chromatic aberration in such a lens would be perfect, if it were not that, although the extreme rays, violet and red, are thus brought to the same focus, the dispersion of the rest is not equally compensated ; so that what is termed a secon- dary spectrum is produced, the images of ob- jects seen through such a lens being bordered on one side with a purple fringe, and on the other with a green fringe. Moreover such a lens is not corrected for spherical aberration ; and it must of course be rendered free from this, to be of any service, however complete may be its freedom from colour. Opticians have long since been able to effect the required corrections, with sufficient accu- racy for most practical purposes, in the con- struction of large object glasses for telescopes ; the size of which has been only limited by the impossibility of obtaining glasses of large di- mensions perfectly free from faults. But it has been only of late years, that the construc- tion of achromatic and aplanatic object-glasses for microscropes has been considered prac- ticable,— their extremely minute size appearing to forbid the employment of the necessary combinations, since a very high amount of accuracy is required in the several curvatures, in order to obtain any real improvement. About the year 1820, however, the attempt was first made in France by M. Selligues, who was fol- lowed by Frauenhofer at Munich, by Amici at Modena, and by Mr. Tulley of London ; and with these attempts a new era in the history of the microscope may be said with truth to have commenced. The work has been prosecuted, both theoretically and practically, with the greatest zeal, and the result has been most successful. By combining two or three groups of double lenses, each corrected in a particular manner, so that the whole is quite free from aberration, a perfectly sharp and clearly- defined image may now be obtained through a lens of many times the aperture of those formerly in use; and the differences in the representation of the objects under enquiry, between such lenses and a good achromatic, are such as could not have been, a priori, sus- pected. One of the most pleasing results of this improvement has been the greatly-increased unanimity amongst microscopical observers, as to the appearances actually witnessed by them ; for with the old and imperfect instru- ments, great uncertainty could not but exist in regard to many objects, of whose nature every one formed his own opinion, frequently accord- ing to preconceived ideas ; but at present the objects are presented to the sight of each ob- server possessed of a good instrument, with so much more clear and uniform an appearance, that there is much less scope for the play of his imagination as to their real character,— however much he may exercise it upon their history. It would be foreign to the purpose of this article to enter into scientific details upon the minutiae of the construction of achro- matic combinations ; but it may not be amiss to state that, in the opinion of the author, English artists have far surpassed foreigners in the construction of lenses of very short focus, whilst some foreign combinations which he has seen, of low magnifying power, possess an advantage over those of British make, — the constructors of the latter having sometimes sacrificed what he deems adequate correctness in aiming at a very large aperture.* With these preliminary details as to the na- ture of the means by which microscopic power is obtained, we shall proceed to notice their chief applications to practice. Excluding for the present the solar and gas microscopes, in which an image visible to any number of per- sons at once is formed upon a screen, and is viewed by them precisely as other surrounding objects would be, we shall consider the instru- ments (to which the term microscope is more commonly applied), whose effects are produced by their influence on the rays of light which enter the eye of the observer, and which can be used, therefore, by but one at the same time. These are distinguished as single or simple, and compound microscopes. Each of these kinds has its peculiar advantages for the anatomist; and we shall, therefore, describe the construction and uses of both in some detail. Their essential difference consists in this, — that in the former the rays of light which enter the eye of the observer proceed directly from the object itself, after having been subject only to a change in their course, whilst in the latter an inverted image of the object is formed by a lens, which image is viewed by the ob- server through a simple microscope, as if it were the object itself. The simple microscope may consist of one lens, but (as will be pre- sently shown) it may be formed of two or even three ; but these are so disposed as to produce an action upon the rays of light correspondent to that of a single lens. For this kind of mi- croscope, therefore, we prefer the term simple to single. In the compound microscope, on the other hand, not less than two lenses must be employed, one to form the inverted image of the object, and this being nearest to it is called the object-glass, whilst the other mag- nifies that image, being interposed between it and the eye of the observer, and is hence called the eye-glass; Both these may be constructed of several lenses, as will be hereafter shown ; but they are so arranged as to have the func- tions of a single lens, and are only combined * Those who wish to study the principles which now guide opticians in their construction, should refer to Mr. J. J. Lister's paper in the Phil. Trans, for 1829, and Mr. Ross's Memoir in the Trans, of the Society of Arts, vol. it. MICROSCOPE. 337 for the purpose of correcting the defects inci- dental to it. In order to gain a clear notion of the mode in which a single lens serves to magnify minute objects, it is necessary to revert to the pheno- mena of ordinary vision. An eye free from any defect has a considerable power of ad- justing itself in such a manner as to gain a distinct view of objects placed at extremely varying distances ; but the image formed upon the retina will of course vary in size with the distance of the object ; and the amount of detail perceptible in it will follow the same proportion. To ordinary eyes, however, there is a limit within which no distinct ima°e can be formed, on account of the too great diver- gence of the rays of the different pencils which then enter the eye; since the eye is usually adapted to receive and bring to a focus rays which are parallel or slightly divergent. This limit is variously stated at from five to ten inches ; we are inclined to think from our own observations, that the latter estimate is nearest the truth ; that is, although a person with ordi- nary vision may see an object much nearer to his eye, he will see little if any more of its details, since what is gained in size will be lost in distinctness. Now the utility of a con- vex lens interposed between a near object and the eye consists in its reducing the divergence of the rays forming the several pencils which issue from it ; so that they enter the eye in a state of moderate divergence, as if they had issued from an object beyond the nearest limit of distinct vision ; and a well-defined picture is consequently formed upon the retina. But not only is the course of the several rays in Fig. 159. Diagram illustrating (he me o f the Simple 3Iicroscope. each pencil altered as regards the rest by this refracting process, but the course of the pencils themselves is changed, so that they enter the eye under an angle correspondent with that at which they would have arrived from a much larger object situated at a greater distance. The picture formed upon the retina, therefore, corresponds in all respects with one which would have been made by the same object, greatly increased in its dimensions, and viewed at the smallest ordinary distance of distinct vision. A short-sighted person, however, who can see objects distinctly at a distance of three or four inches, has the same power in his eye alone, by reason of its greater convexity, as that which the person of ordinary vision gains by the VOL. III. assistance of a convex lens which shall enable him to see at the same distance with equal distinctness. It is evident, therefore, that the magnifying power of a single lens, depending as it does upon the proportion between the distance at which it renders the object visible, and the nearest distance of unaided distinct vision, must be different to different eyes. It is ordinarily estimated, however, by finding how many times the focal length of the lens is contained in ten inches ; since, in order to render the rays from the object nearly parallel, it must be placed very nearly in the focus of the lens ; and the picture is referred by the mind to an object at ten inches distance. Thus, if the focal length of a lens be one inch, its magnifying power for each dimension will be ten times, and consequently a hundred super- ficial ; if its focal distance be only one-tenth of an inch, its magnifying power will be a hundred linear or ten thousand superficial. The use of the convex lens has the further ad- vantage of bringing to the eye a much greater amount of light than would have entered the pupil from the enlarged object at the ordinary distance, provided its own diameter be greater than that of the pupil. It is obviously neces- sary, especially when lenses of very high mag- nifying power are being employed, that their aperture should be as large as possible ; since the light issuing from a minute object has then to be diffused over a large picture, and will be proportionally diminished in intensity. But the shorter the focus the less must be the dia- meter of the sphere of which the lens forms a part; and unless the aperture be proportionally diminished, the spherical and chromatic aber- rations will interfere so much with the distinct- ness of the picture, that the advantages which might be anticipated from the use of such lenses will be almost negatived. Nevertheless, the simple microscope has always been an in- strument of extreme value in anatomical re- search, owing to its freedom from those errors to which, as will hereafter appear, the com- pound microscope is subject; and the greater certainty of its indications is evident at once from the fact, that the eye of the observer receives the rays sent forth by the object itself, instead of those which proceed from an image of that object. A detail of the means em- ployed by different individuals, for procuring lenses of extremely short focus, though pos- sessing much interest in itself, would be mis- placed here ; since recent improvements, as will presently be shown, have superseded the necessity of all these. It may, however, be stated that Leeuwenhoeck, De la Torre, and others among the older microscopists, made great use of small globules procured by fusion of threads or particles of glass. The most im- portant suggestion for the improvement of the simple microscope composed of a single lens proceeded some years ago from Dr. Brewster, who proposed to substitute diamond, sapphire, garnet, and other precious stones of high re- fractive power, for glass, as the material of single lenses. A lens of much longer radius of curvature might thus be employed to gain z 338 MICROSCOPE. an equal magnifying power, and the aperture would admit of great extension without a pro- portional increase in the spherical and chro- matic aberrations. This suggestion has been carried into practice with complete success as regards the performance of lenses executed on this plan ; but the difficulties of various kinds in the way of their execution are such as to render them very expensive ; and as they are not superior to the combination now to be de- scribed, they have latterly been quite super- seded by it. This combination was first proposed by Dr. Wollaston, and is known as his doublet. It consists of two plano-convex lenses, whose focal lengths are in the proportion of one to three, or nearly so, having their convex sides directed towards the eye, and the lens of shortest focal length nearest the object. In Dr. Wollaston 's original combination no stop was interposed, and the distance between the lenses was left to be determined by experiment in each case. A great improvement was subse- quently made, however, by the introduction of a stop between the lenses, and by the divi- sion of the power of the smaller lens between two; this is due to Mr. Holland.* By these means a combination may be produced, in which the errors are made to correct each other so nearly that all the advantages of a wide aperture with a very short focus may be gained. The general nature of the performance of a doublet or triplet may be understood from the adjoining figure, (Jig. 160,) in which L 0 L' is Fig. 160. Diagram of the passage of rays through a doublet. the object, P a portion of the pupil, and D D the stop. The pencils of light from the two extremities, L L', of the object cross each other in the stop, and consequently pass through the two lenses on the opposite sides * Trans, of Soc. of Arts, vol. xlix. of the axis O P ; so that each becomes af- fected by opposite errors, which to a certain extent balance and correct one another. To take the pencil L, for instance, which enters the eye at R B, R B; it is bent to the right at the first lens, and to the left at the second ; and as each refraction alters the direction of the blue rays more than of the red, and more- over, as the blue rays fall nearer the margin of the second lens, where the increased power of the refraction, consequent upon the distance from the centre, compensates in some degree for the greater focal length of the second lens, the blue and red rays will emerge very nearly parallel, and are therefore colourless to the eye. At the same time the spherical aberration has been diminished by the circumstance that the side of the pencil, which passes one lens nearest the axis, passes the other nearest the margin. This explanation applies only, how- ever, to the pencils near the extremities of the object. The central pencil, it is obvious, will pass through the same relative portions of the two lenses, and only an imperfect correction will therefore take place, and of those issuing from the intermediate points the amount of correction will vary with their proximity to the centre or to the circumference. Hence a dou- blet is not a perfect magnifier ; but it is very much superior to a single lens, and may be so constructed as to show many of the usual test- objects, — especially those in which a moderate amount of penetration is sufficient, provided the definition be good, — in a very beautiful manner. Its angle of aperture, however, by which is meant the angle of the apex of the conical pencils of rays admitted by it, cannot be advantageously increased much beyond 40° or 45°. But when the smaller lens is replaced by a combination of two others, so as to form a triplet, their joint aberration is so much less Fig. 161. A B Diagram to illustrate angle of aperture. A, lens with small opening, admitting only pencils of rays diverging at an angle of 15u ; B, lens with large opening, admitting pencils of 50°. that it is more counterbalanced by the third lens placed above the stop. In this manner the transmission of a still larger angular pencil, — even to 65°, — is rendered compatible with distinctness; and great penetrating power is thus combined with perfect definition, as well as with brilliancy of illumination. For the purposes of anatomical investigation, as we shall hereafter state, we consider good doublets and triplets, where circumstances admit of their employment, superior to any other kind of magnifying instrument. The principal disadvantages which the use of them involves are the close proximity to the object required by their very short focus when a high MICROSCOPE. 339 magnifying power is employed; and the strain- ing of the eye, which is occasioned by their very minute aperture. Thus a triplet in our possession, which will show the most difficult test-objects, has a focal distance of only about jUth of an inch, and an aperture through which the smallest pin would scarcely pass. But the first of these disadvantages is more apparent than real. The object should be always co- vered with talc, (which may be easily split into laminae of the g^th of an inch in thickness,) for the purpose of protecting both it and the lens from injury by accidental contact; and the magnifier should not be screwed into the arm which carries it, but loosely fitted, so that, if the observer should happen to bring the arm too near the stage, he may not force down his lens upon the object. As Mr. Holland justly ob- serves, " Should the proximity of the object to the lowest lens of the triplet be urged as a material objection to its usefulness, it may be answered that the whole microscope is a mass of delicacies ; consequently, it cannot be al- lowed that a line be arbitrarily drawn, beyond which every thing is to be considered as too delicate." The second of the above objections must be obviated by never continuing the use of deep powers in a simple microscope for any length of time at one sitting, and by taking care to adjust the instrument in such a manner that the head may be as little inclined forwards as possible. The only other form of simple microscope which we shall notice is one commonly known under the name of the Coddington lens. The first idea of it was given by Dr. Wollaston, who proposed to cement together two plano- convex, or hemispherical lenses, by their plane sides, with a stop interposed, the central aper- ture of which should be equal to |th of the focal length. The great advantage of such a lens is that the oblique pencils pass, like the central ones, at right angles with the surface ; and that they are consequently but little subject to aberration. The idea was further improved upon by Mr. Coddington, who pointed out that the same end would be much better an- swered by taking a sphere of glass, and grind- ing away the equatorial parts, the groove being then filled with opaque matter, so as to limit the central aperture. Such a lens gives a large sphere of view, admits a considerable amount of light, and is equally good in all directions; but its powers of definition are by no means equal to those of an achromatic lens, or even of a doublet. This form is very useful, there- fore, as a hand lens, in which a high power is not required, but has no particular advantages for magnifiers of short focus, nor for the object- glasses of a compound microscope.* It may be desirable to mention that a magni- fier, now known under the name of the Stan- hope lens, and much praised by those interested * We think it right to state that many of the magnifiers sold as Coddington lenses are not really (as we have satisfied ourselves) portions of spheres, but arc manufactured out of ordinary double-con- vex lenses, and will be destitute, therefore, of many of the above advantages. in its sale, is nothing more than a double con- vex glass, much thicker than ordinary, so that an object in contact with one of its surfaces shall be in focus to the eye placed behind the other. This is an easy method of applying rather a high magnifying power to scales of butterflies' wings and other similar flat and minute objects; but the instrument is totally destitute of value as a means of scientific re- search, and must be regarded as an ingenious philosophical toy. Compound Micro- scope. — The com- pound microscope es- sentially consists, as already stated, of two lenses, which are so disposed that one of them receives the rays of light from the object, and forms an image by its refraction of them ; and this image is seen by the eye through the second lens, which acts upon it as a simple mi- croscope. The princi- ple of such a micro- scope will be at once understood from the adjoining diagram (fig. 1 62). According to the laws already stated, if the object be at a less distance from the lens than its diameter of cur- vature (supposing it to be a double - convex lens, or twice that dis- tance of a plano-con- vex) the image will be larger than the object ; and this in proportion as the latter is brought nearer to the principal focus, at which it can give rise to no image, as its rays after refrac- tion become parallel. Hence, by the use of the same object-glass, a considerable variety of power might be ob- tained ; for, if the image be formed near the lens, it will be small ; but if . „ the object be caused to A B' t,,c ohJect' of which approach it, the image will be thrown to acon- siderable distance, and will be proportionably magnified. The eye- piece would of course require, however, a cor- responding re-adjust- ment; and, in fact, the construction of the whole instrument would need modifica- an amplified image is formed by the object- glass C D, in the con- trary direction, at A' 15', by the convergence of the rays of the several pencils to a focus. These again diverging are re- ceived by the eye-glass L M, which gives them the nearly parallel di- rection necessary for them to enter the eye, and causes the apparent size of the image to be E. z 2 340 MICROSCOPE. tion. Further, the optical disadvantages of such a plan would be considerable, for the nearer to the principal focus of the lens the object is brought, the more obliquely will the rays fall upon its surface, and the greater, therefore, will be the errors of aberration. This method of augmenting the power of a microscope has been adopted in spite of these disadvantages,* but it is not found to answer. Nevertheless, it is capable of being made of great utility, as we shall presently show, to a limited extent. A much more generally convenient method of varying the power of the microscope is to employ, as object-glasses, lenses of different foci ; and thus, as the same distance between the image and the lens is constantly maintained, whilst that of the object varies, the number of times that the latter is amplified is changed in a like proportion. In whatever mode addi- tional amplification be obtained, two things must always result from the change; the por- tion of the surface of the object, of which an image can be formed, must be diminished, and the quantity of light spread over that image must be proportionably lessened. In the use of high magnifying powers, the compound microscope has the great advantage over the simple, that the object need not be brought to nearly the same proximity with the lens, and that much more of it can be seen with comfort at a time. The long focus and large aperture with which the eye-piece is usually made pre- vent even the prolonged use of the instrument from acting prejudicially on the visual powers, except in cases of peculiar tendency to nervous disorders of the eye. And as the power of the eye-piece as well as that of the object-glass can be raised, there are scarcely any limits to the magnifying power that may be obtained. Practically, however, there are limits, arising from the fact that, as the amplification is greater, the aberrations will be increased in even an augmented proportion; so that these com- pletely antagonise the benefit otherwise deri- vable from the employment of high powers. The aberrations can only be diminished by contracting the aperture of the object-glass; and this renders the image so dark that no real advantage is gained. Moreover, the imperfec- tions necessary to the best compound micro- scope, in which ordinary lenses are employed, are further augmented by the slightest error in the centering of the lenses, so that their axes do not coincide. In addition to the two lenses of which the compound microscope has been stated essen- tially to consist, another is usually introduced between the object-glass and the image formed by it. The ordinary purpose of this lens is to change the course of the rays in such a manner that the image may be formed of dimensions not too great for the whole of it to come within the range of the eye-piece, and consequently to allow more of the object to be seen at once. * We have seen a microscope, constructed by Chevalier, in which the tube was capable of being drawn ou> to the length of between three and four feet ! Fig. 163. Section of Compound Microscope, with field-glass introduced. A A, the image which would be formed by the object-glass alone ; B B, the image formed by the interposition of the field-glass F F ; the whole of this image is within the range of vision of the eye-glass E E, and the field of view is therefore increased. Hence it is called the field-glass (fig. 163). It may be so adjusted, however, in regard to the eye-glass, as to correct its errors in almost a perfect degree ; and it is now, therefore, usually considered as belonging to the ocu- lar end of the instrument, — the eye-glass and the field-lens being together termed the eye- piece. Various forms of this eye-piece have MICROSCOPE. 341 been proposed by different opticians, and one or other will be preferred, according to the purpose for which it be required. It may be laid down as a general principle, however, that to give the higiiest effect to the microscope, in regard to clearness of view and penetrating power, no more than two lenses should be employed; and that when a certain amount of these may be sacrificed to gain a large flat field, three is the largest number which can be introduced with any benefit. This prin- ciple is founded on the fact that, whenever light impinges on the surface of even the most transparent body, a part of it only is trans- mitted, the remainder being reflected. In the passage of light through ordinary lenses, there- fore, a certain quantity is lost by reflection at each surface; and every multiplication in the number of lenses entails, therefore, a positive evil, which may or may not be counterbalanced by the good it effects. In the doublet or triplet already described, the correction of the aberrations is an advan- tage much greater than the injury resulting from the substitution of four or six surfaces for two ; but this is by no means the case in the eye-piece, in which (from their low power) the aberrations are much less. Hence, when too many lenses are employed in it, although the field of view (that is, the circle within which the image is comprehended) may be very much enlarged and rendered flatter, the brilliancy and sharpness of the image are so much im- paired, and it is invested with so much false colour, that, for all scientific purposes, the instrument is rather deteriorated than im- proved. The eye-piece which may be most advan- tageously employed with achromatic object- glasses, to the performance of which it is desired to give the greatest possible effect in regard to defining and penetrating power, with- out the necessity of a large field, is that termed the lluyghenian, having been employed by Huyghens for his telescopes, although without the knowledge of all the advantages which its best construction rendered it capable of afford- ing. It consists of two plano-convex lenses with their plane sides towards the eye. These are placed at a distance equal to half the sum of their focal lengths ; or, to speak with more precision, at half the sum of the focal length of the eye-glass, and of the distance from the field-glass at which an image of the object- glass would be formed by it. A stop or dia- phragm must be placed half-way between the two lenses. By Huyghens this arrangement was intended merely to diminish the spherical aberration ; but it was subsequently shown by Boscovich that the chromatic dispersion was also in great part corrected by it. Since the introduction of achromatic object-glasses for compound microscopes, it has been further shown that all error may be avoided by a slight over-correction of these, so that the blue and red rays may be caused to enter the eye in a parallel direction, and thus to produce a colour- less image, though not actually coincident (Jig. Fig. 164. Section of Huyghenian cue-piece, adopted to oner- corrected achromatic). L M N, the two extreme rays of three pencils, which, \viihout the field-glass, would form a blue image convex to the eye-glass at li B, and a red one at R R. By the field-glass, however, a blue image, concave to the eye-glass, is formed at B' B', and a red one at R' R'. As the focus of the eye-glass is shorter for blue rays than for red rays, by just the difference in the place of these images, their rays, after refraction by it, enter the eye in a parallel direction, and produce a picture tree from false colour. If the object- glass had been rendered perfectly achromatic, the blue rays, after passing the field-glass, would have been brought to a focus at b, and the red at r, so that an error would be produced, which would have heen increased instead of antago- nised by the eye-glass. 164). Further, the image produced by the meeting of the rays after passing through the field-glass is by it rendered convex towards the eye-glass, instead of concave, so that every part of it may be in focus at the same time, and the field of view thereby rendered flat. Those who desire to gain more information upon this sub- ject than they can from the accompanying dia- gram and the explanation of it, may be re- ferred to Mr. Varley's investigation of the pro- perties of the lluyghenian eye-piece in the 51st volume of the Transactions of the Society of Arts, and to the article "Microscope" in the Penny Cyclopaedia. By an achromatic object-glass for a com- pound microscope, therefore, is not meant one which simply contains within itself a perfect correction for its own errors, but one in which (he usual order of dispersion is so far reversed that the light, after undeigoing the series of changes effected by the eye-piece, shall come uncoloured to the eye. " We can give no spe- cific rules," says the writer of the article just MICROSCOPE. 343 that a considerable general advantage is hence derived. We can regard no microscope as complete, without an eye-piece of this kind, with a set of ordinary objectives of low powers; for it will certainly do what no other combi- nation with which we are acquainted can effect. The great improvements recently made in the construction of achromatic objectives, and the unquestionable fact that, for exhibiting the minute details of objects, they are infinitely superior to all other kinds, have had, we think, a tendency to blind microscopists to the ad- vantages afforded by other combinations, where it is desired to obtain a view of the general arrangement of the parts of a large object, rather than to investigate its minutiae. We should recommend, therefore, that every achromatic microscope should be fitted with at least two Huyghenian eye-pieces, adapted ex- pressly to the achromatic objectives; and that it should also have a meniscus eye-piece, with a set of ordinary object-glasses of long focus. And the best substitute for such a microscope, at least for the purposes of anatomical or phy- siological research, we believe will be found in Mr. Holland's doublet microscope, which should be furnished with his eye-piece for doublets already described, and with a me- niscus eye-piece and ordinary object-glasses of low power. In this last form of compound microscope, there is the further advantage, that the high magnifying power of the doublets and triplets employed as objectives renders them available as simple microscopes ; and this cannot be said of achromatic object-glasses, which have not yet been usually made of shorter focus than one-tenth of an inch, and which are not, therefore, of much use in them- selves. No one, however, can be regarded as entitled to form positive conclusions in regard to difficult questions of microscopic enquiry, until he has availed himself of the very best means of observation at his command ; and these are certainly to be found only in achro- matic microscopes of the highest class. For viewing large opaque objects, achromatic objectives of low power are often very useful, on account of the large quantity of light they admit, which supersedes the necessity of arti- ficial illumination ; this is a particular advan- tage in anatomical investigations, in which it is often especially necessary to avoid the re- flection of condensed light from the surface of the object, on account of the confusion which is thereby occasioned. The achromatic objectives at present usually made on the continent consist of sets of three or more, of which one, two, or three may be used at once. In this manner considerable variety of power may be gained ; but the highest degree of perfection in the performance must be sacrificed to obtain it, since no single objective consisting of two lenses only can be thoroughly corrected, and each combination ought to be corrected for itself alone. The best achromatics made by British artists consist of combinations of two or three compound lenses, which cannot be separated ; and thus Fig. 165. Section of the English achromatic combination. every required power must be furnished by a distinct combination. The expense of a mi- croscope fitted with the requisite number of these, however, is a great bar to its general employment. Other combinations have been constructed, therefore, in which the lens next the object may be removed, so as to diminish the magnifying power considerably ; and the corrections are so adjusted as to be nearly the same when the two or when three compound lenses are used together. The difference be- tween the performance of the best of these, and that of those most perfectly adjusted, is not, for general purposes, of much importance. Two sets of these separating lenses, — a high and a low one, — giving four powers, therefore, which may range from an inch and a half to one-eighth of an inch focus, will adapt the microscope, with the eye-pieces we have men- tioned, to a great variety of purposes. The power may be further varied by length- ening the body of the microscope, by drawing out the eye-piece, which should always be made capable of this kind of movement. This operates by increasing the distance from the object-glass of the image formed by it, and therefore augmenting the size of the image ; the object must of course be brought some- what nearer on the other side. We have al- ready stated that the length of the body cannot be much increased with advantage; but a mo- derate variation will be found useful in many ways. It enables the magnifying power to be adjusted to almost any point intermediate between those given by the different objectives. Thus, one may give a power of 80 diameters, and another a power of 120 ; by using the first, and drawing out the eye-piece, the power may be increased to 100. Again, it is often very useful to make the object fill up the whole, or nearly the whole, of the field of view. This is especially the case, when it is itself not very transparent, and requires a strong light to render its details visible ; in which condition a glare entering around its edges would very- much interfere with its distinctness. When opaque objects, also, are being viewed by con- densed light, in the modes hereafter to be stated, it is often extremely desirable to make them, or the discs on which they are mounted, fill up the whole field. In either case the 344 MICROSCOPE. drawing out of the eye-piece until the end is accomplished answers the object most simply and effectually. In the use of the micro- metric eye-piece, also, which will be presently described, the capability of adjusting the mag- nifying power to a certain definite amount will be found of very great utility. It is to be borne in mind, however, that for giving the highest effect to the achromatic objectives, a certain fixed distance of the eye-piece is neces- sary ; this is usually adjusted by the maker; but it may be easily determined by trial, since at any other the want of correction of the chro- matic aberration will make itself apparent (however slightly) by the presence of coloured fringes around the images. The degree of perfection in the construction of the optical part of a microscope, whether simple or compound, is judged of by the dis- tinctness and comfort (by which we "mean the freedom from strain or effort on the part of the observer) with which it exhibits certain objects, the details of which can only be made visible by combinations of lenses of high magnifying power and a near approach to correctness. Such are called test objects. They are of various degrees of difficulty. For testing the penetrating powers of a microscope, the lined scales on the wings and bodies of certain in- sects are commonly employed. The scales from the wings of many Lepidoptera are so coarsely marked, that a good ordinary com- pound microscope, or deep single lens, will make the lines apparent. But there are many others, which, under such magnifying powers, only show a flat unmarked surface, requiring lenses of large angular aperture to make their lines visible. One of the most beautiful of these, and at the same time most easily re- solved, is the scale of the Menelaus butterfly ; its longitudinal strife may be seen in the best ordinary microscope, but they require a cor- rected object-glass to be well made out; and its transverse markings are only to be seen distinctly with a superior instrument. A scale with more delicate lines than these is the larger of those of the hyesna Argus; the smal- ler one will be presently noticed. The most difficult of the test-scales, however, is that of the Pudura plumbea, or common spring-tail ; and a microscope which will distinctly exhibit its markings may be regarded as, for this class of objects, of the highest order. For defining power, however, another class of objects is needed. Among these one of the best is the small scale of the Lycana Argus (or battledore), which, with an inferior instrument, appears covered with coarse longitudinal lines; but these, when more perfectly defined, are found to be resolvable into separate circular or oval dots, arranged in a linear manner. The curi- ous hair of the Dermestes, and that of the Bat, require a microscope of good defining power to represent their forms with clearness and accuracy. We have ourselves been accus- tomed to employ the branching hairs of the common bee as tests of the correctness of a microscope of moderate power; for they have a remarkable tendency to produce fringes of colour, under most of the ordinary modes of illumination, unless there is a perfect freedom from chromatic aberration. The spiral fibres lining the tracheae of many insects, also, will be found good tests of the defining power, and freedom from aberration, of a microscope. For still lower powers, we consider the glan- dular dots in the woody fibre of the resinous trees (especially those of the order Conifera) as very advantageous tests. They ought to be rendered distinctly visible with an object-glass of half an inch focus ; and the depression in the centre should be clearly made out, with a perfect freedom from colour. We have seen objectives of English construction (in which a large aperture for showing opaque objects was the chief point aimed at) so defective in this respect, as to be far inferior in their exhibition of these and similar objects to French acro- matics of much smaller aperture. We may here repeat the general rule, that those micro- scopes are, ceteris paribus, the best, which will show the most with the lowest magnifying power. It will sometimes happen that, al- though the details of an object may be made out with tolerable clearness, there is a sort of thin fog or mist over the whole field. This fault may proceed from the too great enlarge- ment of the aperture of the objective, or from a faulty mode of illumination ; or it may result from the imperfect extinction of the rays re- flected within the body of the microscope from the surfaces of the lenses of the eye-piece, and from the interior of the tube itself,* — a fault which may be obviated by carefully coating the inner surface with a black covering, adapted to absorb all the false light. Black velvet may be advantageously used for this purpose. If the aperture be too great, the fault may generally be corrected by the use of stops beneath the stage, by which it may be diminished as required. This plan, which will be presently described more in detail, will be found very much to increase the applicabi- lity of low-power achromatic lenses of that large aperture which is desirable for opaque objects. II. Of the mechanical arrangements OF MICROSCOPES. Having now described, with as much detail as the nature of this article permits, the prin- ciples on which the operation of the micro- scope depends, we shall next proceed to con- sider the means of arranging the optical por- tion of the instrument, so as to confer upon it the best and most varied application, keeping especially in view, however, the wants of the anatomist and physiologist. We shall begin by stating what, in any form of microscope, we regard as the essential conditions to be attained in its construction. 1. Steadiness and firmness in all its parts, * [Or it arises, as suggested to the Editor by Mr. Powell.lhe eminent optician, from imperfection in the correction of the objectives. — Ed.] MICROSCOPE. 345 so that it may be free from vibration. An amount of vibration, which is imperceptible when low powers are used, is sufficient to render the most perfect optical arrangements for high magnifying powers next to useless. That the whole instrument should be secured as much as possible from vibration, by being placed upon a steady table, and this on a steady floor, is of the first importance for its advantageous employment. But, as an entire freedom from this cause of vibration can rarely be obtained in an ordinarily-constructed house, the next point to be aimed at is such an ar- rangement of the optical portion of the instru- ment in regard to the object, that any vibra- tion which takes place may affect both alike, in which case it will be scarcely perceptible. In many microscopes of ordinary construction the stage is comparatively motionless, whilst the body (containing all the optical portion) is subject to tremor; and in such instruments, when a high magnifying power is employed, the object is seen to oscillate so rapidly upon the slightest cause of vibration (such as a per- son walking across the room or a carriage rol- ling by in the street) that it is frequently almost indistinguishable. Various modes have been devised for obviating this inconvenience, the chief of which we shall hereafter notice. 2. Capability of accurate adjustment to every variety of focal distance, without move- ment of the object. It is now a principle almost universally recognised in the construc- tion of good microscopes, that the stage on which the object is placed should be a fixture; and that the movement by which the focus is to be adjusted should be effected in the body or optical portion. Several reasons concur to establish this principle, which was, we believe, first insisted upon by Dr. Goring.* Among the most important we consider to be that, if the stage is made the moveable part, the ad- justment of the illuminating apparatus must be made afresh for every change of magnify- ing power, whilst, if the stage is a fixture, the illumination having been once well adapted, the object may be examined under a great variety of magnifying powers, without its being changed in any respect. Moreover, if the stage is the moveable part, it can never have that firmness given to it, which it ought for many purposes to possess. It is almost im- possible to make a moveable stage free from some degree of spring; so that, when the hands bear upon it in adjusting the position of an object, it yields to an amount which, however trifling, becomes apparent with high powers by the alteration of the focus. We might add many more reasons, but these will here suffice. It having been determined, then, that focal adjustment should take place in the optical portion of the microscope, the next point for consideration is the mode of effecting it. This should be such as to allow free range from a minute fraction of an inch to three or four * See Pritchard and Goring's Microscopic Illus- trations. inches, with equal power of obtaining a deli- cate adjustment at any part. It should also be so accurate that the axis of the instrument should not be in the least altered by movement in a vertical direction ; so that, if an object be brought into the centre of the field with a low power, and a higher power be then substituted, it should be found in the centre of its field, notwithstanding the great alteration in the focus. In this way much time may often be saved by employing a low power as a finder for an object to be examined by a higher one; and, when an object is being viewed by a suc- cession of powers, no readjustment of its place on the stage is required, such as would other- wise be necessary for each. The best modes of securing these ends, also, will be considered in their proper place. 3. The power of placing the instrument in either a vertical or a horizontal position, or at any angle with the horizon, without deranging the adjustment of its parts to each other, and without placing the eye-piece in such a posi- tion as to be inconvenient to the observer. It is certainly a matter of surprise that opticians should have so long neglected the very simple means which are at present so commonly em- ployed, of giving an inclined position to mi- croscopes ; since it is now universally acknow- ledged that the vertical position is, of all that can be adopted, the very worst. We do not ourselves consider the horizontal position of the body and its appendages at all an advan- tageous one, although it has been adopted in some of M. Chevalier's latest and best instru- ments. In the first place it requires that the whole microscope should be raised so much above the level of an ordinary table, as to bring the eye-piece to the height of the eye of the observer when sitting upright at his ease ; if this be not done, a constrained and conse- quently disadvantageous position of the head is required on his part; and if it be, all the manipulations must be executed at an elevation very inconvenient and fatiguing to the arms. Moreover either the stage must be rendered vertical, in which case all the objects must be so secured (to prevent their slipping) as to render the necessary movement of them very difficult; or, the stage being horizontal, the direction of the rays must be changed, after they have passed through the object-glass, by a prism or a mirror placed at an angle of 45° in their course, as in M. Chevalier's construc- tion, which we think a decided disadvantage, as introducing another source of imperfection and error. We believe that it will be gene- rally acknowledged, that an inclination of about 45° to the horizon is the most convenient for unconstrained observation ; and the instrument should be so arranged, that, at such an incli- nation, the stage may be so far elevated above the table, that, when the hands are employed at it, the elbows may rest upon the table. In this manner a degree of support is attained, which gives such free play to the muscles of the hands, that movements of the greatest nicety may be executed by them ; and the 346 MICROSCOPE. fatigue of long-continued observation is greatly diminished. Such minutiae may appear too trivial to deserve mention ; but no practised microscopist will be slow to acknowledge their value. At the inclination we have mentioned, the departure of the stage from the horizontal position will not be such as to render it neces- sary to confine the objects with more than a slight force, and accordingly they may be moved by the hands with considerable free- dom ; and light objects may be placed upon a slip of glass without any confinement, or co- vered with talc if necessary, and yet be in little danger of falling off it. These are con- veniences which are of more value in practice than they may appear in theory ; for it will often be found that the saving of a little time in the adjustment of the microscope is of great importance in the observation of objects which are undergoing change. There are some objects, however, which can only be seen in a vertical microscope, as they require to be viewed in a position nearly or entirely horizontal ; such are dissections in water, saline solutions under- going chrystallisation, &c. For other purposes, again, the microscope should be placed hori- zontally, as when the camera lucida is used for drawing or measuring. It ought, therefore, to be made capable of every such variety of position. 4. The last principle on which we shall here dwell is simplicity in the construction and adjustment of every part. Many ingenious mechanical devices have been invented and executed, for the purpose of overcoming dif- ficulties which we cannot but regard as trivial. If all these were combined in one instrument, a degree of complexity would be thereby engendered, which would prevent it from be- ing generally available. Our own experience leads us to the conclusion, that a moderate amount of dexterity in the use of the hands is sufficient to render most of these superfluous ; and without such dexterity, no one, even with the most complete mechanical facilities, will ever become a good microscopist. We shall hereafter describe, however, some of those which are in most general use ; premising that we cannot speak from much experience of their applicability, since we have ourselves found no difficulty in doing without them, as we recommend our readers to do. Although a large box, well filled with glittering brass im- plements of various shapes and sizes, may have a very inviting appearance, it will often be found that these are more for show than use, and add to the expense of the instrument in a proportion far exceeding their utility. Among the conveniences of simplicity, the practised microscopist will not fail to recognize the saving of time effected by being able quickly to set up and put away his instrument. Where a number of parts are to be screwed together before it can be brought into use, interesting objects as well as time are not unfrequently lost ; and the same cause will often occasion the instrument to be left exposed to the air and dust, to its great detriment, because time is required to put it away. With those who are not practised in mechanical manipulation, this is especially necessary ; indeed we have often known a slight advantage on the side of sim- plicity of arrangement cause an inferior in- strument to be preferred to a superior one. Yet there is, of course, a limit to this simpli- fication ; and it ought never to interfere with due attention to the principles already spe- cified. Before proceeding to notice any of the ordi- nary forms of stands for simple or compound microscopes, we shall make a few remarks on the best means of carrying on a dissection under a magnifying power. The simplest of all means of effecting this, where the object is large and opaque, and a low magnifying power only is requisite, is to fasten it down upon a board, to any part of the edge of which may be affixed, by means of a small clamp, a jointed stem, carrying a socket or cell, into which a lens mounted in the usual manner may be dropped. This stem, being capable of movement in every possible direction, but having also sufficient stiffness in its joints to remain in any position in which it may be placed, appears to us preferable to any other plan of supporting the lens. The object may be illuminated, if necessary, by light condensed through a convex lens, or reflected from a con- cave mirror. If the dissection must be carried on under fluid, the only variation necessary is the use of a shallow trough, instead of a board, which may be filled with water, dilute spirit, or oil of turpentine, as the case requires; to the edge of this trough the clamp may be fixed in the most convenient position; and the bot- tom of it (if of metal) may be covered with a piece of cork, or a layer of resin and bees- wax, for the purpose of receiving the pins necessary to fix the object. Where the object is smaller, and the dissection may be carried on under a higher magnifying power, we can strongly recommend the use of Mr. Slack's dissecting microscope, of which a description and figures may be found in the 49th volume of the Transactions of the Society of Arts.* Dissecting instruments. — The instruments employed in microscopic dissection must of course vary with the nature and size of the object. The following will, we think, be found most generally useful. Small pointed scalpels. The iris-knife is a convenient size and form for many purposes. Scarpa's curved cataract needle is an instrument which we have found extremely serviceable. Fine scissors, one leg of which should be fixed in a long handle, and the other kept apart from it by a spring, so as to close by the pressure of the finger and to open of itself ; the blades should both be pointed and sharpened on a hone ; these will * [Mr. Powell, the optician, Clarendon-street, Somers' Town, has enlarged and improved con- siderably Slack's dissecting microscope ; and Mr. Ross, of Regent-street, has also on sale a conve- nient form of dissecting microscope, which is deli- neated in the Penny Cyclopaedia, art. ' Micro- scope.'— Ed.] MICROSCOPE. 347 be found much superior to any form of knives for cutting through delicate tissues without disturbing them. Swammerdam is said to have made great use of such implements, in his dissections of insect structures, which, from the accounts of them on record, seem almost to have surpassed any which have been since executed. The curved forceps recom- mended by Mr. Slack, we also have used with much advantage. For more minute dissection we can strongly recommend common needles, and cutting implements which may be easily manufactured from them, by grinding down their sides upon a hone. These may either be fixed in wooden handles, or, which is much better, held in little instruments resembling crayon-holders, specially constructed for their reception. The dissector is thus enabled to give to his needle the effect of a long elastic point or of a short stiff one, by simply altering the part at which it is held. In the ivory handles of these holders, also, there is a receptacle for the needles, which makes the whole of this useful little apparatus complete in itself.* Many microscopists, especially on the conti- nent, are in the habit of making great use of the compressorium, an instrument in which an ob- ject may be submitted to graduated pressure between two plates of glass, the parallelism of which is perfectly maintained. The results obtained by such compression, however, must be accepted with great caution, and need to be corrected by those views of the object which are gained without that distortion of it to which it is liable in this method. The class of inves- tigations in which the compressorium is most valuable, is that m which such structures as the minute ovum need to be closely scrutinized, without any further change in their shape than may render their contents more distinctly visi- ble. For such purposes we believe that a steady hand and a well-made aquatic box will answer the purpose sufficiently; but to those who prefer relying on mechanical assistance, the compressorium will be a useful instru- ment. We shall now proceed to describe some of the modes of mounting and arranging simple and compound microscopes, which appear to us most convenient. The first that we shall notice is a form which has cheapness and sim- plicity to recommend it, and which, if well made, is capable of an adjustment sufficiently delicate for all ordinary purposes. It is a slight modification of one of Mr. Pritchard's.f A (Jig. 166) is the stand, or basis, into which the pillar is screwed. This may be variously constructed, according to the purpose for which it is designed. If hulk be an object, it may be a round disk of lead ; but if weight must be avoided, a thick tablet of mahogany about six inches square, or five inches by seven, (the longest side being in the direction of the movement of the pillar,) is preferable. If great * Such needle-holders are sold by Mr. Pritchard, Fleet-street, London. t Microscopic Illustrations, 2nd cd. p. 82. Fig. 166. Elevation of ordinary compound or simple microscope. A, base ; 13, hollow pillar, with joint at bot- tom; C, triangular rack; D, nut by which it is moved ; E, bar carrying compound body ; F, other end adapted for simple magniliers ; U, compound body ; H, objective ; I, spring fork ; M, mirror attached to sliding tube, tightened by the nut, N ; S, stage. portability be desired, the pillar may be made to screw into the top of the box that holds the apparatus; but this plan should not be adopted, unless all the smaller fittings be contained in a tray which may be lifted out, in order that there may be no necessity for opening the box when the instrument is in use. The pillar is a thick tube of brass about six inches long, with a large screw at the bottom for being attached to the stand, and a joint above this, for allow- ing it to be inclined at any angle. If this joint be well constructed, the instrument will remain in any position in which it is placed, without any steadying rod or perceptible vibration. Within the tube is a triangular bar, with a rack cut on its posterior edge ; this may be raised or depressed from the top of the tube, by turn- ing the milled head, which carries a pinion working into the rack. Particular attention 348 MICROSCOPE. should be paid to the action of this rack ; it should work through a triangular socket at the top of the pillar of at least an inch long, closely embracing the bar, so that it may be moved up and down without the least shake, or variation from its axis, or tendency to slip, when loaded with the full weight it has to carry ; at the same time, it should be sufficiently sensitive to be moved by the slightest rotation of the pinion, which may be effected, not only by the milled head, but by a lever, as in Mr. Holland's mi- croscope. Such a rack will afford the means of focal adjustment for doublets and triplets of high power, as well as for ordinary magnifiers. If it be considered desirable to vary the length of the pillar, and consequently the height of the stage, this may be effected by attaching the rack, stage, &c, to a piece of tube which shall slide within the one that is attached to the base ; if the top of the lower one is sprung, and surrounded by a clamping screw, the upper one may be firmly fixed at any elevation. This plan lias been proposed by Dr. Goring for the pillar of his engiscope; but we consider it per- fectly inapplicable to a large instrument, of which the pillar should be solid, in order to avoid oscillation. The triangular bar carries at its top a double arm, attached to it with a screw and a small milled head, by which its movements may be rendered more or less free. This arm should be thick and well hammered, in order that, when it carries the compound body, it may not be subject to vibration. The object of the double bend in one side of it is to allow the no.se of the body, which is screwed into the hole on that side, to project below it, so that the magnifiers may be attached on its un- der side ; by this means, the necessity for un- screwing the body every time that the magni- fier is to be changed (which is requisite where the magnifier is screwed into the arm and the body into it) is avoided, without any increase in the length of the rack, which would other- wise be necessary for low powers. The other side of the arm carries the magnifiers, when employed as single lenses ; the same set may be used as are fitted to the compound body, their interior being screwed for attachment to it, and their exterior being adapted to drop loosely into the hole of the second arm. For such a microscope, we should recommend a series of ordinary lenses from 2J or 2 inches focus to ^th of an inch, and two or three dou- blets from -,'gtli to 5'Bth, with a triplet of g'gth. These may all be used as objectives with a meniscus eye-piece ; though, for the latter, Mr. Holland's will, in most cases, be preferable. The stage of this microscope may be a simple plate, attached to the top of the pillar, as in jig. 166, with a spring stage and other appurte- nances adapted to it. We are inclined to re- commend for such a microscope, however, for the sake of simplicity and facility of use, a stage in which the ordinary principle of fixity is in some degree departed from. The upper part of it consists of a thick and strong fork, projecting about 2 inches and about \\ inch broad, of well-hammered brass, firmly attached to the top of the pillar ; at about |ths of an inch below this is a plate of similar dimensions, with an aperture of about an inch. Bearing upon this lower plate by a spiral spring, and guided by vertical pins working through aper- tures in it, is a thin moveable plate, which is constantly being pressed upwards by the spring against the fork. This stage combines, in a degree which renders it an extremely conve- nient one, the advantages of the ordinary spring- stage, and the fork. The objects, whether placed in sliders, on slips of glass, or in aquatic boxes, are readily slid under the prongs of the fork (which should be bevelled off on the under side so as to allow them to enter), and are held by the spring with sufficient firmness in any position, whilst ready movement is also per- mitted them. The fork may have a vertical hole drilled in it on each side, for holding the stage forceps or other such instrument; and it may be made thick enough to allow of a la- teral hole for fixing the condenser, without being too much weakened. The thickness of the fork will be of no kind of inconve- nience, as the nose of the microscope will have free play from side to side between its prongs. To the lower plate may be attached ground- glass, stops, condensers, polarising apparatus, or any other required fittings. The disadvan- tage of this stage is that it affords no firm sup- port to the object, which is in some instances of importance. This may be obtained by sim- ply adapting a plate to the upper side of the fork, which may be received into grooves on its lower surface; and this plate may then be con- sidered as the stage. Whenever such an in- strument is being adapted to the purpose of dissection, all that is necessary is to raise up a support for the hands on each side of the stage, which may consist of books, or still better of blocks of wood cut to the form of the outside of Mr. Holland's case; and the height of the stage being then adjustible by the sliding tube of the pillar, all the advantage of Mr. Holland's microscope, except its setf-containedncss, may be secured. We have only further to mention the mirror, which should be at least two inches in diameter, and have one of its sides plane, and the other concave. Its stem should be attached to a short piece of sprung tube sliding over the pillar, and capable of being secured in any situation by a clamping screw. If a still more portable microscope be re- quired, combining considerable range of power with great exactness of adjustment, we can strongly recommend an instrument constructed upon the plan of the large one subsequently to be described, (jig. 167,) but upon about two- fifths of the scale. Its pillar may either be screwed into the lid of the box containing the apparatus, or mounted on a tripod similar to that which is used for portable telescopes, — the tripod being reversed, and the legs being folded round the stem, when it is packed in its box. The delicate focal adjustment of which this microscope is susceptible renders it more ad- vantageous than the one last described, when deep magnifying powers are being employed ; MICROSCOPE. 349 and its portability is a great recommendation. The one in our own possession is packed, with its tripod, into a box whose outside dimensions are 7| inches by 5, and its depth only 2, and this also contains a short body with meniscus eye-piece, four ordinary magnifiers, and three doublets and triplets, which may be used singly or as objectives, illuminating lenses and speculum, aquatic boxes, and other small ap- paratus,— the weight of the whole being no more than 2^ lbs, although a magnifying power of 450 diameters, with sufficient penetration to exhibit the markings on the Podura, and with perfect steadiness, may easily be obtained by it. The instruments we shall now describe are not adapted for use in any other way than as compound microscopes. Their size and weight are such as would render them far less conve- nient than the smaller forms already described for use with simple lenses, although there is no other reason why they should not be thus em- ployed. Every constructor of microscopes has his own favourite model ; and there are few re- cently made instruments of the highest class which do not possess some particular recom- mendations. Amidst the numerous claimants to our notice, we shall select two ; of which the first is the form adopted by one of the best constructors of achromatic objectives in this country ; and the second is the one which we have ourselves had in use for several years, and which we do not desire to lay aside for any we have seen. With respect to the former, our limited space compels us to refer to the article Microscope in the Penny Cyclopaedia, where a delineation and full description of Mr. Ross's Microscope will be found.* We shall now de;cribe the microscope * [Without wishing in the least degree to detract from the merit of Mr. Ross's microscope, (to which, on the contrary, he bears willing testi- mony,) the Editor deems it but justice to refer to a very beautiful instrument constructed by Mr. Powell, wbich he has employed for some time, and which is also used by several observers in this city. The body of the microscope moves on a triangular bar, having a bearing of three inches, which ren- ders it very steady. The coarse adjustment is ob- tained by a rack and pinion, attached to which are two large milled heads, which allow of the body being adjusted with either hand. The fine adjust- ment has also two milled heads, only two inches apart from the coarse one, and their axis being horizontal and parallel to each other, renders the motion of the hand from one to the other perfectly easy, without removing the eye from the body of the microscope. The stage is seven inches square. The convenience of its being thus large is, that the hands do not interfere with the object when adjust- ing it. The heads that move the stage have their axis in the same line, and so placed that with the same hand the stage may be moved in all direc- tions ; this is convenient when viewing an object, the surface of which is very irregular ; with the right hand you can move the stage, and there being two heads to the adjustments for the body, with the left the object can be adjusted into focus. There are likewise two milled heads to one motion of the stage, by which means both hands may be employed at the same time, which is sometimes requisite. On the same bar that the body rests, moves the " achromatic condenser," by which arrangement it is certain to move in the same line with the body, which we have ourselves been accustomed to employ, and state what we regard as its advan- tages; not omitting to notice the objections which may be brought against it, and bearing in mind that every microscopist is naturally most partial to the form which he has himself adapted to his own ideas of convenience. It is principally constructed according to the plans of Mr. Pritchard and Dr. Goring ; and we may observe in limine, that the objections which have been brought against any form of construction in which the body is screwed by its lower extremity to a horizontal arm, as placing it in the most unfavourable position for vibration, independently of the stage, are ap- plicable only to instruments which are not made with sufficient solidity ; for, having had an opportunity of comparing- the quality in this respect, of Mr. Ross's microscope, with our own, the two being placed in exactly the same circumstances, we could not find that there was any inferiority on the part of the latter. It must be borne in mind, that every increase in the size and power of a microscope must be accompanied by mure than a corresponding increase in solidity, in order to guard effec- tually against oscillation. The stand or basement is a slab of solid mahogany 12 inches square and 1£ inch thick, loaded with lead at the corners, and having a strip of thick baize, about l£ inch broad, glued round the edge of the under side ; the whole weight bears upon the baize, which does not readily communicate vibrations; and the large surface over which the pressure is distributed gives the instrument a degree of imperturba- bility which would scarcely have been antici- pated. The slab is surrounded by a slightly elevated rim ; and it thus serves as a most con- venient little table, on which the various pieces of apparatus required for microscopical obser- vation may be carried about with the instru- ment without any danger. The pillar of the microscope carries at its lower extremity a screw, above which is a flange or shoulder of 2 inches diameter; the screw is received into a socket let into the wooden foot, and firmly attached to it, and itself having a shoulder of equal size; so that, when the pillar is firmly screwed down upon it, there is not the least tendency to vibration between the two. The socket is not let into the middle of the base, however; but its centre is only 2 J inches from one of the sides, and 9£, therefore, from the other ; so that, in fact, when the microscope is placed vertically, the centre of the stage pretty nearly corresponds with the centre of the foot. The object of this is to give a decided prepon- derance in weight to the front of the foot in all positions of the microscope ; for we are inclined to think that much of the oscillation so fre- quently complained of in microscopes is to be which is most essential, for unless it did so when using different power object-glasses, the axis of the lenses would not coincide. There are many other conveniences and improvements to this microscope which cannot be mentioned in this brief notice. — Ed.] 350 MICROSCOPE. Fig. 167. Superior Compound Microscope. A A, base; B, pillar with joint at the top; C C, stem, containing square tube D, which is moved by a fine screw turned by the nut E ; within this tube slides the square bar F, carrying the arm G ; into this is screwed the tube H, within which the compound body slides ; I, the objective ; K, stage-fork ; L, sprung tube, tightened by the nut N, carrying the frame of the mirror M. attributed to the fact, that, when the instrument is much inclined, the hinder foot receives nearly the whole weight, and the portions of the instrument on the two sides so nearly counterpoise each other, that a very slight cause will communicate an oscillation to the whole. We can strongly recommend to our readers a basis of this kind, having not only our own ex- perience of its benefit to guide us, but that of friends whom we have induced to adopt it, and whose previously unsteady microscopes have been greatly improved thereby. It certainly does not possess the merit of portability ; but this, in a large microscope for observations of the highest kind, ought not to be a considera- tion. Nothing is easier than to have a separate tripod of the ordinary kind for use when occa- sion requires. To such a tripod Mr. Ross* has recently applied a method of construction, which he states to be very effectual in obviating vibration ; but we cannot speak from experi- ence in regard to its use ; and being well satis- fied with our own much simpler and less ex- pensive plan, we do not see the necessity for it. The pillar is just an inch in diameter, and consists of a stout brass tube loaded with lead. On the firmness of this part much depends. It is 8 inches from the foot to the centre of the joint. The middle piece of the joint is Jth of an inch thick ; and to this is attached a tubular clamp with a binding screw, which closely em- braces the stem. This mode of construction we adopted in accordance with the recommen- dation of Dr. Goring and Mr. Pritchard ;* but we are doubtful if its advantages counterba- lance the disadvantage of a certain want of fixity which it imparts to the remainder of the instrument supported by it. The stem is a thick brass tube of about f^ths of an inch in diameter; to the upper part of it is firmly at- tached the stage, which is composed of a simple plate of well-hammered brass, \ of an inch thick ; its length from the front of the pillar is 4 inches, its breadth 2g inches, and the diame- ter of its aperture lj inch. The only fitting constantly attached to it is the fork, of which the two wires work through sockets projecting from the under side of the stage. This fork is made sufficiently thin to possess a certain de- gree of elasticity ; and, being firmly held in any position by the friction of its wires, it is a very useful means of holding aquatic boxes, slips of glass, large sliders, &c, affording, by its wide opening, (2 inches,) considerable free- dom of movement to the object. The utility of this fork will depend upon the goodness of its construction in the first instance; it ought to work easily, and yet hold tightly in any po- sition. The sockets through which its wires pass should be sprung, so that they may be tightened at pleasure, should they work loose. The stage has a slight rim projecting into the lower side of the aperture, in order to hold various fittings which are attached to it by a bayonet catch, and holes are drilled in various parts of the stage (the massiveness of which prevents its being weakened thereby) for the reception of the pins of the forceps, condenser, &c. The stem carries a sprung tube, to which the minor is attached, in the manner to be presently noticed. From the top of the stem projects a square tube, a little more than f5ths of an inch each way, the upper end of which is sprung, so as to grasp with sufficient firmness a solid bar of half an inch square, which slides up and down within it. The upper end of this bar carries the arm to which the body of the microscope is attached ; on the accuracy of its formation the truth of its movement will of course depend ; but if well made, a rise and fall of 3g inches may be allowed to it, without the slightest alteration in the position of the axis of the body which it carries. The advantages of this sliding move- ment over the rack commonly employed for the coarse adjustment we regard as considerable; very much time is saved ; for the arm may be shifted from its greatest to its least distance from the stage, in scarcely more time than is * Microscopic Journal, No. 2. * Op. cit. MICROSCOPE. 351 required for making the slightest adjustment. The axis of the body is never changed in the least degree, — which we have rarely found in rack adjustments, owing to the pressure of the pinion against one side of the bar; and thus an object is always kept in the centre of the field, whatever change made be made in its focal distance by an alteration of the magnifiers. By a little practice, the power of making adjust- ments of extreme minuteness may be obtained, if the bar have been originally filed so true that it works with perfect smoothness in every part. An additional adjustment, which may be made of any required fineness, is provided for, however, by making the square tube or socket itself moveable, and connecting it with a micrometer screw worked by a large milled- head at the bottom of the stem. By turning this screw, the socket, and the bar which it carries, are raised or depressed in any minute degree ; and the socket being made to work through stuffing - boxes closely packed with cork, all twisting on its axis by the action of the screw is avoided. On the fineness of the screw the delicacy of the adjustment will of course depend. That which we have employed has forty turns to the inch; and the milled- head being 1£ inch in diameter, or about 4f inches in circumference, a movement of one- fiftieth of its periphery, or something less than -['jthofan inch, will affect the ai m to the amount of ^th of an inch. We should recommend, however, a screw rather finer than this. By dividing a circle on the milled head, and affix- ing an index-point to the bottom of the stem, the amount of motion given may be known to a great nicety, and thus the thickness of a mi- nute object laid upon any surface may be mea- sured. If its upper side be brought exactly into focus, and it be then removed, and the surface on which it has lain be brought into focus by the micrometer screw alone, the num- ber of divisions over which the index has passed will of course indicate the thickness. This me- thod, which was proposed by Mr. Valentine,* answers very well for such objects as the vessels of plants, scales of insects, &c. which can be completely isolated, when a sufficiently high power is employed, so that distinctness can only be obtained at one point. We consider it a great advantage of this kind of adjustment, that it is effected at a considerable distance from the stage, and that the hand is therefore in no danger of deranging the position of ob- jects or apparatus connected with it. The arm which carries the body is attached to the top of the bar by a screw-pin passing through the former, by which it is enabled to traverse from side to side. This movement will often be found extremely useful, both in the examination of different parts of objects which it is desirable not to move, and in chan- ging magnifiers, &c. on the body ; the want of it we consider one of the chief inconveniences in Mr. Ross's form of construction. The arm is jjths of an inch thick, and broad enough at the part farthest from the centre to receive the * Trans, of Soc. of Arts. body, which is not made tapering in the usual manner, but is attached by a screw of l^inch diameter, with a large shoulder above it. By this mode of attachment, and by the massive- ness of the arm itself, all vibration from the top of the bar is prevented ; at least we have not been inconvenienced by it. When the bar is pushed into its socket, so that the arm ap- proaches the stage, (as when high powers are used,) no oscillation can arise from its vibra- tions ; and the socket itself works through an aperture in the stage-plate, to which it is so closely fitted that no oscillation can arise in that point; so that, both in theory and prac- tice, we find the form here proposed unobjec- tionable on this score. It is true that, when the bar is drawn out to its full extent, oscilla- tion may arise ; but this is never the case, ex- cept when low powers are being employed, and then we altogether fail to perceive it. In the construction of the body there is nothing worthy of peculiar remark ; and, as we have already de- scribed the various modes of magnifying the object, we shall therefore now pass on to con- sider the best means of illuminating it. The perfect illumination of the object is a matter of the utmost importance, especially when high magnifying powers are being em- ployed. There are many difficult objects which require to be viewed under a great variety of aspects, in order that their true characters may be determined ; and there are not a few whose structure cannot be understood at all, even with the most perfect arrangement of the optical portion of the microscope, unless similar atten- tion be bestowed on the concentration of the light by which they are viewed. We shall, therefore, bestow on this subject more attention than it has ordinarily received. For transparent objects of large size, which are being viewed with low powers, such as sec- tions of wood, wings of insects, &c. we find a concave mirror by far the most simple and, at the same tune, effective means of illumination ; and the optical errors to which it gives rise are not such as to interpose any practical difficulty in its use. It should be, for such a microscope as we have described, of greater size than that ordinarily employed ; three inches may be re- garded as a good diameter. It should be set, by an universal joint, upon a piece of tube fitted to slide stiffly up and down the stem which descends from the stage. In this man- ner its distance from the object may be readily varied ; and the degree of concentration of light effected by it will thus be easily adapted to the character of the object to be viewed. Thus, if it be pushed near the stage, the pencil of con- vergent rays will not be nearly brought to a focus, and a large surface will be illuminated with a moderate light. But if it be drawn nearer the opposite end of its range, the rays will be more concentrated, so that a smaller suiface will be illuminated, but with much greater brightness. By the former adaptation we are enabled to illuminate, with great equa- lity, and by means of the ordinary lamp-flame, an area of three-eighths of an inch in diameter, with sufficient intensity to produce a very bright 352 MICROSCOPE. field of fourteen inches. In viewing large ob- jects for which great perfection is not required, we find it advantageous to interpose a ground- glass at about half or three quarters of an inch distance beneath them ; this is easily adapted to the under side of the stage. It serves to pro- duce an extremely equable diffusion of the light over a large field, and to deaden the glare which is occasioned by the direct admission of so large a quantity ; but, if applied to objects which require to be seen with great distinct- ness, it will be found to produce a kind of fog which seriously impairs the power of the micro- scope; and with objects of any difficulty it is quite inadmissible. In viewing objects, how- ever, of the largest size that the microscope can receive, by a good diffused daylight, the ground- glass is never required. A bright cloud, oppo- site to the sun, is then the best source of illu- mination. For the purpose of effecting these and other adjustments of the mirror, we have found it convenient to have the tube which carries it sprung, so as to slide rather loosely on the stem, and to secure it in any particular situation by means of a large milled head which screws on one end of the tube, and clamps it upon the stem. The plane mirror, with a condensing lens between it and the stage, is preferred by many to a concave mirror; and for certain objects it is, without doubt, superior. For ordinary use, however, we prefer the concave mirror, for the following reasons : — Its effects are obtained by a single adjustment ; whereas, in the use of the plane mirror and lens, two adjustments are re- quired : and if (as we shall presently state to be often desirable) the mirror be thrown quite out of the axis of the optical part of the instru- ment, it is difficult to adjust the condenser with correctness. Further, in order to obtain light enough for a field such as we have men- tioned, the condensing lens must be nearly three inches in diameter, and thus becomes very cumbrous and inconvenient. For objects of a high class the concave mirror should of course not be employed ; but for these the common condenser is by no means adapted, and must be put aside for a superior one, such as we shall presently describe. The plane mir- ror and condenser enable the observer, how- ever, to obtain an additional variety of illumi- nation, which is often advantageous ; and by a simple modification, proposed by Mr. Varley, the light of a bright cloud may be artificially imitated by them. The means of doing this consist in covering the surface of the plane mirror with carbonate of soda or pounded glass, by which the direct solar rays are reflected very much as by a white cloud. We have also seen a plaster of Paris mirror employed for the same puipose, and with good effect, where, on ac- count of the transparency of the object, it was necessary to reduce the amount of light sent through it, without interposing any screen that should produce indistinctness. It is often very desirable to throw the centre of the mirror a good deal to one side of the axis of the body of the microscope, so that the reflected rays may fall very obliquely upon the object, and cause its prominences and depres- sions to exhibit shadows of much greater depth than can ever be seen with more direct light. No microscope, in which there is not a provision for this movement, can be regarded as having its resources properly developed ; and we have seldom seen one which comes up to our ideas of the degree in which it should be permitted. In general, the mirror-frame is immediately fixed to the sprung tube which carries it; and thus it can only be turned out of the axis at an angle which will evidently interfere with its use. In our own microscope, the mirror-frame is connected with the tube by a stalk of an inch in length, so that the centre of the mirror is three inches from the stem. This, of course, involves a lengthening of the stage, and of the arm which carries the body, in order that the centre of the apertures of all three may be in the same line; but the disadvantage hence resulting is easily avoided by increasing the strength of these parts. The variety of illumi- nation which may be given by a mirror fitted in the manner we have described, is very great ; and some very curious and unexpected pheno- mena are not unfrequently disclosed by means of it. For example, the field may be rendered almost dark, by turning the centre of the minor considerably out of the axis, so that none of the rays reflected by it pass up the body of the microscope; whilst objects of great delicacy will frequently appear brilliantly illuminated, on account of their retention of a part of the light which is passing obliquely through them. In this manner we have often been enabled to see an immense number of the minutest ani- malcules (monads) rapidly moving through water, in which, with direct light, none but the larger ones could be distinguished ; and the inteiest of the spectacle is heightened by the phosphorescent glow which the animalcules appear to have when thus illuminated.* A similar effect may be produced without the use of the concave mirror, by causing a direct pencil of rays from a lamp or candle to be thrown very obliquely upon the object by means of a condensing lens. In the examination of many delicate objects with high powers, direct light will often be found more advantageous than reflected. This may be obtained with facility, by placing a lamp or wax-candle behind the stage, the mirror being turned out of the way. In the day-time the direct light of a bright cloud will often be found to produce an extremely beautiful effect; but in order to attain this without an inconve- nient position of the head, the microscope stand must be elevated to such a height, that, when the stem is horizontal, or even inclined in a position contrary to the usual one, the eye-piece may be at a convenient height for the eye. The different modes of illumination best suited to different objects can only be found out by ex- perience, since achromatic objectives vary in their relative effects with each. * This method of viewing objects was publicly noticed, a few years since, as a new discovery ; it had long, however, been familiar to ourselves, and, we believe, to most other scientific observers. MICROSCOPE. 353 When condensed light is employed with deep powers, great care is necessary in order to bring out the best effects of a microscope, with difficult objects. These remarks apply to the simple as to the compound forms of the instrument. We do not ourselves consider the ordinary condenser as of much more value for the higher than for the lower class of trans- parent objects ; and we think that it may be discarded from the instrument without dis- advantage. Great assistance may be obtained, however, from a well-constructed condenser, in the resolution of the more difficult class of microscopic objects. That which was pro- posed by Dr. Wollaston for use with his doublet consists of a tube about six inches long, having at the lower end a diaphragm with a circular perforation about three-tenths of an inch in diameter, through which light, proceeding from a radial point or surface, is reflected by a mirror below it. At the upper end of the tube is a plano-convex lens, about three-fourths of an inch focus, with its plane side next the observer ; the object of which is to form a distinct image of the circular per- foration in the plane of the object, which should be at about eight-tenths of an inch from the lens. We consider this instrument to be theoretically faulty; inasmuch as the point from which the illuminating rays di- verge, and the limiting aperture are not co- incident, so that pencils brought to a focus for the former are not for the latter. The length of the tube, again, is an inconvenience, espe- cially in the case of small microscopes. Never- theless, it is much superior to the ordinary form of condenser. An improvement was suggested by Dr. Goring, which consisted in shortening the tube below the lens, and re- moving the stop from that end of it to the other, so that it should be just beneath the object; in this manner the illuminating rays may be brought to a focus on the object, the superfluous ones being cut off by the stop. We have derived much advantage from the use of this condenser in the small doublet mi- croscope already noticed, and by a slight mo- dification of it we can obtain a variety of illumination, which is often very useful. Our condenser consists of three tubes, one sliding within the other; the outer one is fixed to the under side of the stage; the second carries at its upper end the stop, the distance of which from the object may thus be changed, and the inner one carries the condensing lens. A stop may be screwed into the bottom of the latter, if it is desired to adopt Dr. Wollaston's plan. We have derived the greatest advantage from the use of this condenser, however, by using it with direct light from a radiant point at some distance, — a bright cloud, for instance, in the day-time, — and a lamp or candle on the opposite end of the table at night. In either of these cases, the focus of the illuminating rays may be made coincident with the plane of the object, without that glare which will almost certainly be produced if the source of light is nearer and move intense. When thus used, Dr. Goring's condenser approaches in its VOL. III. character to that of Sir D. Brewster,* which we shall now describe, adding some ideas of our own in reference to its construction. The principle of illumination on which Sir D. Brewster lays great, and we think fully- deserved stress, is, that the focus of the illu- minating rays shall be coincident with the object, so that there shall not be two sets of rays at different angles, one proceeding from the luminous object and the other from the object to be magnified. This can only be attained in any degree by making the image of the illuminating body coincident with the object; and it will be perfectly accomplished, in proportion as the rays forming that image are themselves free from aberration. If, for example, the white rays have been separated into their component colours by the condenser, these colours will be imparted to the object, the appearance of which will also be rendered less distinct by the spherical aberration of the condensing lens. Hence an achromatic lens, or, if this be objected to on account of its expense, a Herschel's aplanatic doublet, should be used as the condenser ; the latter we have found to answer very well, as the centre of the circle illuminated by it is very nearly free from false colour. Further, if a mirror be employed to change the course of the rays, it should be of metal, in order to avoid the false rays reflected from the first surface of the glass. If day-light be employed, no other precaution is necessary; but if the illumination be obtained from a lamp or candle, it will be necessary to limit the amount of light ad- mitted. This must not be by a stop placed beneath the lens, for the reason already speci- fied ; but it should be accomplished by a stop or shade placed as near as possible to the flame, so that the image of that and of the flame may be brought— virtually if not exactly — to the same focus. We have found that the same end may be attained by removing the lamp or candle to a greater distance, so as to diminish the intensity of the light to the required amount, and only a very low flame will then be required, as the condensation of the rays is much more perfect than with the ordinary lens. The achromatic condenser is strongly recommended also by M. Dujardin, an eminent microscopist of France; and we know that it is now considered an indispensable addition to microscropes of the highest class, affording, as it does, the means of resolving objects, previously considered too difficult to admit of a clear view of their nature. We are disposed to think, however, that some improvement is necessary in order to develope the highest powers of this instrument. The rays of light proceeding from the radiant point or object, being brought to a focus by the condenser on its surface, cross each other there, and should proceed to the object-glass of the microscope, as if they came from the object itself. Now, unless they are made to converge upon the object at the same angle at which they diverge * Treatise on the Microscope, from th« Ency- clopaedia Britannica. 2 A 354 MICROSCOPE. to enter the objective, we cannot but think that a source of error still remains, and that the most perfect image possible, formed by an achromatic object-glass, of an object which is artificially illuminated, can only be produced when the rays from the source of light take exactly the same course as if they proceeded from the object itself. That they may have this course, they must be made to converge upon the object by a condensing lens, whose focus for parallel rays (if the illuminating point be very distant) shall be the same as the acting focus of the objective. A different condenser would thus be required for every objective; but the expense of these would be sufficient to preclude their general employment. The same condenser might be employed, however, for several low powers; the highest having their own expressly adapted to them. We may mention it as a fact for which we cannot very well account, that we have been able to obtain a very beautiful and distinct illumina- tion by the use of an aplanatic-doublet con- denser, receiving its rays from the ground glass globe of the common table-lamp, which would not seem to furnish any of the conditions that we have dwelt on as of theoretical impor- tance. Opaque objects may be illuminated in two principal ways, either by a light cast obliquely upon them by a condensing lens, or by rays thrown upon them perpendicularly by a silver speculum fixed to the object-end of the body, which receives them from the mirror below. Both these modes have their peculiar advan- tages, and will be found by experience to be applicable with advantage to different classes of objects. No general directions on the sub- ject can, however, be given. The condenser to be used by lamp-light for large opaque ob- jects should be a bull's-eye or hemispherical lens of four inches in diameter ; by this, even from a common candle or flat-wicked lamp, a sufficient light may be attained for almost any purpose, and with an Argand lamp a very powerful illumination is obtained. For the parallel rays of day-light, however, an ordinary double-convex lens of the focus of two inches or more may be employed ; this may be mounted upon a separate stem and foot, as the bull's-eye should always be, or it may be attached to some part of the micro- scope itself. We have seen foreign instru- ments in which it was fixed to the object-end or nose of the body ; a construction which we deem essentially bad, inasmuch as it then re- quires to be readjusted every time that the focal distance is changed by the substitution of one objective for another. A better mode in our opinion is to attach it to the side of the stage by a jointed arm possessing a pin which may be fitted into one of three or more holes drilled in the side of the stage with sufficient tightness to remain in any position. If the wire to which the lens-frame is attached be made to pass through a sprung socket con- nected by a ball-and-socket-joint with the jointed arm, an immense variety in position may be readily given to the condensing lens, which will render a separate mounting for it unnecessary. The metallic speculum, or Lieberkuhn, for throwing down rays directly upon the object, is sometimes attached to the objective itself, sometimes to a tube which maybe drawn down over it to the required amount. The former con- struction is the most perfect, each magnifier having its own speculum ; but the latter is most economical, as one speculum serves for many objectives. When the latter construc- tion is employed, the tube should be marked with the numbers of the magnifiers at the points at which it may be best adjusted for each, so that, when the object is in the focus of the objective, it may be in full receipt of the rays reflected from the speculum. In this mode of illumination the size of the concave mirror will be found to have a considerable influence ; and the capability of adjusting also its distance from the speculum gives a useful variety to the mode of illumination. It can never be too fully kept in mind, that, in the examination of doubtful objects, no really satis- factory result can be attained, until they have been viewed in every possible way. When the object is not perfectly opaque, or does not fill up the whole of the field of view, it should always be placed on an opaque disc, which should be large enough to interrupt all the rays passing directly upwards from the mirror to the eye. The colour of this disc may be advan- tageously varied for certain objects, but in general we consider a dead black the best for giving them effect. As a general rule it may be remarked, that the fewer the rays entering the eye except through the object, the more perfect will be the view of it ; and if there be anything approaching to a glare around an opaque object, whether the light proceed di- rectly from the mirror, or be reflected back from the too-bright surface of the disc, it is equally injurious, and will occasion a mis- tiness over the object itself. It is evident, how- ever, that the size of the disc must be governed by that of the field of the objective employed ; for, if too large, it will interrupt too much of the light impinging on the speculum. A piece of black glass, mounted upon a long strip of common window-glass, will be found very useful where the object is such that it can be laid upon it when the microscope is in- clined. When the object requires to be held in the stage-forceps, however, a disc of black card may be placed behind it, so as to afford it a back-ground. And for some delicate opaque objects, it is most advantageous to em- ploy little concave discs or cups, with their interior blackened, in front of which the ob- jects are to be placed. Similar dark back- grounds are useful when oblique light is em- ployed. III. Magnifying power of micro- scopes. The next point to which we shall advert is the mode of estimating the magnifying power of microscopes, and of measuring the real size of objects under examination. Our esti- MICROSCOPE. 355 mate of the magnifying power of a microscope must depend upon the standard which we assume as the ordinary distance at which the object is seen with the naked eye; since, if brought within five inches, it is seen under double the angle, and therefore of double the size which it appears to possess at ten inches. If, therefore, the former distance were taken as a standard, the magnifying power of a lens or microscope will only be half that at which it would be estimated with reference to the other. Nearly all opticians, however, have agreed in considering ten inches as the standard of com- parison ; and when, therefore, an object is figured as magnified 100 diameters, it is meant that this figure placed at ten inches distance from the eye is 100 times the dimension, each way, of the real object seen with the eye alone at a similar distance. The measurement of the magnifying power of simple or compound microscopes by this standard is attended with no difficulty. All that is requisite is to have a glass or thin slip of ivory accurately divided to a small fraction of an inch (ifojth will usually answer very well), and a common foot-rule, divided to tenths of an inch. The glass or ivory micrometer being adjusted to the focus of the magnifier, the rule is held parallel with it, at the distance of ten inches from the eye. If the second eye be then opened, whilst the other is looking at the object, the circle of light included within the field of view, and the object itself will be seen faintly projected upon the rule ; and it will be very easy to mark upon the latter the apparent distances of the divi- sions on the micrometer, and thence to ascer- tain the magnifying power. Thus, supposing that each of the divisions of ,Lth of an inch corresponded with 1£ inch upon the rule, the linear magnifying power is 150 diameters; if it corresponded with half an inch, the mag- nifying power would be 50 diameters. The superficial magnifying power is of course esti- mated by squaring the linear ; but this is a mode of statement never adopted by scientific observers, although often employed to excite popular admiration or to attract customers by those whose interest is concerned in doing so. When the magnifying powers of the several objectives of a microscope are known, it is easy to make a fair approximation to the real size of an object under examination, by projecting its image, as before, upon a foot-scale held at ten inches distance ; and the apparent dimensions it there exhibits, divided by the magnifying power employed, will of course be its real size. More accurate measurements are generally re- quired, however, although the foregoing may serve as a sufficiently near approximation for ordinary purposes. Various methods of ob- taining these have been devised. The most perfect measurements are obtained by a fine micrometer-screw, by turning which either the object or the body will be made to execute a transverse movement; just as, in the fine ad- justment of the focus, the body is made to approach or recede from the stage. This ap- paratus may be attached to the stage, if it be thought preferable to move the object, or to the arm if the body be made to traverse. In proportion to the fineness of the screw, and to the size of the milled-bead, will measurements be obtained of minute accuracy. In the focus of the eye-piece a very fine thread is placed ; and one edge of the image being brought against it, the position of the micrometer is noticed ; and the other edge being then brought to the same line, the number of divisions of the micrometer-screw, which have passed over the index, will indicate its size. The expen- siveness of this micrometer, when made with sufficient accuracy and minuteness, is the only bar to its general employment. Other means have been devised, however, which are scarcely inferior; and the simplest of these requires only the use of an eye-piece of a construction different from the ordinary, with coarsely di- vided glasses. The micrometer eye-piece is made upon the principle of Ramsden's. The optical part of it differs from that in common use, in having the plane side of the field-glass turned towards the object; and in the adjust- ment of the foci of its lenses in such a manner that the image to be viewed by it must be beneath the field-glass instead of being be- tween it and the eye-glass. In its focus there is placed a plane glass with divisions on it ; these may be from j'jth to T^th of an inch apart ; the latter will enable very minute mea- surements to be taken. By this arrangement, when the object is brought into focus, it ap- pears as if it were traversed by cross lines ; since its image is coincident with the divided glass, and is, like it, viewed by the eye-piece as by a simple microscope. The value of these divisions will, of course, depend upon the degree in which the object is magnified in the image ; and they must be ascertained for every objective, by the divided glass or ivory mi- crometer. This being brought into focus, and so placed that the direction of its two sets of lines shall correspond with those of the divided glass in the eye-piece, the number of divisions in the latter, corresponding to each division of the former, must be observed, and their value will be thus ascertained. Thus, if one divi- sion on the T^Bth inch micrometer be found to coincide with eight on the eye-piece, these eight will together indicate a dimension of jLjth of an inch upon the object; and each division of the eye-piece will of course be equivalent to the gijth of an inch. If there is not an exact correspondence, or if it be desired to obtain a power which can be expressed in round numbers, a little alteration in the length of the body, made by drawing out his eye- piece, will enable the microscopist to effect this ; but the eye-piece should be marked, so as to be adjustible to the same point again, when the same magnifying power is employed. When the value of the divisions on the glass in the eye-piece is ascertained for every mag- nifier, the object-glass micrometer may be put aside altogether; since by the use of the eye- piece alone, a series of lines, the real distance corresponding to which is known, is projected 2 a 2 356 MICROSCOPE. upon the object ; and, with a little practice, a very close estimate may be formed of the proportional size of the object, when it only extends over a part of a single division. This, for ordinary purposes, is by far the most con- venient mode of measurement. The camera lucida, however, which has been adapted to the microscope for the purpose of delineating representations of microscopic ob- jects, may be most advantageously applied also to micrometry. By this instrument (of the construction of which we shall presently speak) a highly magnified picture is projected upon a surface on which its outlines may be easily marked, and on which their size may, therefore, be determined with the greatest nicety. Here, as in former cases, the micro- meter object-glass must first be employed, in order to fix the standard. If one of these be placed in the focus of the microscope, and the camera lucida be so adjusted, that an image of its lines be thrown upon a piece of paper at a fixed distance from it, the distance of these may be marked with precision ; and subdivi- sion on the paper may be carried to any re- quired extent, so as to afford the means of at once ascertaining the size of an object placed in the field. Thus, if the magnifying power and the distance of the paper be so adjusted, that the lines which are really T^jth of an inch apart are projected upon it at five inches distance from each other, every inch on the paper will of course be equivalent to ^th of an inch on the object. Lines of ^jth of an inch apart may easily be drawn on the paper; and the distance between each of these will represent T^th of an inch on the ob- ject. In this manner the size of an object may be known with great nicety, and with less lia- bility to error than in the use of the screw mi- crometer. It is easy to increase the apparent size of the image thrown by the camera lucida to almost any required extent; so that even greater minuteness may be attained. The dis- tance between the eye-piece and the paper may be increased, — either vertically by placing the latter upon a chair or even on the floor, — or horizontally, by turning the prism or mirror a quarter round, and projecting the image in the direction of the side of the room, so that the range of distance is much increased. Such a plan is, of course, of no use in delineation ; but in micrometry it may be had recourse to with advantage, especially when comparing the relative sizes of similar objects, such as the blood-discs. For every magnifying power, whether gained by changing the objective or by increasing the distance of the screen, a determi- nate value must of course be ascertained for the divisions of the latter. The camera lucida of Dr. Wollaston is some- times applied to the eye-piece of the micro- scope for the purpose of delineation and micro- metry ; but it is much inferior for these pur- poses to other plans which have been devised. Probably the best of these consists of a mirror composed of a thin piece of rather dark-coloured glass cemented on a piece of plate-glass, in- clined at an angle of 45° in front of the eye- glass. Of the light which passes out from the latter, a sufficient quantity is reflected by the mirror to give a distinct image; and yet the paper and pencil can be distinctly seen through the glass, though rather darkened by the co- loured glass, which thus serves to render the image more brilliant. A lens is placed below the reflector, which causes the rays from the paper and pencil to diverge at the same angle with those received from the eye-glass ; so that both the object and the pencil are seen with equal distinctness. The use of a small highly- polished steel mirror, fixed in the focus of the eye-piece, and inclined upwards towards the eye at an angle of 45°, is by some preferred to this. The mirror being smaller than the pupil allows the rays from the paper to pass up into the eye around it ; and thus the image is seen as upon the screw. In the use of either of these instruments, the chief difficulty (as in the use of the common camera lucida) is for the delineator to see both the image and pencil with sufficient distinctness to enable him to make an accurate tracing of the former. Much will depend upon the advantageous adjustment of the amount of light upon the object and the paper respectively. In drawing or measuring by lamp-light, we have found it useful to place a small taper near the screen, so that its direct rays may fall upon it, whilst the lamp is used for illuminating the object ; and when the screen is illuminated by daylight it is prefer- able still to use the lamp for the other purpose. The point of the pencil should be blackened. The micrometer eye-piece also may be em- ployed for drawing ; its squares being repre- sented by squares on the paper ; and the por- tion of the object between each beingdelineated, in the manner commonly practised by artists. No assistance of this kind, however, can supply that skill to the microscopic draughtsman which is required for making finished delineations of any object. Accuracy of outline is all that they can ensure. Under this head it seems not inappropriate to introduce a few remarks on the degree of minuteness in the structure of objects, which the magnifying power of the microscope ena- bles us to detect. Much speculation has taken place amongst philosophers at different times, relative to the possibility of detecting the ultimate atoms of material, especially organic, substances ; and microscopists have occasionally hazarded state- ments in regard to their size, which an in- creased knowledge has shown to be invalid. It was a favourite theory about fifteen years since, that all organized bodies are made up of globules, which cannot be resolved into any other kind of structure, the diameter of which was stated at about g^jth of an inch. The great improvements which have been recently made, however, in the microscope, and the general advance of knowledge on the subject of the ultimate constitution of organized struc- tures, have shown the erroneous nature of this view, by proving that there is no body, however MICROSCOPE. 357 minute, which is not capable of being resolved into smaller particles, as far as our means of observation can carry us; and the absurdity of the particular dimensions assumed is further shown by the fact, now well known, that there are very numerous species, and countless indi- viduals, among the Polygastric animalcules, whose whole bulk is much less than that of one of the so-called ultimate particles, and which contain within this a considerable number of different organs. The following statements made some years since by Ehrenberg will give a very good idea of the mode in which the size of such organs and of their component parts may be approximately known, when they are themselves too minute for measurement. "I could plainly distinguish with a micro- scope magnifying nearly 800 diameters, Mo- nads, which were filled with colouring nutritive substances, and which possessed voluntary mo- tions, but the entire and greatest diameter of whose body only amounted to the 1555th or 3555th of a Parisian line. I could perceive in the largest individuals of this form as many as six, and in the smallest as many as four, in- ternal sacs coloured blue by indigo, which at times did not occupy half the internal dimen- sion of the animal. Such a sac, therefore, of an animalcule measuring -j^jth of a line, and if we suppose only four sacs occupying the half of it, (therefore not one of the smallest,) is 15555th of a line in size. Further, if we suppose the single colouring particles, with which the stomachs are filled, not to be nume- rous, it would be against all probability not to think that they were filled by several particles. Let us, however, only suppose each sac to be filled with three colouring atoms, — which, from the roundness made perceptible by the motion communicated to them when diffused through the water, we may well admit, — this alone affords a proof of the existence of material colouring particles of red and dark blue moving freely in water, which measure 35555th of a line, or 335555th part of an inch in diameter; and calculating these objects from the smallest of the animalcules, which by actual observation were found to be 5555th of a line in size, and which sometimes contained four coloured points in the hinder part of the body, these particles, which cannot be distinguished individually by the eye with a magnifying power of 800, but which are yet to be recognized as corporeal, would amount to ^g^th of a line, or 57S55„th of an inch. Further, the smaller monad -stomachs are seen isolated in the body, and with sharp outlines. In larger Infusoria, which are ^th of a line, or more, in diameter, these internal receptacles are recognized as evi- dent membranaceous sacs, which often make their appearance isolated, when the animalcule is pressed, or when it divides itself, and which have been supposed to be separate infusoria, internal monads. It can be distinctly seen that, when two such digestive sacs touch one another, the thickness of the partition between them is, in comparison with the diameter of the stomach, extremely small, so that the former is scarcely perceptible ; it may be reckoned as at the most 35th of the latter, Granting, how- ever, the thickness of the partition to be as much as T'5th the diameter of the sac, this would amount to ^mtb of a line, or 7555555 th of an inch, in monads 5555th of a line in size, in which the stomachs measure but one- eighth of the whole length of the body, and are therefore -,5555th of a line in diameter." When similar views are extended to the young of the species on which this calculation is founded, or to smaller species in the existence of which there is good reason to believe, the minuteness of structure thus disclosed becomes still more wonderful. " Let not these calcu- lations," it is justly remarked by Ehrenberg, " be regarded as playful ; they are so far in earnest, that they are founded on the contem- plation of nature, and are not to be considered as a groundless speculation. They plainly de- monstrate an unfathomableness of organic life in the direction of the smallest conceivable space; and if the word infinity be too much for what we know at present, let the •word unfa- thomableness, which I have purposely em- ployed, avert from me the reproach of exagge- ration, and establish the direction which the physical, chemical, and physiological enquiries of our days, should they be rendered fruitful by new powers, have to take, and what deviations they have to avoid." To these enquiries Ehrenberg has subjoined an attempt to calculate the power of vision for the human eye, and the ultimate power of the microscope. From his experiments on the smallest square magnitudes which are ordina- rily visible at any distance by the human eye, he finds that they vary in different cases from ugth to yigth of a line ; but when strongly il- luminated, much smaller bodies can be seen, metallic particles of ^th of an inch being visible in common daylight ; and non-transpa- rent threads of ^th of a line in thickness being distinguished, when held between the eye and the light. Hence the size of the mi- nutest objects visible with a given magnifying power of the microscope might be determined by dividing their apparent dimensions, as just stated, by the magnifying power; thus no square corpuscles of less dimension than 3So0th or fjggiti of a line could be seen with a magnifying power of 100 diameters. In practice, however, owing to the degree of im- perfection which must necessarily attend the best-constructed instruments, the minuteness of the smallest visible objects cannot be judged of entirely by this rule ; since, in order that it should be correct, it is necessary that the object of ^g'r^th or 3555th of a line in dia- meter, should be represented to the eye as clearly by a microscope magnifying 100 dia- meters, as a real object of ^th or ^th of a line would be; this is very far from being the case, owing to the loss of light by reflection in passing through the lenses, as well as to the errors of the lenses themselves, which can never be perfectly corrected. With a magnifying power of 1000, which is perhaps the highest that has yet been employed to real advantage, the minutest particle which could possibly bo 358 MILK. distinguished would be s^th or 7540th of a line square, and thus they would be much la. •ger than those of whose existence a very simple process of reasoning is sufficient to con- vince us. Bibliography.— The following works may be referred to. — Hooke, Micrographia, Loud. 1665. Baker, Of Microscopes, Lond. 1785 Adams, On the Microscope, Lond. 1787. Brewster, Treatise on the Microscope from Encyclopaedia Britannica, also Treatise on new Philosophical Instruments. On Optics, Lardner's Cyclopaedia. Lister, in Phil, Trans. 1829. Chevalier, Des Microscopes, Par. 1839. Mandl, Traite Pratique du Microscope, Par. 1839. Pritchard and Goring, Micrographia ; also, by the same authors, Microscopic Illustrations and Microscopic Cabinet. Slack, Holland, and Turrell, in Trans. Soc. Arts, vol. 49. Penny Cyclop, art. Microscope. Hildebraudl, Anatomie, Band. i. p. 128. ( W. B. Carpenter.) MILK.— (r**«, Gr.; lac, Lat.; le hit, Fr.; die Milch, Germ.; latte, Ital.) The secretion of the mammary gland. In treating of the milk it will perhaps be best, previous to entering upon its description as produced by the human subject, to give a general account of the secretion as obtained from the cow, such being the most familiar example afforded to us. Milk may be regarded as a serous fluid, hold- ing in suspension minute white globules com- posed of casein and fatty matter. These glo- bules have been microscopically examined by Raspail, who states them to have a diameter of .00039 inch, and to disappear on the addition of a solution of potassa. The most recent microscopic observations on the milk are those of Professor Nasse, of Marburg,* who gives the following as the constituents of the normal secretion of the mammary gland: — 1st, smooth, homogeneous, transparent oil globules and large oil globules, also the common milk globules; 2d, cream globules, distinguishable by their facette-like appearance; 3d, granu- lated yellow corpuscles; 4th, the lamellae of epithelium ; 5th, the more or less turbid medium in which the four preceding kinds of corpuscles are suspended. The common milk globules are composed of fatty matter, which dissolves rapidly in ether. No membrane can be seen investing them. The first nine days after delivery the largest globules measure ^th of a line in diameter, but subse- quently become as large as -r^th, but they vary in size throughout lactation. The cream glo- bules are considered by Professor Nasse to be formed after the milk has been drawn or exposed to the air, for in fresh woman's milk no globules but the common milk globules above described are discernible : the cream globules occur as large as j'jth of a line in dia- meter. The yellow granulated corpuscles are peculiar to the colostrum ; their diameter is from i^th to jigth of a line ; some are found mea- suring J5th of a line in length and ^th in breadth. They are composed of fatty matter. The author considers them analogous to the mucus cells cast off from mucous membranes, and thinks that perhaps they come from the gland ducts. From my own observations I am inclined to * Muller's Archiv, 1840, Heft iii. p. 258. think that the cream globule of Nasse exists even in fresh milk, and may easily be seen in specimens containing but little fatty matter. I lately saw them in the milk of a woman who had suckled for seven months. I have not been able to rid the milk of globules by ether or liq. potassED. If milk be agitated with ether, then allowed to stand, and the lower stratum of fluid examined, we can detect distinct globules in it — globules of all sizes, and having the appearance described by Nasse as belonging to the cream globule. From the variety in size which I have so constantly observed, I cannot understand how any author can have made up his mind to give an admeasurement to the globule of milk; for my own part, after much careful observation, I feel convinced that the milk contains nothing which deserves the name of a true organic globule. That globules exist I do not deny, and these I believe to be what have been described by Nasse as cream glo- bules, appearing when milk has creamed, be- cause the adhering fatty matter is separated ; but, notwithstanding, being very obvious before creaming occurs, in specimens of fresh milk containing a small proportion of fatty matter. The serum in which these particles float is composed of water, holding in solution an alkaline lactate and chloride with traces of sulphate and phosphate, lactates of lime and magnesia, sugar of milk, and animal extractive. Oxide of iron and an earthy phosphate are to be detected in the ashes of milk, but these, in all probability, are derived from the casein of the secretion. When milk is allowed to remain at rest for some hours, a pellicle forms on its surface, varying with the nature of the milk : this is what is called the cream, and consists of the fatty or butyraceous matter of the milk in combination with a varying proportion of casein. It is from this cream that butter is obtained by churning, by which operation the butyraceous particles unite into a mass to the exclusion of the casein, which remains suspended in the serum, and thus forms a mixture known by the name of butter-milk or lait de beurre of the French. The whole of the casein, however, cannot be removed from the butter by churning, its minute particles being entangled by the cohering fatty globules, and it is in a great measure owing to its presence that butter is more or less prone to become rancid and de- composed. Milk from which the cream has been removed still retains the greater part of the casein, and when this is precipitated from it by the action of rennet, we obtain a curd, which, being pressed and dried, constitutes cheese. The clear liquor separated from this curd contains the more soluble matters of milk, viz. the alkaline salts with the sugar of milk, and in Switzerland a considerable quantity of this sugar is manufactured from whey and used for household purposes. I have thought it best to notice the various operations in domestic economy to which the milk is subjected, not only because by them several of its proximate elements are eliminated, but likewise that the reader may have some familiar object with which to connect the following account of the MILK. 359 chemical properties of the constituents of the fluid. The fatty matter of milk obtained by churn- ing cream, and which is known by the name of butter, differs from the other forms of animal fat in several particulars. It yields about 88.5 per cent, of fixed acids on being saponified, for which purpose it requires no more than four- tenths of its weight of caustic potassa ; it there- fore unites with alkali very easily. Of these acids the margaric and oleic are in large propor- tion, the stearic existing as a mere trace. Glyce- rine, as is the case with other fats, is a constant product of the saponification of butter. The great distinguishing peculiarity of this form of fatty matter consists in the production of three volatile acids as results of saponification; these have been carefully examined and distinguished by Chevreul in his admirable work, " Sur les Corps gras." He has named them the butyric, caproic, and capric acids. The production of these acids by the action of alkali has been traced by Chevreul to the existence of a new form of fat which he detected in butter mixed with the stearine and elain, and to which he gave the name of butyrine : thus butter may be regarded as composed of three different kinds of fatty matter — stearine, elain, and butyrine — the two former yielding by saponifi- cation the margaric, oleic, and stearic acids, and the latter the three volatile acids above mentioned. The proportions of the three kinds of fat vary considerably in different specimens of butter. The solubility of butter in alcohol is stated by Chevreul to be 3.46 parls in 100 at a boiling temperature, the specific gravity of the menstruum being 0.822. The stearine obtained from the alcohol by cooling is more crystalline and of a more brilliant white than that obtained from common fat, and 1.45 parts require 100 parts of alcohol of specific gravity 0.822 for its solution. The elain obtained from butter possesses no peculiar characteristics. The butyrine when separated from it, which is only to be accomplished with difficulty, pos- sesses the following qualities : — it is an oil generally of a yellow colour, but some speci- mens of butter yield it perfectly white; it con- cretes at 32° Fahrenheit, and possesses the smell and taste of butter; it mixes with boiling alcohol in ali proportions; it is soluble in anhydrous alcohol. Potassa and the other alkalies are not the only substances capable of producing the volatile acids by acting on buty- rine. Alcohol if long digested produces a similar effect, as does strong sulphuric acid, and if butyrine be allowed to putrify these acids are developed. The casein or cheesy matter of milk which is obtained with some slight admixture of the fatty matter in the production of cheese from the skimmed milk has the following chemical properties. It is soluble in water after long digestion ; but this is most likely owing to some decomposition which occurs in it, and it is certain that casein in its pure, undecom posed, and dry state is quite insoluble in water. Casein, as it exists dissolved in skim milk, is precipitable by the mineral acids and also by the acetic acid. The process which Berzelius recommends in order to obtain this substance is as follows : — Skim milk is to be mixed with a small proportion of dilute sulphuric acid, which unites with the casein and precipitates it in the form of a white clot. This is to be well washed with distilled water on a filter in order to separate the whey which it contains. After this carbonate of baryta and water are to be mixed up with the mass, by which means the acid is separated and the casein remains dissolved in the water, and may be separated from the carbonate and sulphate of baryta by filtration. Casein obtained by this process is more or less soluble in water, and is precipi- tated from its aqueous solution by the acids. It rapidly undergoes the putrefactive fer- mentation. It is soluble in the alkalies and in alcohol both boiling and cold, but far more so in the former, from which it rapidly deposits on cooling. Casein, when dissolved by the assistance of the acids, is precipitated by the ferro-cyanide of potassium. It is distinguished from albumen, with which it possesses many physical and chemical properties in common, by being precipitated from solution on the ad- dition of acetic acid, and the precipitate so formed being with difficulty soluble in an excess of the precipitant. It must not be imagined, however, that albumen under all circumstances cannot be precipitated from so- lution by the addition of acetic acid, for when dissolved in an alkaline solution, that proxi- mate principle is immediately thrown down on the addition of the acid. Casein, like albu- men, always contains some sulphur as a neces- sary element in its composition ; the presence of this body may be easily shown by boiling casein in a concentrated solution of potassa, when the liquor rapidly assumes a brown colour, and gives out ammonia, an alkaline hydro-sulphuret remaining dissolved, which may be proved by the solution becoming of a deep black colour on the addition of a salt of lead. The aqueous solution of casein is pre- cipitated by all the earthy and metallic salts which precipitate albumen in the dissolved state. Tannin precipitates it even from its solution in alcohol, notwithstanding that men- struum protects it from the precipitating action of the acids. The ultimate analysis of casein is, according to Thenard and Gay Lussac, carbon 59.781, nitrogen 21.381, hydrogen 7.429, and oxygen 11.409. Caseous matter, as precipitated by rennet in making cheese, is liable to a peculiar kind of putrefaction, which has been investigated by Proust and Braconnot; the latter obtained as a product of putrefaction a peculiar crystalline substance, to which he gave the name of aposepedine, from utto and o-r)iri$ui>, indicative of its origin. Proust had before noticed this substance and called it caseous oxide. It may be prepared very easily by allowing cheese to putrify under water and evaporating the solution so obtained to dry- ness ; the dried mass is then to be treated with alcohol until that menstruum exerts no further solvent action ; the portion insoluble in alcohol, on being dissolved in water, and digested with 360 MILK. animal charcoal, yields us by filtration and evaporation pure crystals of aposepedine. This substance has the following properties : it is somewhat bitter to the taste, very slightly so- luble in alcohol, soluble in water, and of greater specific gravity than that fluid. It sub- limes when heated strongly, but always un- dergoes a partial decomposition. It contains sulphur. In addition to aposepedine, cheese when decomposing has been found to contain acetic acid, acetates of ammonia and potassa, chloride of potassium, ammoniaco-phosphate of soda, margarate and phosphate of lime, and a peculiar extractive matter. I shall now proceed to consider the sugar of milk which is left in the whey after the sepa- ration of the cheese by rennet, and exists in solution with the salts of the milk, lactic acid, and animal extractive matter. Sugar of milk may be obtained from whey by evaporating it to the consistence of a syrup, and setting it aside for a length of time, when small granular crystals of the principle are observed to deposit. The following are the principal qualities of sugar of milk. It has a sweetish taste, the grains crushing with dif- ficulty between the teeth ; its specific gravity is 1.543. It contains about 12 per cent, of water, which may be separated by carefully fusing it ; when fused it is still quite white if the heat be not too strongly urged. It is solu- ble with difficulty in water, requiring three parts of boiling water and six of cold for that purpose. It is very slightly soluble in alcohol, and quite insoluble in ether. When acted on by concentrated nitric acid it becomes trans- formed into a mixture of oxalic, malic, and muric acids. By the action of caustic potassa it is changed to a brown-coloured bitter mass, which is insoluble in alcohol. Sugar of milk has been stated to be in- capable of undergoing the alcoholic fermen- tation; but late experiments by Hess (Poggen- dorff, Annalen der Physick) shew that such will occur, and an intoxicating liquor has been long known among the Tartars, which is pre- pared from the milk of the mare, and to which they give the name of Koumiss. Sugar of milk has been analysed byBerzelius: including its 12 per cent, of water, its composition is as follows : Carbon.... 40.125 or 1 atom, Hydrogen.. 6.762 or 2 atoms, Oxygen.... 53.113 or 1 atom: or deducting the 12 per cent, of water, Carbon .... 45.94 or 5 atoms, Hydrogen . . 6 00 or 8 atoms, Oxygen. . . . 48.06 or 4 atoms. It will be observed, on comparing the ana- lysis of hydrous sugar of milk with that of starch, that they accord very nearly, and sugar of milk is convertible, as is the case with starch, into true sugar, by the action of sulphuric acid ; these facts strongly point out the curious ap- proach to vegetable matter which is made by this constituent of an animal secretion. After the crystallization of the sugar of milk from the whey, we have left in solution, accord- ing to the experiments of Berzelius, lactic acid and lactates, chloride of potassium, an alkaline phosphate, phosphates of lime and magnesia, and traces of oxide of iron. I shall not here enter upon the question whether or not lactic acid be the peculiar acid of milk, or whether the substance receiving that name be only a modification of the acetic ; the matter is to be found noticed at length in the 7th volume of the French edition of Ber- zelius' Chemistry. For my own part I can only wish that one quarter of the animal acids mentioned in our modern chemical works had the same right to be distinguished as peculiar animal principles. Mons. Lassaigne, in his work bearing date 1836, when speaking of lactic acid, says," regarde pendant long temps comme de l'acide acetique modifie par une matiere organique, M. Berzelius a etabli d'une maniere incontestable sa veritable nature." Anhydrous lactic acid has the following ulti- mate composition. Carbon 50.50 Hydrogen 3.60 Oxygen 43.90 Berzelius' analysis of skimmed cow's milk is as follows : Caseous matter with some butter 2.600 Sugar of milk 3.500 Extractive, lactic acid, and lactates 0.600 Chloride of potassium 0.170 Alkaline phosphate 0.025 Earthy phosphates, trace of oxide of iron 0.220 Water 92.875 The cream from this milk yielded the follow- ing result : Butter 4.5 Caseous matter 3.5 Whey 92.0 The specific gravity of this milk was 1.0348, and that of the cream 1.0244. A specimen of cow's milk which I lately examined was of sp. grav. 1.0338, and its solid contents 121.85 in 1000 parts. The ashes of cow's milk, according to Pfaff and Schwartz, are composed of phosphates of lime, magnesia, and iron, phosphate of soda, chloride of potassium, and soda, which, before incineration, had existed in combination with lactic acid. They found 1000 parts of the milk yielded 3.742 parts of ash. According to the experiments of Van Stip- trian, Luiscius, and Bondt, the proportion of cream which separates from cow's milk is about 4 per cent, of its weight. They ob- tained from milk 2.68 per cent, of butter, 8.95 of casein, and 3.60 per cent, of sugar of milk. The first milk which is observed in the breast after parturition has received the name of colos- trum ; it differs somewhat from ordinary milk. It has been stated by some authorities that scarcely any cream can be obtained from the colostrum, and that no butter can be obtained by churning. According to Stiptrian, Luiscius, and Bondt, however, the colostrum from the cow yields 11.7 per cent, of cream, 3 of butter, and 18.75 of cheese. They state the specific gravity of the colostrum at 1.072 ; dried and in- cinerated it yielded 5J per cent, of ash. They MILK. 361 do not mention sugar of milk as a constituent, and in this respect agree with MM. Chevallier and Henry, who do not mention it in their analysis of the colostrum of the cow. Donne has observed a microscopic difference between the globules of the colostrum and those of milk. He states the colostrum globule to be made up of small granules united together, or enclosed in a transparent envelope. They dis- appear in ether, and when the fluid is evapora- ted, small tufts of acicular crystals are observed. Donne traced these globules in milk secreted twenty days after parturition. M. Giiterbock has also observed these compound globules, and says he could detect the transparent membrane after the ether had dissolved the enclosed granules. M. Mandl has not been able to detect these compound globules, and believes them to be made up of agglomerated milk glo- bules. The following is the result of a com- parative analysis of colostrum and true milk by F. Simon. Colostrum. Common milk. Casein .... 4 per cent. 3.5 per cent. Sugar 7 „ 4.7 „ Butter 5 „ 2.3 ,, I shall now proceed to the consideration of the milk of the human subject, which differs in some respects from that obtained from the cow; its general characters are, however, iden- tical. One of the principal differences to be observed consists in the caseous matter of human milk not being so universally preci- pitable by acids as that which exists in the secretion from the cow. Meggenhofen found but three out of fifteen specimens which he examined that could be precipitated by the hy- drochloric or acetic acids. Three specimens of human milk examined by myself were found not to be precipitable either by the muriatic, nitric, or sulphuric acids. Although human milk resists the coagulating power of the acids, it is, notwithstanding, easily precipitable by rennet; but the curd so formed is some time in collecting, owing to the minute size of the pre- cipitating flocculi ; thus there appears both a physical and chemical difference between the caseous matter from the human subject and that from the cow. The casein of human milk being incapable of forming insoluble combina- tions with the mineral acids, may be regarded as bearing chemically the same relation to the casein of cow's milk that the albuminous matter of the chyle bears to that principle as it exists in the blood. The butyraceous matter of hu- man milk has been stated by some chemists to be too liquid to admit of the formation of butter by churning; this, however, has been proved incorrect by the experiments ofPleischl, who succeeded in obtaining butter from the cream of human milk, which was similar in appearance to that from cow's milk, and expe- riments into the nature of this form of butter have been made by Meggenhofen, who considers it as identical with that obtained from the cow. The specific gravity of human milk has been stated so low as from 1.020 to 1.025, but this is certainly far too low ;.for out of six specimens which I examined the specific gravities varied between 1.030 and 1.035. The proportion of solid matter contained in milk is, according to Meggenhofen, 11 to 12.5 per cent, and some- times more. I have had occasion to verify this result, having obtained 64.15 of solid matter from 500 grains of milk. The specific gravity of this specimen was, however, as high as 1.0358. Human milk when fresh is either neutral or slightly alkaline. Its analysis, according to Meggenhofen, is as follows, being the results obtained from milk from three different sub- jects. No. 1. Alcoholic extractive, but- ter, lactic acid and lac- tates, chloride of sodi- um, traces of sugar of milk 9.13.. 8.81.. 17.12 Aqueous extractive, sugar of milk, and salts 1.14.. 1.29.. 0.88 Caseous matter (coagula- ted by rennet) 2.41 . . 1.47. . 2.88 Water 87.25. .88.35. .78.93 The specific gravity of the milk appears to increase as the woman continues suckling, this increase ceasing at some period which is as yet undetermined. Milk at three days after partu- rition I found of specific gravity 1.0310, at four days 1.0334, and at six weeks 1.0358. Payen has analysed three specimens of human milk with the following results : — Butter 5.18.. 5.16. . 5.20 Caseous matter 0.24.. 0.18.. 0.25 Residue of evaporated whey (containing the extractives, salts, and sugar of milk) 7.86.. 7.62.. 7.93 Water 85.80. .86.00. .85.50 Berzelius remarks upon these analysis, and says that a considerable portion of caseous matter remained in all probability in the whey, and was estimated in the residue obtained by evaporation. According to Meggenhofen the salts contained in milk amounted to from 0.5 to 1.25 parts in 500 of the secretion. In an experiment made by myself, 500 grains of milk yielded 1.20 grains of salts. Pfaff and Schwartz obtained 4.407 parts of ash from 1000 of milk, which they found to be composed as follows : — Phosphate of lime 2.500 Phosphate of magnesia 0.500 Phosphate of iron 0.007 Phosphate of soda 0.400 Chloride of potassium 0.700 Soda from decomposed lactate 0.300 4.407 Berzelius very naturally expresses surprise that no carbonate of lime, chloride of sodium, or alkaline sulphate, is mentioned in this ana- lysis, since casein always yields the earthy salt, and chloride of sodium is constantly present in animal matters which are intended for the nou- rishment of man. The absence of alkaline sulphate is quite inexplicable, as it is always a 362 MILK. product of the combustion of animal substances containing an albuminous or caseous consti- tuent. The proportion of cream contained in milk from the human subject has been deter- mined by Sir Astley Cooper at from one-fifth to one-third by measure, varying with the health, the food, the habits, and state of mind of the mother. The colostrum or first milk which is observed in the human breasts has been examined by Meggenhofen. He states that it contains more saline matter than the after milk, and describes it as having the ap- pearance of a weak solution of soap containing oleaginous particles. It is very prone to be- come sour and decompose, and becomes viscid by exposure to the air, hence its name from KoAAtiju-at, to agglutinate. Several instances are on record of the exis- tence of milk .in the male breasts, and the ana- lysis of a specimen lately published by Mayer in Schmidt's Jahrbucher, July 1837, is as fol- lows : — Fatty matter 1.234 Alcoholic extractive .... 3.583 Watery extractive 1.500 Insoluble matters 1.183 Total solid contents .... 7.500 in 100 parts of the fluid. It was slightly alkaline. The following were the physical properties of this milk: when left at rest it quickly coagulated, and cream soon sepa- rated ; after some hours butyraceous globules collected on the surface. Its specific gravity was 1024. Milk from several of the herbivorous Mam- malia has been examined by Stiptrian, Luiscius, and Bondt, with the following results : — The milk of the ass has a specific gravity of 1.023 to 1.0355; it yields a white and light butter which is very apt to become rancid. The caseous matter does not separate so easily as in cow's milk ; the whey, however, can be obtained very clear, and is found to contain more sugar of milk than that from the cow. An analysis yielded the following result : Cream 2.9 per cent. Casein 2.3 „ Sugar of milk .... 4.5 „ The milk of the mare has a specific gravity of 1.0346 to 1.015; it yields but little cream, but contains a very large proportion of sugar; the analysis gave : 0.8 per cent, of cream, 1.61 „ caseous matter, and 8.75 „ of sugar of milk. The milk of the mare, as also that obtained from the ass, very rapidly commences the alco- holic fermentation, an effect which cannot be produced but with the greatest difficulty in cow's milk. Goat's milk has a specific gravity of 1.036 ; it possesses a very disagreeable odour of the animal, and the more strongly so if the goat be dark-coloured ; it yields a large quantity of cream and butter; the latter contains, in addi- tion to the usual acids of butter, a peculiar acid to which the name of hircic acid has been given ; it is to this principle that goat's milk owes its peculiar unpleasant odour. This milk contains also a large quantity of caseous matter of a firm dense character. Payen found goat's milk composed as follows : Butter 4.08 Casein 4.52 Sugar, salts, and extractives . . 5.86 Water 85.50 Stiptrian, Luiscius, and Bondt procured 7.5 per cent, of cream, 4.56 of butter, 9.12 casein, and 4.38 per cent, of sugar from the milk of a goat. The milk of the sheep has a specific gravity of 1.035 to 1.041; it yields a larger propor- tion of cream : the butter is semifluid and pale yellow in colour ; it putrifies very easily. This milk yields 11.5 per cent, of cream, 5.8 of butter, 15.3 of caseous matter, and 4.2 per cent, of sugar of milk. The milk of the bitch and also of the por- poise have been lately examined by Dr. Bird ; the former contained 15.8 per cent, of casein, and 7.2 of butter mixed with some sugar of milk. That from the porpoise contained 23.00 per cent, of oily matter, and a volatile ingre- dient supposed to be phocenic acid. The spe- cific gravity of bitch's milk is stated at 1.024. The milk is very prone to become contami- nated by various ingesta ; that of the cow is frequently impregnated by the odours derived from particular pasturage, and if saffron or in- digo be mixed with their diet the milk has been observed to assume more or less the colour of those pigments. Chevallier, Henry, and Peligot made expe- riments on the milk of asses to whom several different substances had been exhibited ; they were enabled to detect the oxides of iron and zinc, the trisnitrate of bismuth, common salt, and sesquicarbonate of soda with great ease ; sulphate of soda required to be administered in very large doses before it could be detected in the milk, and sulphate of quinine could not be discovered, though large quantities were intro- duced into the stomach. These gentlemen state likewise that the iodide of potassium cannot be detected in the milk unless exhibited in doses of upwards of a drachm. This rule, however, cannot apply to the human subject, as I lately very readily detected it in the milk of two of my patients, one of whom had taken only 45 grains of the iodide in divided doses of 5 grains each, administered three times a day for three days; and the other 105 grains in 21 doses of 5 grains each, administered in like manner. It is probable that many substances enter the milk which the present state of che- mistry does not admit of our detecting, and every practitioner is aware of the danger in- curred to the child by exhibiting any active medicine to the mother during the period of lactation. There is perhaps no animal secretion which bears so strongly-marked an analogy with the blood as the milk, and which promises us so fair a prospect of discovery in the mysteries of secretion, and we cannot but hope that as animal chemistry advances we may be able to imitate those changes which occur in the minute MOLLUSCA. 363 parts of the mammary gland, where, though each constituent of the blood be changed in its character to form milk, yet each constituent of that secretion retains an obvious type in the fluid from which it was eliminated ; thus if we compare the blood and this secretion side by Blood separating into side, we remark not only identical physical changes to occur, but also the existence of a set of proximate elements, which, though pioper to each, still possess many chemical qualities in common ; for instance — Milk separating into Clot and { Fibrin ) Red particles ("Albumen I Alcoholic extractive, viz. lactates Serum Aqueous extractive; albu- minate of soda Alkaline salts _Fatty matter The similarity of reaction between fibrin, albumen, and casein is well known to chemists, and the derivation of the latter from the former can scarcely admit of a doubt ; the only dif- ference acknowledged between fibrin and albu- men is a physical one, and it would be exceed- ingly interesting to ascertain whether or not the casein, which, like fibrin, separates on stand- ing, be not physically different from that por- tion of casein which remains in the fluid after the milk has creamed. The red particles of the blood certainly bear no analogy whatever to the butyraceous matter of milk in its perfectly formed state ; it is a curious fact, however, noticed by Sir Astley Cooper, that the colos- trum at its first appearance is occasionally of a red colour, and the cream which separates is of a still deeper red tinge, thus rendering it probable that the fatty matters are in this in- stance the colouring ingredient. I may men- tion, in addition, that it is not easy to obtain hrematosine quite free from fatty matter; there appears to exist a natural affinity between them. The alcoholic extractives of blood and milk are too obviously analogous to need comment, as are the salts and likewise the fatty matters adherent to the casein of the milk and the albumen of the serum. The sugar of milk appears in all probability derived from the aqueous extractive of the blood, an ingredient which has scarcely attracted sufficient attention, and the development of whose chemical rela- tions may perhaps assist us greatly in obtaining a further insight into the true nature of those changes which are effected in the minute struc- ture of secreting glands. I have thought it right to mention the above resemblance, as I cannot help thinking that we may be greatly assisted hereafter in the physiology of secretion by attempting to reduce each proximate ele- ment of a secerned fluid to some type in the blood, and afterwards endeavouring artificially to produce those substances from their ana- logues in the circulating fluid; as nature may perhaps in this way form them for the various secretions, by the so-called chemistry of vita- lity. Physiologists and chemists are, in the present day, too prone to attribute the forma- tion of those substances contained in secretions, Cream and Milk or skim milk Casein ) Butyraceous matter ) Casein Alcoholic extractive, viz. lactates and lactic acid Aqueous extractive, with f sugar of milk Alkaline salts Fatty matter and which cannot be detected in the blood, to changes occurring among the ultimate ele- ments of organic matter, changes of a character too intimate and obscure ever to be induced by those reagents which non-vital chemistry applies in effecting transformations. Such a conclusion is founded on the assumption that organic chemistry is not to make that progress which we now see in almost every branch of inquiry, a progress marked by the develop- ment of new laws which not only become valuable as indicators for the ascertainment of new facts, but which have a retrospective in- fluence on science, rearranging and altering the bearings and relations of previously ascertained phenomena. (G. O. Rees.) MOLLUSCA, (Lat. mollis,) Malakia and Ostracoderma of Aristotle ; Mollusqites, Fr. ; Weichthicre, Mollusken, Germ.; Mollusks, Engl.; invertebrated animals, distinguished by Bruguiere from insects by the negative cha- racters of the absence of bones, of stigmata, and of jointed feet; and first accurately de- fined by Cuvier as a primary division of the animal kingdom, with the following anatomical characters. The Mollusks are animals without an articulated skeleton or a vertebral column. Their nervous system is not concentrated in a spinal marrow, but merely in a certain number of medullary masses dispersed in different points of the body, the chief of which, termed the brain, is situated transversely above the oesophagus, and encompasses it with a nervous collar. Their organs of motion and of the sensations have not the same uniformity as to number and position as in the Vertebrata, and the irregularity is still more striking in the viscera, particularly as respects the position of the heart and respiratory organs, and even as regards the structure of the latter : for some of these respire elastic air, and others water, either fresh or of the sea. Their external organs, however, and those of locomotion are generally arranged symmetrically on the two sides of an axis. The circulation of the Mol- lusks is always double; that is, their pulmo- nary circulation describes a separate and dis- tinct circle. The blood of the Mollusks is white 364 MOLLUSCA. or bluish, and it appears to contain a smaller proportionate quantity of fibrine than that of the Vertebrata. The veins probably fulfil the functions of absorbent vessels. Their muscles are attached to various points of their skin, forming more or less dense and complex tis- sues. Their motions consist of various con- tractions, which produce inflections and pro- longations of their different parts, or a relax- ation of the same, by means of which they creep, swim, and seize upon various objects, just as the form of these parts may permit, but as the limbs are not supported by articu- lated and solid levers they cannot advance rapidly. Nearly all Mollusks have the body enveloped by a duplicature of soft and usually muscular integument, which bears more or less resemblance to a mantle: it is sometimes nar- rowed into a simple disc, sometimes prolonged into one or more tubes, or is extended and divided in the form of fins. The JSaked Mollusks are those in which the mantle is simply membranous or fleshy. In most of the species one or more plates, of a substance more or less hard, are developed in its substance, usually in successive layers, which increase in extent as well as in thick- ness as they are successively formed. When this substance remains concealed in the thick- ness of the mantle, it is still customary to style the animals ' Naked Mollusks.' Most com- monly, however, it becomes so much deve- loped that the contracted animal finds shelter beneath or within it, and it is then termed a shell, and the animal is called a Testaceous Mollusk. The mode of generation is too varied in the Mollusks to afford any common character to this sub-kingdom : but, being for the most part sluggish and feeble animals, with low and little varied instincts, they are preserved chiefly by their fecundity and vital tenacity. The nervous system of the Mollusks may consist of one or more ganglionic masses ; but these are scattered, often irregularly or unsym- metrically, through the body, and the inter- communicating chords never form a symme- trical knotted pair along the middle line of the ventral surface of the body ; whence the term ' Heterogangliata,' expressive of the charac- teristic condition of the nervous system, with which the unshapely and often unsymmetrical figure of the whole body corresponds. The number of the ganglia follows closely the progressive development of the muscular system : the first is that which is found between the anal and respiratory tubes of the Ascidix, and which regulates the elongator and sphincter muscles of these tubes. The development of a muscular heart and of a bivalve shell with its adductor muscle is accompanied with the appearance of a second ganglion or centre of the nerves which supply that muscle: a second adductor muscle, with the superaddition of a muscular foot and its retractors, produces an additional ganglion or ganglions, and the com- plication of the nervous system is further aug- mented when the breathing and anal siphons are unusually prolonged, and provided with strongly developed annular contractile muscles and with proportionately powerful retractors. The progressive development of the nervous system may be traced thus far in the tunicated and bivalve Mollusca without its reaching the stage which is marked by the appearance of a distinct supra-oesophageal ganglion or brain ; the species have, in fact, no distinct head, and are termed Acephalous Mollusks. The first appearance of this important part with its appendages, which are usually subservient to the organs of special sense, is associated with an accumulation of nervous matter, in the form of a transverse chord, with a ganglion or gang- lions, above the commencement of the oeso- phagus, forming the brain; whence these Mol- lusks are termed ' Encephalous.' The development of the brain proceeds directly as the organs of the senses increase in number and complication, and consequently reaches its maximum in the higher Cephalo- pods with highly complex eyes and distinct organs of hearing; and in these the brain is protected by a cartilaginous cranium, forming the first representative of the true internal skeleton which is met with in the Invertebrate division of animals, and one of the main organic characters by which the higher Mol- lusks surpass Articulates in the ascent to the Vertebrate type. The nervous system of the Mollusks is re- markable for the peculiar and distinct colour of the ganglions in certain species, as the fresh- water Muscles and Unios ; and for the contrast between the density of the cellular sheath of the nerves and the semifluid pulp which it contains. This structure allows of an artificial injection of the nerves, which has led some anatomists to describe them as parts of an absorbent system. Although the bivalve Mollusks are headless and without brain, some of them have mani- fested signs of a perception of light, and in a few species simple ocelli have been detected on the verge of the mantle. In the Encephalous Mollusks the eyes, when present, are small, never exceed two in number, and are usually supported on flexible peduncles or tentacula; but in the Dibran- chiate Cephalopods they are large, always ses- sile, and highly complicated. The organ of hearing is peculiar to the Ce- phalopods in the present division of the animal kingdom. The organ of smell, as a special and cir- cumscribed part, has likewise been recognized only in the highest class : but Cuvier observes, that the skin of the Mollusks so clearly re- sembles in its softness and lubricity a pituitary membrane, that they probably may recognize odours at every point of their external surface. Professor De Blainville conjectures that in the Gastropods the soft extremities of the first pair of cephalic tentacles may be the seat of the organ of smell. An organ of taste has of course been recognized only in the Encephalous Mollusks, in many of which the tongue is large MOLLUSCA. 365 and complex, and in the Cephalopods is evi- dently provided with gustatory papillae. The sense of touch is in this as in other groups of animals the most generally possessed and the most widely diffused over the body. The mar- ginal fringe of tentacles on the mantle of most Bivalves ; the branched processes of the skin in certain Pteropods and Gastropods ; the ce- phalic tentacles or ' horns,' as they are termed, in the Snail and allied Mollusks; the rich and varied apparatus of cephalic and labial ten- tacles— nearly one hundred in number — in the Nautilus ; and the extremities of the acetabuli- ferous arms of the higher Cephalopods, may all be regarded as organs of delicate sensa- tion : the same opinion may reasonably be entertained of the highly vascular surface of the ventral locomotive disc or ' foot' in the Slug, Snail, and other Gastropods. The voluntary muscular fibre of the Mollus- cous animals is distinguished from that of the Articulate and Vertebrate animals by the ab- sence of the transverse striae, and in most of the Acephalous Mollusks it is antagonized by a merely elastic gelatinous fibre. In the Tuni- caries the flexible outer coat obeys and opposes the change of form which the inner muscular envelope occasions. In the Bivalves, whose shell affords firm levers of attachment to the muscles, the antagonizing elastic force is im- planted at the hinge of the shell ; and some of the species ( Mollusca subsilentia of Poli) can, by virtue of this mechanism of solid lever with its attached muscular and elastic fibre, execute short leaps. The Encephalous Mollusks with a cerebral centre of nervous influence antagonize one series of muscles by the regulated action of another series, and are no longer dependent on mere elastic fibres for their movements. The musculo-cutaneous mantle is produced in the form of fins in the Pteropods, Iieteropods, and some Cephalopods ; or there is an accumula- tion of longitudinal fibres, intersected by ob- lique or transverse ones on the ventral surface of the mantle, producing the thick contractile disc, which is termed the foot. This some- times extends the whole length of the body, as in the Gastropods, sometimes is developed only from the region of the neck, as in the Trache- lipods. The attachment of the body to the shell in these Mollusks, the presence of, and power of retracting and elongating, a siphon or breath- ing tube, the movements of the head and its appendages, especially when these are deve- loped into instruments of progressive motion and prehension, as in the Cephalopods, are the chief conditions of the progressive advance- ment and complication of the muscular system in the Molluscous sub-kingdom. The heterogangliate type of the nervous sys- tem, with the correspondingly low condition of the muscular and other organs of relation, which, commencing in the Ciliobrachiate Po- lypes, is established in the Mollusks, is on the whole very inferior to the conditions and powers of the sensitive and motive systems in the Arti- culates : but, on the other hand, " the organs of growth and reproduction become more evolved ; and in the Mollusca we are presented with a perfecting of the internal organs, which is to prepare for and to be more fully deve- loped in the higher animals."* The alimentary canal is provided with a se- parate mouth and vent : the stomach may be distinguished from the oesophagus and intes- tine, and a liver is present in all the Mollusks, and is remarkable in most for its large size and complicated lobular form. The bile is secreted from arterial blood. The mouth in the Ace- phalous Mollusks is generally concealed in the interior of the pallia! cavity, but is always si- tuated at the anterior part of the body, or that which is opposite to the excrementory and re- spiratory tubes or orifices. There are neither jaws nor salivary glands in this division. Among the Encephala, however, in which the mouth is armed with horny plates representing in diffe- rent species the knife, the saw, the rasp, or the scissors, the salivary system attains an extraordi- nary degree of development, especially in the Cephalopods, in which the mandibles resemble those of the Raptorial bird, and sometimes have their margins armed with a calcareous dentated plate. In the Cephalopods the pancreas makes its first appearance. The special forms of the progressive complications of the digestive sys- tem in the present division of animals will be found amply illustated in the articles Tuni- CATA, CoNCHIFERA, PtEUOPODA, GaSTKO- poda, Cephalopoda. The circulating system, which, as has been stated, is complete and double in all the Mollusks, is provided in all the species with a systemic heart, and in the highest organized species with a distinct heart for the lesser or branchial circulation. The systemic heart first appears in the sessile Tunicaries as a vasiform undivided ventricle, which, however, is in- closed in a distinct pericardium. It is concen- trated into a more compact muscular organ in the Conch ifers, and divided into a venous and arterial chamber ; but the auricle, and some- times also the ventricle, as in Area, is sub- divided and segregated, according to the law of self-repetition, which is exemplified in all the systems of organs at their first appearance in the animal kingdom. The heart of the Gastropods exhibits the higher type of a single auricle and ventricle, both placed at the termi- nation of the lesser and the commencement of the greater circulation. In the highest Cepha- lopods the course of the blood is accelerated in both circulations by a muscular ventricle, but the superadded analogue of the pulmonic heart here, likewise, at its first appearance illustrates, by its separation into two distinct ventricles, the law above alluded to in reference to the systemic heart of the lower Mollusks. The respiratory organ is distinctly developed in all Mollusks, and is subject to the greatest variety of forms in this division of the animal kingdom; yet, with the exception of the small sessile order of Ascidians at the lowest extreme, * See the eloquent and philosophic ' Recapitu- lary Lecture' of Prof. Gieen, Vital Dynamics, 8vo. 1840. 366 MONOTREMATA. connecting the Mollusks with the Zoophytes, it affords perhaps the best positive character of this great primary group of the animal king- dom; for whereas, in the Articulate division, the breathing organs are lateral or open upon or towards the sides of the body, and in the Vertebrate division communicate with the oral extremity of the nutritive canal, in the Mollusca they are connected with the anal outlet. The uropoietic system, where traces of it are recognizable, as in most Gastropods and in Cephalopods, likewise communicates with the respiratory cavity. The rich endowment of vibratile cilia de- serves to be noticed as characterizing the. bran- chial organs, and constituting the chief mecha- nism of respiration in most Mollusca. The organs of vegetative life subservient to the pro- creation of the species are not less remarkable for bulk, variety, and complexity than are those which minister to the preservation and growth of the individual. Although comparatively simple and reduced to the essential formative organs in the Acephala, they are, with very few exceptions, placed in distinct individuals, that is to say, one Ascidian or Oyster possesses only the testicle, and is a male ; another only the ovarium, and is a female. In the order Conchifera, the females have the gills modified to serve as a receptacle for the impregnated ova during foetal development. Among the Encephalous Mollusks are many hermaphroditical species, some with the male and female organs terminating sufficiently close together for independent or self-impregnation; others having the outlets of the two organs remote, and requiring the concourse of another individual in reciprocal fecundation ; or the same individual is impregnated by another and impregnates a third, as is curiously exempli- fied in the nuptial chain thus formed by nu- merous individuals of the Marsh-snails ( Lym- ntza). The Trachelipods and Cephalopods are again dioecious, like the lowest classes of Mollusks, but exhibit the generative organs under the highest stage of complication; and some of the latter class are remarkable for the expulsion not only of the ova aggregated in groups contained in special receptacles, but also of the spermatozoa in a similar state of aggregation in cylindrical cases, which, by the arrangement of their elastic tissue, manifest movements, prior to their rupture, which have long excited the surprise and admiration of the physiological observer. A large vitellus, among the numerous nucle- ated cells of which it is often difficult to recog- nize a single one as the centre of development, or as the germinal vesicle, characterizes the ovum of most Mollusks. In most species also the early formation of vibratile cilia on the surface of the germinal membrane, and the rotation of the embryo upon its axis produced by their action, are striking thoughnot peculiar phenomena. The adherence to a uniform type in the earlier pe- riods of growth is singularly manifested in the young of Tritonia, Doris, Aplysia, and other naked Mollusks, which are protected for a cer- tain period by an external spiral univalve shell. The classification of the Molluscous animals has exercised the judgment and discrimination of some of the ablest Zoologists, and is a sub- ject too expanded for the limits assigned to the present article. The principles of a natural distribution into the larger groups according to general organization seem to be adhered to in the following system. Taking the nervous system as a guide to the divisions of highest value and extent, the Mollusca separate themselves, as already shown, into Acephala and Encephala. The Acephala may be divided according to the nature of their external covering into Tu- nicata, where this is continuous, flexible, and elastic; and into Conchifera, where it is tes- taceous and divided into two or more valves. The Conchifera may be subdivided according to the modifications of the respiratory organs into Palliobranchians and Lamellibranchians. Respiratory characters likewise mainly distin- guish the sessile Tunicaries or Ascidians, and the floating Tunicaries, or Salpaceans. The Encephalous Mollusks are classified ac- cording to their organs of locomotion, as Pte- ropods, Gastropods, and Cethalopods. The respiratory organs afford the best charac- ters for the subdivisions or orders of these three classes. (Richard Owen.) MONOTREMATA, Gr.^o»o?,sj'wg/e,T§t!/*a, hole, in reference to the single cloacal excre- mentory and generative outlet ; Fr. Mono- tremes ; Ger. Monotremen ; Eng. Monolremes. An order or primary group of the Implacental subclass of Mammalia, representing the Eden- tata in that subclass; allied to the Marsupialia by the absence of the corpus callosum and by the presence of the marsupial bones, but differ- ing in the absence of the abdominal pouch and scrotum, in the absence of teeth, in the sim- plicity of the bigeminal bodies, and in some remarkable modifications of the skeleton and generative organs. As the order Bruta or Edentata is that which exhibits the lowest modifications of the Pla- cental type of the Mammalian structure, and offers in some respects the nearest approach in that subclass to the Ovipara, so the Monotre- mata present the extreme modifications of the Implacental type, and make the last step in the transition from the Mammalian to the Oviparous classes. The Monotremes are, however, true Mam- malia in all essential points of structure : they possess functional mammary glands, which are largely developed at the breeding season : their lungs consist of a spongy tissue, sub- divided throughout into very minute cells; they are suspended freely in a thoracic cavity, separated by a complete muscular and aponeu- rotic diaphragm from the abdomen : the arch of the aorta bends over the left bronchus : the larynx is superior, and is defended by a well- developed epiglottis : the kidneys are compact conglobate glands with distinct cortical and medullary substances, secreting the urine from arterial blood, and returning the blood to the MONOTREMATA. 367 cava by a single large vein. The lower jaw articulates with the base of the zygomatic, and not with the tympanic element of the temporal bone, and tbe cranium articulates by two dis- tinct condyles with the atlas. The quadrupeds which combine these essen- tial mammalian characters with the oviparous modifications above-mentioned are peculiar to Australia and Van Dieman's Land ; they form three well-marked species, referable to two distinct genera. One of these genera, called Echidna by Cuvier, is characterized by an elongated slender muzzle, terminated by a small mouth, and containing a long and exten- sible tongue like that of the Ant-eaters. The jaws are edentulous, but the palate is provided with many rows of small, sharp, hard, epidermal spines, which are directed backwards, and the base of the tongue is similarly armed. The feet are short, but remarkably broad and strong, and are each provided with five very long and strong claws. The upper part and sides of the body ate defended by spines similar to but larger than those of the hedge-hog. The tail is very short. The genus Echidna contains two species, one ( Ech. hystrix ) characterized by a more complete armour of spines, with a scantier admixture of darker coloured hair; the other C Ech. setosa ), by being clothed with a greater proportion of lighter coloured hair, which half conceals the spines. These characters are constant in both sexes, and as well marked in the mature as in the young individuals. Both species of Echidna are terrestrial and fossorial ; they feed almost exclusively on ants, and abound in certain districts of both Australia and Tasmania, playing there the same part in the economy of Nature which is assigned to the Pangolins ( Munis ) in Asia and Africa, and to the Ant-eaters ( Myrmecophaga) in South America. The Ornithorhynchus — the second genus of the Monotrematous order — is an aquatic Insec- tivore,* but combines water-snails, worms, and other small Invertebrata with the insects that constitute the staple article of its food. These it obtains, not by its tongue, which is short and inextensible, but by its lips, which are largely developed, and supported by singularly modified intermaxillary and lower maxillary bones ; the whole mouth presenting a close resemblance to the broad and flattened beak of a duck. The similarity is increased by the lateral lamella- of the lower jaw; but both jaws are provided with four horny teeth ; the anterior one on each side, both above and below, is long, narrow, and trenchant ; the posterior one is broad, flat, and shaped like a molar tooth. The feet are short, broad, armed each with five claws, but less robust than in the Echidna. The fore feet have a web, which * See No. 041, 13. Physiological Series, Museum Royal College of Surgeons, London. " Debris of Insects belonging to a genus of the Nauccrida;, which were found in the check-pouches of the OrnithoTh.ynch.ua panidnxus." Mr. Bennett (Zoo!. Trans. 1834, p. 239) found in the cheek-pouches of the Ornithorhynchus mud and gravel, with frag- ments of insects and shell-fish. not only unites and fills the interspaces of the toes, but extends beyond the extremities of the claws; the web of the hind foot terminates at the base of the claws. With these swimming- feet is associated a strong, broad, horizontally flattened tail, which completes the organic locomotive machinery for the aquatic existence of an air-breathing and warm-blooded quadru- ped. The body is clothed with a dense coat of hair, which consists of a fine fur, intermixed with long, stiff, flattened, and sharp-pointed hairs, that seem to represent the spines of the Echidna. Only one species of Ornithorhynchus is as yet satisfactorily defined ; it occurs in the fresh-water rivers, ponds, and lakes of Australia and Van Dieman's Land. As external ears and large eyes would be it! suited to the habits either of a burrowing or a swimming animal, both genera of Monotremes are characterized by the absence of the auricle and the small size of the visual organs. The male in both genera bears a horny pointed spur upon the heel, which is perforated, and trans- mits into the wound it inflicts the secretion of a peculiar gland. This singular repetition of an offensive mechanism, which, prior to the discovery of the monotrematous mammals, was known only in certain insects and serpents, completes the anomalous combinations in the external characters of the present order. Echidna hystrix and Ornithorhynchus para- doxus were first described and figured by Dr. Shaw ; the former as early as the year 1792 in the third volume of the Naturalists' Miscellany, under the denomination of Myrmecophaga acu- leata ; the latter in the tenth volume of the same work in the year 1799, by the name of Platypus anatinus. In the following year this more extraordinary animal received a further description, together with its present zoological denomination from Professor Blumenbach, in " Voigt's Magazin fur den neuesten Zustand der Naturkunde, Bd. ii, 1800 ;" and soon after Sir Everard Home gave an account of some of its ana- tomical peculiarities, which appeared in the Philosophical Transactions for the year 1800. As these observations, however, were limited to the head and beak, they rather tended to perplex than guide the naturalist in assigning the position of the animal in the natural system. Professor Blumenbach, in his Elements of Natural History, placed the Ornithorhynchus paradoxus among the Pulmata of his mamma- logical system, between the otter and the walruss ; while Dr. Shaw more naturally re- ferred it to the Bruta of Linnaeus; but being limited to such points of comparison as the exter- nal form alone presented, he merely discerned the affinities of the Platypus and the Echidna to the Myrmecophaga. The real value and extent of these affinities could only be deter- mined by a deeper insight into their respective organizations. The important memoirs on the anatomical structure of both these animals read before the Royal Society by Sir Everard Home, and published in the Philosophical Transactions for 1802, drew the attention of the scientific 368 MONOTREMATA. world more strongly towards their remarkable peculiarities and deviations from the ordinary structure of the Mammalia. In these investiga- tions the author having brought to light nume- rous instances of mutual affinity, before con- cealed under very dissimilar exteriors, grouped the two animals together under the same generic appellation, adopting that of Ornithorhynchus, proposed by Blumeubach. He likewise ex- pressed his opinion that they differed consider- ably in their mode of generation from the true Mammalia, on the ground of the peculiarities of the organs themselves, and on the absence of nipples in both species, and especially in the female of the Ornithorhynchus paradoxus. The opinion of Sir Everard Home was soon after adopted by Professor Geoffroy St. Hilaire, who, in the Bulletin des Sciences Philomathiques, (torn, hi.), constituted a new order for these animals under the term ' Monotremata;' having been led to believe, from an imperfect dissec- tion, that the genital products of both sexes as well as the urine and excrement, were voided by a single common outlet. Concluding, also, by inference that the mammary glands as well as nipples were wanting, and strengthened in his belief of the oviparous nature of the Mono- tremata by some accounts from New South Wales respecting the discovery of the eggs of the Ornithorhynchus,* he subsequently sepa- rated the Monotremata altogether from the Mammalia, and characterized them as a class intermediate to Mammalia, Birds, and Reptiles. This mode of viewing the Monotremata was not, however, generally assented to. The Baron Cuvier, who in one of his earliest works * had separated the Myrmecophaga aculeata of Shaw from the true Anteaters under the generic term ' Echidna,' and who afterwards made con- siderable additions to its anatomical history, as well as to that of the Ornithorhynchus para- doxus, in the Lecons d'Anatomie Compulse, whilst he adopted the collective term ' Mono- tremata,' admitted it in the ' Regne Animal ' as indicative only of a tribe or family in his order Edentata. Spix, Oken, and De Blainville more decidedly opposed the opinion of Geof- froy, and the latter naturalist in an express dis- sertation on the place which the Ornithorhyn- chus and Echidna ought to hold in the animal kingdom, after adducing the numerous instances in which the structure of the Monotremes agrees with that of the true Mammals, ex- presses his opinion that the mammary organs will ultimately be detected, and considers the animals themselves as most closely allied to the Marsupial order. The exact position of the Monotremata, their natural affinities, and the value of the group, could, however, be only a matter of speculation before their organization, and especially their cerebral structure, had been thoroughly eluci- dated ; the consideration of these points will therefore be resumed after the requisite anato- mical and physiological details have been given, for a knowledge of which, as regards the Orni- thorhynchus, science is chiefly indebted to the celebrated Meckel.f Fig. 168. Skeleton of the Echidna Hystrix. ( Pander and D' Alton, corrected from Nature. ) Osteology. Of the skull. — The skull in both genera of Monotremata is long and depressed, but is cha- racterized by a relatively larger cranium in pro- portion to the face than in the Marsupials. The parietes of the expanded cerebral cavity are rounded, and their outer surface is smooth. These characters are most conspicuous in the Echidna, in which the jaws are slender, elon- gated, and gradually diminish forwards to an * See Linn. Trans, xiii. p. 621. obtuse point, so that the whole skull resembles the half of a pear split lengthwise. The facial angle of the Echidna is 36°, that of the Orni- thorhynchus 20°, being almost the lowest in the mammiferous class. The cranial bones and their constituent pieces continue longer dis- tinct in the Echidna than in the Ornithorhyn- chus ; and their relative position, their con- * Tableau Elementaire de l'Histoire Nat. 1797. t See his beautiful Monograph, " Ornithorhynchi ParaUoxi Deseriptio Analomica," folio, 1826. MONOTREMATA. 369 nections, and the proportions in which they enter into the formation of the skul!, have heen in great measure determined and described in that genus.* I have had the opportunity of investigating the composition of the cranium, a point so im- portant in regard to the natural affinities of the Monotremata, in the young Ornithorhynchi transmitted to the Zoological Society of Lon- don by Dr. Weatherhead ; and the comparison of this part of their anatomy has enabled me Fig. 169. better to appreciate and understand peculiarities of the same part in the Echidna, the skull of which is here also described from original spe- cimens. In the cranium of a young but full-grown specimen of Echidna setosa, (g, fig. 169, 170, 171,) the four elements of the occipital bone are unanchylosed and are joined together by smooth linear harmonise. The basi-occipital (Jig. 170, a) presents a six-sided rhomboidal figure, with the posterior margin notched to complete the lower Shull of Echidna setosa. ( Original.) boundary of the large vertical occipital foramen, and thickened and smoothly rounded to form the inferior extremities of the two occipital con- dyles. These condyles are principally deve- loped from the ex-occipital elements (fgs. 169, 171, b, b), which are expanded superiorly and terminate in an angle wedged in between the supra-occipital and petrous bones ; they extend, but do not meet, above the occipital foramen, being separated by a notch closed by membrane in the recent state. The supra- occipital element (figs. 169 & 171, c) is a transversely oblong quadrilateral plate of bone ; its short lateral margin is joined by a linear harmonia with the upper part of the os petro- sum, on each side ; the wide anterior mar- gin is similarly articulated with the single parietal bone, and is slightly overlapped by its posterior margin ; this representative of the deltoid suture runs straight across the posterior and upper part of the skull. Fig. 171. Occipital and sphenoidal cranial vertebra;, Echidna setosa. ( Original.) * See Lemons d'Anatomie Coinpan'-e, Kd, vol. in. 1837. Occipital region of shull, Echidna setosa. ( Original. ) In the specimen in which the preceding condition of the occipital vertebra was mani- fested there was no trace of sagittal suture ; the upper and middle region of the cra- nium was covered by a single broad, slightly convex, parietal bone, (fig. 169, d,) joined posteriorly, as above described, with the supra- occipital, laterally with the petrous and sphe- noid bones, and anteriorly with the sphenoid and frontal bones, which the parietal overlaps; 2 B 370 MONOTREMATA. by a squamous modification of the coronal suture. The part described in this Article as a lamelliform portion of the petrous bone, (Jig- 169, e,) which extends upon the lateral and part of the posterior region of the skull, is regarded by the Editors* of the Lemons d'Ana- lomie C'omparee, Ed. 1837, as the squamous portion of the temporal ; and the flat oblong bone, (fig. 169, B,) which forms part of the la- teral wall of the cranial cavity and the posterior half of the zygomatic arch, and which supports the articular surface for the lower jaw, is thought to be the malar bone. But when we consider the low development or total disappearance of the malar bone in the skull of the Insectivora generally, as in Echinops and Centetes among the Fera, and as in the edentate Manis and Myrmccopliaga, it is unlikely that the malar bone should attain so superior a size and fulfil such important functions in the Monotrema- tous Edentata, in which its condition, according to the above views of the editors of the Lecons dAnat. Comparee, would be unique in the mammiferous class. It appears to me to be more reasonable to regard the malar bone as either altogether absent in the Echidna, as it is in the Manis, and the zygomatic arch as being completed in the Echidna by a greater exten- sion of the zygomatic processes of the tem- poral and superior maxillary bones; or else to suppose that these are actually united, at an earlier period, by a separate intervening jugal style, which, however, I have not been more successful in finding than the Continuators of Cuvier. With respect to the great develop- ment which the petrous bone, according to my view, must present in the Echidna, it may be observed that this bone forms part of the occi- pital region of the skull in most Marsupials, and also contributes as large a proportion to the lateral parietes of the skull in certain Ro- dents, as the Helamys, as it is here described to do in the Echidna. The side of the cranium is principally formed by the largely developed petrous bone (fig. 170, e) and the great ala of the sphenoid, which meet and are joined in the interspace separating the parietal from the squarno-temporal bone, by a nearly vertical harmonia half an inch long ; this harmonia is crossed at nearly right angles by a deep groove, which in some parts sinks through the wall of the cranium and exposes its cavity. The groove or canal first runs be- tween the squamous and petrous elements of the temporal bone, and is a conspicuous fea- ture in the skull of the Ornithorhynchus. The lower part of the side of the skull of the Echidna is closed by the squamous element of the temporal, which overlaps a large portion of the petrous bone, and by a small portion of the sphenoid : it is represented detached from the skull at fig. 169, B. The lower boundary of the squarno-temporal forms a straight line, from which the glenoid surface for the lower jaw (f) is extended inwards at a right angle, upon the base of the skull; the anterior part * The very able anatomists, MM. Laurillard and Duvernoy. is continued forwards, protecting the temporal fossa by a thin vertical plate of bone, and then diminishes to a slender, straight, styliform, zygomatic process which rests obliquely on a corresponding process of the superior maxil- lary bone. The tympanic cavity is shallow, and exca- vated in the basal part of the petrous bone, where it is widely open in the macerated skull : it is figured closed by the tympanic bone and membrane atg^g. 170, and exposed by their removal at e" fig. 170. The plane of the mem- brana tympani is horizontal, and its exter- nal surface looks nearly downwards. Three- fourths of its circumference are implanted in the groove of the very slender incomplete hoop formed by the detached tympanic bone, which is figured with the anchylosed malleus at c,fig. 169. The petrous bone is continued from the tympanic fossa forwards and inwards, in the form of a broad and nearly horizontal process, (fig. 170, e',) to the pterygoid plate of the sphe- noid, (j', i',) which is also horizontal. The pe- trous and pterygoid plates are joined by an oblique harmonia, and both contribute to extend the bony palate backwards. The palatal pro- cess of the petrous bone is abruptly terminated behind by the Eustachian groove (fig. 170*). The frontal bone (fig. 169, A) in the cranium here described was divided by a median frontal suture, toothless like the rest; the angle be- tween the superior and the orbital plates is rounded off ; the orbital plate joins the great ala of the sphenoid by a deeply sinuous suture. The anterior part of the frontal is largely over- lapped by the bases of the nasal bones, which encroach upon the interorbital space. The nasal bones (fig. 1 69, n) receive the upper edge of the superior maxillary bone into a groove at their outer margin, and articulate anteriorly with the intermaxillaries (fig. 169, o); but these meet above the nasal canal in front of the nasal bones for an extent of about three lines, and thus exclusively form the boundary of the single, oval, and terminal external nostril. The lower or palatal process of the intermaxillary extends backwards in the form of a long and slender pointed process which is wedged into a fissure of the superior maxillary bone. The anterior palatal or incisive foramen is a single large elongated fissure extending from the narrow anterior symphysis of the inter- maxillaries backwards, for some distance, be- tween the palatal processes of the maxillaries. At the back part of the bony palate a narrow fissure extends forwards between the pterygoid bones, and the intermediate extent of the bony palate is entire, or presents only a few minute perforations. The palatal bones, if originally distinct, soon become confluent with the maxillaries. There was no separate osseous style representing the malar bone between the zygomatic processes of the maxillary and tem- poral bones in the skull here described.* The zygomatic process of the superior max- * Cuvier says, " Entre ces deux apophyses est un tres-petit filet qui represent le jugal." Cuvier, Ossem. Foss. 4to., vol. v., p. 145. MONOTREMATA. 371 Mary bone (Jig. 169, m ) extends backwards as far as the posterior boundary of the zygomatic or temporal fossa; the palatal process extends along the floor of the orbit in a similar form and to nearly the same extent. The orbit is marked off from the temporal fossa by merely a slight ridge extending down and across the suture joining the frontal and sphenoid bones. The skull of the Echidna differs from that of the edentulous Manis and Myrmecophaga in the completion of the zygomatic arches, in the unclosed state of the tympanic cavity, in the large size of the foramen incisivum, and the surrounding of the external nostrils by the intermaxillary bones alone : it differs also in the smaller relative distance between the poste- rior palatal fissure and the superior maxillary bones, and in the apparent absence of the pala- tine bones, the presence and interposition of which between the pterygoid and maxillary palatal plates elongates the palate in the pla- cental Anteaters at the part where it is rela- tively shorter in the Echidna. In the modi- fication of the pterygoid plates of the sphenoid to complete the posterior nasal canal, the Echidna manifests an interesting resemblance with the great Anteater; but it differs from this, as from every other mammiferous species, in the palatal plates contributed by the petrous bones to the broad posterior part of the roof of the mouth which supports the horny palatal teeth. Cuvier describes the posterior palatal fissure as extending between the palatine bones, and therefore regards the plates, which are here affirmed to be developed from the petrous bone, as being the pterygoid processes of the sphenoid ; and, according to this view, he truly observes that their horizontal position is very remark- able;* but he might have added, that their share in the formation of the tympanic cavity was not less so. The same determination of the bones composing the posterior part of the osseous palate of the Echidna is repeated in the Lemons d'Anatomie Comparee, 1837, p. 454. If, however, the sphenoid be sepa- rated from the occipital bone, which was easily done in the young skull of the Echidna repre- sented in figs. 169 and 170, the horizontal plates, described by Cuvier as pterygoids, are left behind, not as separate bones, but as conti- nuous portions of the petrous elements of the temporal, which form, at the same time, part of the base of the cranial cavity, complete the inner wall of the tympanum, and the anterior part of the Eustachian groove. The palatines of Cuvier are developed from the sides of the basi-sphenoid, and almost immediately bend inwards and meet below the nasal canal, which they thus prolong posteriorly, as in the Myr- mecophaga ; and they are separated poste- riorly, also, as in that genus, by an acute fissure, presenting unequivocally the same modifications * Cuvier says, " Une echancrure dignc et pro- fonde scpare les palatins cn arriere. Le plan The pyramidalis, or superficial rectus (4), is here, as in the ordinary Marsupials, of very large size; it arises from the whole inner margin of the marsupial bone ; its fibres converge to- wards and are confluent at the linea alba with those of its fellow, and it gradually terminates in a point opposite the posterior part of the sternum. It depresses the ribs, shortens the abdomen, and protracts the marsupial bone. The rectus abdominis, or posterior rectus (5), arises from the posterior margin of the marsu- pial bone, and is inserted into the cartilage of the first rib, the manubrium sterni, and the coracoid bone. The diaphragm presents the structure which is characteristic of the true mammiferous ani- mal. The lesser muscle arises from the first lumbar and four last dorsal vertebra, and ex- pands to be inserted into the central tendon, which chiefly receives the fibres of the greater muscle arising from the cartilages of the eleven inferior pairs of ribs. The pectoralis (2) is of very striking dimen- sions; the origin of the superficial portion extends from the acromion, along the sternum and linea alba, almost to the pubis ; a deeper- seated portion arises from the six osseous sternal ribs ; the fibres of both portions con- verge to be inserted into the largely-developed pectoral or anterior crest of the proximal half of the humerus. The pectoralis minor is attached to the cora- coid, and the subclavius is likewise inserted, as in some other quadrupeds, into this bone, which is no longer a subordinate process of the scapula in the Monotremes. The subscapularis is a narrow muscle, and narrower in reality than at first sight it appears to be, since the supra-spinatus, from the inflec- tion of the spine and acromion, arises from the same aspect of the scapula, and appears to form the anterior fasciculus of the subscapularis ; its distinct insertion into the anterior tubercle of the head of the humerus points out its true nature. The infraspinatus (20) and the large teres major cover the whole external surface of the scapula. The deltoid is divided into an anterior and a posterior portion. The anterior portion (19) arises from the anterior extremity of the cora- coid, and is inserted into the summit of the deltoid crest of the humerus : the posterior part (21) arises from the anterior and superior apex of the scapula, and is inserted into the lower half of the deltoid crest. There are also two muscles to which the name coraco- brachialis may be applied, a superior one (22) and an inferior one (25). The biceps brachii arises by two heads ; one (23) arises from the sternal extremity of the coracoid, the other (24) also arises from the coracoid ; the common tendon is inserted into the middle of the radius. The other muscles of the anterior extremity adhere closely to the mammalian type. The extensor carpi radialis (30) sends three ten- dons, to be inserted respectively into the second, third, and fourth metacarpal bones. There is a single common Jiexor digitorum, as well as extensor digitorum (27). The extensor digit i minimi (26), the indica- tor (28), the extensor pollicis (29), the prona- tor teres (32), and the Jiexor carpi radialis (33) are all remarkable for their strength in the Ornithorhynchus, and are still more powerfully developed in the Echidna. The most remarkable muscle on the palmar aspect of the fore arm is the Jiexor ca7pi ulnaris, which arises by two separate heads, the longer one from the broad olecranon, the shorter one from the internal condyle of the humerus ; the common tendon is attached to the os pisiforme and the metacarpals of the fourth and fifth digits. The psoas minor from its insertion into the pelvic arch should be regarded as a muscle of the pelvic extremity, and it is one of the largest of these muscles. It arises from the sides of five dorsal vertebra, and its strong tendon is implanted in the remarkably-developed ilio- pectineal process. It depresses the pelvis , 382 MONOTREMATA. and with it also the tail and the pelvic extre- mities. The psoas magnus and Mucus internus form a single muscle, having the usual origins, and inserted by a common tendon into the large internal condyle. The gluteus externus is larger than is usually the case with quadrupeds; its tendon is inserted into the plantar fascia and the bone which sup- ports the spur. The gluteus medius, gluteus inte?-nus, pectineus (45), biceps flexor cruris, gracilis (34), sartorius (35), rectus J'emor is (36), adduc tores J'emor is (46), semitendinosus (47), semimembranosus, vastus externus, offer no notable deviations from the usual structure. A strip of fibres (49) descends from the gracilis to the sphincter cloaca (H). A muscle, called by Meckel ' flexor accessorius a Cauda ad tibiam tendens ' (51), arises from the transverse pro- cesses of the anterior caudal vertebrae, and converges to be inserted into the tibia. Another peculiar adductor of the leg, which might be termed ' intertibialis ' (52), is attached by its extremities to both tibia; its fleshy belly passes across the sphincter cloacae (H), and is connected with a strip of the panniculus carnosus (i). The gastrocnemius (48) derives its largest origin from the produced and expanded head of the fibula, and its smaller belly from the internal femoral condyle; its tendon is implanted in the calcaneum. The analogy between the gastro- cnemius and ulnaris internus is strikingly illus- trated in the Ornithorhynchus. The soleus arises from the head of the fibula and from a large proportion of the tibia ; it is nowhere blended with the gastrocnemius, but is inserted by a thick and short tendon into the astragalus. The abductors of the outer digits of both the hand and foot are well developed for the purpose of expanding the web which connects the toes. In the figure the following muscles of the leg are shown, viz. 37, tibialis anticus, 38, ex- tensor hallucis longus, 39, peronaus longus, 40, peronaus ■ brevis, 41, extensor digitorum communis profundus, brevi analogus, 42, exten- sor digitorum communis sublimis, 43, a portion of the same muscle corresponding with the indicator of the fore leg, 44, extensor dig it i quinti accessorius. NERVOUS SYSTEM. Brain. — In the male Ornithorhi/nchus Meckel found that the brain weighed two drachms, German weight (about four drachms avoirdupoise), and bore a proportion to the weight of the body as 1 to 130. It was in- closed by a pretty strong dura mater, of which the fold corresponding with the bony falx ad- hered but slightly to that process. The cere- brum weighed one drachm and a half, German ; neatly the whole of its superficies was smooth ; a few vascular impressions marked the side of the anterior lobe : its shape was triangular, depressed; the contracted anterior lobes form- ing the obtuse apex of the triangle : the pos- terior lobes are wide and cover the corpora bigemina. The surface of the cerebrum is smooth and unconvoluted (Jig. 181). Fig. 181. Side view and base of brain, Ornithmliynchus . ( Meckel.) In describing the structure of the cerebral hemispheres Meckel observes, with reference to the most characteristic part of this structure in the Mammalia, " Corpus callosum adest quidem, sed breve, quam baud quatuor lineas longitudine aequet, memorabilius etiam videtur, in dimidia duo lateralia, linea mediana haud confluentia, esse disjunctum. Equidem sal- tern in faciebus sese spectantibus internis nul- lum dilacerationis vestigium invenire potui." — L. c. p. 33. During my investigations of the structure of the brain in the Marsupial animals,* I had in memory the apparent exception to the bird- like condition of the corpus callosum, which the Ornithorhynchus, according to the above description, presented, but which each suc- cessive example of the brain of the Marsupial quadruped served to establish more firmly as the rule of structure in the higher order of the Implacental sub-class. It was difficult to believe that in the lower or Monotrematous group, the cerebral organ, which indicates so accurately the true affinities and natural posi- tion of the Vertebrate animal, and which fol- lows so faithfully the degradation of the general organization of each species, should offer so abrupt an ascent to the cerebral condition of the placental Mammalia, as would be indi- cated by a corpus callosum of four lines long in a brain of which the hemispheres measure only fourteen lines in length (German scale). The strong suspicion of an error in the cele- brated anatomist's description justified a re- serve in acknowledging this exception until the opportunity of testing it by a dissection of a brain of a Monotrematous quadruped should have presented itself ; and my doubts as to the great development of the corpus callosum of the Ornithorhynchus were further justified by the indication of its nearer ap- proach to the Oviparous type afforded by the simple bipartite condition of the tubercules * Philos. Trans. 1837, p. 87. MONOTREMATA. 383 called ' quadrigemina.' Well preserved speci- mens of Ornithorhynchus presented to me by Mr. Thomas Bell, surgeon R. N., in 1838, have ena- bled me to determine this question. There is neither corpus callosum nor septum lucidum in the Ornithorhynchus. The part described by Meckel as the corpus callosum corresponds with the fornix and hippocampal commissure, as it exists in the Marsupialia, excepting that the essential func- tion of the fornix, as a longitudinal commis- sure, uniting the hippocampus major with the olfactory lobe of the same hemisphere, is more exclusively maintained in the Ornithorhynchus, in consequence of the smaller size of the trans- verse band of fibres uniting the opposite hip- pocampi, and representing the first rudiment of the corpus callosum, as it appears in the development of the placental embryo. The thin internal and superior parietes of one lateral ventricle are wholly unconnected with those of the opposite ventricle. Meckel makes no mention of the fornix or hippocampus major: the latter forms a large pyramidal prominence at the outer and pos- terior part of the ventricle, and is confluent with the inferior and external parietes of that cavity. The corpus striatum is long and nar- row : the thalamus opticus small, and is united with its fellow by a soft commissure, which rises to the same level, whereby they appear to form a continuous body. The anterior com- missure is very large, as in the Marsupials. The posterior bigeminal body is much smaller than the anterior, and the trans- verse depression which divides them is very feebly marked : the longitudinal groove is equally feeble on the ' nates,' and is alto- gether absent in the ' testes,' which thus form a single small tubercle. It is in the condition of these parts, recognized, but too briefly no- ticed by Meckel, that the brain of the Orni- thorhynchus deviates most essentially from the Marsupialia, and offers the most direct step in the descent to the Oviparous type. The cerebellum is modeiately large, highest in the middle, but with small lateral append- ages : the median or vermiform part is traversed by transverse furrows; and its vertical section exhibits an ' arbor vitse.' The medulla oblongata is broad and de- pressed : its inferior surface exhibits the corpora pyramidalia (fig. 181, a), the corpora olivaria («'), which expand as they advance forwards, apparently in relation to the immense size of the trigeminal nerve. Their anterior extremi- ties are crossed by large trapezoid bodies (b), (figured by Meckel as the pons Varolii) ; and anterior to those is the true ' nodus er.cephali' (c), which is narrow, in correspondence with the small lateral lobes of the cerebellum ; and from this there emerges on each side a large gan- glioid body (c'), from which the trigeminal nerve (5) arises. The under surface of the medulla oblongata is traversed by a deep median lon- gitudinal groove. The brain of the Echidna is relatively larger, and its external surface is complicated by convolutions.* It weighs twelve drachms and thirty grains avoirdupoise,and bears a proportion to the weight of the body as 1 to 50. The cerebral hemispheres conceal the bigeminal bodies, but do not extend over the cerebellum. The broad posterior part of each hemisphere is disposed in three nearly parallel transverse convolutions, the outer extremities of which Fig. 182. Brain of the Echidna, right hemisphere dissected. ( Original. ) incline forwards (fig. 182) ; anterior to these is a larger convolution bent upon itself at a right angle, one crus running transversely ; the other longitudinally, and forming the inner boundary of the anterior half of each hemisphere : this convolution was not divided by a transverse anfractuositv, as in the figure in the ' Voyage de la Favorite,' loc. cit. On the outside of the longitudinal convolution there are two or three oblique folds which converge towards the contracted anterior part of the brain, or descend to its under surface : besides these principal and more constant convolutions there are a few smaller and less regular ones at the lateral and inferior parts of the hemispheres, especially on the great natiform protuberances. The principal anfractuosities sink more than a line's depth into the substance of the he- misphere: the posterior convolutions are con- tinued upon the median surface of the he- misphere, and interlock with those of the cor- responding hemisphere. The depth of the me- dian fissure of the hemispheres is from five to six lines: the hippocampal commissure (o) one line and a half in antero-posterior diameter is seen at the bottom of the fissure which divides the hemispheres. The dura mater in the Echidna is thin and * See the figures and description of the external characters of the brain of the Echidna, given by MM. Eydoux and Laurent in the 'Voyage dc la Favorite,' 8vo. 1839, torn. v. pi. 9, p. 161. 384 MONOTREMATA. transparent ; the membranous falx is less deep than the osseous one of the Ornithorhynchus. I found no bony plate between the hemi- spheres in the Echidna. The arachnoid is transparent, but relatively strong. The cere- bellum is traversed by several narrow trans- verse anfractuosities, disposed as in fig. 182. The vermiform or median lobe, as in the Ornithorhynchus, is larger in proportion to the lateral lobes than in the Marsupialia, and the limits between them are much less dis- tinctly defined. The base of the brain in the Echidna (fig. 183) is remarkable for the deep and wide excavations at the under part of the anterior Fig. 183. Base of brain of Echidna. ( Original.) lobes, forming the base of the enormous olfactory nerves. The natiform protuberances are unusually large. The medulla oblongata is broad and flat, but contracted anteriorly to an angle ; the pyramidal bodies ( a) long and narrow; the olivary bodies (b) broad, but flat. The pons Varolii ( c) presents, as in the Orni- thorhynchus, a low development proportion- ally to the size of the brain : it is not raised beyond the level of the under surface of the medulla oblongata : it is of a triangular form with the obtuse apex turned forwards : the median longitudinal groove formed by the ba- silar artery is well marked : the trapezoid bodies are relatively narrower than in the Ornitho- rhynchus. The pituitary gland (p, Jig. 183) is one line and a half in length and one line in breadth : its under surface adheres closely to the dura mater of the sella turcica. The corpus mam- millare is single, broad, and but little ele- vated. The internal, superior, and posterior walls of the lateral ventricle are from one line to two lines in thickness ; the outer wall is between two and three lines; when the roof of the ventricle is removed, as in Jig. 184, two elongated convex bodies are exposed, as in the marsupial brain : the posterior and Fig. 184. largest (//) is the hip- pocampus major: the anterior body (s) is the corpus striatum. The whole internal wall of one ventricle is quite disunited from that of the opposite hemisphere.* The contracted an- terior parts of the hip- pocampi are connected together by the short transverse commissure above mentioned, which is the sole re- presentative of the cor- pus callosum and for- nix. The septum luci- Right lateral ventricle laid dum and fifth ventricle Vfh Echidna. are entirely absent. (Original.) The pia mater, which accompanies the ven- tricular artery into the floor of the ventricle, at the base of the hippocampus, spreads over the optic thalami, and sends upwards a smooth fold of membrane, one line and a half broad, between the hippocampus and the corpus striatum. The free margin of this fold is slightly thickened by the choroid artery. It is necessary to remove the hippocampus and posterior part of the hemisphere, in order to bring into view the optic thalami and bige- minal bodies. The optic thalami (fig. 182, /) and nates appear as one convex body slightly contracted laterally, and divided from each other by a sig- moid linear fissure : the testes are only half the breadth of the nates, and the median longitudinal line of division, which is very faint in the larger bodies, is not visible in the smaller and pos- terior tubercle. The Echidna corresponds in this characteristic modification with the Orni- thorhynchus.f * The internal structure of the hemispheres of the Echidna's brain is not described in the ' Voyage de la Favorite.' f MM. Eydoux and Laurent have thrown into the following tabular form the published results of the dissections of the brains of the Impla- cental Mammalia as compared with Placental Mammals and Birds. MONODELPHES. DlDELPHES. Oknithodelphes. OlSEAUX. Corps calleux . . . . Pont de Varole . . Lobes optiques . . . existe. existe. quadrijumeaux et superieures. manque, existe. quadrijumeaux et superieures. manque, existe. bijumeaux et superieures. manque, manque, bijumeaux et lateraux. They add : " En indiquant ce resultat des ob- servations de M. R. Owen, aux-quelles nous avons joint les observations de Meckel en les rectifiant, nous devons faire remarquer que Meckel a cepen- MONOTREMATA. 385 The medullary fibres of the optic thalami (fig. 182, t ) and bigeminal bodies (r, s) form a thin stratum above a third ventricle of unusual capa- city, the relative size of which appeared somewhat larger than was natural from the decomposition of the medullary matter of the soft commis- sure. The principal commissure of the he- mispheres is the anterior one, which is sub- cylindrical, and measured two lines thick verti- cally, and one and a half horizontally. The pos- terior commissure is a narrow strip of medullary matter, which thickens the upper part of the valvula Vieussenii. The ' iter' or canal from the third to the fourth ventricle is proportion- ally wide. The arbor viup, as displayed by a vertical section of the vermiform process, sends off four principal and some minor medullary branches. The spinal chord in the Ornithorhynchus is long and slender, but fills closely the spinal canal : it is thickest at its commencement and at the lower two-thirds of the cervical region ; it is more slender in the dorsal region, espe- cially near the loins; it is slightly enlarged in the lumbar region, and gradually terminates in a point in the canal of the sacral vertebrae : the cauda equina is very feebly represented. In the Echidna the form and proportions of the spinal chord (Jig. 185) are strikingly dif- ferent: it is here nearly as short and thick, relatively, as in the hedge-hog, and terminates in a point, at d, before it has reached the middle of the dorsal region. Nevertheless, in this short tract the two usual enlargements, giving origins respectively to the nerves of the pec- toral and pelvic extremities, are clearly marked ; the slightly contracted intermediate portion being extremely short : the cauda equina is remark- able for its length. The nerves escape, as usual, from the intervertebral foramina, and have a longer course in the spinal canal, in proportion as they supply parts more distant from the chord. It is interesting to find the peculiar structure of so important a part as the spinal chord re- peated in two species, which, with the excep- tion of the dermal spines, and their common characters as Mammalia, differ in other respects as widely from one another, and occupy such distant places in their class. Can the short- ness of the solid chord, and the great length of the nerves within the spinal canal, have any physiological relation with the habit, common to both the placental and monotre- matous hedgehogs, of rolling the body into a ball when torpid or asleep, or when the tegu- mentary armour is employed in self-defence?* The olfactory nerves are large in the Orni- thorhynchus (fig. 181, 1,1). The external root dant admis, dans les figures relatives a l'encephale dc l'ornithorhynque I'existence du corps calleux; mais, en ttudiant avec soin l'encephale de notrc echidne, nous nous avons reconnu que les descrip- tions de M. R. Owen sont plus exactes que celles de Meckel, et que les determinations de I'anato- miste Anglais doivent etre adoptees." — Voyaye de la Favorite, p. 166. * " Cet echidne passait la majeure partie de son temps dans une espece d'engmndissement, blotti, enroule a la manierc des ln'rissons." — Voyage de la Favorite, p. 159. vol. nr. M Fig. 185. is remarkable for its length and relative size: it arises from the poste- rior surface of the cere- bral hemisphere imme- diately behind the bige- minal body; bends round the crus cerebri to the inferior surface; and is continued forward to join the internal root which rises from the base of the anterior lobes of the brain. In the Echidna the olfactory nerves may be described as enormous. The external root (fig. 183, 1 a) arises from nearly the whole anterior part of the natiform pro- tuberance, which extends its origin, as in the Or- nithorhynchus, to the pos- terior part of the hemi- sphere. The internal root (183, 1 b) is also very large : the lateral ventri- cle is prolonged forwards into the olfactory nerve, which would appear like a continuation of the en- tire hemisphere, were it not that it is overlapped by the anterior convo- lution. The extent and com- plications of the olfactory cavity are proportionate in the two Monotremes to the size of their respec- tive nerves. The optic nerve {fig. 181, 183, 2) is smal'l in both Monotremes, in ac- cordance with the dimi- nutive size of the eye : the two nerves are joined by a transversely oblong chiasma. The eye is protected, in the Ornithorhynchus, by a cartilaginous plate continued from the upper part of the orbit, which Meckel compares with 1 " ' the bony palpebral plates Brain and spinal chord, in the Crocodile. Both Echidna, Half natural Monotremes have a well size. (Original.) developed membrana nic- titans : there are also an upper and a lower eyelid, each of which has its proper apertor muscle. In the Ornithorhynchus the sclerotic is carti- laginous, the cornea flabby, the retina very thick : there is no trace of pecten or marsu- pium : the lens is very small, two lines in vertical and transverse diameter, one line in antero-posterior diameter; the anterior surface 2 c 386 MONOTREMATA. is nearly flat, the posterior very convex. The choroid is black, without a tapetum lucidum : the pupil is circular. The nerves of the third pair (fig. 183, 3) have the usual origin and destination, and are like- wise very small : the fourth nerve is still more minute. The fifth pair in the Ornithorhynchus ex- ceeds, in relative magnitude, that of any other animal; though large, also, in the Echidna, its size is much less remarkable in this Mono- treme. The trigeminal nerve in the Ornithorhynchus, (fig. 181, 5,) emerging from the ganglion an- terior to the pons, soon divides into three branches ; the first and second appearing as one. The first and smallest division divides into two equal branches: the superior or ethmoidal branch enters the nose, emerges from a canal in the upper part of that cavity, and supplies the skin at the upper part of the face; and, by a branch continued from between the nasal and intermaxillary bones, is distributed to the nostrils and contiguous integument. The second division of the fifth is two lines broad and one line and a half thick ; it passes through the foramen rotundum, and the chief part of it passes into the ant-orbital canal. On its emergence it divides into two branches, distributed, the one to the nasal or upper pa- rietes of the face, the other to the lateral or labial integuments. The palatine branch di- vides into a posterior smaller nerve, which passes through the posterior palatine foramina : the anterior and larger branch emerges from the anterior palatine canal and supplies Jacob- son's organ and the surrounding palatine mem- brane. The third division of thefifth(5') is broader but thinner than the second ; it leaves the cranium by the foramen ovale, and is distributed as usual, in part to the manducatory muscles, but mainly to the sensitive labial integument of the lower jaw (Jig. 180, a a). The sixth nerve (fig. 183, 6) is as small as the third. The seventh and the acoustic pre- sent half a line in diameter. The acoustic nerve is expended upon a labyrinth remarkable for the small relative size of the semicircular canals, and .their free pro- jection into the cavity of the cranium. The cochlea is wide, but not high ; it is bent around a modiolus, and divided as usual into a superior and inferior scala. The foramen ovale is nearly circular, and opens into the wide but shallow tympanic cavity. It is naturally closed by the base of a small columelliform and imperforate stapes (fig. 173, d, d) : the stem of this ossicle is articulated with a triangular plate of bone (c), representing, according to Meckel, the incus. This bone is connected with a small bent os- seous style (b), which serves to complete, with the similarly-shaped tympanic ossicle (a), the frame supporting the membrana tympani. This membrane is concave externally, and forms the inner extremity of a long and narrow meatus auditorius externus, which is strength- ened by a cartilaginous incomplete cylinder, protected by a valve, but not provided with an external auricle. The auricle is equally wanting in the Echidna, in which the external aperture of the auditory canal presents the form of a vertical slit, shaped like the italic S, one inch and a half in length : the margins of the slit are tumid, and support a row of bristles which protect and cover the orifice when recumbent. The meatus is remarkably long ; the tube is strengthened in this Monotreme by a series of incomplete cartilaginous hoops, connected to- gether by a narrow longitudinal cartilaginous band, so that its structure closely resembles that of a trachea (fig. 188, a, a). The tym- panic fossa is almost entirely encircled with a slender hoop of bone (fig. 169, c) consisting of the anchylosed tympanic bone and malleus. The portion which represents the tympanic bone (a), and which can be separated from the malleus in theyoungsubject, is a slender osseous filament bent into three-fourths of a circle, and placed upon the inner margin of the tym- panic fossa, its concavity looking outwards: this concavity is impressed with a fine groove for the insertion of the membrana tympani : the posterior part of the hoop passes across the commencement of the Eustachian canal, and terminates in a free point upon the pos- terior wall of the tympanic fossa : the anterior end of the hoop is applied to and usually anchylosed with the longitudinal bar of the malleus (b). Only a small portion of this ossicle is con- tained within the cavity of the tympanum ; the principal portion forms the external and part of the posterior boundary of the bony meatus auditorius, and is then continued forwards in the form of a slender pointed process; the bone slightly expands as it extends backwards, and its broadest part is abruptly bent inwards until it nearly meets the posterior end of the tympanic hoop. From the extremity of this in- flected portion a slender compressed process (f) extends to the centre of the space encircled by the bony hoop ; it is attached by its whole length to the membrana tympani, and repre- sents the handle of the malleus. At the pos- terior margin of the broad incurved part of the malleus there are two minute tubercles nearly a line apart: the short and simple columelliform stapes (rf) ascends vertically from the inner- most of these tubercles, with the upper surface of which it is articulated ; its opposite ex- tremity closes the foramen ovale in the form of an expanded plate. The membrana tym- pani is concave outwardly at its middle part. The eighth and ninth pairs of nerves have the usual origins and proportions. The pneumogastric nerve (fig. 180, d) is closely attached, at its origin, to the hypoglossal (fig. 180, b), but is quite distinct from the sympathetic (fig. f) : it gives off the superior laryngeal, and then proceeds along the neck to the chest : the right nerve here sends its recurrent branch, in the usual manner, round the arteria innominata; the left branch (fig. 187, k) winds round the aorta : the trunk of the pneumogastric is then expended in the MONOTREMATA. 38? cardiac, pulmonic, oesophageal, and gastric nerves. The spinal accessory nerve (fig. 180, c) is thicker than the pneumogastric, and has the usual distribution. The brachial plexus is formed by the five posterior cervical and the first dorsal nerves. The third cervical nerve is shown at g,fig- 180 . The median nerve perforates the inner condyle of the humerus. The lumbar plexus is formed by the two posterior dorsal, the two lumbar, and the first sacral nerve. The great ischiadic nerve divides into the peroneal and tibial branches before it quits the pelvis. The crural nerve is shown at h (fig. 180). DIGESTIVE SYSTEM. The Ornithorhynchus, which subsists on aquatic insects, larvae, mollusks, and other small invertebrates which conceal themselves in the mud and banks of rivers, is provided with a mouth which most nearly resembles the flat and sensitive bill of a lamellirostral bird. The singularly modified jaw-bones, already de- scribed, are invested by a smooth coriaceous inte- gument, (fig. 173, A, E, a,) devoid of hair, but perforated by innumerable minute foramina. At the base of the jaws this integument is produced into a free fold, which overlaps the hairy covering of the cranium immediately behind it. The integument covering the upper mandible ex- tends beyond the margins of the bone, and forms a tumid, smooth, and highly sensible lip ; the narrower and shorter under jaw is more closely invested : the oral or upper sur- face of the lateral part of the under jaw sup- ports a series of about twenty nearly transverse folds, increasing in breadth as they approach the angle of the jaw : the corresponding sur- face of the upper jaw is smooth. The two anterior horny teeth in both jaws are elongated, narrow, with their outer part raised into a trenchant edge in the lower jaw. The two posterior teeth (fig. 173, h, and f) in both jaws are flat, with two broad and slight excavations, corresponding with the two parts into which each molar may be divided in the young animal. Immediately on the outside of the posterior part of each molar in the lower jaw, is the orifice of an oblong cheek-pouch (fig. 180, f, f), about two inches in length, and half an inch in diame- ter : the pouch is continued backwards, and is lined with a hard dry cuticle. The tongue (fig- 186) consists of two parts, the normal, anterior, narrower portion (e), and a broad, raised posterior lobe (f), analogous to the intermolar eminence of the tongue in certain Rodents. This part is pro- duced anteriorly into a free projecting apex in the Ornithorhynchus, and is rendered still more remarkable in that animal by being armed with two short thick horny spines (g,g), projecting forward. The anterior part of the tongue is beset with rather coarse papillae, and extends into the posterior interspace of the incisive teeth, but with the apex more than an inch distant from Fig. 186. the anterior aperture of the mouth. The raised pos- terior lobe of the tongue must impede the passage of unmasticated food to the pharynx, and doubtless tends to direct it on each side into the cheek-pouch- es; whence the Ornitho- rhynchus may transfer its store at leisure to the mo- lar teeth, and complete its preparation for degluti- tion. An air-breathing- warm - blooded animal, which obtains its food by the capture of small aqua- tic animals, while sub- merged, must derive great advantage from the struc- ture which enables it to transfer them quickly to a temporary receptacle, whence they may be ex- tracted and masticated while the animal is floating on the surface or at rest in Tongue and larynx of jts burrow. the Ornithorhynchus. The soft lat ;s tmck ( Meckel. ) , , , r, . . , , ' 1 ' broad, and divided poste- riorly into three fimbriated lobes. The pharynx is narrow, and is singularly en- compassed by two posterior processes of the thyroid cartilage (fig. 189, c,c). The oesophagus becomes slightly dilated near the diaphragm, below which it expands into a moderate-sized membranous stomach (fig 187, I), which is chiefly remarkable for the close approximation of the cardiac and pyloric ori- fices. The intestinal canal is moderately wide, five feet three inches and a half in length, and provided, at a distance of four feet three inches from the pylorus, with a small and slender ccccum (w). The small intestines are chiefly remarkable for the extent of the mucous coat, which is disposed in numerous folds or valvulne conni- ventes : these are transverse at the beginning of the duodenum, but are placed more or less obliquely in the rest of the small intestine; they are about two lines broad, and placed very close together in the duodenum, but diminish in breadth and number as they ap- proach the coecum coli. There are about fif- teen longitudinal folds in the first half of the colon ; the remainder of the intestine has a smooth inner surface. There is no valvula coli. The rectum (z) terminates at the anterior and dorsal part of the vestibular compartment of the cloaca. In fig. 191 a probe (b ) is passed through this termination. On each side of its termination there is an oblong glandular pro- minence, about four lines in length and two in breadth, on which there are about ten ori- fices of glands, which Meckel considers as analogous to the anal glands of other quadru- peds. The long, slender, tubular mouth of the 2 c 2 MONOTREMATA. Fig. 187. Thoracic and abdominal viscera, Ornitkorhynchus. ( Meckel.) Echidna is unprovided with teeth ; but the palate is armed with six or seven transverse rows of strong, sharp, but short retroverted spines. The tongue is long and slender as in the true Anteaters ; its dorsum is broad, flat, callous, and beset with hard papillae, and the insects are doubtless crushed and lacerated between these and the pa'atal spines. As, how- ever, the food undergoes less comminution in the mouth of this Monotreme than in that of the Ornithorhynchus, the pharynx and oesophagus are wider, and a dense epithelium lines the inner surface of the latter tube, and is conti- nued over the capacious stomach to the py- lorus, near which orifice it is developed into numerous horny and sharp papillae. The sub- jacent mucous membrane is smooth; the tunics of i he stomach are very thin, except at the pylorus, which forms a prominent protuberance in the duodenum. The intestinal canal of the Echidna is seven times the length of the body; the mucous membrane is not raised into val- vular folds ; a small vermiform and glandular coecum divides the small from the large intes- tines ; the rectum terminates as in the Ornitho- rhynchus. Salivary glands. — There appears to be no parotid gland in the Echidna, and it is doubt- ful whether the thin flat stratum of glandular substance (Jig. 180, E), which extends from the meatus auditorius to the check-pouch in the Ornithorhynchus, can be so regarded. The submaxillary gland (Jig. 180, jD) is a mode- rately-sized, oval, compact body, situated be- hind and below the meatus auditorius; it mea- sured five lines in the long diameter and four in the short diameter. The duct is very small, scarcely admitting an absorbent injecting pipe ; it passes under the omo-mylo-hyoideus(10),and then, contrary to the usual mode, begins to be disposed in a series of about twelve close trans- verse folds, and terminates by a single aperture at the fraenum linguae. The submaxillary gland (Jig. 188, b) is of unusual dimensions in the Echidna, in which it extends from the meatus auditorius along the neck, and upon the anterior part of the thorax : it is a broad, flat, oblong lobulated body, nar- rowest at its anterior extremity, from which the wide duct emerges. When the duct has reached the interspace of the lower jaw it dilates, and then divides into eight or ten undulating branches, which subdivide and ultimately ter- minate by numerous orifices upon the mem- branous floor of the mouth. This modification, which escaped the observation of Cuvier and M. Duvernoy, appears to be unique. The large size of the glands and the mode in which the secretion is spread over the floor of the mouth, relate to the lubrification of the long, slender, and extensible tongue, and to its fit- ness as an instrument for obtaining the insect food of the Echidna. The liver (Jig. 187, r, r) closely retains the mammalian type of the organ in both Mono- tremes. Four lobes may be distinguished in the Echidna: the principal or cystic lobe re- ceives the suspensory ligament in a fissure ; the large gall-bladder is placed a little to the right ; the left lobe occupies the left hypochondrium ; the Spigelian lobule is of moderate size; it is an appendage of the right lobe. The liver pre- sents nearly the same form in the Ornithorhyn- chus, which has likewise a large gall-bladder (fig- 187, s). There are three hepatic ducts in the Echidna which join the cystic, and the common canal terminates in the duodenum rather more than an inch from the pylorus. In the Ornithorhyn- chus the two chief hepatic ducts join the cystic near the neck of the bladder; the third hepatic joins a more distant part of the cystic ; the ductus choledochus receives the pancreatic duct about nine lines before its termination, as in the Marsupials, where its coats are thickened and glandular, and opens into the duodenum about eight lines from the pylorus. The pancreas in the Ornithorhynchus is a thin lobulated gland bent upon itself; the left and larger portion descends by the side of the left MONOTREMATA. Fig. 188. 33S> lobe of the spleen.* The pancreas is thicker in the Echidna, and enlarges considerably to- wards the duodenum. The principal difference occurs in the place of termination of the pancreatic duct, which, in the Ornithoihynchus, joins the ductus chole- dochus, but in the Echidna terminates sepa- rately in the duodenum and nearer the pylorus than does the ductus choledochus. The arrangement of the hepatic and pan- creatic ducts is thus conformable to the Mam- malian type, and the Oinithorhynchus, in the place of the junction of these ducts near the commencement of the ductus choledochus, ma- nifests its affinity to the Marsupials, as the same structure occurs in the Dasyure. The spleen (Jig. 187, u, u) consists of two lobes bent upon each other at an acute angle, * Meckel, loc. cit. p. 46. Submaxillari/ glands. Echidna selosa {Original.) in which the Monotremes again resemble the Marsupials. In the Ornithorhynclius the ante- rior and right lobe is four inches long, the pos- terior and left lobe two inches and a half ; the right lobe is bent upon itself. In the Echidna, besides the two lobes which are continued for- wards from the left side, there is a third shorter descending appendage.* The lobes are thin and moderately broad in both Monotremes, and in structure, size, situation, and general figure, the spleen conforms to the Mammalian type, al- though this is exhibited under a more than usual complication of external form. CIRCULATING SYSTEM. Blood of the Ornithqrhynchus. — A Mammal presenting such striking resemblances in cer- tain parts of its organization to the oviparous * Cuvier, 1. c. t. iv. p, 591. 390 MONOTREMATA. modification of the Vertebrate type as does the Ornithorhynchus, is one of which it was obviously most interesting to ascertain the form of the blood-discs. I have made appli- cations to different professional and zoological correspondents in Australia on this subject, for the transmission of a portion of recently drawn blood thinly spread and dried on glass, or preserved in its fluid state in brine and other menstrua of the same density as serum, and for the results of observations on the blood-discs of both the Ornithorhynchus and Echidna. Mr. Hobson, of Hobart Town, Van Diemen's Land, an accomplished sur- geon and comparative anatomist, has made the required observations on the blood of the Ornithorhynchus, of which he has trans- mitted to me the following account: — "The globules of the blood of the Ornithorhyn- chus are discoid, and measured about the 3553th of an inch, calculating two-and-a-half millimetres to the line. The human blood- globules were placed side by side with those of the Ornithorhynchus, and both in shape and size so nearly resembled each other that it was impossible to say which was human and which was Ornithorhynchus. These examinations were made in the presence of Mr. Ronald Gunn, by means of one of Oberhauser's mi- croscopes ; the powers used were 250, 400, and 800. In order to be sure that there was no delusion, I placed the elliptical globules of a Lizard's blood beside those of the Ornitho- rhynchus. The tenacity and high florid colour of the blood, together with the greater propor- tional number of globules in a given quantity" (in the Ornithorhynchus) " is most interesting in an analogical point of view." From the preceding highly valuable observa- tions we may infer that the Oi-nithorhynchns resembles the Mammalia in the circular form, the size, the proportional number, and florid colour of its blood-discs, which correspond in size with those of the only Edentate species yet examined, viz. the Armadillo,* and conse- quently with those of the Quadrumana and of Man. The blood-discs of the Echidna, according to the observations made by Dr. John Davy on a portion of blood of that animal, transmitted to England in brine, are likewise circular. Heart. — The heart of the Ornithorhynchus (Jig. 187, a, b, c) presents a rounded oblong form ; it is situated in the middle of the ante- rior part of the chest, parallel with the axis of the cavity. It is inclosed in a thin subtrans- parent but strong pericardium. The right auricle (b) is larger and longer than the left; its appendix is free and is slightly bifid, as in the Marsupials. It receives the venous blood, also, as in that order, by three great veins; the left vena innominata (f) de- scending behind the left auricle to join the termination of the inferior cava (A). The coro- nary vein also terminates in the auricle to the right of the inferior cava. The right superior * See Medical Gazette, Nov. 18, 1840. cava (e) is joined to the left by a transverse branch (g). Meckel found in the heart of both the Ornithorhynchi dissected by him a deep but closed fossa ovalis, near the upper extremity of the septum. This structure would indicate that the intra-uterine existence of the young was of longer duration than in the Marsupialia. The right ventricle (a) is capacious, with thin parietes. The tricuspid valve I found to consist of two membranous and two fleshy portions : the smallest of the latter was situated nearest the origin of the pulmonary artery, and seemed to correspond with the lesser fleshy valve observ- able in the heart of certain birds, as the Ostrich ; it is attached to the whole of the side of the first or adjoining membranous portion. The second fleshy portion may be described as ana- logous to the muscular valve in the Bird's heart, if the lateral margin of this were detached from the wall of the ventricle, and the connection of its two extremities was preserved, the one to the angle between the fixed and moveable wall of the ventricle, the other to the auriculo-ven- tricular orifice. The two edges of the lower half of the second fleshy portion of the valve in the Ornithorhynchus are free ; but those of the upper half are attached to the two mem- branous portions of the tricuspid valve ; the margin of the membranous part of the valve is attached to the fixed wall of the ventricle by two small chordae tendineaa; and the structure of the valve thus offers an interesting transi- tional state between that of the Mammal and that of the Bird.* The origin of the pulmonary artery is pro- vided with the three usual sigmoid valves. The left ventricle has very thick parietes, which form the apex of the heart; the mitral valve is membranous ; the larger flap is at- tached to two strong columnar earner ; the smaller flap to three smaller columns. The small left auricle (c) receives two pulmo- nary veins. In the Echidna the free appendix of the right auricle is slightly indented. The ter- minal orifice of the superior cava is protected by a membranous semilunar valve, extending from its left side. The musculi pectinati di- verge from a strong fasciculus, which extends from the appendix to the orifice of the in- ferior cava ; this fasciculus bounds the left side of a wide fossa ovalis, which is imper- forate. The inferior cava is protected by a large membranous Eustachian valve ; the left vena innominata terminates by a distinct aperture to the left of the preceding, and is also defended by a process of the Eustachian valve. The inner surface of the right ventricle is more irre- gular than in the Ornithorhynchus ; the free wall is attached to the fixed one by several columnar carneae and short chordae tendinex; the tricuspid valve is membranous and consists of one principal portion attached to the exterior * " Similitudo quaedam cum avium valvula ve- nosa dextra et propter carnositatem et propter figuram minime prastervidenda adest." — Meckel, 1. c. p. 31. MONOTREMATA. 391 circumference, and a smaller portion closing the outer angle ; the free margin of the valve is attached to the extremity of a large fleshy column, arising by different roots from both the fixed and the free walls of the ventricle ; a short fleshy column is attached to the left ex- tremity of the valve; some chordae tendinea? are fixed to the right angle of the valve. The rest of the structure of the heart corresponds with that in the Ornithorhynchus. The aorta (fig. 187, d) bends, as in the Mammalia, over the left bronchus. The pri- mary branches come off from the arch, in both Monotremes, as in Man, viz. arteria in- nominata, left carotid, and left subclavian. The innominata divides, after a course of three lines, into the right subclavian and carotid (fig. 187, i), the latter being the smallest branch. Both subclavians emerge from the thorax above the first rib, and pass between it and the coracoid. The phrenic, coeliac, and mesenteric arteries are given oft' from the abdominal aorta; the renal artery is short, wide, and single; there is no inferior mesenteric artery, but the abdominal aorta terminates by dividing into the two com- mon iliac and the caudal arteries, the arterial system agreeing in this and the other essential characters with the Mammalian type. The crural artery is shown aty, fig. 180. Each of the superior vena; cava receives the azygos vein of its respective side. The inferior cava has a long course in the thorax ; it is greatly dilated in the liver in the Ornithorhyn- chus, as it is in the Placental divers, the Otter and Seal for instance.* The veins of the kidney are continued from the renal artery, and communicate solely with the inferior cava. The vena porta? is consti- tuted as in other Mammalia. RESPIRATORY SYSTEM. The lungs of the Monotremata are con- fined to the thoracic cavity, and suspended freely in compartments partitioned off' by du- plicatures of the pleura. The right lung is divided, in the Ornithorhynchus, into three lobes, of which the smallest (Jig. 187, n) fills the interspace between the heart and diaphragm : the left lung (o) is undivided. The structure of the whole is spongy, and divided into minute cells. The trachea (fig. 187, m) is wide, as in most aquatic mammals : the cartilaginous rings, fifteen in number, are broad and slightly overlap each other : the bronchial annuli are bony, and are continued of that texture through a great part of the lungs. In the Echidna the trachea is narrower than in the Ornithorhynchus : there are twenty-two tracheal hoops, which are disunited behind ; very firm cartilaginous annuli are continued along the larger branches of the bronchus for some way into the lung, but the smaller branches are membranous. There is no trace of inferior larynx in either * Meckel, 1. c. p. 32. Monotreme. The superior la- Fig. 189. rynx is conformable to the Mam- a malian type, but presents some remarkable modifications in the Ornithorhynchus. The thyroid cartilage (fig. 189, c) in this animal is very broad; its middle part is prominent and acuminate : the lateral ala? are bony, and each of them divides, and sends one of the processes to the posterior Larynx of part of the pharynx (fig. 186, c), Ondthorhyn- where it becomes cartilaginous, chtis. and is confluent with the corres- (Meckel.) ponding process of the opposite side. The cri- coid cartilage (Jig. 189, d) is ossified at its middle anterior part. The arytenoid cartilages, (fig. 189, e, e) present the usual triangular form, and are of large size. The epiglottis (fig. 189, a) is remarkably broad, with an acuminated and notched apex. Besides a small thymus gland, Meckel found in the Ornithorhynchus two other lateral glands on the external part of the chest, extending be- tween the scapula and humerus, covered only by the panniculus carnosus and the trapezius. These presented a reddish colour, a tabulated structure, and pretty firm texture. RENAL SYSTEM. The suprarenal bodies (fig. 190, b, b) are of moderate size, of the usual structure, and have the ordinary situation internal to the anterior extremities of the kidneys. The kidneys {a, a), in both Monotremes, are smple, compact, conglobate glands, situated, as usual, far forwards on the loins, the right a lit- tle in advance of the left. The external surface, after the removal of the capsule, is smooth. The renal tissue consists of the two usual por- tions; the cortical, or softer and more vascular part, being easily distinguishable from the more compact medullary part. The tubuli uriniferi terminate on the concave surface of a small and simple pelvis. The ureter (fig. 190, c, c) takes the usual course to the contracted neck of the bladder, but terminates, in the male, in the urogenital canal, below the vasa deferentia; and, in the female, ( fig. 191,/, I,) beyond the uterine orifice, which thus intervenes between the ureter and the orifice of the urinary bladder. In all respects, save the place of termination of the excretory ducts and their relation to the reservoir of the renal secretion, the Mono- tremes adhere closely, in regard to their urinary system, to the Mammalian type. The circum- stances in which they deviate from the higher mammals approximate them closely to the Iteptilia, and especially the Chelonia ; and it is to be observed that the deviation commences where the urinary system begins to be connected with the generative organs, in which the ovipa- rous type of structure is especially manifested. Organs of generation. The male organs in both Monotremes con- sist of a testis, vas deferens, Cowper's glands, and penis : there are neither prostatic glands nor vesicula? seminales. 392 MONOTREMATA. Fig. 190. Male organs, Ornithorhynchus. {Meckel.) The Monotremes are true testiconda, and in this respect differ from the Marsupial animals. In the Echidna each testicle is situated imme- diately below, or sacrad of, the kidney, and is suspended to that gland by a fold of peritoneum; the same fold is continued to the neck of the bladder, inclosing the vas deferens, which is disposed in a S2iies of close transverse folds throughout its whole course. It corresponds closely, in these respects, with the Ornitho- rhynchus. In neither Monotreme is there any disparity of size between the right and left testicle : the latter is figured in situ at a, fig.187. The vas defeiens ( fig.\90,J') emerges from the upper or atlantal extremity of the testis (e) ; and, from its peculiarly extended, plicated, or folded course, seems to prolong the epididymis nearly to the neck of the bladder ; the folds gradually diminish, and the duct itself enlarges, as it approaches its termination, which is in the beginning of the urogenital canal (g). This canal is continued through the pelvis and termi- nates in the vestibular passage, anterior to the orifice of the rectum (f the Shrews which secrete " a mucus possessing a very powerful odour," says, " I should not be surprised, if this mucus, more abundant and more substantial in the Monotremata, became the nutriment of the young after their hatching. The Monotremata would act, in this respect, like some aquatic birds which conduct their young after hatching to the water, and assist them in their sustentation. The maternal instinct would lead the female Ornithorhynchus to effect the contraction of the gland, which is possible by the efforts of the panniculus carnosus and the great oblique muscle, between the fibres of which the gland is seated, and thus procure for the young, at several periods of the day, by way of nutri- ment, an abundant supply of mucus. If this edu- cation is carried on in the water, where we know, by the history of the generation of frogs and the nutrition of their tadpoles, that the mucus com- bines with the ambient medium, becomes thick, and supplies an excellent nutriment for the early age of these reptiles, we shall understand the utility of the ventral glands of the Ornithorhyn- chus, as furnishing a source of nutriment for the young of these animals, — for young Ompura newly hatched."— Gazette Medicate, Feb. 18th, 1833.— Proceedings Zool. Society, March 1333, p. 29. MONOTREMATA. 401 to be granted to it in order to direct its move- ments. The privation of this sense, on the contrary, implies a confinement to the nest, and a reception on land of the mammary secretion of the parent. The auditory orifices (fig. 196, d) are situated about a line behind the eyes. The general form of the body and the carti- laginous condition of the bones of the extre- mities equally militate against the young Orni- thorhynchus possessing, at this period of its existence, active powers of swimming or creep- ing. The head and tail are closely approxi- mated on the ventral aspect, requiring force to pull the body out into a straight line ; and the relative quantity of integument on the back and belly shows that the position necessary for the due progressive motions is unnatural at this stage of growth. The toes on each of the four feet were com- pletely formed, and terminated by curved, co- nical, horny claws ; but the natatory fold of membrane of the fore foot had not the same proportional extent as in the adult, and the spur of the hind foot did not project beyond its socket in either specimen. In the smaller one, which was a male, it presented the form of an obtuse papilla; while in the larger specimen, although a female, it was more plainly developed and more pointed (fig. \97, f). This circum- Fig. 197. Hind-foot and spur, yonnp female Ornithorhynchus , magnified. ( Owen, Zool. Trans.) stance is inexact accordance with the known laws of the development of sexual distinctions, espe- cially of those of secondary importance, such as beards, manes, plumes, horns, tusks, spurs, &c, which do not avail in distinguishing the sexes till towards the period of puberty. As the spur is the only obvious distinction of the sexes in the full-grown Ornithorhyrichus, I was compelled to refer to the internal essential organs, in order to determine the sex of the specimens here described. The ventral surface of the smaller specimen was carefully examined with a lens ; but no trace of an umbilicus could be satisfactorily determined. In the very young or newly born Kangaroo, a longitudinal linear trace of the attachment of the umbilical vesicle is at that time apparent, but it is rapidly obliterated ; as is probably also the case in the Ornitho- rhyrichus. In the smaller specimen the intromittent organ projected a little way beyond the excre- VOL. III. mentory orifice, as in the young Marsupial ia ; but it was not continuous, as in them, with the anterior margin of that outlet. In the larger female specimen the corresponding organ was visible just within the verge of the opening ; but this clitoris, remaining stationary in its development, is afterwards, as I have shown in my paper on the Mammary Glands of the Mo- notremes,* removed to a distance from the preputial aperture by the elongation of the sheath, just as the minute spur of the female lies concealed at the bottom of the progres- sively elongated tegumentary socket, and as the tongue is left at the back of the oral cavity by the growth of the jaws. The following; anatomical appearances were noticed in these young Ornithorhynchi : — On laying open the abdomen in the larger specimen, the most prominent viscus was the stomach, which was almost as large as in the adult animal, deriving at this period no assist- ance from the preparatory digestive cavities, the cheek-pouches, which were not yet deve- loped. The stomach extended in a curved direction across the epigastric and down the left hypochondriac region to the left iliac re- gion. It was full of coagulated milk. In the smaller specimen the stomach was empty; when distended with air it exhibited a less disproportionate development. It was situated in the left hypochondriac and lumbar regions. The intestines contained air, with granular masses of a mucous chyme adhering to their internal surface. This condition of the digestive canal would seem to show that no long period had elapsed since the birth of the specimen, and that either lactation had not been in full action, or that the young one had been deserted by the parent for some time before it was taken. In both specimens the spleen bore a propor- tionate size with the stomach ; and as the dif- ference in the development of the stomach was considerable, the correspondence between the condition of the spleen with that of the diges- tive cavity was made very obvious. The difference in the development of the liver was not greater than corresponded with the different size and age of the two specimens. But the pancreas in both bore the same ratio to the stomach as the spleen. This, therefore, would seem to afford some indication of the organs with which the function of the spleen is more immediately related. The intestinal canal in the larger specimen was situated almost entirely on the right side of the abdomen. The carum in both was very minute and filamentary. I examined the ileum, and more especially in the usual situation above the ccecum, but could not perceive any trace of the pedicle of the umbilical or vitelline vesicle. The other vestiges of foetal organization were more obvious than in the ordinary marsupial or ovoviviparous Mammalia. In both specimens, but more especially in the smaller one, the umbilical vein was seen, extending from a linear cicatrix of the perito- * Phil. Trans, for 1832, p. 525. 2 n 402 MONOTREMATA. neum, opposite the middle of the abdomen, along the anterior margin of the suspensory ligament to the liver. It was reduced to a mere filamentary tube, filled with coagulum. From the same cicatrix the remains of the umbilical arteries extending downwards, and near the urinary bladder, were contained within a duplicature of peritoneum, having between them a small flattened oval vesicle, the re- mains of an allantois, which was attached by a contracted pedicle to the fundus of the bladder. As both the embryo of the Bird and that of the ovoviviparous Reptile have an allantois and umbilical vessels developed, no certain inference can be drawn from the above appear- ances as to the oviparous or viviparous na- ture of the generation of the Ornithorhynchus. But the structure of the ovary and that of the ovum, both before and after it has quitted the ovisac, afford the strongest analogical proof of the intra-uterine developement of the embryo, and at the same time accord with the ascer- tained fact of the mammary nourishment of the young animal. The kidneys were situated remote from the pelvis and high up in the lumbar region. The situation of the kidneys with respect to each other varied in the two specimens ; in the larger one, the left was a little higher than the right; in the smaller one it was a little lower; the latter is the ordinary position in the adult. The supra-renal glands did not correspond with this arrangement, but in both instances the right was higher than the left, agreeing with the relative position of the testes in the male, and the ovaries in the female. In Man the large size of the supra-renal glands is noted as a foetal peculiarity, but in the Ornithorhynchus they are of minute size, their greatest diameter not exceeding one-eighth of a line in the smaller specimen here described ; and they increase in size progressively with the growth of the ani- mal, and in a greater proportion than the kid- neys, which increase would appear, therefore, to have relation to the development of the ge- nerative organs. There were no traces of the corpora Wolffiana. The testes in the small male specimen were situated a little below the kidneys: they were of an elongated form, pointed at both ends, with the epididymis folded down, as it were, upon their anterior surface. In the female, the ova- ries were freely suspended to the loins in a similar position, the right being at this period as large as the left : it is the persistence of the latter at an early stage of development which occasions the disproportionate size of the two glands in the adult. The still greater inequa- lity of size in the oviducts of the Bird arises, as is well known, from a similar arrest of the development of the one on the right side, but both are equal at an early stage of existence. The uteri were straight linear tubes, scarcely exceeding the size of the ovarian ligaments. The lungs were found amply developed in both specimens ; the air-cells remarkably ob- vious, so as to give a reticulate appearance to the surface, and a resemblance to the lungs of a turtle. They had evidently been permeated by air in the smaller specimen. The heart, in both specimens, was of the adult form, with the apex entire ; but the left auricle was proportionately larger than in the adult heart. The ductus arteriosus was here very evident, and formed a filamentary chord in the usual situation between the aorta and pulmonary artery, but proportionately longer than in the true viviparous Mammalia. Here also we have the indication of a more prolonged foetal existence than in the marsupial animals, there being no trace of a ductus arteriosus either in the uterine or mammary foetus of the Kangaroo. The Ornithorhynchus also deviates from the ordinary Marsupialia in having the thymus gland. This is situated in front of the great vessels of the heart, and consists of two lobes, of which the right is the largest. The traces of foetal structures presented by these young Or- nithorhynchi, and especially the allantoic dila- tation of the urachus, indicate that the Mono- tremata differ from the Marsupialia in a longer continuance of the true foetal or intra-uterine existence. Mammary organs. — In this section will be adduced the evidence in proof of the essentially Mammalian nature of the Monotremes which the presence and ascertained function of the mammary glands have yielded. The most important result of Professor Mec- kel's anatomical investigations of the Ornitho- rhynchus was his discovery of the two large abdominal subcutaneous glands : these he con- cluded to be the mammary organs, which until that period had been supposed to be absent in the Ornithorhynchus. Subjoined is the figure which Meckel has given of one of these glands in its natural relative position, jig. 198. It measured four inches and a half in length, two inches in breadth, and half an inch in thickness. From this apparently conclusive evidence of the affinity of the Ornithorhynchus to the Mam- malia, Professor Meckel, however, is far from drawing conclusions as to the identity of their mode of generation. For assuming that the difference between the bringing forth of living young and of eggs is really very small and by no means of an essential nature, and remarking that birds have accidentally hatched the egg within the abdomen and so produced a living foetus, — an occurrence which has also been in- duced by direct experiment, and that, lastly^ the generation of the Marsupial animals is very similar to the oviparous mode, he deems it very probable that as the Ornithorhynchus ap- proaches still nearer than the Marsupial ani- mals to Birds and Reptiles, its mode of gene- ration may be in a proportionate degree analo- gous. For an animal possessing mammary glands he claims, however, the right to rank with the Mammalia, agreeing with Professor Geoffroy only so far as to consider the Mono- tremata as a distinct order of quadrupeds, which he places, as Cuvier has done, next to the Edentata. Against this conclusion, however, Professor MONOTREMATA. 403 Fig. 193. Mammary (jhtnil, Ornithorhynchus, nearly arrived at full size. ( Meckel.) Geoffroy has argued (Annales des Sciences Nat. ix. 1826, p. 457) that the subcutaneous abdominal glands considered by Meckel as mammary, possess none of the characters of a true mammary gland ; he states that he exa- mined them with the greatest attention, com- paring them with the human mammary glands, and especially with those of Marsupial animals, and that they were of a totally different texture, consisting of a vast number of ccecums placed side by side, all directed to the same point of the skin, where only two excretory orifices were to be perceived, and these orifices so small that the head of the smallest pin could not be made to enter them. That above all there was no trace of nipples ; that in the specimen examined by him, which had the size and ap- pearance of an adult female, the apparatus in question was not more than a fourth part the size of that observed by Meckel. But a mam- mary gland, Professor Geoffroy observes, when arrived at its full development, occasions an enlargement of all its constituent parts, the nipple acquiring additional bulk even before lactation commences, and that there was no appearance of this kind in the Ornitho- rhynchus. He considers, therefore, these ab- dominal glands as analogous to those which are situated along the flanks of Salamanders, and still more to the odoriferous glandular ap- paratus which is concentrated at the sides of the abdomen in the Shrews. In the absence of direct testimony of the nature of the secretion of the abdominal sub- cutaneous glands of the female Ormthorhyn- chus, the next obvious step was to test their disputed nature and office by an examination of their periods of increase and functional activity, as compared with those of the ovaria. If these glands had been analogous to the scent- glands of the flanks in the Shrews, and if their secretion had been destined to attract the male to the sexual intercourse, as suggested by Pro- fessor Geoffroy, their development ought to have proceeded pari passu with that of the ova- ria, and the enlargement of both organs ought to have simultaneously reached its maximum. But in specimens in which the ovisacs were enlarged so as to indicate the ova to be ripe for development, I found* that the abdo- minal glands had made a comparatively slight progress to their full size (fig. 199). This Fig 199. a Mammary gland, Ornithorh.yneh.ua, natural size at non-brecdini) season. (Owen, Phil. Trans. 1832.j * Philos. Trans. 1832, p. 525. 2 d 2 404 MONOTREMATA. condition was only manifested in the females with ovaria, large indeed, but without promi- nent ovisacs, and in which the recent corpora lutea were almost absorbed. These facts were established by the dissection of five female Ornithorhynchi. In each of these specimens the mammary gland was composed of between one hun- dred and two hundred elongated subcylin- drical lobes, forming an oblong flattened mass, and converging to a small oval areola in the abdominal integument, which areola is situated between three and four inches from the cloaca, and about one inch from the mesial line. The lobes in the fully developed glands are rounded and enlarged at their free extremities, and measured at that end three or four lines in breadth, and became narrower to about one-third from the point of insertion, where they end in slender ducts. Almost all the lobes are situated at the outer side of the areola, and consequently converge towards the mesial lineof the abdomen. Between the gland and the integument the panniculus carnosus (fig. 199, a) is interposed, closely adhering to the latter, but connected with thegland by loose cellular membrane. This muscle is here a line in thickness, its fibres are longitudinal, and, separating, leave an elliptical space for the passage of the ducts of the gland to the areola. On the external surface of the skin, when the hair is removed, this areola can only be distinguished by the larger size of the orifices of the lacteal ducts, compared with those for the transmission of the hairs. Fig. 200. Mammary areola, Ornithorhynchus , natural size. (Owen, Phil. Trans. 1832.) The orifices of the ducts thus grouped together form an oval spot, which in the female with the largest glands measured five lines in the long and three in the short diameter. In none of the specimens was the surface on which the ducts terminated raised in the slightest degree beyond the level of the surrounding integument. Meckel was disposed to believe that the ducts terminated on a small eminence about the size of a millet-seed, but did not succeed in demonstrating the fact by injection of the ducts.* * Meckel writes : " Dnctuli excretorii, maxime attenuati, in glandular medio extrorsum aperinntur. Quamvisneque setas, neque mercuriam per duetus.et per se, utmonui, angustissimos, et spiritu vini con- Not any of the specimens of Ornithorhyn- chus examined by me have presented a mammary eminence of any dimensions ; on the contrary, I have succeeded in demonstrat- ing the termination of the lacteal ducts on the flat areolar tract. Having in vain at- tempted to insert the smallest absorbent pipe into the mouths of these ducts, I thrust it into the extremity of one of the elongated lobes, and after a few unsuccessful efforts at length saw the mercury diffuse itself in mi- nute globules through the parenchyma of the lobe, and at a distance of an inch it had evi- dently entered a central duct, down which it freely ran to the areola, where it escaped exter- nally from one of the minute orifices just de- scribed. This process was repeated on most of the lobes with similar results, the greater part of them terminated by a single duct open- ing exteriorly and distinct from the rest, but in a few instances the ducts of two contiguous lobules united into one, and in these cases the mercury returned by the anastomosing duct and penetrated the substance of the other lobe as freely as that into which the pipe had been inserted. Some of the lobes injected by the reflux of the mercury through the duct, and of which it was more certain that the glandular structure and not the cellular membrane was filled, were dried, and various sections were submitted to microscopical examination. At the greater extremity they are minutely cellular, the cells communicating with each other, and elongating as the lobule grows narrower, first at the centre, so as to form apparently minute tortuous tubes, which tend towards and terminate in a larger central canal, or receptacle, from which the ex- cretory duct is continued. On making a sec- tion of the corium through the middle of the areola the ducts are seen to converge slightly to the external surface, but there is no inverted or concealed nipple at this part, as in the Kan- garoo. ( Fig. 201 is a sketch of a magnified view of this section, with the section of one of the dried and injected lobules.) Thus, prior to and independently of any direct observation of the secretion of the ab- dominal glands, the anatomical facts brought to bear upon their disputed function were in- dubitably more favourable to the opinion of the German than of the French Professor ; for, 1st, the glands are confined to the female, and vary in degree of development at dif- ferent periods in individuals of equal size, at- taining in some an enormous development ; 2nd, the secretion is conveyed outwardly by means of numerous long and narrow ducts, tractos, et fiuido concreto repletos.trajicere potuerim, area tamen indicatur in cute. Quamvis pili hanc par- tem tegant, apparet tamen, hos si abstuleris, plaga, quinque circiter lineas longa, tres lata, foraminulis, iis, e quibus pili egrediuntur, majoribus, nigris, circiter octoginta stipata, forsan ductuum excre- torium ori6ciis. Praeterea in hujus medio depres- siuncula duarum linearum diametri adest, pilis destituta, sed eminentiunculis ina?qualis, inter quas prascipue una, milii granum haud aequans, reliquas antecellit. Hae sine dubio papillae et ductuum ori- ficia sunt." — Loc. cit. p. 54. MONOTREMATA. 405 Terminal ducts, and lube of mammary gland, injected twice natural size. strongly implying its fluid nature, and most contrary to the mode in which odorous sub- stances are excreted ; 3rd, the excretory ori- fices are by no means extended over so wide a space, in proportion, as in the Shrew, but col- lected into a point which we know to be not disproportionate to the size of the mouth of the young animal, and this point is situated in a part of the body convenient for the transmission of a lacteal secretion from the mother to her offspring. Compared with an ordinary mammary gland, that of the Ornithorhynchus differs chiefly in the absence of the nipple, and, consequently, of the surrounding vascular structure necessary for its erection. But the remarkable modifica- tion of the mouth in the young Ornithorhynchus removes much of the difficulty which previously attached itself to the idea of the possibility of an animal with a beak obtaining its nutriment by suction. The width of the mouth in the smallest observed Ornithorhynchus corres- ponds with the size of the mammary areola; and the broad tongue, extending to the apices of the broad, short, and soft jaws, with the fold of integument continued across the angle of the mouth, are all modifications which pre- pare us to admit such a co-adaptation of the mouth of the young to the mammary outlet of the parent, as, with the combined actions of suction in the recipient, and compression of the gland in the expellent, to effect this essen- tially Mammalian mode of nourishment. We may presume that a corresponding mo- dification of the mouth of the new-born animal obtains in the Echidna, since the mam- mary glands in this Monotreme* correspond in structure, and mode of termination of the excre- tory ducts, with those of the Ornithorhynchus. As yet the secretion of the mammary glands of the Echidna has not been observed; but that of the Ornithorhynchus has been detected not only in the stomach of the young (ante p. 401), but oozing from the lacteal pores of the female, and by more than one competent observer.f Mr. George Bennett, describing his dissection of a female Ornithorhynchus shot at Mun- doona, New South Wales, on the 14th of November, the day before his arrival at that place, and which " had evidently just produced her young," and had very large mammary glands, thus records his obser- vation of their secretion. " The glands were very vascular on the surface, the mammary artery ramifying over them in a most beautiful and distinct manner. The fur still covered that portion of the integument on which the ducts terminated, and there was no appear- ance of a projecting nipple." " How different was the appearance in the recent state of this mammary gland from that which I had pre- :, viously seen at the Royal College of Sur- geons, in a specimen long preserved in spirits, in which I had the opportunity of witnessing the injection of the ducts with mercury by my friend Mr. Owen, the mercury exuding, as I , have seen the milk from the similar ducts, upon the integuments." — Zoological Trans- actions, vol. i. p. 251. In a female Ornitho- rhynchus, which with her two full-furred young were captured alive by Mr. Bennett on the 28th of December, he says, " The milk that could be expressed from the glands was but trifling in quantity ; and, in the mother of these young animals, such would have been expected to be the case, for they were capable of feeding upon more substantial diet." — Ibid. p. 254. Crural gland and spur.\ — This remarkable * Sec Phil. Trans. 1832, p. 537, pi. xvii., figs. 2 and 3. t Hon. Lauderdale Maule, Proc. Zool. Society, part ii. p. 145. G. Bennett, Esq. ib. part i. p. 82. Part ii. p. 141-11. % Meckel, loc. cit. p. 54, calls this peculiar sexual gland ' femoral,' observing, " ne ipso no- mine de fnnctione judicium proferam, forsan re- trahendam, hoc nomen a situ impono." As, how- ever, the femoral position is peculiar to the Orni- thorhynchus, the gland being popliteal in the Echid- na, I prefer a name derived from the word ' eras,' which has a move extended signification to the whole hinder extremity. 406 apparatus in the Mo- notrematous quadru- peds must be classed with the accessory or- gans of generation in the same category with the antlers of Deer, the spurs of the Cock, the claspers of the Shark, and other peculiar characteristics of the male sex. It has been already shown, in the description of the young Ornithorhyn- chus, that the external parts of the apparatus are not so developed as to distinguish the sex at that immature period ; a small spur, concealed in a cavity or socket of the inte- gument covering the heel, the bottom of which closely adheres to the accessory tarsal ossicle, exists in both sexes; a magnified view of the part in the young female is given at fig. 197. As the young animal advances to maturity the cutane- ous socket increases in width and depth in the female, but without any corresponding growth of the rudimentary spur, of which in aged female Ornithorhynchi sometimes no trace remains. In the male Ornilhorhynchus the tarsal spur soon begins to rise above the socket, and finally attains a length of ten lines with a basal breadth of five lines, apparently everting the tegumentary socket in the progress of its growth. The spur (Jig. 173, k, e; fig. 202, e) consists of a firm semitransparent horn-like substance: it is coni- cal, slightly bent, and terminated by a sharp point; its base is expanded, and notched at the margin for the implantation of the ligaments which connect the spur with the accessory flat tarsal bone ( os basilare, Meckel,) (fig. 173, k, d; Jig. 202, d.) The base of the spur is co- vered by a thin vascular integument. The spur is traversed by a canal which commences at the centre of the base and terminates by a fine longitudinal slit, about one line distant from the point, closely resembling in this respect the canal that traverses the poison fang of the venomous snake.* Like that canal also the spur of the male Monotreme is sub- servient to the transmission into the wounds it may inflict of the secretion of a peculiar gland. This gland («, Jig. 202) is situated in the Ornithorhynchus at the back part of the thigh, between the femur and the long process from the head of the fibula, covered by the integu- MONOTUEMATA. Crural gland and spur, male Ornithorhynchus, (Meckel.) ment and the cutaneous muscle. It is of a triangular or reniform figure, convex above, concave below, or towards the leg; from twelve to fourteen lines in length, seven or eight lines broad, and three or four lines thick, with a smooth exterior, invested by a thin capsule, on the removal of which the gland may easily be divided into a number of small lobes. Its intimate structure, as displayed by a successful injection of mercury, is minutely cellular, like that of the glandula Harderi of the hare or goose, but with the ultimate secerning cells more minute ; the excretory duct is continued from the concave side of the gland, and small clusters of vesicles are developed from parts of its expanded commencement.* The duct, (fig. 180, l,) which is about a line in width and with pretty strong tunics, descends straight down the back of the leg, covered by the flexor muscles and posterior tibial nerve, to the posterior part of the tarsus, where it sud- denly expands into a vesicle (l>, Jig. 202) about three lines in diameter ; the vesicle is applied to the base of the spur, and a minute duct (c, fig. 202) is continued from it into the canal which traverses the spur. The tarsal perforated spur and its glandular apparatus are both relatively smaller in the male Echidna than in the Ornithorhynchus. The gland is situated lower down, in the popliteal region, between the insertions of the deep-seated fasciculi of the adductor femoris and the origins of the gastrocnemius ; it is of subspherical form, about the size of a pea, with a smooth exterior; the excretory duct, wide at the commencement, soon contracts into a filamentary canal, which again enlarges to form a small reservoir for the secretion just above the base of the spur. The true nature and use of this apparatus has not yet been determined. Its close analogy with the poison apparatus in other animals obviously suggests the idea of a corresponding function, but no well authenticated case of symptoms of poisoning consequent upon a wound inflicted by the spur has been recorded. It seems on the contrary that the Ornithorhyn- chus possesses not the instinct of availing itself of a weapon so formidable, as upon this theory the spur must be, when attacked or annoyed. Mr. George Bennett tried the following experi- ment with a full grown wounded but lively male Ornithorhynchus : — " I commenced by placing my hands in such a manner, when seizing the animal, as to enable it, from the direction of its spurs, to use them with effect; the result was that the animal made strenuous efforts to escape, and in these efforts scratched my hands a little with the hind claws, and even, in consequence of the position in which I held it, with the spur also. But although seized so roughly, it neither darted the spur into my hand nor did it even make an attempt so to do. As, however, it had been stated that the creature throws itself on the back when it uses this weapon, (a circumstance not very * De Blainvillein Bulletin de la Soeietc Philo- * Miillcr, Dc Glandularum penit. Struct, p. 43, mathiquc, 1817. tab. ii. fig. 10. MOTION. 407 probable to those who have any knowledge of the animal,) I tried it also in that position; but though it struggled to regain its former posture, no use was made of the hind claw. I tried several other methods of effecting the object I had in view ; but as all proved futile, I am convinced that some other use must be found for the spur than as an offensive weapon. I have had several subsequent opportunities of repeating the experiments with animals not in a wounded state, and the results have been the same."* Evidence to a like effect is given by the zoologists of the French expedition in the Astro- labe, in reference to the male Echidna.f An objection to the theory of the spur and gland being a defensive apparatus is their absence in the female. Since then this apparatus forms a sexual character, it may be presumed that its func- tion is connected with that of generation. Whether the spur be a weapon for combat among the males, — or, like the spiculum amoris of the Snail, be used to excite the female, the injected secretion being an additional stimulus, — or whether the spur be mechanically useful in retaining the female during the coitus, — are conjectures which must be verified or disproved by actual observation. BIBLIOGRAPHY.— Shaw, Naturalists' Miscellany, 1798. General Zoology , vol. i. 1800. Iilumenbach, Philos. Transactions, 1800 ; and Voigt's Magazin f ur den neuesten Zustand der Naturkunde, Band 2, 1800. Home, Philos. Transactions, 1802, pp. 67 and 356. Ibid. 1819. Lectures on Comparative Anatomy, passim. Cuvier, Lecons d'Anatomie Comparee, 1799-1805, passim. Ossemens Fossiles, 4to. vol. v. 1823. Peron and Lesueur, Voyage de dccouvertes aux Terres Australes, 1807. Meckel, Beitrage zur Vergleichenden Anatomie, 1808. Fro- riep's Notizen, 1824. Ornithorhynchi paradoxi de- scriptio anatomica, fol. 1826. De Bluinville, Dis- sertation sur la place que la famille des Orni- thorynques et des Echidnes doit occuper dans lcs series Naturelles, 4to. 1812. Bulletin de la Socicte Philomathique, 1817. Nouvelles Annates du Mu- seum, torn. ii. 1832. Geoffroy St. Hilaire, Ana- tomie Philosophique, torn. i. 1818. Mcmoire sur les Glandes Abdominales des Ornithorhynques faussement presumees mammaires, lesquelles se- cretent, non du lait, mais du mucus, &c. Gazette Medicale de Paris, 1833. Sur des Glandes Abdo- minales chez l'Ornithorhynque dont la determina- tion, comme mammaires, fut en Allemagne, et est de nouveau en Angleterre tin sujet de controversie, 8vo. 1833. Rudolphi, Abhandlungen der Berliner Akademie der Wissenschaftcn, 1829. Jaffe, Thesis inaug. de Ornithorhyncho paradoxo, Berolin, 1823. Traill, Edinburgh Philos. Journal, 1822. Hill, Linnaean Transactions, vol. xiii. 1822. Knox, Wernerian Transactions, vol. v. Van der Hoeven, Nova Acta Physico-Medica, torn. xi. 1823. Pander and D' Alton, Skelete der zahnlosen Thierc, 1825. Grant, ( Dr. R.) Annales des Sciences Naturelles, 1829, torn, xviii. Mutter, De Glandularum Secernen- tium Structura penitiori, fol. 1830. Owen, Philos. Transactions, 1832, 1834. Proceedings of the * Zoological Transactions, vol. i. p. 236. t " Nous n'avons point entendu parler d'accident occasionne par cette piqure, et nous-memcs nous avons touche, irrite cet Echidne sans qu'il ait ja- mais cherche a se servir de son arme, pas meme lorsque nous exercions sur elle une assez forte prcs- sion." — Zoologie du Voyage de 1'Astrolabe, p. 124. Zoological Society, October, 1832, March, 1833. Zoological Transactions, vol. i. 1834. Bennett, G. Zoological Transactions, 1834. Eydoux § Laurent, Voyage de la Favorite, 1836, 8vo. (R. Owen.) MONSTROSITY. — See Teratology. MOTION ANIMAL, ANIMAL DY- NAMICS, LOCO-MOTION, or PRO- GRESSIVE MOTION OF ANIMALS.— Amongst the infinite number of objects pre- sented by the Deity to our contemplation in the sublime spectacle of the universe, there are none, relating to the economy of animal life, more important in their consequences, more calculated to awaken inquiry, or deserving of more profound research, than the phe- nomena of progressive motion in man and animals. Life, in virtue of which animated beings possess sensation and exhibit the play of the vegetative functions, endows the muscular system with contractility, and is the funda- mental cause of all the motor power of animals. The theory of the progressive motion of animals presents a most extensive field for anatomical and physiological inquiry, far too extensive indeed for the space here allotted to this subject; it will therefore be treated only in outline. The automatic, and several of the voluntary motions which belong to the vegetative functions of the animal economy, though de- rived from the same source as those of progres- sive motion, will not be included in this investi- gation. The theory of locomotion relates to those mechanical functions by which animals are capable of changing their relative positions or distances with respect to surrounding ob- jects supposed to be stationary or fixed. The locomotive organs of the higher animals are composed of a system of levers of various forms, orders, and dimensions, so united or ar- ticulated at the joints as to give them the re- quisite mobility as well as direction of motion. The fulcra to these levers are the earth, the air, or the water ; the active agents of mo- tion are the muscles which constitute a complex system of contractile organs, firmly attached to the levers, whereof the points of connexion, amount of contraction, and direc- tion of force, communicate to the levers, to which they are firmly attached, all the move- ments necessary for progression. The progression of some animals, such as the Annelida and Ophidian Reptiles, is effected by the alternate contraction or flexion and elongation, or by undulatory movements of the body ; in others, as Bipeds, Quadrupeds, Fishes, Birds, &c, by the alternate approxima- tion and angular separation of the levers which form the organs of progression. These prin- ciples apply to animals, whether their levers are represented by wings, fins, or legs, and whether the progression is effected on solids, in water, or in the air. The various modes of animal progression 408 MOTION. are swimming, flying, crawling, climbing, leaping, running, walking, &c. The con- sideration of these diversified methods of progression involves the theory of the mo- tion of bodies in general, of the lever, the pulley, the centre of gravity, specific gravity, and the resistance of fluids, &c. ; and, as we shall have occasion for constant refer- ence to the mechanical principles connected with these subjects, they will be first dis- cussed; but for the convenience of those who are unacquainted with the algebraic method of computation and analysis, the latter will generally be separated from the text. Fundamental Axioms. — First, every body continues in a state of rest or of uniform mo- tion in a right line until a change is effected by the agency of some mechanical force. Secondly, any change effected in the quiescence or mo- tion of a body is in the direction of the force impressed, and is proportional to it in quantity. Thirdly, reaction is always equal and con- trary to action, or the mutual actions of two bodies upon each other are always equal and in opposite directions. Thus if M (fig. 203) be a particle of matter free to move in any direction, and if the lines MA, MB, represent the intensity of two forces Fig. 203. M -A B acting on it in the direction MC, the particle M will move towards C by the combined action of the two forces, and it will require a force in the direction of CM, equal to MA+ MB to keep it in a state of rest: but if MA and MB (Jig- 204) represent the intensities and directions of two forces acting on the par- ticle M in opposite directions, if MA be Fig. 204. greater than MB, the particle M will be moved towards A by the difference of these two forces, and it will require a force equal to that difference to keep it at rest. The composition and resolution of forces. — In the composition of forces it is proposed to find the resultant, arising from any number or system of forces acting upon a given point. The resolution of forces, which is the converse of the former process, consists in discovering what forces acting in given directions would com- bine to produce a given resultant: Thus, if there be two forces F F' (Jig. 205), whose directions and magnitudes are represented by F N, F' N, and if FR, F'R be drawn respectively parallel to F'N, FN, then by the composition of forces we find the magnitude and direction of the equivalent or resultant of these two forces to be RN, and conversely it may be resolved into a pair of forces as RF, RF' represented by the adjacent sides of any parallelogram, of Fig. 205. which RN is the diagonal, and consequently into an indefinite number of such pairs.* This construction is called the parallelogram of forces. The resultant of any number of forces meeting in a common point may be ascertained thus : first, let the resultant of any two forces be found as before, and substitute this one force for the two components pro- ducing it ; then combine this new force with one of the remaining forces, and continue this process until all the forces are reduced to a single force, which is the resultant sought. The following geometrical solution will render the subject more apparent : let P, P', P", &c. (Jig. 206) represent a number of forces meeting in the common point A, and let A P, A P', A P" be proportional to these forces respectively : through P draw PR equal and parallel to AP', and through R draw It It' equal and parallel to AP", and through R' draw R' It" equal and parallel to A P'"; join A It", which represents the resultant of the four forces A P, AP', AP", AP"'. A similar opera- tion will serve for any number of forces. This figure is denominated the pohj- C gon of forces. If the directions of three forces are rectangular, and in dif- ferent planes, the resultant may be found as follows: let PC, PC, PC", (fig. 207) be the intensities and directions of three forces, complete the parallelopiped BD; then the forces PC, PC have P r for an equivalent, therefore P r may be substituted for these two forces; and by compounding the forces PC", P r, we get PR the diagonal of the parallelo- piped BD r for an equivalent to the three forces. This construction is called the parallt lopipedon of forces.f An equilibrium cannot subsist be- iB tween any two forces acting upon a point of matter, if the lines represent- ing the directions of the forces be inclined to each other at any angle ; but a third force, equivalent to their resultant and in an oppo- • Vide Gregory, vol. iii. ch. ii. p. 23. t From the same construction the resultant of a system of forces maybe found, disposed in different planes by the method of rectangular co-ordinates : let P C = x, PC =y, P C" = z, (fig. 207 ), by the 47 Euc. Lib. I. we have Pr2 = PCl+ Cr2 = x2 + y2, and Pll!=Pr! + )'R! = x2 + 2/ 2 4" z 2> whence the resultant PR = v/ x2+y 2 -+- z2. The position of the resultant is thus determined ; let r, r', r" denote the un- known angles formed by the direction of the re- sultant with each of the co-ordinates, and R cos. r, R cos. R cos. r" will represent the equivalents of the resultant in the several directionsot theaxes, hence we have R cos. r = x, R cos. r ~ y, R cos r" = z, . •• Cos. r = u' cos. r' _ V cos. r = b ' MOTION. 409 site direction to it, will produce an equilibrium. Fie. 206. Let N ( fig. 205) be the point acted upon by any two forces N F, N F', which form an angle FNF', and the line NR their resultant, which will draw the point in the direction NR. But if a third force NR', equal and opposite to NR, be applied, it will destroy the motion in NR, and the point N will remain at rest by the simultaneous action of the three forces NR', NF, NF. Fig. 207. c •p D CP Centre of gravity. — The centre of gravity of any body is a point about which, if acted upon only by the force of gravity, it will ba- lance itself in all positions; or, it is a point which, if supported, the body will be sup- ported however it may be situated in other respects; and hence the effects produced by or upon any body are the same as if its whole mass were collected into its centre of gravity. To find the centre Fig. 208. of gravity of any plane body mechanically, let the plane a e d b (fig. 208) be sus- pended freely by a string from the point a j to which a plumb- line a b is also at- tached — the latter will coincide with the vertical line a b, which is to be marked with a pencil: then suspend the plane and plumb-line from a second point e, when the plumb-line will hang vertically in the line e d, inter- secting a b in c,the point c will be the centre of gravity of the plane. To find the distance of the head and feet from the centre of gravity of the human body in a horizontal position ; balance the body placed upon a plane a b on a triangular prism de, as in fig. 209 ; then draw a line on the plane Fig. 209. close to the edge of the prism ; again balance the body in another position and draw a line as before, the vertical line passing through c, the intersection of these lines will pass through the centre of gravity. After the plan of Borelli, Weber balanced a plank across a horizontal edge, and stretched upon it the body of a living man : when the whole was in a state of equilibrium, in which the method of double weighing was adopted, by accurate measurements he found the total length of the body m.m. in. = 16G9.2 = 65.30853 the distance of the centre of gravity below the vertex = 721.5 = 28.406455 above the sole of the foot = 947.7 = 37.310949 above the transverse axes of the hip-joints = 87.7 = 3.454729 above the promontory of the sacrum = 8.7= 0.341519 As the horizontal plane of the centre of gravity lies between three-tenths and four-tenths of an inch above the promontory of the sacrum, it must traverse the sacro-lumbar articulation which is intersected by the mesial plane, be- cause the body is symmetrical, and by the transverse vertical plane, the sacro-lumbar arti- culation must, therefore, contain the common point of intersection of all three planes, which coincides with the position of the centre of gra- vity of the body when standing; but this point varies in different individuals in proportion to the difference of the weight of the trunk to that of the legs, as well as by any change of the position of the limbs. The centres of gravity of particular figures may be found geometrically and analytically, as shewn in mechanical treatises ; but these methods require computations too detailed for our limits. The attitudes and motions of every animal are regulated by the positions of their cen- tres of gravity, which, in a state of rest and not acted on by extraneous forces, must lie in vertical lines which pass through their bases of support. Thus, if g (Jig. 210, a and n) be the common centreofgravityoftwobodies whose re- spective centres of gravity are g, II, in A 410 MOTION. the whole mass will be supported, whilst in B it will fall over on the side of H. A Fig. 210. B In most animals moving on solids, the centre is supported by variously adapted organs; during the flight of birds and insects it is suspended ; but in fishes, which move in a fluid whose density is nearly equal to their specific gravity, the centre is acted upon equally in all directions. The lever. — Levers are commonly divided into three kinds, according to the relative po- sitions of the prop or fulcrum, the power, and the resistance, or weight. The straight lever of each order is equally balanced when the power multiplied by its distance from the fulcrum equals the weight, multiplied by its distance, or P the power, and W the weight, are in equilibrium when they are to each other in the inverse ratio of the arms of the lever, to which they are attached : the pressure on the fulcrum however varies. In straight levers of the first kind, the ful- crum is between the power and the resistance, as in fig. 211, where F is the fulcrum of the Fig. 211. A T B lever A B ; P is the power, and W the weight or resistance. We have P : W : : B F : A F, hence P. AF=W. BF, and the pressure on the fulcrum is both the power and resistance, or P+W. In the second order of levers (fig. 212) the resistance is between the fulcrum and the power ; and, as before, P : W : : BF : AF, but the pressure of the fulcrum is equal to W — P, or the weight less the power. Fig. 212. W In the third order of lever the power acts between the prop and the resistance (fig. 213), Fig. 213. where also P : W : : BF : AF, and the pressure on the fulcrum is P — W, or the power less the weight. In the preceding computations the weight of the lever itself is neglected for the sake of sim- plicity, but it obviously forms a part of the elements under consideration, especially with reference to the arms and legs of animals. To include the weight of the lever we have the following equations : P. AF+AF. i AF= W. BF+BF. a BF; in the first order where AF and BF represent the weights of these portions of the lever respectively. Similarly, in the second order P. AF — W. BF+AF- ~> and in the third order P. AF=W. BF+BF. BF 2 In this outline of the theory of the lever, the forces have been considered as acting ver- tically, or parallel to the direction of the force of gravity. The head moving backwards and forwards on the atlas acts on the principle of the first kind of lever, the fulcrum being placed between the power and the resistance. The tibia resting on the astragalus acts on the prin- ciple of the second order of lever, when the heel is raised by the tendo Achillis, the re- sistance being between the power and the fulcrum, or between the heel and the toes. In lifting a weight by the hand and bending the elbow-joint, as in fig. 214, in which p the power, or biceps muscle is inserted at a between the fulcrum }', and the resistance w or b, we act on the principle of the third order of lever. In the latter case, however, the power, in- stead of acting vertically, is applied obliquely, and the lever, instead of simply resting on the fulcrum, turns upon a point at f, fig. 214. Instead, therefore, of estimating the values of p and w as before, according to their reciprocal distances from the fulcrum, we resolve each of them into two other forces by perpendiculars drawn from the fulcrum f to the directions of the forces p and w. Thus, in fig. 214, p will not be to w as b f to a f \ but as the perpen- diculars from f on the vertical line through b to that on a c the direction of the insertion of the muscle. The pulley. — The principles of the simple pulley are introduced into the mechanism of animals for the production of motion, and to change the directions of the motions of several organs in reference to that of the tendons MOTION. 411 Fig. 214. moving them. There are no examples of the compound pulley in animal structures. We recognise the simple pulley in the trans- mission of the tendons of the peronei muscles through the groove of the external malleolus of the human ankle-joint, in the tendon of the obtu- rator internus gliding through the groove in the os ischii, in the tendon of the circumflexus palati passing through the hamular process of the sphenoid bone, in the tendon of the obliquus superior gliding through the ring attached to the frontal bone, and in several other instances where a change of the directions of the limbs results from tendons passing over joints, through grooves in bones, or under ligaments, by which the muscles are capable of producing effects on distant organs without disturbing the sym- metry of the body, an effect which, owing to the limited power of contraction in the muscles, could be accomplished in no other way. Of uniform motion.— If a body move constantly in the same manner, or if it pass over equal spaces in equal periods of time, its motion is uniform. The velocity of a body moving uniformly is measured by the space through which it passes in a given time.* The velocities generated or impressed on different masses by the same force are reci- procally as the masses.f Motion uniformly varied. — When the mo- tion of a body is uniformly accelerated, the space it passes through during any time what- ever is proportional io the square of the time. In the leaping, jumping, or springing, of animals in any direction, (except the vertical,) the paths they describe in their transit from one point to another in the plane of motion are pa- rabolic curves. The legs move by the force of gravity as a * Thus if v be the spare passed over by the body in an unit of time, that space X by t, or t v will be the space s passes over in t units, that is, s = tv (1). t If a force communicates a velocity » to a mass m, and a velocity v' to a mass m, then we have fflii = m't)' (2). Generally, if /be the accelerating force, the space s=hft\ (3). and s= — (4). 2 pendulum. — To the many instances already recognised of the connexions subsisting be- tween the functions of living animals and the physical sciences, another remarkable con- tribution has been recently added by the Pro- fessors Weber, whose experimental researches satisfactorily demonstrate that the swinging forwards of the legs of animals in progres- sive motion obeys the same laws as those of the periodic oscillations of the pendu- lum. In order to ascertain these relations, MM. Weber instituted a series of experi- ments upon legs of given lengths, both in the living and dead subject, and under variously modified circumstances. Having removed a leg from the trunk at the hip- joint, and suspended it by a short thread that it might move as if upon the axis of the head of the femur; upon giving it an im- pulse they found it oscillated nearly in the same time as in the living state. They next communicated a vibratory motion to a leg sus- pended to the acetabulum by the ligaments of the hip-joint only, the muscles having been previously cut through : in this experiment the oscillatory movements were rather less than in the preceding. The oscillations of the leg of a dead person after the rigidity of the muscles had subsided, were still further diminished. On comparing the durations of the vibrations of the legs in these several states with those of the living, they found their periods nearly equal or in the following proportions. Half Length dura- of leg. tion of No. in me- tres.* oscilla- tion. m ii 1 0.831 0.3/0 An exarticulated freely suspended leg. 2 0.866 0.371 The same. c A leg suspended to the trunk by the < ligaments only, the muscles of the ( hip joint having hecn cut through. 3 0.831 0.355 4 0.831 0.355 f A leg of the dead body in its natural 1 state. 5 0.860 0.346 f A living leg swinging uninfluenced t by the action of muscles. 6 0.860 0.322 A living leg walking on the heel, r A living leg walking on the hall of I the foot. 7 0.860 0.323 ! A metre = 3.2808992 feet. A millimetre = 0.03^7 inch. 412 MOTION. From this table it appears conclusive that no muscular force is employed or required to pro- pel the leg forwards after it has been raised and bent by the flexor muscles, and that the force of the earth's gravity alone on the leg is suffi- cient to accomplish that purpose. The diffe- rence found between the oscillation of the legs in the living and the dead body is very small, and is attributed by those authors to the elas- ticity of the ligaments connecting the leg to the trunk, and some trifling differences in the length of the legs, but decidedly not to muscu- lar action. An application of the principles of the pendulum to the legs of animals mov- ing in a vertical plane shows that the durations of their periodic oscillations must be respec- tively as the square roots of their lengths,* estimated by the distance of the centre of oscillation ; or the time of a complete oscillation of any leg from behind forwards when in- fluenced only by gravity is to the time in which a heavy body would fall through half the length of the leg, considered as a com- pound pendulum, as the circumference of a circle is to its diameter. It further results from the periodic move- ments of the legs being subordinate to the force of gravity, that the same individual would necessarily walk slower as he ap- proached the equator, and quicker as he ap- proached the poles, all other circumstances being equal. For example, let us suppose any two persons to be walking in different latitudes, whose legs are of unequal length, and acted on by unequal gravitating forces, then by the theory of the pendulum the time of the swinging forward of their legs respectively will be as the square roots of their lengths directly and as the square roots of the gravitating forces in those latitudes inversely .f Mechanical effects of fluids on animals im- mersed in them. — When a body is immersed in any fluid whatever, it will lose as much of its weight relatively as is equal to the weight of the fluid it displaces. In order to ascertain whether an animal will sink or swim, or be sus- tained without the aid of muscular force, or to estimate the amount of force required that the animal may either sink or float in water, or fly in the air, it will be necessary to have recourse to the specific gravities both of the animal and of the fluid in which it is placed. The specific gravities or comparative weights of different substances are the respective weights * Let I and I' equal the lengths of any two pendulums, 1 1' the times of vibrations, g the force of gravity, it to i the ratio of the circumference of a circle to its diameter, then .-. t : t' : : s/l : J V (5.) t For as t = w /\J ~ ' anc^ — * \/~r' hence t : t' : : A / — : \ I — (6.) of equal volumes of those substances* When any solid body is immersed in a fluid and left to itself, it will sink if its specific gravity is greater than that of the fluid ; but if its specific gravity be less than that of the fluid, it will rise to the surface and be sustained there ; and when the specific gravity of the solid and fluid are equal, the body will remain stationary wherever it is placed. When the weight of any body taken in a fluid is subtracted from its weight out of the fluid, the difference is the weight of a volume of the fluid equal to that of the solid; this is to its weight in air, as the specific gravity of the fluid to that of the solid ; so that generally the specific gravities of solid bodies are as their weights in the air directly, and their losses in water or any other fluid inversely.f The specific gravity of air, water, and mer- cury, when the barometer stands at 30 in. and the thermometer at 55°, being to each other as If, 1000, 13600, it results that all those ani- mals whose specific gravities approximate to that of water are nearly 1000 times heavier than air, and more than thirteen times lighter than mercury, and consequently animals that would sink and perish in water could walk on the surface of mercury. The human body in a healthy state, with the chest filled with air, is specifically lighter than water, and its sinking generally depends upon the air in the lungs escaping under the pressure of water upon its immersion. Dr. Ainott remarks that if this truth were generally and familiarly understood, it would lead to the saving of more lives than all the mechanical life-preservers which man's ingenuity will ever contrive. Atmospheric pressure produces a great va- riety of mechanical effects on animal structures. If we estimate the surface of a man to be equal to 2000 square inches, the pressure of the atmo- sphere on his body with the barometer at 30 in. will amount to 30,000 lbs., or about 15 tons ; when the barometer falls from 30 to 27 inches, the pressure is reduced from 15 to \Z\ tons ; we need not, therefore, be surprised that variations of atmospheric pressure should be attended with corresponding sensations in living animals. The pressure of the atmosphere enables some animals (as we shall subsequently prove) to fix themselves to rocks with great force, to walk up the surfaces of glass windows, to sustain themselves in an inverted position on the * If W, w are the weights of two substances, V, d their volumes, S, s their specific gravities, then S : s : : — : V v t Let W — the weight of the body in air, W' — its weight in water or any other fluid, S — the specific gravity of the solid, s — the specific gra- vity of the fluid, then we shall have the following proportions ; W — W' : W : : « S: hence and W — W' S = w w w — w (7-) (8) MOTION. 413 ceilings of rooms in opposition to the force of gravity, and to hold the mechanism of the joints together with a force proportional to their respec- tive areas. The air being elastic, its density decreases as the elevations above the earth's surface increase, and when the heights increase in an arithme- tical progression the densities decrease in a geometrical progression ; hence, in the flight of birds, the weight of air which they displace, and the effective force of their wings must continually vary with every change of eleva- tion. Animals moving in water at various depths are not subjected to the same variations of den- sity that are experienced in air, since water, being nearly incompressible, suffers no sensible change of volume at the greatest depths of the ocean ; but although the density remains nearly con- stant, the pressure increases with the depth, being equivalent to about one pound on the square inch for every two feet. The specific gravity of water being from 800 to 1000 times greater than air, its pressure becomes very great at the known depths to which many fishes and cetaceous animals descend. Resistance of fluids. — Animals moving in air and water experience in those media a sensible resistance, which is greater or less in proportion to the density and tenacity of the fluid, and the figure, superficies, and ve- locity of the animal. An inquiry into the amount and nature of the resistance of air and water to the progression of animals will also furnish the data for estimating the proportional values of those fluids acting as fulcra to their locomotive organs, whether they be fins, wings, or other forms of lever. The motions of air and water, and their direc- tions, exercise very important influences over velocity resulting from muscular action. The resistance of a plane moving perpendi- cularly to itself in a fluid, equals the weight of a column of the fluid of which the base is equal to the plane, and the altitude to the depth through which a body would fall to acquire by gravity the velocity of the plane.* If the directionf of the motion, instead of being perpendicular to the plane, as before supposed, be inclined to it at any angle, the * Let a represent the area of the plane, v the velocity, p the specific gravity of the fluid, then the height due to the velocity being-!!, the whole resistance will be diminished in the triplicate ratio of the sine of the angle of inclination. When a body is termi- nated by a curved surface generated by the revolu- tion of a plane round its axis, and moves parallel to that axis, the amount of resistance may be ob- tained by the formulae and analysis subjoined.* Tig. 216. resistance is a p _ 2g- .(9.) hence, cwteris paribus, the resistance is as the square of the velocity. t Let a b (fig. 215) be the plane, and b d the direction of its motion, a n d the angle whose sine is s, the number of particles which strike the plane, as well as the force of each particle, will be dimi- nished in the ratio of 1 to .1, therefore the whole resistance will be diminished in the ratio of 1 ; s2, but the effective part of the resistance being per- pendicular to the plane, the whole resistance in the direction a e is to the effective part in the direction b e perpendicular to a b, as a e and b e, But the forms of animals, though symme- trical, can rarely be considered as mathemati- cally regular figures, and consequently many of the data for calculating the resistance to their movements must be derived from experi- ment. Passive organs of locomotion. Bones. — The solid framework, or skeleton of animals which supports arid protects their more delicate tissues, whether chemically composed of entomoline, carbonate, or phosphate of lime; whether placed internally or externally ; or whatever may be its form or dimensions, presents levers and fulcra forthe action of the muscular system, in all animals furnished with earthy solids for their support, and possessing locomotive power. The form, strength, density, and elasticity of skeletons vary in relation to the bulk and locomotive power of the animal, and to the media in which it is destined to move. or as 1 to s. Hence the whole resistance in the direction of the motion will be diminished in the ratio of 1 : s3, and will therefore be a p »s s? .(10.) * Let if ad (fig.2\U)be the section through the axis ca of thebody whose motion is in the direction of c a, draw the tangent e g to any point of the curve meeting the axis produced in g, draw the ordinates e / and e f indefinitely near each other, also draw e' a parallel to g c, then let cf ~ x, e f ~ y, b e ~ z, and s the sine of the angle g to the radius 1 ; then 2 tt y is the circumference of the circle whose radius is e f and 2 nt y x e e' or 2 it y d z is the surface described by e e in its re- volution about the axis c a, which is the quantity represented by (a) in the preceding note, therefore lit viz. or— ! ydz (11.) 2g J ' g . . will be the resistance on that ring or the differen- tial of the resistance to the body whatever its figure may be. — (See Gregory's Mechanics, chap. v. p. 521.) 414 MOTION. The number of moveable articulations in a skeleton determines the degree of its mobility within itself; and the kind and number of these articulations of the locomotive organs determine the number and disposition of the muscles act- ing upon them. See Articulation. The strength, density, and elasticity of the external skeleton of animals have been but very partially investigated or made an ob- ject of either physiological or mechanical en- quiry, notwithstanding their great importance in the animal economy generally, as well as their office in locomotion. A superficial inspection, however, is suffi- cient to detect that the shells of those animals which reside constantly at the bottom of the sea, as the Astrea triduina, Phombus, &c. are more dense, and contain a greater number of calca- reous laminae than those which swim or float, either by means of specific organs of progres- sion, such as the Tanthina vulgaris, the Lymnse, and Hyalaea, or upon hydrostatic principles, as in the Nautilus, assisted, it is believed, by the siphon. Shells are formed with a design to resist the greatest external pressure, consistent with the least expenditure of materials, and with regard to the habits of the animal. The bones of vertebrated animals, especially those which are entirely terrestrial, are much more elastic, hard, and calculated by their chemical elements to bear the shocks and strains incident to terrestrial progression than those of the aquatic vertebrata; the bones of the latter being more fibrous and spongy in their texture, the skeleton is more soft and yielding. The bones of the higher orders of vertebrata, such as the Mammalia, which are designed to afford large surfaces for the attachment of their powerful muscles of locomotion, are constructed in such a manner as to combine lightness with strength ; therefore their surfaces are convex ex- ternally, concave within, and strengthened by ridges running across their discs : such are the forms of the scapular and iliac bones. The long bones of the legs and arms of Mammalia are piled on each other endwise, forming a series of moveable columns, which in the standing position are directed vertically ; these are designed to support the head, neck, and trunk, with all their contents and appen- dages, together with their own weight, and to elevate the trunk to some variable height above the plane of position. It would indeed be a problem of no small difficulty, if it were proposed to an artist to erect a moveable column, composed of a de- finite number of rods, so united and inclined as to fulfil all the objects, for which the long bones of the extremities are designed when viewed only mechanically, and adapted to support the weight of the superincumbent or- gans, to present the lengthened dimensions ne- cessary to raise the trunk often far above the plane of motion, the strength requisite to bear the shocks directed upon them both vertically and laterally, the symmetry of form and beauty of proportion corresponding to the outline and functions of other organs, their extremities being furnished with articulating surfaces for the joints, with ridges and protuberances for the at- tachment of muscles, and with levers adapted to perform all the varied offices of locomotion. In quadrupeds, which have four osseous columns to support the superincumbent organs, the pressure of the trunk on each leg is only half that in bipeds; but owing to the hori- zontal inclination of the trunk and the projec- tion of the neck and head, the anterior osseous pedestals have to sustain the largest proportion of the weight ; and we consequently find that the angle formed by the bones of the anterior ex- tremities at the joint are less, and the directions of the bones nearer the vertical plane in these than in the posterior: this arrangement is most conspicuous in the larger Ruminantia and Pachydermata, especially in the Elephant, Horse, &c. We may, therefore, readily per- ceive why the shafts of the long bones of the legs and arms of most Mammalia are par- tially hollow cylinders; the prismatic outline predominates in the Elephant and Megatherium. The weights which cylindrical or prismatic flexible columns will support perpendicularly when their bases and composition are equal is, according to Euler,* in the inverse ratio of the squares of their lengths, therefore if we take any bones, of similar materials and thickness, but of which the lengths are as 1,2, 3, 4, 5, they will support weights without flexion rela- tively in the proportions 1, \, ^ so that whilst the lengths increase in an arithmetical progression, the weights will decrease in a geometrical progression ; the necessity, there- fore, for dividing the columns which sustain the trunk by means of the joints, independently of the use of the latter for locomotion, is obvious. According to Galileo, the power of a beam or bar to resist a fracture by a force acting late- rally, is as the section of the beam, where the force is applied, multiplied into the distance of the centre of gravity of the section from the point or line where the fracture will end. By applying this principle to the case of bones, we deduce the following propositions, which must, however, be regarded only as approximations to the truth. The lateral strength of two cylindrical bones of equal weight and length, of which one is hollow and the other solid, are to each other as the diameters of their transverse sections. Thus, let ab, d e (jig. 217, A, B,) be the sec- tion of the two bones : then the strength of the tube d e is to that of the solid a b as d e to a b. Fig. 217. A a I * De curv.is elasticis, No. 37. MOTION. 415 Fig. 217. 13 e Upon the principle of this proposition, it was long since observed by Galileo that nature greatly augments, in a thousand ways, the strength of bodies without increasing their weight, and that if a wheat straw which sup- ports the ear, that is heavier than the whole stalk, were made of the same quantity of mat- ter, but solid, it would bend or break with far greater ease than it now does. The feathers of birds as well as the bones of animals pre- sent similar provision for the combination of strength, lightness, and economy of material. The strength of bones, however, cannot, as might possibly be inferred from the preceding proposition, be increased with the same quan- tities of matter indefinitely, because when the diameter of the tube exceeds certain dimensions it will become so thin and fragile as to break almost without offering any resistance. The lateral strengths of prismatic bones of the same materials are as the areas of their sections and the distances of their centres of gravity directly; and their lengths and weights inversely. From the deductions which may be drawn from the preceding proposition Galileo very justly concludes that " there are limits set to the magnitudes of the works of nature and art, and that the size of ships, palaces, and temples, trees and animals, cannot surpass certain dimensions ; and lie observes that large animals have neither the strength nor speed proportionate to their bulk, and if there were any terrestrial animals much larger than those we know, they could hardly move, and would be much more subject to the most serious acci- dents : and also that it is impossible for nature to give bones to men, horses, or other animals, if they were enlarged to immense heights so as to perform their offices proportionally unless the structure of bones were composed of ma- terials much more firm and resisting, or that they were made of a thickness out of all proportion, which would render the figure and appearance of animals monstrous." Mr. Banks has found that an oak rod one inch thick, sup- ported at each end, will break by its own weight at the length of 57.45 feet, and a similar one of iron at 38.223 feet; Emerson also found that the cohesive strength of bone is double that of oak, whilst its specific gravity is only to that of the latter as 1656 to 1170, or as 92 to 65. In the Megatherium and Elephant the length of the bones of the legs is small com- pared with their diameters, and consequently they possess greater comparative strength as columns in supporting their ponderous super- structures. In the thigh bones of most animals an angle is formed by the head and neck of the bone with the axis of the body, which prevents the weight of the superstructure coming vertically upon the shaft, converts the bone into an elastic arch, and renders it capable of supporting the weight of the body in standing, leaping, and in falling from considerable altitudes. Joints. — Where the limbs are designed to move to and fro simply in one plane, the gin- glymoid or hinge-joint is applied ; and where more extensive motions of the limbs are requi- site, the enarthrodial, or ball and socket joint, is introduced. These two kinds of joints predo- minate in the locomotive organs of the animal kingdom. Though the ginglymoid joint re- stricts the movements of the limbs to one plane, yet it secures that precision of direction and firmness of step recognized in their motions, as well as the steadiness with which they sup- port the trunk. The elbow, knee, and ankle- joints, in man more especially, though gingly- moid, are differently constituted and possess different degrees of mobility. The limbs re- volving upon the elbow-joint move in concen- tric planes, whilst those articulated at the knee allow, according to Weber, a rocking motion upon each other; the ankle has the greatest latitude of motion of these three ginglymoid joints. The enarthrodial joint has by far the most extensive power of motion, and is therefore selected for uniting the limbs to the trunk, as it is at the enarthrodial joints that the planes in which all the limbs move is determined. The enarthrodial joints permit of the several motions of the limbs termed pronation, supi- nation, flexion, extension, abduction, adduc- tion, and revolution upon the axis of the limb or bone about a conical area, whose apex is the axis of the head of the bone, and base cir- cumscribed by the distal extremity of the limb. In consequence of the structure of the ankle- joint, the foot may be directed out of the plane of the leg's motion. The limbs, in moving upon or about the heads of bones, describe arcs of circles, of which the centres of motion are the axes of the heads of the bones or the tubercles on which they revolve. Ligaments. — The office of the ligaments with respect to locomotion is to restrict the degree of flexion, extension, and other motions of the limbs within definite limits. The strength, form, elasticity, and points of attachment of ligaments are sufficient to effect the objects above mentioned ; they are, how- ever, destined mechanically to limit the motions rather than to expend their forces in supporting the weight of the limbs suspended beneath the joints to which they severally belong. The influence of atmospheric pressure in supporting the limbs was first noticed by Dr. 416 MOTION. Arnott, though it has been erroneously ascribed by Professor Miiller to Weber. Subsequent experiments made by Dr. Todd, Mr. Wormald, and others, have fully established the mecha- nical influence of the air in keeping the mecha- nism of the joints together. The amount of atmospheric pressure on any joint depends upon the area or surface presented to its influence and the height of the barometer. The forces acting in opposition to the weight of the limb are the pressure of the air, and a force em- ployed by the ligaments and muscles equal to the excess of the weight of the limb, if any, above that of the pressure of the atmosphere. According to Weber the atmospheric pressure on the hip-joint of a man is about 26 pounds. The pressure on the knee-joint is estimated by Dr. Arnott at 60 pounds. This estimate agrees with our measurement of the area of the surface of the knee-joint in an adult female, but is too small for an adult male which is about 90 pounds. In the Elephant and Megatherium, the pressure of the air upon the joints is greater in proportion to the increased bulk and weight of their limbs. In the latter the area of the plane bounded by the edge of the coty- loid cavity, is an ellipse whose diameters are seven and eight inches, and therefore present a plane surface exceeding 43.9824 square inches, which, being multiplied by fifteen, with the barometerat 30inches,willbe=43.9824 X 15, or about six hundred and sixty pounds pres- sure upon the cotyloid joint of this greatest of terrestrial Mammalia. Muscles. — The amount and effects of mus- cular contraction, the absolute and relative power of muscles in reference to their length, mass, and obliquity of direction, and the ex- penditure of their power to support given weights, will now be either simply noticed or briefly estimated. In the application of muscles to the purposes of locomotion we find them so arranged as to produce great velocity, and at the same time to admit a great extent of motion, still preserving the beauty of proportion. These objects are obtained, 1st, from the oblique directions of their fibres towards the tendons ; 2d, from the obliquity of the direction of the tendon to the bones on which they act ; 3d, from the proxi- mity of their points of insertion to the articu- lations of the bones, or axes of motion in the joints. The muscles are capable of contracting (ac- cording to the researches of MM. Prevost and Dumas) about f033 or nearly one-fourth their whole length, which, owing to the circumstances just mentioned, is sufficient to produce all the positions and motions observed in animals. It has been already determined by experi- ment that the volumes of muscles do not alter by contraction, their thickness only increasing as they decrease in length, and vice versa. The comparative power of muscles in the same animal, according to Borelli, may be thus estimated: — When two muscles are composed of an equal number of fibres, or are of equal thickness but .of unequal lengths, they will suspend equal weights, but their motor powers and the height to which they are capable of raising the weights will be as the lengths of the muscles. 2d. When the lengths of the muscles are equal and their thicknesses unequal, their rela- tive powers will depend upon their thicknesses, but they will raise weights to equal heights. 3d. When the lengths and thicknesses are unequal, the weights they will raise will depend on their thicknesses, and the heights to which they will raise them will be as their lengths. When the fleshy fibres of a muscle lie pa- rallel to the tendon, the space through which they will draw it equals the contraction of the fleshy fibres ; but when they are inserted ob- liquely into the tendon, the space through which they will draw it will vary with the in- clination. Thus, let two equal fleshy fibres, AC, B C, (Jig. 218) similarly situated with respect to the tendon C D, be inserted obliquely at C, join A B, and produce D C to meet it in P, then D P is perpendicular to A B. Now if the points at A B be considered as fixed, and the angle A C P be such that radius : its sine : : A C : to the length of A C when contracted, then the joint action of the fibres will draw the point C to P. Fig. 218. For with A B, as centres describe the circular arcs P E, P F, touching each other at P, then it is evident that the point C will, after the contraction of C A, be somewhere in the arc E P, because the radius of E P is the length of A C when contracted ; for a similar reason C will be somewhere in F P; therefore it will be at P, their point of contact. The same result becomes apparent from the consi- deration that the forces in the direction C A, C B are equivalent to forces in the direction C P, P A and C P, P B respectively, of which the forces in the direction C P are not counter- acted, but gradually diminish and become zero when the fibres are at right angles to their tendon, that is, when C coincides with P. It is here assumed that there is no ob- stacle to the free motion of the tendon in the line C P. If the obliquity of the fibres be less than A C P, the arcs will intersect in some point between P and C, and the contractile force will be insufficient to draw C to P. If, on the contrary, the obliquity be greater than the angle AC P, the arcs will not meet, but C MOTION. 417 will be drawn to P. In this case the contrac- tile force is more than sufficient for the object to be attained. All other things remaining the same, the space C P will be greatest when the obliquity is that which is stated in the proposition. If A P = | A C, the l_ A C P is 48° 35' nearly. From the researches of the Professors Weber we learn that the weight of the extensor muscles generally predominates over that of the flexors; those of the leg being selected, their propor- tions in two well-formed healthy subjects were found to be as ('2403.2 + — — ) : 810.3 1 091 1 j = 2913.75 : 1320.85 * or as 11 T 2 to 5 in favour of the extensors, the proportions are divided by 2, or halved, to allow for the double office which some muscles perform of both flexion and extension, according as either end becomes the fixed point. The pre- ponderance of the weight of the extensors be- comes greater if the double action of each be omitted in the computation and the whole weight of each set be substituted ; the pro- portion then becomes, 2403.2 : 810.3, or as 3 to 1 nearly. The weight of the extensor muscles, when compared with that of the rest of the leg, is in the proportion of 5 to 9, and to the whole of the muscles, including the flexors, as 3 to 4, consequently the extensor muscles of the leg weigh three-fourths of the whole series. Borelli has given approximate values for the powers of a great number of the muscles of the human body, from which we select a few computations which will convey an idea of the enormous amount of their absolute power and the large proportion of it which is sacri- ficed in order to gain velocity. Borelli states that the whole force expended by the muscles of the arms, when stretched horizontally, is 209 times greater than that of any weight sus- pended at its extremity, and that the force of the biceps to that of the brachialis is as 3 to 2.6, or as 15 to 13, and their absolute forces as 300 to 260. He estimates the force of the deltoid at 61600 pounds, the sum of the forces of the intercostal muscles at 32040 pounds, and of the glutei at 375420 pounds. The extensor muscles of the hip, knee, and ankle-joints have also a large proportion of their power sacrificed to velocity ; the amount of this inter- change has been estimated upon the following principles of Borelli. Let us suppose a porter carrying a weight to be in the act of stooping in order to enter a door- way with his load; his body is bent, with one leg raised from the ground, and the heel of the * 2403.2 = the weight of the muscles in grammest acting over one joint of the leg, viz. the glutei =: 936.0, vasti and cruralis = 1092.0, so- leus = 375.2, and 1021.1 = the weight of those flexors and extensors of the leg acting over two joints, viz the rectus = 199.2, semitendinosus = 128.2, semimembranosus = 206.5, biceps s= 129, gastrocnemius 358. t A grain = 0.007508 gramme. VOL. III. Fig- 219. other elevated, as injig. 219 ; he is sustained in this position by the glutei (f), the quadratus femoris ( (/), and the gastrocnemius and soleus (/). Then if the weight r = 120lb., the weight of the porter 1501b., the line r s be the direc- tion of the force of gravity cutting the femur and tibia in c and x, the centre of gravity of the man be at b, and the common centre of gravity of the man and his load be at a, then the weight of the man from the head to b will be = '™lb. = 75lb., and of the section b to c, by supposition, is = 47, therefore the weight of the arc a b c = 75 + 47 = 122, also by supposition the section c v x = 20, and consequently the whole arc a b v x = 142, also the distances of the directions of the muscles from the axes of the joints to the dis- tances of the line of gravity are, according to Borelli, in the following ratio: * the distance b is to the distance m b as 1 is to 8; \ o v is to t v as 1 to 6 ; \ k d is to p d as 1 to 3 ; and t v to b m as 3 to 4 ; hence we derive these proportions : — t v : b m '. : r + a b v x : z, or 3:4:: 120 + 122 : 322§lb. = the pressure of the weight of man and load at the point x. a p : b m : : r + a b v d f : s, or 3 : 8 : : 120 + 150 : 720 = trie force of thij whole weight at s. J b / : in b ; : r + a b c : g., 2 E' 418 MOTION. or 1 : 8 : : 120 + 122 : 1936 : = the force re- sisted or employed by the glutei muscles. I v o : t v : : z : y, or 1 : 6 : : 2322§ : 1936 : =* the power exerted by the quadratus femoris; \ k d : d p : : s : I,* or 1 : 3 : : 720 : 2160. The last proportion gives the force exerted by the gastrocnemius and soleus muscles to sustain the weight of the man together with the weight r ; now as the sum of the forces exerted by the muscles / ' + y + I = 2 X (1936) + 2160 = 6032, and the weight supported being only 120lbs., it follows that the extensor muscles of the leg, to sustain this weight, exert a force = 6032lbs., being more than fifty times the weight. Force of muscles at various stages of their contraction. — The variations which the force of muscles undergoes in different states of their contraction have not yet been thoroughly in- vestigated ; though it is a subject not only susceptible of being pretty accurately deter- mined, but also leads us to form a more cor- rect hypothesis of the laws which regulate the contraction of the muscular fibres, and of the physical operation of the vital agents which are the immediate causes of the contraction. The force of muscles, according to the ex- periments of Schwann, increases with their length, and vice versa. His experiments were made on the gastrocnemius muscle of a frog. The apparatus which he employed consisted of a board, to which the frog was fixed, with the thigh in the horizontal position, the leg being raised so as to be perpendicular to the board, and the foot again flexed to the horizontal position, in which posture the limb was firmly fixed; a rod or beam was suspended over the board and made capable of turning upon it as its axis of oscillation. This balance beam was unequally divided with respect to its axis of motion, one arm being to the other 'as 1 to 6. To the longest arm of the beam a scale was separated; to the other arm the tendo Achillis (which had been carefully exposed and detached from the heel) was attached by means of a thread ; by this method a very small contraction of the muscle caused the other end of the beam to revolve through a much greater space, so that the slightest con- traction of the muscle became very apparent. The ischiatic nerve was then laid bare, cut through high up in the thigh, and drawn out, great care being taken not to injure the sur- rounding vessels. The nerve was then laid upon two wires, connected with a galvanic battery, consisting of a single pair of plates, one of the wires being connected with one pole of the battery, and the other made to commu- nicate with the opposite pole by using a slight pressure upon it. The skin was left entire, except where the tendon and nerve were ex- posed. By this simple apparatus, Schwann observed that the force of the muscle was at a maximum when at its greatest elongation, and * This computation differs from that in the 53d prop, of Borelli,. where he has substituted new and arbitrary values for s and z in the two last pro- portions, which diminish the values of y and /. at a minimum at its greatest contraction. In a series of five experiments, whicli were repeated at equal intervals, the forces of the muscles at different lengths were in the following propor- tions : — Force of No. of Muscle Comparative Difference Experi- in grains length of in ments. weight. Muscle. length. r o i4.i 60 17.1 3. 1. ■< 120 19.7 2 6 | 180 22.6 2.11 l_ 0 end of experiment. ( 0 13.5 2 J 100 18.8 4.3 ' }200 23.4 4.6 V 0 end of exp. 14.4 f 0 13.7 | 50 18.7 4.3 3. ■{ 100 20 3 2.1 50 17.7 (_ 0 end of exp. 14.1 r 0 13.5 5.6 4. -? 100 19.1. 4.1 (.200 23.2 f 100 16.8 ', 0 12.17 4.1 . J 100 16.1 2.4 ] 200 18.7 100 16.1 I 0 11.17 This table shows that twice the comparative length coincides with twice the force of the muscle, and that at its greatest contraction the force = 0. In the first two experiments the increase of force and length of muscle were uniform ; but in the last three the ratios of the force and the length varied ; the earliest ex- periment, however, was performed when the animal might be supposed to be nearest to its normal condition, and therefore when the re- sult approximated most nearly to the healthy play of the muscle. These experiments of Schwann are opposed to the hypotheses of Prevostand Dumas, as well as to those of Meissner, who regard the pheno- mena of muscular contraction to be due to the force of electric attraction, but as the latter in- creases in force the more nearly the attracted bo- dies approach each other, and decreases as they recede in the inverse ratio of the square of the distance, and as the force of elastic bodies varies in a ratio differing from that of muscles, when their length and force affecting them vary, we conclude that the contraction of muscles does not depend upon any of the known laws connected either with electro- dynamics or the forces regulating the molecules of elastic matter. If we conclude from the experiments of Bergolotti, Mayo, and Prevost and Dumas, that the contraction of muscles is unaccom- panied by a diminution of bulk, and that the aggregate molecules present equal volumes and are at equal distances from each other, whe- ther contracted or not, the electric force would remain constant, whilst the muscular force varied; or if with Professors Gruithuisen and MOTION. 419 Ermann, that the molecules approximate during contraction, the magnetic force would increase at the same time, and the muscular force is observed to decrease, therefore both of these hypotheses are inconsistent with the theory of the identity of the magnetic and muscular forces. The power of muscles, however, rapidly decreases by exertion, especially in some of the lower animals, such as the Ophidian and Batra- chian reptiles; the ratio of decrease is in pro- portion to the energy of action, until, by con- tinued exertion, locomotion becomes impos- sible. It has now been sufficiently demonstrated that muscles are capable not only of moving the levers on which they act with great force and velocity, and of prolonging their action for a greater or less period, but that they are endowed also with a surplus of force beyond what is necessary for locomotion, and which is applied to the various purposes of life. Having now given a brief statement of the mechanical principles applicable to the loco- motion of animals, we shall proceed to give an outline of their various modes of progression according as it is performed in air, in water, or on solids ; and in the first place, for example, we shall select those that move by means of an aeriform medium. Sect. II. Flying. — Flying depends on the power which animals possess of raising them- selves in the air, and of moving through it with considerable velocity in every direction. The power of flight is denied to a large proportion of the animal kingdom, and requires for its exercise a certain configuration of body, adjust- ment of parts, and modification of structure, based on the most profound principles of dyna- mics. In flying, as in swimming, the animal moves in a medium which furnishes a suitable fulcrum to its levers or locomotive organs, whatever may be their kind or form. Air sup- plies the medium to animals that fly as water to those that swim. Air, however, being more than eight hundred times lighter than water, gives a proportionably diminished support to the animals which move in it; consequently, instead of having the whole or nearly the whole weight of the body sustained, as when plunged in water, the same animal weighs as much more in air as corresponds to the difference in the specific gravities of the two fluids, or nearly as 1| to 1000. The weight of the volume of air displaced by the equal volume of any insect or bird indicates the amount of buoyancy or force acting vertically upwards, in opposition to the force of gravity on the mass of the body of the animal acting vertically downwards. The difference between the specific gravity of animals and that of the atmosphere represents the weight necessary to be overcome in flying by the action of their locomotive organs; or, in other words, whatever may be the amount of the force of gravity on the mass of particles composing the whole animal in a direction •vertically downwards, and the resistance of the air on its surface due to its velocity, an equal force acting vertically upwards will be required to sustain it in the air, and a still greater force to cause it to rise. It is the vast preponderance of the weight of most animals over that of the air they displace, which con- stitutes the chief obstacle to their flight, in addition to their inappropriate form and the unsuitable organization of their locomotive organs. Flight of insects. — The flight of insects depends on the same principles as that of birds, notwithstanding the dissimilar structure of their bodies and wings. The skeleton of insects is both light and dense, and, without greatly adding to their weight, affords the necessary fulcrum for the action of an elaborate muscular system. The mobility of the seg- ments of the abdomen upon the thorax enables the insect to bend upon itself, and to adjust the position of the centre of gravity, with respect to the articulation of the wings during flight. The attachment of the wings to the trunk lies above the centres of magnitude and gravity, so that the insect is kept steady whilst flying. Compared with their volume, the weight of insects is less than that of birds : the lightness of their skeletons and the diffusion through their bodies of trachea? and air cavities, greatly tend to diminish their specific gravity and the quantity of muscular action em- ployed during their flight. The form of their bodies is very irregular, but being for the most part either cylindrical or ellipsoidal, is well adapted to pass through the air with little resistance. In the Diptera, the single pair of wings is articulated to the meso-thorax ; in the- other orders with two pairs of wingSj the first pair is also articulated to the meso-thorax, and the second to the meta-thorax. The wings are composed of a duplicature of the common integuments continued from those parts of the body. In the Diptera and Ilymenoptera the ratio of the areas of the wings to their weight is much less than in the Lepidoptera; and as this ratio decreases, the number of the vibrations of the wings in a given time proportionally increases. Hence it is vastly greater in the two former orders than in the latter. The neurse when injected with air and fluid assist in giving expansion and tension to the wings ; an office compared by Jurine to the support given to a sail by its cordage. Insects are capable of varying the area of their wings during their elevation and depression, by alternately filling and exhausting the tubes, which movements follow synchronously the expansion and con- traction of the thorax. The muscles which act indirectly on the wings at the same time effect changes in their surfaces, angular inclinations, and ratios of velocity during their ascent and descent. There is an elaborate mechanism pro- vided in the structure of insects relating to their flight. The surfaces of their wings, like those of birds, are in general slightly convex above and concave below. In the Strepsiptera, Or- thoptera, and Hemiptera their figure approaches that of the quadrant of a circle. In the Diptera, Coleoptera, and diurnal Sphinges it is ellip- soidal. The figure of the wings varies, how- 2 e 2 420 MOTION. ever, considerably in different orders of insects, and they are here described rather in the language of geometry than in that of entomo- logy. The ratio of the area of the wings to the weight of the insect varies in each order, and approximates to a constant quantity only in the same order. The wings of insects dimi- nish in thickness from their base to their apex, and from their anterior to their posterior margin;* the strongest nervures traverse the anterior margin of the wing, and confer on that portion the greatest resisting power. The posterior margin being weaker is inclined upwards and backwards in reference to the direction of its stroke. The plane of the wing, as Straus has correctly remarked, is therefore inclined at a different angle to the horizon at every moment of its descent. By the composition of forces the obliquity of the wings backwards and downwards gives to the centre of gravity an impulse upwards and for- wards. The radial and cubital nervures in insects supply the place of the bones of the arm in birds; and though different in structure, they have the same mechanical effect. The anterior nervures being articulated to the apo- * See Chabrier sur le vole des insects, c. i. p. 424. physes of the wings, and being fixed at their extremities upon the two axillary first pieces, the latter, with the wings, form a lever of the first order, and when the internal borders of the two axillary pieces are lowered the wings are raised, and vice versa ; or as the axillaries are articulated upon the border of the clypeus, the movements of elevation and depression in these produce the contrary movements in the wings.* The wings of insects oscillate during flight through arcs of various lengths, which depend on the distances of the centres of the wings from their axes of motion, and other dy- namic conditions. In the Lepidoptera they appear to describe an arc of 180°, so as to meet each other at each elevation and depres- sion. In some other orders the arc of oscilla- tion appears to be much less. Amongst the Coleoptera, in some of which the elytra assist the under wing in flight, according to Chabrier, the latter describe an arc four times as great as the former.f In estimating the number of * See Straus-D'urckheim, loco cit. 212. f Daus les hannetons chaque aile, en volant paroit decrire un arc de plus de 200° cent, tandis que celui trace dans le meme temps par les elytres est peut-etre au dessous de 50° cent. See Chabrier, sur le vole des insects, p. 31. MOTION. 421 strokes made by the wings of insects as well as of birds during flight, it is necessary to take into the account the length of the arc in which they oscillate. The oscillations of the wings of insects are too rapid to be numbered by common observa- tion. The principles of optics,* acoustics, and dynamics have been employed to determine them during their flight. According to Bur- meister the pitch of the sound made during flight varies with the number of strokes made by the wings, although the production of the sound is perfectly independent of them.f If the number of strokes is synchronous with the number of vibrations which produce the sound, we can ascertain the number of their oscillations very readily ; but we are not yet furnished with sufficient evidence that each stroke of the wing is coincident with one musical semi-vibration to determine this ques- tion with precision. According to the analysis made on the flight of birds, if the same data may be considered applicable, we shall see by Chabrier's investigations when all other things remain the same, that the number of strokes made by the wings of insects will vary as the square roots of the weight directly, and of the area of the wings inversely. In the Coleoptera, the ratio of the area of the wings to the weight of the insect is small in comparison with other orders. The elytra of the Coleoptera add to their weight and surface in passing through the air, without contributing either to the vertical elevation or horizontal velocity of the insect; on the contrary, as their surfaces are inclined to the axis of the body and the direction of motion, they retard the velocity of the beetle in moving against the wind. The centre of the forces lies posterior to the articulation of the wings, and as the angle of inclination of the elytra tends to ele- vate the head and depress the abdomen by its resistance to the wind, the axis of the body becomes inclined vertically during flight. In a stag beetle weighing forty grains, the area of each elytra measured 0.366364 of a square inch, and the true wings, calculated as the quarter of an ellipse, gave 0.6263565 of a square inch each, or 1.2527126in. for both. The same measured by a graduated scale gave 0.62240 in. each, which shows how nearly the form of the true wings approaches to a segment of perfect ellipse. Those Coleoptera in which the ratio of the surface of the wings is very small cannot fly against a strong wind. Olivier says, " None of this class can fly in opposition to the wind," but this assertion is opposed by Kirby, who states that the Melolonthae Iloplise fly in all directions; others, as the Cicindelce, take short flights, and may be easily marked down by the entomologist. The Cetoniae expand their wings in flight without elevating their elytra, as is done by other Coleoptera. The Dcrmaptera, though generally on their legs, take flight towards evening. The wings * See Nicholson's Journal, 4to. vol. iii. p. 38. t Remarks on the causes of sound produced by insects in flying, by Dr. H. Burmeistcr. Taylor's Scientific Memoirs, vol. i. p. 378, 1837. of the earwigs are ample ; the nervures radiate from a common centre to the external margin of the wings, which they expand like a fan. According to Kay, the tegmina of the Orthop- tera assist the wings in flight. The Grillus domesticus flies with an undulatory motion like the woodpecker, alternately making a few strokes with the wings in order to give a pro- jectile velocity to the body upwards, and then folding the wings to descend on the opposite side of the vertex of a parabolic curve. Owing to the analogous structure of their wings, the Gryllus campestris and Gryllotalpa are capa- ble of using them in a similar manner. The Hemiptera employ their hemi-elytra to assist the wings in flying* By this means the area of the wing is increased, a greater surface is given to it for striking the air, the ratio of the surface of the wings to the weight of the body is augmented, the quantity of action and the number of vibrations necessary to sustain it in the air is diminished, and the power of flight is consequently increased. The Lcpidoptera are furnished with a far greater area of wing in proportion to the weight of their bodies than is observed in any other flying animal. The under wing approaches in figure to the quadrant of a circle, and in many species the two meet posteriorly and form a semicircle. The anterior and under wings are locked together during their descent so as to give them a synchronous action, and a compact surface to resist the air. The surfaces of the two wings on each side increase with the distances of their sections from the axes of motion; in the Morpho automedon (Jig. 220), in which the areas of the sections of the wings lying between the parallels 1, 2, 3, 4, drawn at equal distances from the axis of the body, will _ be seen to increase (the last one excepted) as the distances from the centre of motion of the wings increase ; the effect of which is, to throw the centre of resistance to a greater distance from the axis of motion, so that the muscles of the wing act at a mechanical disadvantage ; and the weight of the body being small in proportion to the area of the wing, the body oscillates considerably at each elevation and depression, and its flight is rendered un- steady. The surface of the anterior wing is less than that of the posterior, being as 2.08 : 2.4483471 square inches, and the sum of the surfaces of the four wings is =9.0566942 inches. As the solid contents of the body are very small when compared to the surface of the wings, we naturally conclude that the Morpho has pro- longed powers of suspension. The great mag- nitude of the wings of the Lepidoptera are generally in proportion to the weight of their bodies, and the force of their muscular system endows them with great powers of flight; but it is most frequently accomplished in a zig-zag path. In the Pontia brassicae the weight of the insect is found to be 1.525 gr. ; the area of the anterior wing 0 6 square inch, the area * See Dr. Rogct's Bridgewatcr Treatise, third edition, vol. i. p. 313. 422 MOTION. of the under wing 0.65 ; the sum of the areas of the two wings consequently is —1.25 ; but when placed in tire position of flight, as the anterior wing lies partially over the under wing, the whole effective surface of the two wings measures 0.83, and that of the four 1.66 in. During repose the dorsal planes of the wings of the diurnal Lepidoptera are directed verti- cally and brought into contact. Nocturnal Lepidoptera. — Many of this order have large organs of flight; their wings, which in repose lie in or beneath the horizontal plane, are triangular, their apices being the most dis- tant points from the body when the wings are extended, and their areas are in the inverse ratio of their velocities, and their distances from the centre of gravity. Thus in the Erebus Strix (fig. 221) the wings are greatly expanded and of a form the best calculated for rapid flight, the areas of the sections of the wing being, for the most part, in the inverse ratio of their distances from the axis of motion; consequently the reverse of that of the Pontia, the Morpho, and most of the diurnal Lepidoptera. The anterior wing is much larger than the posterior, being as 7.175 to 5.095 square inches. The area of the four wings is therefore about 12.270 inches, which, being very considerable in proportion MOTION. 423 to the cubic contents of the body, endows this insect with great powers of suspension in the air and with great velocity of motion. The triangular figure of the vvings prevents the un- steady undulating progression observed in the diurnal Lepidoptera, and the flight is conse- quently more direct as well as more rapid. The wings of many of the moths are of considerable dimensions. The largest male Atlas moth in the collection at the British Museum measures 5^ inches on each side, estimated from their axes of motion to the apices of the wings, pre- senting a total area of 26§ square inches. If the force of the muscles acting on the wings is proportional to their areas, they must possess the most extensive power of flight. TheBombyx mori, or silk-worm moth, is stated to travel more than a hundred miles a day.* The Neuroptmi have a separate set of muscles appropriated to the movements of each wing, which being detached can be moved either synchronously or independently of each other: the muscles also are actually inserted into the wing, instead of moving them indirectly, as in other orders of insects. The surfaces of the four wings of the Libellulae, or dragon-flies, are nearly equal in most species ; they are always expanded in repose, and ex- tended horizontally at right angles to the axis of the body, so that they take flight in an in- stant. Their figure is lanceolated. The ratio of the united areas of the four wings to the weight of the body is greater than in the Cole- optera and Ilymenoptera, and the muscular power is proportionally augmented. The arti- culation of the wings being situated above the centre of gravity keeps them steady in flight : their velocity is very great, exceeding that of the Swallow. Leeuwenhoek once observed one of this tribe in a menagerie 200 feet long, chased by a swallow ; the insect flew with such velocity, and turned to the right and left in all directions so instantaneously, that the swallow, with all its powers of flight and tact in chasing insects, was unable to capture it, the insect always keeping about six feet in advance of the bird. The great length and surface of the wings of the Libellulae, and the power of the muscles acting on them, is such that they appear to be never tired of flying in quest of their prey. In a specimen of the ^.shna maculatissima, which weighed fourteen grains, the area of the anterior wing was 0.7324 in. the posterior 0.8988 in. and the area of the four wings 3.26408 square inches. The preponderance of surface in the posterior wing enables the Libel- lula to change the direction of their path of motion with great facility, and to capture their prey on the wing. Previously to taking flight, this TEshna exerts a vibratory movement with its wings; the oscillations are made in very minute arcs, and with great rapidity, producing a faint though distinct sound. The pitch indi- cates that the wings perform ninety-six vibrations in a second. On taking flight the wings oscil- late through larger arcs, with a less number of vibrations, the amount of which it is not easy * Lin. Trans, vol. iii. p. 40. to determine, and does not depend, as some distinguished entomologists have supposed, on their mutual friction. In a Triphavna pronuba, weighing 8.545 grains, the area of the anterior wings measured 0.6213, and that of the under wings 0.68 square inches, making the sum of the areas of the four wings 2.6026 square inches. In the ilymenoptera the ratio of the areas of the four wings to the weight of the insect is less than in the Neuroptera, and they are consequently obliged to make a greater number of strokes in the same inter- val of time in order to suspend themselves in the air. The areas of the upper are greater than those of the under wings. When ex- panded they are retained in the same place, and are linked together by means of small hooks, so that the upper and under wings act simultaneously and with greater power. A humble bee, which weighed 6.2 grains, had wings the sum of whose areas measured 0.366 of a square inch, or rather more than 5'5th of a square inch to each grain weight of the body. Bees are not only celebrated for the geo- metry displayed in the structure of their cells, but also for the precision with which they re- turn to their homes by the shortest path or in a straight line. The collectors of honey make use of this fact to discover their nests. Having captured two of these insects, they separate them some yards from each other, and on setting them free, ascertain with an instrument the angles respectively made by the lines of their flight with that between the points of their de- parture, then the point where the two lines of direction intersect each other indicates the posi- tion of the nest. The humble bee, wasp, and hornet fly with great force, but owing to the weight of their bodies, compared with the areas of their wings, cannot fly with much speed against a strong wind, so that a person might easily outstrip them by running in the same direction against the wind. When disturbed, or before leaving their abode, they wheel round the spot in a large circle, and then fly off at a tangent to some part of the curve. The Ichneumons are provided with a far greater expansion of wing, in proportion to their weight, than the Bees, and can consequently sustain themselves in the air with less expenditure of muscular action. In a species of ichneumon allied to Ophion luteus, which weighed 0.5 gr. the areas of the anterior wing measured 0.0832 in. the poste- rior 0.0480 in. the sum of the two wings = 0.1322 in. and that of the four = 0.2644 in. The Diptera are furnished with only two wings, which when in repose lie directed obliquely backwards upon the abdomen; their figure is nearly that of an ellipse, and their areas are ample when compared to the weight of their bodies. Three examples of MusctB vo- mitories for instance were found to weigh 2.4375 grains, which gives for the mean weight of each 0.8025 gr. and the mean areas of both wings were found to be from -^th to tgth of a square inch. Instead of posterior wings they have poisers, the articulation of which to the thorax is placed more posteriorly than in the four- 424 MOTION. winged insects, so as to lie above the centre of gravity. According to Dr. Derham, if either a poiser or vvinglet be cut off, the insect flies as if one side overbalanced the other, till it falls to the ground ; and if both be removed, it flies unsteadily. Shelver states that the removal of either winglets or poisers deprived the insect of the power of flight altogether. The pneumatic pressure which retains them inverted to the ceilings of rooms, gives them a position favour- able for flying oft' instantaneously, the centre of gravity being below the articulation of the wings, enabling them to regain the pendant position of the trunk in flight. In the crane fly the centre of gravity is ad- justed, and the direction of flight directed by its long legs ; the two fore legs being extended forwards, and the four hind legs backwards. According to Kirby, the one represents the prow, the other the stern of a ship. The velo- city of the house, and large flesh flies (Muscce domestica et vomitoria) appears to be from five to six feet in a second, or about four miles in an hour ; but if favoured by the wind, they are seen flying round the ears of horses when tra- velling at the rate of from ten to twelvemiles in an hour.* The following table presents at one view the proportions of the areas of the wings in square inches to their weight in grains of various spe- cies of insects which have been already de- scribed in the text. Order. coleoptera . . Hymenoptera DlPTERA Lepidoptera , Neuroptera , Species. Lucanus cervus Bombus Ophion luteus Musca vomitoria Pontia brassicae Triplrsna pronuba . . . iEshna maculatissima Area of Wings in square Inches. 1.2527126 0.366 0.2644 0.083333 or-,L... 2.50 2.6026 3.26408 Weight of Body in Grains. 40. 6.2. 0.5. 0.8025. 1.525. 8.545. 14. By the help of this table we are enabled to compare the proportions of the area of the wing to the weight of the insect in different orders, and to estimate the relation between these pro- portions and the absolute powers of flight, when the latter have been ascertained by expe- riment. If the velocity and power of suspension varied in insects precisely in the same ratio as the areas of the wings to the weight of their bodies, we should be enabled to compare with tolerable accuracy the relative powers of the flight of in- sects from data similar to the preceding, but there are several other mechanical and physio- logical conditions involved ; such as the ratio of the force of the muscles to the areas of the wings, and the figure and structure of the latter. The Lepidoptera which have the greatest surface of wing in proportion to their weight, should surpass all other insects in power of flight, yet the diurnal section at least yield to the Libellulce in velocity, if not in the duration of their suspension in the air. From the pre- ceding data we conclude, that to render a man, whose weight is 150 pounds, capable of sus- pending himself in the air by the assistance of artificial wings, with the same facility as in- sects, would require an extent of surface be- yond the control of his muscular force, and consequently that the act is impossible. Flight of Birds. — In the organization of birds, we observe that many parts common to other animals are modified, the power of the muscular system is increased, and new forms of matter are introduced to confer on them the power of flight. The bulk of birds is less than that of quadrupeds of equal strength, and owing to many of their bones being per- meated with air, and their skin clothed with feathers, their specific gravity, and conse- quently the demand on their muscular power are diminished.! Instead of the cylindrical form observed in animals which move ex- clusively on solids, the anterior extremity of birds is expanded into a triangular surface, of which the apex is the distal, and the base is the proximal section of the wing in reference to the axis of rotation. The arm is articulated to the trunk by a ball and socket joint, permitting all the freedom of motion necessary for flight, whilst in consequence of the axes of motion in the gyngli- moid joints of the fore-arm being directed either perpendicularly or obliquely to the ascent and descent of the wing, it is prevented from yield- ing to the resistance of the air during elevation and depression, and is more conveniently folded on itself during repose. The surface of the wings may be increased or diminished by abduction and adduction, in consequence of which the resistance of the air to their motion may be proportionally varied in the up and down strokes. The amount of this resistance is also varied by the surface of the wing being convex above, and concave below. The feathers are moreover provided with a curious me- chanism by which the barbules lock into each other, so as to unite all the parts of the vane, and present a continuous surface to the air. The ten primary and the secondary feathers, which have the greatest leverage, are inserted into the arm and fore-arm, and directed so as to produce the greatest surface of wing * See Kirby and Spence. vol. ii. p. 357. t 1. The Pelicanus cmocrotalus is five feet in length, but its skeleton weighs only twenty-three ounces, whilst the whole animal weighs twenty-five pounds. See Roget's JJridg. Treat, vol. i. p. 490. 2. The skeleton of the Carrion Crow when dry weighs only twenty-three grains. Jaquaniin, An. Sci. Nat. series 2, 11, p. 2718. 3. Many entire Humming Birds weigh only one- eighth of an ounce, or one drachm. MOTION. 425 without very sensibly increasing its weight. The scapulars which have the least velocity are shorter and weaker. The length and strength of those feathers which contribute so largely to increase the area, vary directly with the velocities of that portion of the wing to which they belong. The ratio of the area of the wings of birds to their weight is by no means constant. It is least in the Cursores, such as the Ostrich, Cassiowary, and Emeu ; greater in the Insessores, as the Raven, Crow, and Humming-bird ; and greatest in the diurnal Rap- tores, as the Eagle, Falcons, and Vultures. The power of flight in birds, provided the muscular forces vary in proportion, is as the areas of their wings directly, and as their specific gravities in- versely. Owing to the triangular figure of the expanded wing, the area of its sections dimi- nishes as their distance from the centre of gra- vity increases, and from the same cause the areas are in the inverse ratio of the velocities corres- ponding to the distances of the sections from the axis of motion. The centre of resistance coincides very nearly with the middle of the length of the wing from the shoulder-joint to the tip. The wing is moved on the princi- ple of the third order of levers, and the power is applied sufficiently near the axis of motion to produce a considerable relative velocity. The power of the muscles acting on the wing is increased in proportion to their mass, being to those of the inferior extremity (according to Borelli) in the proportion of more than three to one, their absolute power in proportion to the weight of the bird being as 10 000 to 1. In order to give the osseous framework the surface and strength necessary for the attachment of the great pectoral muscles which act on the wing, the sternum is carinated, whereby its surface is increased in proportion to the mass of the mus- cular fibres which are inserted into it, and the shoulder-joints are strengthened by the elonga- tion of the coracoid processes, and the magni- tude of the clavicles. The fixed condition of the ribs and vertebral column tends also to strengthen the thoracic sections of the bird, and enables it to resist the enormous muscular force applied to it during flight.* This brief outline of the manifold adaptations necessary for aerial progression will give some idea of the number and complication of the elements which enter into the composition of so small a fabric, and of the enormous muscular power with which birds are endowed, compared with their bulk and weight. When a bird rises from the ground, and at the moment it begins its flight, the first impulse is communicated to its centre of gravity by the sudden extension of the legs, as in leap- ing. During this action the humerus is raised ; the wings are unfolded and spread out hori- zontally by the extension of the fore-arm, and of the carpal, metacarpal, and phalangeal bones. The force resulting from the sudden extension of the legs elevates the whole mass of the bird above the plane of position, and the body thus raised being deprived of the support previously afforded would begin again to fall by its own weight, as soon as the projectile force became insufficient to sustain it, but the wings having in the meantime been spread out to their fullest extent, are made to descend with great velocity by the contraction of the powerful pectoral muscles. In consequence of the planes of the wings being disposed either perpendicularly, or obliquely backwards to the direction of their motion, a corresponding impulse is given to the centre of gravity. The resistance of the air to the wings during their depression through a greater or less arc of a circle becomes greater than the force of gravity on the mass of the bird, together with the resistance of the air on its body due to its velocity, and consequently the bird rises. During the ascent of the wing, the opposite effect takes place. The bird has not only to encounter the resistance which the air opposes to the motion of the wing during its back stroke, but also the resistance due to its figure when in motion, as well as the force of gravity. These are so many forces tending to neutralize the down stroke of the wing, and to produce an opposite effect, so that there will result a motion, the amount of which may be pretty nearly ascertained when the necessary data are obtained by experiment. The principal data required for computing the quantity of muscular action expended, the velocity of the centre of the wing, and the num- ber of its periodic oscillations necessary to sus- tain the bird in the air, may here be briefly stated. 1st. The area of the horizontal section of the body of the bird. 2d. The area of the two wings whilst they are lowered. 3rd. The area of the wings whilst they are raised. 4th. The velocity with which the bird is driven through the air. 5th. The velocity with which the wings are lowered. 6th. The velocity with which the wings are raised. 7th. The respec- tive durations of the elevation and depression of the wings. 8th. The weight of the whole bird. 9th. The weight of an equal volume of air. loth. The resistance of the air due to the figure and velocity of the bird. 11th. The ratio of the resistance which the air opposes to the wings during their elevation and depression. 12th. The ratio of the resistance of the air to the time of an elevation of the wings to that of a depression. These are the principal data which are deemed necessary for estimating by dynamics the amount of the force employed by birds during their flight.f If the area of the wings of birds always preserved the same ratio to their weight, the * The position of the scapulo-humcral joint with respect to that of the great pectoral muscles throws the centres of gravity and figure below the axis of articulation of the wings, so that the animal is kept steady in flight, whilst its figure is such as to enable it to glide through the air with the least pos- sible resistance. t Let us suppose the bird to endeavour to rise perpendicularly in the air by equal flappings of its wings in a vertical direction, and let s = the area of the transvere section of the bird, A = the area of the wings whilst they are depressed, A ' = the area of the wings whilst they are elevated, u = the velocity with which the bird rises in the air, V = the velocity with which it depresses its 426 MOTION. velocity of the centre of the wing would he the descent in the wing were constant, the number same in all birds, and if the arc of vibration of flappings would vary inversely as the dis- and the ratio of the time of ascent to that of tance of the centre of the wing from the axis of wings, V ' = the velocity with which it elevates its wings,* I — the time reckoned from the mo- ment when the wings begin to be depressed, t = the time of a depression, t ' = the time of an elevation, W — the weight of the bird, it = the weight of a cubical foot of air, g = the velocity acquired by gravity in an unit of time, k — a constant coefficient, by which we multiply the product s " — it, in order to get the expression for the resistance of the air to the rising of the bird, which u2 is therefore it k s — > K — a similar coefficient for the expression of the resistance of the air to the depression of the wings, K' = a similar coefficient for the resistance of the air to its elevation. During the depression of the wing the bird is drawn downwards by the force W, arising from its own M2 weight, and by the resistance of the air to its rising, namely, it k s — 7 but it is driven upwards by the resistance which the air opposes to the motion of the wing, that is, it K A ^ "\ , hence the equation to the motion will be W du v . (V— k)! . u2 ... — — — it K A i. £_ — it k s — W. g dt 2g 2g or 2 W lif = it K A (V— u)2— it ksvP— 2 W g (12) These are approximative values. The motion of the wing being very quick, we may consider « to be constant during a depression, and if u0, ul be the values of u, at the beginning and end of the depression, equation (12) will become 2 W («,— «0) = t { w K A (V— «0) 2 — it ks ul — 2 W g} (13) Similarly if wv w2 be the values of u at the beginning and end of an elevation, the equation for the motion will be 2 W (a2 — tit)=— i/{wK'A'(V + «,) 2 + „ k s 2 Wg} (14) By adding the two latter equations together we have 2W(«3-w0)=T{*rKA(V-u0y>— wfes«2-2Wg}-T'{^K'A'(V'+Hiy+^ ^* «I+2 W^}.. (15) Since, at the end of every flapping the wings are supposed to be in the same position as they were at the beginning of it, we must have V t = V r (16) The two equations (15) and (16) express the conditions under which the bird may acquire a given motion, the nature of which is shown by the variation n2 — u0 which the velocity u undergoes in the time t + t'. If we suppose the motion of the bird to be uniform during each flapping u0z=ul = u2, and if we take the value of V in equation (16), equation (15) will become 0 = * V it K A (V — «0)2— it K' A' (Vt + m0t')2— (t+t) t' n k s m02— (t + t') t' 2 W g. . .(17) In order to fly, the bird must expend a quantity of force sufficient to overcome the resistance of the air to the motion of the wings, and, considering the velocity of the bird to be constant during each movement of the wings, the quantity of force expended in a depression will be 7rKA(V-Q2VT> and in an elevation itK'A'CC+JhTv'r: If we now suppose «0 =«i as before, and substitute the value of V, we shall have for the whole force expended in an unit of time A KA(V-«0HK1/VT+V'Y \ (18) 2g (T + T ) ( \ T / > Let t' = p r, and K'A' = q K A, equation (17) then becomes h « 2 W tr 0 = p ( Y-u0y-q (V + uB p)2 - (P + ]>2) |L£ ul - (P + /»=) ±2LL * V ami V are supposed constant during the times of elevation and depression, respectively, and are referred to the centres of the wings. MOTION. 4-27 motion ; but according to our experiments the whilst the areas of their wings are respectively weight of the Pigeon is 4347.344 grains; of 0.6198, 1.11, and 0.054 feet : hence, we see the Rook 4170.25 ; and of the Canary 229 ; that in these instances, as probably in other and solving it with respect to V, we have V = p 1+1 u0 + JM C'+i V < +p l±UL k + a w * , (19) p—q V \P— q/ P — 1 ttKA .(20) and supposing the same things in (18), it will become ! >'2 < v-"^2 + 9 (y + 1*0? \ Here we may substitute for V its value found in equation (19). If the bird merely supports itself in the air without rising or falling, v0 = o, and the expressions for V and the force expended in an unit of time, viz. (19) and (20) will become respectively w-£±f jJEEEJE*. (22) pi —p q V p — j jKA We may suppose q to be known from the figure of the bird and the power which it has of expanding the wing in a depression, and closing it during an elevation, so as to increase and diminish the surface and resistance alternately; and in order to find the least quantity of force necessary to sustain the bird, we must give to p such a value as will make the expression (22) a minimum. All other things being the same, we see that the quantity of force expended is proportional to the »/W3, and is also inversely as the ^/density of the air. Let us take, as an example, the data given by M. Chabrier with respect to the Swallow". W = 0.01526 kil. it= 1.25 kil. A = 0.0086 met. car. g = 9.80422 met., now from experiment it is found that a plane surface very nearly equal to the surface of a swallow's wing will produce a resistance in air equal to the weight of a column of fluid, whose base is the plane and altitude between one and a half, and twice the height due to the velocity with which the plane is moving ; if, therefore, we suppose the resistance of the wing to be a little more on account of the concavity of its surface, and consider the altitude just twice the height due to the velocity, K will = 2. It is also evident that p > 1 and q < 1, and by giving different values to q, we may obtain the corresponding values of p. 1. Let 9 = j, then when (22) is a minimum. p =3.073 V = 8m.l8 = 26.8304 feet. (22) = W 10m.36 = 33.784 feet. 2. Let<7 = i p- 1.866. V = 6m.91 = 22.6648 feet. (22)=W 8m.39 = 27.5192 feet. 3. Let ? = | p= 1.6 V = 6m.81 =20.3368 feet. (22) = W 7m.95 = 26.0660 feet. We may observe that the several values assigned to q do not produce any great variations in the values of V and (22), we may, therefore, with tolerable accuracy conclude that a bird which just supports itself in the air, expends as much force every second as would be sufficient to raise its own weight a height of 8 metres or 27.5192 feet. The mean velocity of the descending wing is about 7 metres or 22.96 feet per second, and the velocity of the ascending wing is about one-half of it. Let us now take the distance of the centre of the swallow's wing, from its axis of motion, to be three 2 7T inches, and that it oscillates in an arc of 120°= — . then the length of this arc will be found 3 ' by the following proportion 1:3:: H_f : 2 K = 6.2832 inches ; the velocity divided by this 3 length is = 43.85, being the number of arcs which would be described by the descending wing in one second, but the ascending wing takes 1.866 seconds to describe the same number of arcs, conse- quently this number, divided by the sum of the times taken by each wing, namely, 2.866, gives 15.3, the number of flappings, each consisting of two arcs, per second. Such is the result by Chabrier's formula. If we apply the same formula to the case of the Pigeon, the result is 14.9, or nearly 15 flappings per second; but actual observation proves this to be nearly three limes the real number; a similar discrepancy is observed in the case of the Rook, 428 MOTION. dissimilar orders, the areas of the wings do not vary as the weights of the birds. The ratio of the times of the descent and as- cent of the wing will cause a corresponding difference in the ratio of the resistance of the air, which is not as the velocity simply, but as the square of the velocity. The velocity of the wing varies according to the celerity with which the bird moves, and it moves through a greater or less arc according as the bird merely sus- pends itself in the air or is in rapid motion, on the rational supposition that birds employ their locomotive organs in such a manner as to econo- mize as much as possible the expenditure of their muscular power. We find by the an- nexed analysis that for this purpose the ratio of the time of the descent of the wings to that of their ascent is nearly as one to two, and that the ratio of the resistance of the up to that of the down stroke lies between one-half, one-fourth, and one-fifth. In the Swallow, for example, in order that the bird may merely sustain itself in the air, the centre of the wings, according to Chabrier, must descend with a velocity of about seven metres, or 22 9662944 feet per second, which, we find by the annexed analysis, gives 15*3 for the number of vibrations, and for the minimum amount of action expended in the same time, a force which would raise its own weight to the height of 26-246 feet. The ratio of the time of the ascent and de- scent of the wing becomes much greater when the bird moves against the wind, suppose about forty-eight feet per second, or in rapid flight; and the velocity of the descent of the wings, and quantity of action expended, will augment in proportion. The great quantity of action ex- pended in flight tends to confirm the views of Bo- relli respecting the vast power with which the pec- toral muscles of birds are endowed. In small birds the oscillations are performed with such great rapidity, that they cannot be numbered by the eye ; but in the finches and humming- birds, the oscillations of which produce a musi- cal note, the pitch will enable us to determine with accuracy the number of oscillations in a given time. In large birds, the wings move through arcs of greater circles than in small ones, and the times of their periodic oscilla- tions decrease in the same ratio, and may thus be more easily numbered : the areas of their wings, and the resistance which they encounter, bear some proportion to the greater weight of the body : but although theory ascribes to the wings a large number of oscillations, it by no means follows that they perform the exact number assigned at least for any length- ened period. On the contrary, we observe that many birds, such as the Woodpecker,* and most Insessores, give a few strokes of the wings by which the body acquires a projec- tile velocity sufficient to elevate it through a considerable space, and that when the im- pulse thus given is nearly expended, they re- peat this action, and again suspend it. If they are moving horizontally, their progression is performed in a similar manner; the axis of the bird is inclined upwards at each impulse like a projectile, but the mean motion is horizontal. The curve described during each projection is a parabola. After a few strokes, during the ascent, the wings are folded until the bird has passed the vertex of the curve, and has de- scended to some distance on the opposite side, when they suddenly expand their wings again, and by a few strokes describe a new curve. In this mode of progression the velocity is very variable, being equal to that which a body would acquire by falling through one-fourth of the parameter of each point in the curve. Many large birds, such as the Rooks, Pigeons, &c. when descending from great heights ex- pand their wings, and incline the axis of their bodies obliquely downwards, as in jig. 222. Fig. 222. In this case the air opposes sufficient resistance in a vertical direction upwards to keep in equili- brio the force of gravity acting upon the body vertically downwards, so that the motion of the bird becomes uniform, without requiring any movement of the wings. f Another mode of de- where the formula gi^es 7.38, and observation from 2 to 3 flappings per second. It is worthy of remark, that by supposing V to be equal to the cube root, instead of the square root of ?'f'7) 2Wg p —q ttK A the number of flappings in each of the last two cases by the formula, agrees very closely with the number determined by the mean of several observations. The quantity of force expended would be greater if the density of the air were less, but it would only increase in the ratio of 1.4 to 1 if the air were but half as dense. We may, therefore, conclude that the height to which a bird can raise itself is limited not so much by want of sufficient support in the resistance of the air as by the difficulty of respiring in too rare an atmosphere. * The Rook appears to make from ten to fifteen, and the Pigeon from ten to twenty-three effeclive strokes of the wing in five seconds. t The soft downy feathers which line the wings of the nocturnal rapacious birds, as the Owl, permit the wings to perform its evolutions during flight in search of their prey without noise. On the contrary, in the diurnal species of this order, which chase and capture their prey in open day, and where no secrecy would suffice, the feathers are strong, and their passage through the air is accompanied with a rushing noise. MOTION. 429 scent is performed with greater celerity by ele- vating the wings at an angle of nearly 45° above the plane of the horizon, (as in Jig.223,) by which Fig. 223. c c> the resistance of the air, compared with the re- sistance to the wing when horizontal, is dimi- nished in the ratio of radius to the cube of the sine of inclination, that is, as a b to d c3; con- sequently, a bird with its wings elevated at any angle to the horizontal plane will descend with greater velocity than when they are in the direc- tion of a b. We most frequently observe that Pigeons elevate their wings in this manner until they arrive within a foot or two of the ground, when, to prevent the shock they would otherwise receive, owing to the velocity ac- quired during their descent, they suddenly turn their axis perpendicular, which had previously been parallel, to the direction of their motion, and by a few rapid strokes of the wing neu- tralize their momentum, and thus reach the ground with ease and safety. In order to pro- duce lateral motion one wing oscillates more rapidly than the other, thereby causing the head to turn towards the side to which the latter wing is attached. The tail of the bird performs the office of a rudder in steering its course ; its plane being horizontal tends chiefly, as Borelli has demon- strated, to elevate and depress the head, rather than to turn the axis of the bird laterally. Let us, for instance, suppose that a bird, flying in the direction of its axis gj\ (jig. 224) elevates Fig. 224. its tail into the position b h parallel to o n, the resistance of the air will depress b towards k, and causing the bird to rotate on its centre of gravity c will elevate the head from a to- wards / ; on the other hand, if the tail be de- pressed into the position b i, parallel to / k, by the resistance of the air, the point b will be raised towards n, and the head depressed to- wards o, consequently the direction of the bird in its mesial plane is regulated by the tail.* In the Grallatores the tail is short and its sur- face very small, and the function of a rudder is transferred to the legs, which are projected back- wards in flight, to counterbalance the depressing weight of their long extended neck and head This fact was noticed by Aristotle.f The Swal- lows, which are almost always upon the wing, economise their muscular action by giving a few strokes with their wings, and by keeping them expanded, scud through the air with great velo- city in chace of their prey ; this interval of comparative repose must be of great service to them during their annual migrations across the sea to other countries. The velocity of some birds is very great. The Eider-duck is said to fly 90 miles in an hour, the Hawk 150. The great Albatross wafts itself across the Pacific Ocean apparently with untiring energy, owing to the vast muscular power with which it is endowed. Flight of fish and other animals. — Besides insects and birds, there are some other animals capable of sustaining themselves during a short period in the air by means of membranous ex- pansions or enlarged pectoral fins. The Dac- tilopterus and Exocatus, or flying fish, are en- abled to raise themselves above the surface of the water by the action of their enormous pec- toral fins ; but Mr. Bennett, who appears to have particularly observed their motions, states that he has never seen these fishes sustain themselves for a longer period than thirty se- conds, nor ever witnessed any vibration in their pectoral fins. Captain Basil Ilall estimates their longest flight at about two hundred yards, and they have been sometimes known to rise above the surface of the water as high as twenty feet. The projectile force with which they emerge from the water determines their elevation, and the expanded pectoral fins merely sustain them for a brief interval. The Draco Volans (Jig. 225) is provided with a broad disc on each side, extending from the fore to the hinder extremities. It is covered by the skin, supported by the first six false ribs, and directed horizontally. This membra- nous disc expands and closes like a fan, and is elevated and depressed like the wings of birds to break their fall in descending from trees, but notwithstanding the extent and mobility of their vvings, they are said to be incapable of raising themselves in the air, since their arms are detached, and neither enter into the compo- sition of the wings, nor assist in their elevation or depression. The area of the wings of the Draco volans (Jig. 225)1 estimated from the mesial section of the body is nearly 5'052 square inches. Ano- ther Draco volans which is preserved in spirits * See Borelli, De motu Animal, c. 22, p. 235. t See Taylor's Aristotle's Progressive Motion of Animals, c. x. p. 184. % In consequence of Ihe specimen in the collec- tion of Professor Grant, from which the annexed outline was made, being dry, its weight in the living state could not be ascertained. 430 MOTION. Fig. 225. in the Hunterian Museum, weighs 120 grains, and has membraneous expansions which mea- sure about five square inches, or 24 grains weight to each square inch of wing : the area is as great in proportion to the weight of the ani- mal as in many birds, and greater than in the Stag Beetle. The wings of the Volant Lacerta resemble in structure those of insects rather than of birds, the ribs supplying the place of neurae in the former, and of the osseous framework of the anterior extremity in the latter. They have sufficient membraneous expansion for flight, provided the muscles which move them were so applied, and had sufficient force to elevate and depress them with the necessary velocity. The Galeopithecus, or flying Cat, and the Pteromys, or flying Phalanger, are also fur- nished with lateral membranes extending from the atlantal to the sacral extremities, to both of which they are attached, but they are incapable of raising the animal in the air, and rather per- form the office of parachutes than of true organs of progression. The fossil remains of the Pterodactylus show that it was organized for flight ; the pha- langes of the ulnar finger being greatly elon- gated, apparently for supporting a membrane extending along the whole ulnar aspect of the arm and side of the body to the leg ; a me- chanism which enabled these animals to move through the air like birds. The four other fingers are free to answer the purpose of pre- hension, and are terminated by curved hooks like the thumb of the Bat. The Cheiroptera are endowed with extensive powers of flight. The figure of the Bat pre- sents an outline closely resembling that of birds, and calculated to offer the least resist- ance in the direction of their motion during flight. Their anterior extremities are con- structed like wings, and their whole organization is adapted for aerial progression. The weight of the body compared to the area of their ex- panded wings is very small, and hence they have the power of raising and supporting them- selves in the air. The osseous system is dense, but light, the sternum carinated, the scapulae and clavicles fitted to support the wings, and to MOTION. 431 furnish a large surface for the attachment of the muscles which move them. The fore-arm, con- sisting almost solely of the radius, does not possess the power of pronation and supina- tion, which would tend to lessen the resist- ance of the air to the wing in flight ; the hand rotates on the radius by abduction and adduction, as in birds, so that, when folded, the little finger lies along the outside of the ra- dius : the fingers, which are of great length, contribute to the expansion of the wing in flight ; the thumb, which is not enclosed by the interdigital membrane, terminates by a strong hook for prehension, and for suspending the animal when in repose. The wing, taking its commencement from the neck, extends to the arm, feet, and tail. The interfemoral membrane, when developed, has its margin supported by an osseous extension from the calcanium ; this membrane serves to elevate and depress the axis of the animal, its functions in this respect being analogous to that of the tail of birds. The elastic though delicate membrane of which the wings are composed, gives its stroke upon the air a great mechanical effect. The proportion of the area of the wings to the weight of the body is greater in Bats than in many species of birds, and nearly approaches that in the Lepidopterous Insects, consequently their power of flight is very considerable. Bats are capable of increasing the area of their wings during their descent, and of con- tracting them during their ascent by the alter- nate flexion, extension, abduction, and adduc- tion of their elbows, fingers, and hands ; and they can also vary their velocity, and conse- quently the resistance of the air during the elevation and depression of their wings in the same manner as birds. The ratios of the times and of the resistances during these move- ments of the wings, as likewise the number of their oscillations in a given time, may be computed very nearly by the formula appli- cable to the flight of birds, but owing to the extensive area of their wings compared with their weight, their oscillatory movements are comparatively slow. Their power of flight pre- ponderates greatly over the force of gravity and the mass of their bodies, so that they are ca- pable of flying with great ease, even when laden with one or two young ones. Their centres of gravity and magnitude lie beneath the axes of the articulation of the wings with the trunk, an arrangement which keeps them steady during flight. In repose they suspend themselves by their hind feet to some elevated object, from which on being alarmed they can fly off instantly. Their inferior extremities pos- sess neither the length necessary to raise the body sufficiently to expand their wings, nor the power to project it vertically, like birds on taking flight; but by dropping suddenly from the point of suspension, they are enabled to ex- pand their wings instantaneously and without obstruction in the air. Their velocity is so great that they can overtake and capture their insect food on the wing. The amount of force requisite for aerial pro- gression is so enormous, owing to the rarity of the atmosphere, that it would be impossible for a man to sustain himself in the air by means of his muscular strength alone, in any manner he is capable of applying it. It is calculated that a man can raise 13.25 lbs. avoird. to a height of 3.25 feet per second, and can conti- nue this exertion for eight hours in the day, he will therefore exert a force capable of raising 381600 lbs. in the day to a height of 3-25 feet, or 47700 lbs. to a height of 26 feet, which, ac- cording to Chabrier, is the height to which a bird would raise itself in one second by the force it is obliged to exert in order to sustain itself in the air. Now, if we suppose the con- ditions necessary for flight in man to be the same as for birds, and that a man whose weight is 150 lbs. could concentrate the muscular power of a day's labour into as short a period as the accomplishment of this object required, we might find the time t, during which he could support himself in the air, from the fol- lowing equation : — ■ 150 t = 47700, hence t = 318", or about five minutes. It is, however, impossible that a man could concentrate the force of eight hours' labour into the short interval in which he would have to expend it when supporting himself in the air. The opinions of Borrelli and Chabrier agree with these views, and we are not so sanguine as to suppose with Bishop Wilkins, Sir G. Cayley, and others, that with the assistance of some mechanical contrivance men will some day be enabled to fly by the force of their muscular system. Such hypotheses, like the ancient stories of Daedalus and Icarus, &c. serve only to deceive the ignorant, amuse the credulous, and misdirect the human mind to attempt the accomplishment of impossible objects. Sect. III. Swimming. — In swimming, as in flying, the fulcrum which affords the requi- site resistance to the action of the locomotive organs of animals is the fluid medium in which they move, and as this mediumyields to theforce impressed on it by the organs, it is evident that these modes of locomotion are regulated by different principles from those applicable to animals whose progression is performed upon solids. The reaction of the water in swimming is equal to the action impressed on it by the impulse of the locomotive organs ; and if motion ensues, it results from a surplus force in the body in motion, equal to the difference between the force of the locomotive organs, and the resist- ance of the medium. The motion is accelerated as long as the force of the locomotive organs is greater than the resistance of the medium react- ing against the surface of the animal. When the mean forces urging the animal forwards and the resisting force are in equilibrio, the motion be- comes uniform. When these forces are at the maximum, the velocity is also at a maximum. If the weight of the animal be equal to that of the water it displaces, there will be no ten- dency to rise or sink, as the vertical force of the water upwards will be equal to the force of gravity upon the animal vertically downwards, and forces need only be employed to urge the 432 MOTION. centre of gravity forwards, backwards, or ob- liquely. The case is different with animals moving upon solids, where the weight of the body has to be supported as well as urged for- wards by the instruments of progression. When the weight of the water displaced is greater than that of the animal, the body floats upon the sur- face, as in the Palmipedes ; if, on the contrary, the weight of the animal be greater than that of the water displaced by its bulk, a verti- cal as well as a horizontal force is requisite, equal to the difference of the specific gravities of the animal and the water, to prevent its sink- ing during progression.* The animal kingdom includes a vast number of species which are aquatic and constantly reside in ponds, lakes, rivers, and seas, having their general structures organized for inhabiting in these dense and resisting media, and their locomotive organs adapted for swimming. The number of these is far beyond the reach of calculation. Many of the larvae of insects and the tadpoles of Amphibia, which in their adult state are either entirely or partially terrestrial, commence their career in water; in these not only the locomotive organs, but their respi- ratory systems undergo metamorphosis. Ciliograde animals.- -Under this denomina- tion are comprehended the polygastric and rota- tory animalcules, and many genera of the orders, such as the Porifera, Polypifera, and Acale- pbae, whose locomotive organs are those minute, transparent, elastic, and very flexible conical filaments well known by the name of Cilia. The nature and structure of these organs have been fully detailed in the article Cilia, so as to render any further description here superfluous. The cilia act as levers, to which the water is the fulcrum. We may here referto the Volvox, as affording a familiar example of ciliary locomotion. The figure of this animalcule being spherical, the cilia placed on its surface are all equidistant from its centre, but those possess the greatest mechanical power which are placed at equal distances from either pole of the animal's axis of rotation. The volvox is capable of changing its axis of revolution, or varying its direction, and appears to revolve across the field of the microscope like a planet over that of the tele- scope. In the Rotifera, or wheel-animalcules, the cilia are arranged in rows, around the margin of one or more circular discs, capable of being extended and retracted from the body. * When the tail of the animal is free, it moves by its cilia, pursues, and darts upon its prey in every direction. The Rotifera are also capable of crawling upon solids, by the extension and retraction of the body, the head and tail being alternately fixed points : they are also capable of revolving with great velocity on fixing them- selves by the two posterior exsertile bulbs. Porifera and Polypifera. — The Gorgona and Flustra are for a brief period capable of a cilio- grade mode of progression. In the gemmules of sponges the cilia are spread over about two- thirds of the body. According to Grant, these zoophytes swim in a zigzag course, with the bul- bous extremities directed forwards ; their figure is pyriform ; their migrations are of very brief duration, for after the lapse of a few days only, which are spent in seeking for some suitable locality, they fix themselves during the remain- der of their lives. The Actiniae are capable of gliding upon the discs which form their bases of support. Reaumur asserts that they sometimes invert their position, and employ their tentacles as feet ; they also diminish their specific gravity by augmenting their dimensions through the ab- sorption of water; when detaching themselves at the base, they suffer the current of the sea to drift them from place to place. Unlike most of the Polypes which are fixed, the Hydra viridis is capable of moving in the liquid medium which it inhabits (Jig. 226). It Fie. 226. The Hydra viridis represented in its different stages of terrestrial locomotion, as figured by Tremhley. has three modes of progression ; the first is ac- complished by alternate flexions and extensions of the body ; thus the head being fixed by the oral tentaclesat c (Jig. 227), the little disc terminating the anal extremity is drawn forwards from a, and fixed at b ; the head is then raised and carried forwards, by the exension of the body, towards d; these two actions of flexion and extension complete a step, whose length is = ac — be. The second mode of progression is performed * See theory of Specific Gravities. * See Ehrenberg's Infus. Berlin, 1830. MOTION. Pig. 227. hy a series of somersets, the tail being thrown over the head ; if the head is first made the fixed point at c, as before, the tail will then describe the semicircle a d, which is twice the length of a step, or -ad cd1 in the second movement; the tail being fixed at rf, the head t-urns upon it as the centre of a new circle, and takes a position in advance of d, at a dis- tance equal to c di in these two actions the animal travels over a space equal to a b. In this manner the head and tail are ad- vanced alternately. The third mode of pro- gression is by far the most speedy. The Hydra having crawled to the surface of the water, lifts its tail above it to dry in the air, whereby it exerts a repulsive action on the water ; this hydrostatic apparatus, acting as a float, is ca- llable of suspending the body at the surface of the water in an inverted position ; in this pos- ture it rows itself along, or is drifted by the winds from point to point without effort. In the Beroe Pileus, the motions are partly by cilia attached to rectangular laminae, which are arranged in rows along the eight costse (■ h h, fig. 32, vol. i.) of the eihptically- formed body. According to Dr. Grant, each row contains about forty lamina?, whose transverse section presents literally the appear- ance of the floats upon the paddle-wheel of a steam-boat : when the whole of these lamina? strike the water simultaneously, the resultant of their combined action is in the line of the pro- jection of the axis of the animal, which is usually directed vertically. The direction, however, may be changed by the cilia acting partially, by which the inclination of the axis in the direction of the animal is determined. The Physalus has the power of rendering it- self either specifically lighter or heavier than water, by means of the inflation or contraction of its air-bladder ; with the assistance of which the animal is enabled either lo swim upon the surface, or sink, if alarmed, into the bosom of the ocean. The swimming-bladder of the Physalus is of considerable dimensions, and nearly of an elliptical figure, its longest axis being directed horizontally. The top of this bladder is furnished with a membranous lamina or crest, serving to increase the surface presented to the wind, before which it sails with consi- derable velocity. The Rhizophysa Melon, the Agalma Okenii, and the Diphyes Campanu- lifera, with most of the Acalephae, having al- ready been described and figured in the article Ac a LEPiiiE, the reader is referred to them for further particulars, but it may be remarked that the progression of the Diphyes is performed upon the principle of the Syringogrades, merely by the reception and expulsion of water by VOL. III. their two truncated sections, which, taking place alternately, gives the animal a mean uniform motion of considerable velocity.* Cirrigrude animals. — Unlike the entirely soft gelatinous forms which compose the Pulmograde and Ciliograde Acalepha, the Cirrigrade group have an internal solid skeleton to support their soft and delicate exterior tissues. In the Por- pita this skeleton is composed of a flat, circular, semicartilaginous plate, which lies horizontally on the surface of the water; to this plate are appended numerous cirrhi which perform the office of oars in rowing the animal on the surface of the sea : the Porpita is permeated with pores, which being filled with air render it of less density than the water upon which it floats. The Velella Limbosa has a thin perpendicular crest resting obliquely upon the horizontal plate, which being elevated above the water, and presenting a considerable sur- face to the wind, serves as a sail. In the Kataria cordata,f the crest is furnished with muscular fibres, by which the sail can be ele- vated or lowered at pleasure; but this does not take place without altering at the same time the centre of gravity ; for the position of the body is nearly reversed when the crest is lowered, but it recovers itself on the crest being elevated. Pulmograde animals. — The umbeliiform or mushroom-shaped disc of the Rhizostoma being- capable of expansion and contraction at the will of the animal, is employed not only to keep the body (which is specifically heavier than water) at its surface, but also to propel it along. When the plane of the disc lies hori- zontally, and its whole margin contracts simul- taneously, the percussion given to the water is perpendicular to the plane, or in a vertical di- rection, and the animal receives an ascending impulse equal to the force of the reaction caused by the displacement of the water. In moving horizontally, the centre of the disc is turned in that direction, and the animal can also accelerate its descent by the assistance of the disc. The contractions of the disc are iso- chronous, and repeated about fifteen times in a minute,! or 15 x 60 = 900 times in an hour. The convex surface of the Aurelia aurita is directed forwards in progression ; in this posi- tion the whole margin of the disc is called into action, by which the locomotive force is increased, and owing to the figure of the disc the resistance of the water is diminished, and the speed is consequently accelerated. Si/ringngrade animals. — Under this denomi- nation we shall include the Holothuria,theSalpa?, and the larvae of those insects whose progres- sion is effected by the alternate reception and expulsion of water to and from their respiratory organs by an action similar to that of the syringe. Independently of moving upon solids by means of its tubular feet, the Holothuria, according to Muller, is capable of drawing water into its cloacal aperture, and by means of its muscular system, of expelling it from its respiratory * See vol. i. p. 35 et sea. t Vide Art. ACALEPH.E, vol. i. p. 40, fig. 12. % See Grant's Lectures, Lancet, 1833. 2 F 434 MOTION. organs with sufficient force to propel itself through the surrounding medium. The pro- gression of the Sat pa crislata is effected by drawing water into its body, at an opening si- tuated in the posterior segment of the mantle, where a valve (fig. 228 c) is placed to pre- Fig. 220. Salpa cristata. vent its returning by the same aperture ; the mantle having been distended by the water, contracts upon it, by which action it is ex- pelled at an opening situated at the side of the mouth (a); its progression is retrograde, or in the direction of a b, opposite to that of the fluid in b a. The larvae of some Dragon Flies, such as the Ashna and Libellula, draw in and expel the water alternately at the anus, which they occa- sionally lift out of the water, and project a small stream at a distance above the level of its surface : the hydrodynamic effect of these actions is to give a locomotive impulse to the centre of gravity in a direction opposite to that of the ejected fluid. The reaction of the water, which is equal to the action of the ejected stream, is not only sufficient to overcome the resistance of the surrounding medium and the inertia of the body of the animal, but also to drive it along. The velocity of the Syringo- grades is accelerated during the expulsion of the water, and retarded during its reception ; consequently the motion is never uniform. The Vermiform animals are for the most part destitute of distinct locomotive organs, yet, owing to the flexibility of their lengthened and usually cylindrical bodies, they swim with great faci- lity. They glide by a series of lateral undu- latory movements of the body, with which they strike the water obliquely backwards, and with equal force on each side of the axis of motion, so that the force impressed on the water is trans- lated to the centre of gravity of the animal in an opposite direction forwards ; the compo- sition of all the forces giving a resultant the di- rection of which coincides with the axis of motion. Many serpents whose habits are chiefly terres- trial, swim with the head elevated above the surface of the water; others glide entirely be- neath it. Some of the Entozoa, as the Tenia, and, among the Annelides, the Planariae, when immersed in warm water, swim by similar un- dulations of the body; the latter, however, with the ventral aspect upwards. In the Ophidian Hydrophyli, or water-snakes, the tail is flat- tened ; and its planes being directed vertically, give it the properties of a powerful oar, in striking the water by lateral oscillations. In many chetopod Annelides, the setae and cirrhi form numerous and complex external organs of progression. The Terebella has four rows of setae in tufts ; the dorsal row projecting in the horizontal, the ventral in the vertical plane. They extend along the whole of the elongated subquadrangular-shaped body. In the Eunice Gigantea, which grows to the length of more than ten feet, each ring is furnished with two lateral packets of bristles, and two cirrhi. In the Nereis nuntia the locomotive organs are complex and greatly multiplied. The cirrhi and seta? may propel the body forwards, in- dependently of those undulatory movements which are indispensable for the progression of the apodous Annelides. Aquatic insects. — The perfect insects swim like quadrupeds and birds, by the alternate flexion and extension of their legs. Amongst the aquatic insects the Dvtiscus is one of the best organized for swimming ; its figure resem- bling that of a boat, being calculated to glide through the water with little resistance. The posterior legs are greatly developed, and they are moved by powerful muscles performing the office of oars, and are the principal instruments used in swimming. Their movements forwards are made in a plane nearly horizontal. The haunches being fixed to the thorax, give firm- ness and precision to these legs, which do not differ materially from those of other Coleoptera, with the exception of the tarsi, which are much flattened, and present their broad surfaces to the water. They are furnished with rows of stiff' hairs, which bend when the leg is carried forwards, and become straight when its move- ment is vigorously reversed, thus increasing the Fig. 229. a The Dytiscus, from Struns-Durckheim, showing the various positions which the posterior legs take in swimming. MOTION. 435 effect of the stroke. In the back stroke, the thigh ( d, fig. 229) moves first, describing an arc of a circle about their iliac extremity, from d to d' and d" successively. During this move- ment the legs e and tarsi j are flexed pas- sively, and carried forwards to e',f, so as to act with little effect on the water. The two thighs d" d" begin to approach their greatest flexion forwards, the legs e' c' and the phalanges f"f" extend in succession, so that the water opposes resistance to only one of them at a time. The tarsi (/") having been completely extended outwards, the two legs are suddenly carried backwards, pressing on the water, with the entire plane of the tarsi, and as the silky fringes which cover the phalanges are extended at the same instant, their surface is considerably augmented. The other parts of the two legs press- ing upon the tarsi, as in the walk or the leap, projects the body forward in the direction of its axis. In walking, the two members of the same pair act alternately, in order to serve, each in its turn, as a support to the centre of gravity. In swimming, on the contrary, the body being supported by the water, the two members move simultaneously, in order to give the greater impulse, and it is in this respect that swimming differs essentially from walking, and more nearly approaches leaping. The middle legs of the Dytiscus act in a manner similar to the posterior, but being shorter and weaker, contribute little towards accele- rating the movements of the animal ; the an- terior pair appear to be used chiefly for the purpose of altering the direction of its motion. The motions of insects in the water may be thus explained : let u b (Jig. 230,) be the axis of the body passing through the centre of gravity o ; and let co be the excess of the specific gra- vity of the water over that of the insect, acting in a vertical direction upwards ; and do the re- sistance of the water to the insect moving in a direction oblique to the axis of the body; this Fig. 230. latter force is decomposed into two forces, one in d g parallel, and the other in d c or g o perpendicular to the body, the former of which is lost, and the latter forces it obliquely down- wards and backwards; this force being com- bined with the force of the water c o produces a resultant in h o, opposite to d o, which is the force by which the insect ascends passively. On the other hand, when the insect moves ho- rizontally with its axis inclined in a b, and its centre of gravity in o, (Jig. 231,) let its Fig. 231. '■J A figure from Straus-Durcltlteim, to illmtrate the movements of insects swimming horizontally. velocity be represented by h o, so that the force in this direction may be the resultant of the forces of the locomotive organs, of the water c o, and of the resistance which it opposes to the motion of the body in the direction of d o, opposite to /( o. The resistance of the liquid in d o, acting obliquely upon the plane of the body, a b, (which is known from the velocity of the body and the inclination of its axis to the horizontal plane,) may be decomposed into two forces, one in d g or e o parallel, and the other in d e or g o perpendicular to the body ; the former is ineffective, and the latter tends to force the body backwards and downwards. The force g o, being combined with that of the water c o, produces the resultant i o, which, with the force of the oars, must give the two components of h o. Completing the parallelogram of forces, of which h o is the diagonal, we find that the legs must generate a force represented in magnitude and direction by f o, and it is in the direction of this com- ponent, or, more correctly, in a line parallel to it, that the centre of force of the feet ought to act, which is in fact the case. The Hydrophilus has nearly the same form as the Dytiscus, but is not quite so well or- ganized for swimming. The Gyrinus also, as well as the Hydrophilus, swims in conformity with the same principles as the Dytiscus. The Nepa, being ill organized for swimming, usually walks in the water. The Ih/drometru being so light, and having a little globule of air attached to its feet, has the power of swimming on the water without sinking. The Notonccta, in which the centre of gravity lies above the centre of 2 f 2 436 MOTION. magnitude, swims in an inverted position ; it is propelled exclusively by its posterior legs, which are lengthened, and move in a plane parallel to the axis of the body. The thighs, legs, and tarsi are nearly of equal length ; the two phalanges, which are slightly flattened, are furnished with hairs to strike the water with greater force, and to vary the surface pre- sented in the effective back strokes. When the insect is poised freely in the water, its centre of gravity lies in the vertical line, pass- ing downwards from the centre of the figure. From the singular circumstance of its swim- ming on its back, it has derived the appellation of Notonecta. Decapods. — In the Crustaceous Macrourous Decapods, such as the Lobster, Prawn, and Shrimp, the tail is prolonged, and equals the length of the body. It is the princi- pal organ of locomotion, and the seven seg- ments which compose it are nearly of a semi-elliptical form, the terminal being fur- nished on each side with lamina, which the animal spreads out transversely like a fan, in order to produce a greater surface in striking the water. At the dorsal aspect, the segments of the tail are locked before its extension is com- pleted, but on the abdominal aspect there is greater freedom of motion. The segments of the tail are articulated with each other on both sides by ginglymoid joints, of which the axes of rotationare directed perpendicularly to theplane of the mesial section, consequently their mo- tions are restricted to one plane. A slight eccentricity, however, in the direction of the articulating axes of the joints permits a li- mited obliquity of motion in the tail, but at the expense of muscular power. In swim- ming, the convex surface of the tail is pre- sented to the water during the back stroke, and the concave ventral surface in the effective stroke, by which the force translated to the centre of gravity in flexion is to that of exten- sion nearly as two to one.* During each flexion of the tail the animal is propelled backwards, and its velocity is accelerated, but during each extension it is retarded, so that its movement is retrograde and accomplished by a succession of impulses. In the swimming Decapods, the thoracic stemmata are laminated to assist in progression. The Cephulopods. — The Cephalopods swim according to the same principles as the Holo- thuria, by admitting water into the interior of the body and jetting it through the funnel with sufficient velocity to communicate a locomotive retrograde impulse to the animal, which enables it to traverse the sea with considerable speed. From the time of Aristotle to that of Cuvier, the Argonaut, or Paper-Nautilus, has been sup- posed to have its slight and delicate mono- thalamus shell designed for a boat, and the broad expanded membranes terminating the two dorsal feet organized for sails; but, what- ever poetiy may have been associated with this view, must be abandoned by the Zoologist for * Se^aPrmciplPs of Resistance of Curved Sur- faces moving in Fluids. the more modern and more physiological con- clusions to be deduced from the researches of M. Sander Rang* and Madame Power, who have discovered and assigned the true function of these expansions, the fabrication of the shell. Pterupuda. — Amongst Pteropods, the Clio Borealis presents a conical shaped body about an inch long ; its locomotive organs consist of two uniform expansions attached on each side of the neck, the planes of which lie parallel to the axis of the body. According to Eschricht, the tins are composed of one muscular fasci- culus, which passes through the neck, and this muscle acts in a manner resembling the principle of the double-paddled oar witli which the Greenlander steers his course on the surface of the same seas wherein the Clio is found. The inclination of the planes of the fins to that of the axis of the body determines the direction of the animal. The Clio, how- ever, is destitute of organs of prehension, and consequently incapable of fixing itself to solids ; it must therefore either remain at the bottom of the sea or paddle its course upon the dense medium which it inhabits. Pisces. — Amongst the great multitude of ani- mals moving in seas, rivers, and lakes, Fishes next claim our attention. The medium in which fishes move being nearly of the same specific gravity as themselves, they are sustained by such an amount of hydrostatic pressure as almost to neutralize the force of gravity upon their mass, so that organs of progression, calculated to support nearly their whole weight, such as occur in terrestrial animals moving on solids and in a rarer medium, are unnecessary. We observe also that as they are sustained on all sides by great hydrostatic pressure, they do not require their organs of support to be of that magnitude and density which are requisite to terrestrial Mammalia for resisting the shocks of external forces. In the osseous fishes the bones are, therefore, light and elastic, and in the cartila- ginous fishes the organs of support are still more light and flexible. The specific gravity of fishes, although small, is greater than unity, consequently we know, by hydrostatic principles, that without continued muscular effort, or some provision for rendering themselves of equal or less specific gravity than the water, they must sink to the bottom and remain there ;f but the eco- nomy of a great number of fishes requires that they should sustain themselves permanently far above the solids forming the beds of rivers, lakes, and seas, and that they should be enabled to rise to the surface, or sink into the depths of the ocean in pursuit of their prey. As this, however, would otherwise require a vast and never-ceasing play of muscular action during life, Nature has provided them with an apparatus which prevents this waste of muscular energy by the introduction into their system of the air- bladder. This hydrostatic apparatus is of va- rious shapes, but always of sufficient dimensions to contain, when it is distended, as many cubic inches of air as will render the fish specifically * Vide Gucrin's Magazin de Z ologie. t See Theory of Specific Gravities, sect. 1, p. 412. MOTION. 457 lighter than water, and as tlie specific gravities of air and water are to each other nearly as 1 to 8 i 5, a small bulk is sufficient to render the lesser fishes lighter than the medium they inhabit. The position of the air-bladder being immedi- ately under the spine and above the centre of gravity causes the fish to rise without the danger of turning over on its back. Those fishes which are furnished with an air-bladder are capable of either renewing, expelling, compressing, or dilating its aerial contents, and of varying its area so as to rise, sink, or remain in equili- brio. The air-bladder becomes by this means an important auxiliary organ of locomotion, and affords an illustration of one of the many evidence's of design in the primary formation of aquatic animals. The Diodons and Tetrodom render them- selves buoyant by swallowing air, which filling the first stomach becomes inflated like a bal- loon ; but as the gastric reservoir lies below the centre of gravity, the bodies roll over in an inverted position, and are driven in the direction of the winds and tides without the power of directing their course.* The forms of fishes are considerably diversified, being sphe- rical in the globe tetrodon ; an elongated cy- linder in the Eel; compressed in the Dory and Spah ; flattened into planes parallel to the me- sial section in the Pleuroncctida? ; elliptical in the Salmonidao, Scomberida:, and Mugilidae. In nearly all the orders of fishes the surface presented to the water by the head and shoul- ders inclines more or less to the vertebral axis of the fish, which coincides with the axis of motion, and therefore is adapted to offer resist- ance, which varies with the angle of incli- nation. In the Salmon, Cod, and Mackerel the form of the body approximates to that which is con- sidered by mathematicians to offer the least re- sistance to the surrounding medium. The organs of support are developed principally in the plane of the mesial section, and consist of superior and inferior spinous, interspinous, dorsal, and ventral fin elements, the projections of which prevent motion of the vertebral axis in the plane of the mesial section. The ver- tebrae are short, numerous, and, towards the caudal extremity, destitute of transverse pro- cesses, an arrangement which gives the tail a considerable degree of lateral motion ; owing to which it becomes the most essential organ of locomotion. The locomotive or- gans of fishes are the fins and tail ; the pectoral fins represent the anterior, and the ventral the posterior extremities of the higher orders of Mammalia. In the Cod, the legs are absolutely in front of the arms, being sus- pended under the throat. The Percidac, which are provided with two dorsal, two pectoral, and two ventral, as well as anal and caudal fins, have the greatest number of locomotive organs. The planes of the dorsal and anal fins are in the mesial section of the fish, and being res- tricted in that plane by a kind of ginglymoid joint, are capable only of elevation and depres- * See Dr. Roget's Bmlgewater Treatise. sion. In the Cod, Halibut, and Gurnard, the action of these fins serves merely to increase or diminish the lateral surfaces of the fish, so as to prevent any tendency in the animal either to oscillate laterally, or turn upon its vertebral axis into an inverted position, which it would be inclined to do without some muscular effort, since in the erect posture the centre of gravity lies above the centre of figure.* The plane of each ventral fin is in general nearly horizontal, and perpendicular to that of the caudal ; their action serves to balance the body, to incline it on either side, when one fin only acts, and to elevate and depress the fish by their joint effort. f In many fishes the pectoral fins being at right angles to the tail and vertical, act horizontally, and communicate either a progressive or a retrograde impulse to the body, thus assisting the action of the tail ; if they are both retained in an extended position, they will retard the velocity of the fish ; if one pectoral fin only is extended, it will turn the fish in a curve towards that side ; if the other only, it will turn it on the opposite side: they thus per- form the office of a rudder. When the planes of the pectoral fins are directed obliquely for- wards and upwards, they communicate an as- cending and a retarding impulse to the fish, but the amount of retardation is compensated by the power which the fish acquires of ascending. When the caudal, ventral, and oblique pec- toral fins move simultaneously, there result three forces acting in different planes, whose intensities, estimated in directions perpendi- cular to those planes, are severally proportional to the products of their areas multiplied into the squares of their velocities ;\ the resultant of these forces may be obtained by the law of the parallelogram of forces.§ In the Rays, the pectoral fins are developed to an enormous extent, and being directed horizontally, their action is vertical, like the wings of a bird. They are furnished with a great number of joints, which endow them with considerable mobility ; they have the power to increase the surface of the fin during depression, and to diminish it during elevation. The disc of the ventral fins lies in the same plane as the pectoral, and acts in a similar manner, but the plane of the caudal fin is at right angles to them. The depression of the pectoral and ventral fins elevates the fish, whilst the lateral motions of the tail propel it forwards. The area of the pectoral fins in the Rays is very great compared with that of the caudal ; and * In Piseibus, pars gravissima ossium spins, copi isissima caro musculosa in dorso supremo posita est, vesica vcro arrea in inlimo ventre recon- ditur ; ergo centrum gravitatis Piscium supra cen- trum magnitudinis eorum in supremo dorso repo- situm est; et ideo, dum in aqua innatant, natural) instinctu revolverentur ventre supino, qua- positura cum natalui valde incomnioda sit, cojuntur Pisces artificiose se retinere situ erecto. Borelli, loco cit p 257. t Pinna? duplicatae, quas in duobus locis infimi ventris piscium existunt, non inserviunt ad motum sed ad stationem eorum. Borelli, loco cit. p. 257. | See resistance of fluids. $ See methud of rectangular co-ordinates. 438 MOTION. the intensity of their action (all other things re- maining the same) must be proportional to their areas respectively. Sometimes the Rays glide sideways, in which motion the pectoral and caudal fins exchange their office, the former striking horizontally, and the latter vertically, the result of which may be obtained by the composition of forces, when their directions and intensities are given. The Rays, being destitute of an air-bladder, require a much greater force in the vertical direction upwards to sustain themselves in swimming ; hence the necessity for the power and mobility of the pectoral fins which we find conferred on them. The great lateral development of the surface of the Rays compared with their depth, and the great depth of the Pleuronectides compared with their breadth, entitle the former, rather than the latter, as Mr. Yarrell justly observes, to the appellation of Jlat fish. The first movement of a fish from a state of rest is usually produced by the flexion of its tail, as to a, Jig. 232 ; during this action the centre of gravity (c) recedes slightly from its previous position ; the tail being flexed into the position a, is forcibly extended by the muscles on the opposite side, in the direction of the line a i, perpendicular to its plane. The force of its action upon the water in a i is translated to the body of the fish in i «, causing the centre of gravity c to move obliquely forwards in the direction of c h, parallel to i a. The tail having reached the mesial line c d, its power of urging the centre of gravity forwards not only ceases, but during its flexion in e o, it acts backwards in the direction of o e ; having reached the point o, it is again forcibly ex- tended in the line o e, causing an impulse on the centre of gravity in c b, parallel to o e ; if the two forces c h and c b acted simulta- neously, we should obtain the resultant c J\ but as they do not, the point c will not move ex- actly in the right line c f, but in a curved line, which lies evenly be- Fig. 232. tween d c j' and a line drawn parallel to it through The fish being in motion, the tail describes the arc of an ellipse,* whereas if it were stationary, it would describe the arc of a circle. If we sup- pose the force re- sulting from the flex- ion of the tail to be so great as to neutralise the velocity which the centre of gravity had acquired during its extension, the result would be a state of rest whenever the tail reached the points a and o, and a greater force than this would Borclli, loco cit. prop. 24, p. 259. cause it to recede; which, according to Sir John Lubbock,* is the case, although it has never yet been detected in the movements of the living animal. The minute investigation of this sub- ject, however, embraces a very complex ana- lysis.f There are several circumstances which militate against the hypothesis of Sir John Lubbock ; first, the muscles which move the tail are capable of varying its surface during flexion and extension, and of contracting it during the former and expanding it during the latter action, by which the resistance is propor- tionably varied. Secondly, the muscles of the tail incline its plane to the direction of its mo- tion during flexion, and present its plane per- pendicularly to that direction during extension, which causes the effective resistances in the two strokes to be to each other as 1 : s3, where s is the sine of the inclination of the tail to the horizon. Thirdly, according to Dr. Roget, the water having been set in motion during the ex- tension of the tail, in the same direction, offers comparatively but little resistance in flexion ; on the contrary, when the motion of the tail is reversed, the water meeting it in an opposite direction produces a resistance proportional to the sum of the squares of the two velocities. These are so many causes which contribute to diminish the force of the tail during its flexion, without producing a retrograde motion in the fish. The same demonstration serves when the plane of the tail is directed horizontally, as in the Cetacea and Flat Fishes, but the im- pulse given must be estimated in a vertical in- stead of a horizontal plane. The velocity of some fishes is 1 very considerable, and often maintained for lengthened periods. According to Lacepede, that of the Salmon is eight metres, or 26-24 feet in a second ; others are said also to travel upwards of sixteen miles in an hour ; the Shark, for instance, will often accompany and gambol around a ship in full sail across the Atlantic. In those fishes which have the great- est velocity the tail is forked, the area is in the inverse ratio of the distance from the centre of gravity ; in these the centre of force is one half the distance from the centre of motion. When the tail presents a triangular surface, of which the apex is the centre of motion, the centre of force is three-fourths the distance of its base from the axis of oscillation. With this form of tail the muscles act at a mechanical disadvantage, and consequently the animal moves very slowly. If we consider the density of the medium in which these animals move, the resistance which it opposes to their bodies, and the long periods during which they will continue in progression, we may form some idea of the great energy with which their muscular system is endowed. Aquatic Birds. — In the Aquatic Birds, the thorax and abdominal regions present a form * See Dr. Roget's Bridgewater Treatise, vol. i. p. 369. t See Chabrier, Mem. de l'Acad. des Sc. torn. xi. In this paper formulae are given for find- ing the velocity of the centre of the tail and the quantity of action expended in swimming. MOTION. 439 resembling the keel of a boat. The feathers are furnished with an oleaginous secretion, which prevents the water from penetrating to the skin ; they also enlarge the bulk of the bird without very sensibly increasing its weight. In the Palmipedes, the osseous system, though more dense and less permeated with air than in birds destined for long and continued flight, is yet so light as to render their specific gravity considerably less than water, so that a large proportion of the body is sustained above its level by hydrostatic pressure alone. The in- terdigital membranes which give an expanded surface to the feet of these birds, acting at the end of the long lever, formed by the metatarsal bone, enable them to strike the water with considerable force.* In the effective stroke pro- duced by the extension of the legs, the flat surface of the feet is presented to the water in the direction of motion, whilst in the back stroke they are drawn forwards very obliquely and with less force. In the former action, the centre of gravity is accelerated, but during the latter it is retarded, so that there results a succession of impulses and a variable motion. The Swan and other Palmipedes sometimes spread out their wings as a sail, upon which the wind acts with sufficient force to propel them along without the expenditure of any muscular power. The specific gravity of birds, being much less than unity, enables them to glide upon the surface of the water without any expenditure of muscular action in the vertical, consequently it is required only in the horizontal direction. Quadrupeds. — Many quadrupeds have their feet pal mated to afford a larger surface for striking the water in swimming. Many of the Saurian, Batrachian, and Chelonian tribes have their feet thus organized, though the Caymans are semipalmated. The lateral direction of the locomotive organs of the three former orders enables them to give an oblique stroke down- wards and backwards, so as to communicate an ascending as well as a horizontal impulse to the centre of gravity, and thus to prevent their sinking whilst they are urged forwards. In the common Otter the feet are also palmated, a construction which enables them to move in the water with surprising agility, and with suf- ficient velocity to overtake and capture the fish on which they prey. In a similar manner the feet of the Newfoundland Dog are also furnished with interdigital membranes, but owing to the number of their respiratory move- ments in a minute they are incapable of re- maining below the surface of the water for lengthened periods. The Ruminantia, Carni- vora, and Pachydermata, being all of less spe- cific gravity than water, can swim with facility, and their locomotive organs, acting as in ter- restrial progression, render swimming a task of easy accomplishment. Quadrupeds swim by the alternate extension and flexion of their legs; the effective stroke is performed during extension, and the back stroke during flexion, presenting in the former a larger area to the water than in the latter. In consequence of the difference of their specific gravities, the Horse is capable of swimming even when loaded with the weight of a man, with a large proportion of its body above the surface of the water. The feet of the Solidunguli are well formed for striking the water, the fiat portions of which are employed in the effective and the convex in the back stroke, so that the propor- tion of the resistance of the water in these two strokes, owing to the figure of the foot, are to each other nearly as two to one.* Man. — The figure of the human body, the position of the respiratory apertures, the number of respiratory movements made in a a minute, the different plane in which the loco- motive organs usually act in terrestrial progres- sion, and the small surfaces which the hand and feet present to the water, contribute to render man the least adapted of almost all animals for swim- ming. The specific gravity variesin different indi- viduals; it is rather greater than water when the chest is nearly exhausted, and less when well expanded with air ; hence a man has always an hydrostatic apparatus which will keep him floating, if he has the knowledge of this fact and sufficient presence of mind to employ it. The density and temperature of water produce at the moment of immersion an involuntary expulsion of air from the chest, added to which the consequent alarm and misdirected struggles facilitate the fatal catastrophe of drowning. In swimming, the hands and feet are employed so as to present the least surface to the water in the back and the greatest in the effective stroke ; in the former the hands are brought near the mesial plane, with the palmar surfaces parallel to each other ; they are then thrust forward by the extension of the arm, with the points of the fingers in advance to cut the water with the least resistance ; when the hands have nearly reached their greatest distance from the centre of gravity, they are rotated by pronation, so that the palms are directed at an oblique angle outwards and downwards; they are then forced backwards by the abduction of the whole arm through a large arc of a circle, having the shoul- der-joint for its centre, and the length of the arm for its radius ; the fore-arm is then flexed, and carried into its former position preparatory to making another stroke. During the exten- sion of the arm, the feet are drawn towards the centre of gravity, with their convex surface directed obliquely backwards by the extension of the ankle and flexion of the hip and knee joints, and during the adduction of the arm the flat surfaces of the feet are driven forcibly backwards and downwards by the sudden ex- tension of the leg. From the ratio of the areas of the hands and feet, and the ratio of the dif- ference of their velocities in the two strokes, there results such a preponderance of the force in the vertical direction upwards and in the hori- zontal direction forwards as is sufficient to keep the respiratory openings above the surface of the * See Principles of the Resistance of fluids. * See Resistance of Fluids. 440 MOTION. water, and to overcome the resistance which the water opposes to the motion of the body, due to its figure and velocity. In resisting me- dia, both the facility with which bodies im- mersed are supported, and the difficulty of moving through them, increase with the density of the medium: this arises from the increased resistance which the particles oppose to their displacement ; hence, according to Borelli, fishes expend, in order to acquire a given velo- city, nearly twice as much animal power as birds, but are supported in the fluid without any exertion, whereas birds, as we have seen, are obliged to use considerable force to sustain themselves in the air.* Sect. I V. Pi-ogi-ession on solids. — The pro- gressive motions of animals on solids are ac- complished with much less expenditure of mus- cular action than is employed by animals in swimming or flying. In the various movements of animals upon solids the reaction of the ground is always equal and opposite to the quantity of muscular action impressed on it.f The velocity being equal, muscular action in- creases as the resistance of the solids decreases; hence the augmentation of labour in walking on a loamy or soft soil, such as the sands on the sea-shore. If an animal were projected into space, and moving in an unresisting me- dium, no effort of its limbs would ever enable it to change either the velocity or direction of the motion of its centre of gravity. From these dynamic considerations we perceive the importance of a surrounding resisting medium to animal progression. We shall now trace the modes of terrestrial progression from the lower forms of the animal kingdom succes- sively through the intermediate groups, to man. Radiata. — In the general outline of the Echinodermata we observe great diversity in the structure of the organs of support and locomotion. The Crinoidea belong most gene- rally to those forms of the Echinodermata which are permanently fixed. Amongst the Asterioidea, in the Comatula, the locomotive organs consist of long, complicated, flexiblearms radiating from a common centre, and subdivid- ing into numerous filaments covered with spines, which perform the office of so many legs, enabling the animal to drag itself along the bottom of the sea, or of so many tenta- cula to lay hold of surrounding solids or to seize their prey. In the Ophiura the rays are of considerable length, being composed of a great number of pieces curiously imbricated and connected together by ligaments; they are flexible and moveable in every direction, and act not only as legs for crawling on the ground but also as fins, which, by a kind of undula- tory movement, enable the animal to swim during short intervals. In the Asterias the * See Borelli, >. 260. t Barthez, in opposition to Euler, Borelli, and others, denies that reaction is the cause of progres- sive motion on solids, but in the explanation which he gives of it it is difficult to understand his reason- ing, without taking into account the resistance of the ground. five rays diverge at nearly five equal angles from the axis of revolution. In the Sea-star each ray, according to Reaumur, is composed of seven hundred calcareous plates, of which there are about three thousand five hundred in the whole animal. The rays of the As- terias do not possess the flexibility of those of the Comatula or Gorgonia, and of themselves- would be insufficient to propel the animal along. Nature has therefore substituted other organs of progression in tubular, retractile, fleshy suckers, protruded from oblique ambulacra!1 perforations, by means of which the animal is dragged along the bottom of the sea or upon the vertical surfaces of submarine rocks. If an Asterias left to all appearance motion- less and inanimate by the retiring waves,, be picked up from the beach, and placed in a large glass jar filled with sea-water,, an asto- nishing spectacle will be observed. " Slowly," says Professor Rymer Jones,. " the rays ex- pand to their full stretch;, hundreds of feet protrude through the ambulacral apertures, and each apparently possessed of independent ac- tion, fixes itself to the sides of the vessel ; as the animal begins its march, the numerous suckers are all soon employed in fixing and detaching themselves alternately, some remain- ing adherent, whilst others change their posi- tions; and thus by an equable gliding motion the star-fish climbs the side of the glass." The progression of the Asterias is laboured and exceedingly slow, and ill adapted for traversing such surfaces as the rough shingles of the sea- shore. Echinida. — The Echinus Esculentus is one of the most complicated and elaborately formed species of the whole Echinodermata j its figure is spherical : the five pairs of arched ambulacra!., and five pairs of tubercular columns, are joined to each other by zigzag sutures. The nume- rous spines are connected to the tubercles by a ball and socket articulation. According to Dr. Grant, the skeleton is composed of more than ten thousand pieces, the spines acting as so many inflexible levers, and the numerous suckers protruding through the oblique ambu- lacral foramina, as so many feet, form a double set of organs for progression.* In the Echinus, the spines being perpen- dicular to the shell, elevate its centre of gravity (which, on account of its globular figure, is in the centre of the shell) far above the plane of motion, protect the shell from internal in- jury, and increase the diameter of the whole sphere, with respect to that of the shell alone, by twice the mean length of the spines. From the nature of their articulations, the spines are capable of moving in every direction upon their tubercular attachments; but these alone would be insufficient to enable these animals to climb the sides of submarine rocks and vertical pre- cipices in search of shell-fish on which they prey; but by the aid of their tubular feet, which they have the power of extending be- yond the spines, we behold in the Echini the * Grant's Outlines of Com. Anat. p. IB. MOTION. 441 curious spectacle of globular bodies moving in direct opposition to the force of gravity. The structure of this interesting animal in a mechanical point of view is worthy the pro- found attention of the mathematician, as well as of the anatomist and physiologist. Sect. IV. Annelida. — The terrestrial An- nelides, such as the Lumbrici or Earth-worms, have the body cylindrical, and divided into up- wards of one hundred and twenty segments, which permit of extension and contraction, with the power also of curving the trunk vertically and horizontally, according to the play of the muscular system. The progression of the Lumbrici is aided by their retractile seta?, or conical spines, eight of which are attached to each ring, consequently there are as many or more than 8 X 120 = 960 of these setae in a single worm, to assist its locomotion. As many of the Lumbrici attain the length of nearly twelve inches, there must be about twelve rings or segments in an inch of the body taken longitudinally ; now each ring being arti- culated with great freedom of motion, and the integuments being soft, flexible, and elastic, the trunk possesses very great mobility. The locomotion of the Lumbrici is simple, and performed in the following manner. When the animal is about to advance, the head is raised, and about fifteen or twenty of the an- terior segments are extended and placed firmly upon the plane of position ; the setae and rings assist in fixing the segment in advance ; this being effected, the next fifteen or twenty rings are drawn forwards, and the seta? are again fixed in a similar manner; subsequently a third and fourth series successively complete the pro- gression of a step. The space taken at each ad- vance depends on the energy and magnitude of the animal, and the nature of the surface on which the movements are performed. Some Lumbrici, about six inches in length, having been placed upon a smooth surface, performed a distance equal to their own length at six or seven complete steps, taking about one inch at each advance ; this occupied nearly one mi- nute of time, being a velocity of progression of about thirty feet per hour. The smoothness of the surface retarded the celerity of their move- ments in consequence of the seta? being inca- pable of fixing the segments against any points with sufficient power to enable them to draw the succeeding segments forward ; under these circumstances the mouth was observed to be substituted, and to lay firm hold of the surface, whilst the anterior segments were drawn for- wards. The Lumbrici are capable of ascend- ing a plane inclined at an angle of 45° to the horizon, provided its surface presents suffi- cient irregularities for the application of the rings and setae. The centre of gravity of the Lumbrici is very near the middle of their length. The cylindrical form of the articulata, and the minute dimensions of the setae, render them (with such a limited basis of support) very liable to turn upon their axis, and roll over on their backs, but they readily recover the pendent position of the abdomen by bend- ing the trunk forwards into an arch, with its convexity resting on the plane of motion, and the head and anus raised above it, but inclined to one side : the inclined direction of the raised segments causes the animal to revolve on its axis, and regain its natural position. When irritated, the Lumbrici contract and contort the body into curves resembling in form the letter S ; they appear capable of con- tracting the body to one half of its entire length ; in which condition the integuments present a cor- rugated appearance. The Nais and Naiades are swimmers. The Haemocharis walks like the caterpillar of the Geometra. The Hirudines, or Leeches, are more developed in a transverse direction than the Lumbrici ; in these animals the mouth is surrounded by a lip, and the anal extremity is furnished with a flattened disc, each of which is capable of causing a vacuum, and the head and anus being fixed to the plane of position, whilst the body is elon- gated and contracted alternately, the locomo- tion is effected. Leeches are well known to be capable of thus ascending vertically upon the smooth surface of glass, to which they adhere with considerable force. Insecta. Apode larva of Insects. — The num- ber of segments which compose the lengthened cylindrical form of the Apode larva; and the dis- position of the muscular system permit the trunk to be moved in various directions ; to be elon- gated, contracted, curved upwards, downwards, or on either side, thus contributing to the pro- gression of the Apocles. The cephalic, thoracic, and abdominal sections, which may be consi- dered as merely auxiliary organs in animals furnished with arms and legs, are employed by the cylindrical Apodes as the sole instruments of locomotion. The progression of the Balaneus Nudum, the Maggot of the hazel-nut, is thus performed. Having first laid hold, with the mouth, of some point in the plane of position, the body is con- tracted and curved upon itself, and the anal extremity drawn forwards ; the latter then takes a fixed point for a fulcrum, and the segments which had previously approximated during the contraction, are again separated in succession from behind forwards, causing a slight undula- tion of the body in successive curves, vertical to the plane of motion. The head having been pro- jected forwards by the elongation of the trunk, repeats the same actions, recurring as before, in succession. Their progression is slow and laborious, each step not being more than from one-twelfth to one-fourteenth of an inch. The Cionus Scrofularia?, like the common Snail, secretes a slimy substance which enables it to walk on the leaves of the fiewort, on which it feeds.* The larvae of the Muscida? are pro- vided with unguiform mandibles, with which they maintain a firm hold, whilst the body is contracted and dragged forwards. Other larva?, as the Syrphus, use their mandibles for the same purpose. f Pcdate Larva. — Many of the pedate larva? of insects are furnished with six legs like the * Do Gccr, vol. v. p. 210. t Khby ami Spenco, vol. ii. \i. 272. 442 MOTION. perfect insect, which support the three tirst rings of the trunk. In many larvae there are no organs of locomotion, whilst others are furnished with a variable num- berof rudimental legs, presenting differently constituted organs for progression. Most of the larvae of the Lepidoptera have ten pair of these pro-legs, respectively arti- — culated to the sixth, seventh, eighth, ninth, a and anal segments of the body. One family, the Lophyrus, has sixteen pro-legs. Others, as the Stylotoma, have fourteen, and the Tenthredo twelve. The perfect legs move (according to Kirby and Spence) in the same order as in the imago state ; the pro- legs serve not only to raise and support the abdominal and caudal segments of the trunk, but also to assist in grasping objects in the plane of motion, and in urging the centre of gravity forwards. When the head and thoracic segments are fixed, the body and tail are drawn forwards ; the trunk is arched in the vertical plane ; the tail being fixed, the pro-legs are advanced successively in pairs, beginning from the anal segment; the body is then extended, and the head advanced to take a new position ; a conspicuous undulation of the body is produced, proceeding from the caudal to the cephalic seg- ments. The larva of the Ant-lion (Myrmeleon) moves in a backward direction, even after the removal of its legs. Many larvae, such as the Caterpillar of the Hawk-moth, move with ex- treme slowness, whilst others possess consi- derable powers of locomotion, as the Apotela Leporina, which has received its appellation from the rapidity of its movements. But of all terrestrial larvae, the most remarkable for their altitudes and motions are the Geometrae. The true Geometrae have only two anal, and two in- termediate pro-legs ; with these they grasp any object so as to fix the anal extremity : the trunk, with the head, is then extended, elevated, and inclined from the horizontal towards the vertical position, and the animal appears to be in the act of surveying surrounding objects as repre- sented in Jig. 233. In progression, the head being Fig. 233. fixed on the surface of motion at c (fig. 234) ; the anal extremity is drawn forwards to the thoracic segments, from a to b ; the trunk is then again extended to d, and a series of the same alternate flexions and extensions is em- ployed to carry the larva onwards. During progression, the Geometrae spin a silken cord, which they fix by the head on the plane of position at each step, thus measuring the dis- tance over which they pass. The use of this cord is to enable them to descend from the Fig. 234. be d trees, however lofty, on which they feed, and to reascend by the same means, without the necessity of taking a circuitous route, and encountering the inequalities of the trunk and branches. In like manner the Caterpillars of the Cabbage-butterfly weave a ladder of silk on the plane of a glass-window, which serves as a fulcrum for its legs, and thus enables the animal to ascend. Perfect Insects. — The order in which the legs of the Hexapods move in walking or running has been accurately explained by Professor Miiller. Whilst watching insects which move slowly, he observed that three of their legs were always moving at the same time; these were advanced and put to the ground, whilst the otiier three propelled the body of the insect forwards. The feet, which moved simultaneously, were the fore and hindmost foot on one side, and the middle foot of the opposite side; then the fore and hind foot on this side, and the middle one of the other side, so that in two steps all the six feet are set in motion.* In the first movement, whilst the legs, 1, 2', 3, (Jig. 235) Fig. 235. remain on some solid to support the body, and project it forwards, the other three legs, 1/ 2, 3', are raised and advanced ; then, whilst the legs, 1', 2, 3' are, in their turn, supporting the body, 1, 2', 3 are raised and advanced, and so on alternately. It will be observed, that the base of support in these movements is a triangular plane, with the three feet placed on the three angles ; the base and apex of the triangle alternating at each alternate movement of each set of legs ; so that in the first move- ment, the apex, which is at 2, takes the oppo- site side at 2' in the second step. The Hexa- pods are supported by their three pairs of legs, and the stability of the animal is increased by the horizontal direction of the legs outward, this arrangement affording a larger base for the support of the centre of gravity. The first pair of legs being articulated to the prothorax, the second pair to the mesothorax, and the third to the metathorax, also gives to the longest axis an increased stability. The articulation of * Miiller, by Dr. Baly, p. 970. MOTION. 443 the coxre to the trunk is by cotyloid joints, as in the Rhimophorae, or by ginglymoid joints, as in the Lamellicornes ; and between the trochanter and femur, the coxa and tro- chanter, the femur and tibia, the joints are usually ginglymoid : the axis of each of these joints is turned at right angles to the next, so that, as Dr. lioget remarks,* " there results from the combination of both, a capability in the thigh of executing a circular motion, in a manner almost as perfect as if it had revolved in a spherical socket. The principle of this compound motion is the same as that employed on ship-board for the mariner's compass and other instruments which require to be kept steady during the motion of the ship. For this purpose, what are called gimbals are used, the parts of which have two axes of rotation at right angles to each other, so as to enable the compass to take its proper horizontal position, whatever may be the inclination of the ship." The remaining joints of the legs of insects are also ginglymoid. The tarsi, which vary in number from two to six, terminate by a double hook ; those on the anterior pair of legs are directed backwards ; those on the middle pair inwards ; and those on the tail-piece, forwards ; by which disposition the insect is enabled to lay hold of rough surfaces, and to walk up in- clined or vertical planes with security. In the progression of insects, the fore and middle legs are extended, and the hind legs flexed previously to urging the body forwards ; in doing which, the actions of these legs are reversed. The simple hook terminating the locomotive organs of most insects will not en- able them to walk on water, to climb vertically on glass, or stand inverted on ceilings, actions which many can perform, and for this purpose an additional apparatus is therefore provided. The common Gnat and some Coleopterse which walk on the surface of water, have the tarsi furnished with a brush of fine hairs, which appear, when the surfaces are free from moisture, to repel the fluid with sufficient force to sustain the weight of the animal, and in confirmation of this theory, it is found that if the legs are moistened with spirit of wine, the animal immediately sinks and is drowned. Those insects which ascend vertically on the surface of glass, or remain suspended in an inverted position from the ceiling, are furnished with an additional apparatus. We have a familiar example in the House-fly, which has the extremities of its feet furnished with two funnel-shaped membranous suckers, moveable by muscles in every direction, by which tbey are capable of exhausting the air on very smooth surfaces, thus causing the pressure of the atmosphere to sustain the weight of the body : the area of these suckers is so beautifully adjusted to the weight of the insect, that the pressure of the air alone is more than sufficient to sustain the weight of the insect without ex- ertion, and to suspend its body to a ceiling in an inverted position. The centre of gravity is is thus suspended, instead of being supported, * JSridgcwatcr Treatise, i. 294. the legs having merely to resist the force of gravity upon the body. In the Bluebottle- fly ( Musca Vomitoria) these suckers are conspi- cuous, and the edges being serrated enable them to apply the disc of this pneumatic apparatus to any kind of surface. In the Fig. 236. Fig. 237. Bibio febrilis (fig. 236), the foot is furnished with three suckers, in the Musca domestica with two (fig. 237), and in the Cymbex Lutea with five. Numerous other species, amongst which is the common Wasp, are fur- nished with cushions and analogous suckers, which enable them to ascend vertically on glass. The predaceous insects run with great velo- city in proportion to their height. Those which are furnished with very short legs must ad- vance them at intervals of time corresponding to the square roots of their length, on the supposition that their legs are subject to the same physical laws as those of the human race. Mr. Delisle observed a minute fly run three inches in half a second, making 540 steps in the same time ; each of these steps 3 must have been consequently = 0.0056 ^ 540 of an inch in length. The great number of steps taken by these minute animals conveys to the mind of the observer an impression that the animal is running, whereas it is merely walking, the body not swinging freely in the air, as is necessary, according to the definition of Weber, to constitute the act of running. Myriapoda. — In the Myriapods, the great number of legs and the celerity of their move- ments, as for example, in the Scolopendra, render it difficult to detect the order of their motions. The numerous segments entering into the lengthened form of the trunk, each of which is furnished with a pair of legs, give to the body great flexibility, and enable the Myriapods to turn from a right line to any curved or angular path, or to pass over rough surfaces with facility. The legs, in number from fourteen to forty-two, are short, and directed laterally ; they are composed of four segments; all the joints, except that by which they are attached to the trunk, are ginglymoid, and terminate in a sharp conical claw, which gives precision and security in climbing. The legs appear to move in a determinate order; every 444 MOTION. alternate leg on one side supports the animal, and urges the centre of gravity forwards, whilst the corresponding leg on the other side is raised and advanced to take a new position on the plane of motion. Such, at least, seems to be the process employed, but there is very great difficulty in ascertaining their motions with perfect accuracy ; we therefore give the above in part practically, and in part hypothe- tically. The Myriapods move with considerable agility ; usually run, and if disturbed, continue that pace for a great length of time. They have the power of climbing with facility the per- pendicular surfaces of trees, walls, &c. Arachnida. — The Arachnida are furnished with four pairs of legs, which render their mode of progression more complex, and more diffi- cult of observation, than that of the Decapods.* Their coxaa are articulated to the base of the cephalo-thorax by cotyloid joints arranged in an elliptical form, and directed horizontally outwards ; all the remaining articulations of the legs are ginglymoid, which is the best mode of articulation for the horizontal movements of the leg whilst urging the body forwards ; the tarsi, which are composed of a variable number of segments, terminate by a double or single hook, which affords to this tribe of animals the means of ascending vertically, whenever any surfaces present minute irregularities adapted for pre- hension ; the legs, projecting from the cephalo- thorax horizontally, increase the base of support. The centre of gravity is that of an ellipse. The Arachnida cannot ascend vertically on glass, but are enabled to walk in an inverted position on ceilings or rough surfaces without the assistance of their web. The organs of motion in spiders, though nearly constant in number, differ exceedingly in length; the general principle is, however, the same. After long and repeated observation, I disco- vered the order in which the eight legs of these animals are put in motion. If we first attend to the manner in which the legs are moved on either side singly, they will be found to move first the fore leg, then the fourth, then the third, and lastly, the second leg ; that is, in the order 1, 4, 3, 2. On observing the motion of the legs on both sides of theanimal simultaneously, they are found to move the first right leg, then the fourth left; then the first left and the fourth right ; then the third right and the second left ; and lastly, the third left and the se- cond right (fig. 238). Of these, the first two sets are moved conse- cutively, like those of a quadruped, V, 4, 1,4'; the last two in pairs simultaneously, that is, 3', 2, then 3, 2' ; and whilst the legs of one side of the animal are moving consecutively * The female is furnished with an additional pair, to enable her to carry her eggs. 238. in the order 1, 4, 3, 2, the legs of the other side are moving in pairs in the inverted order 4', 1', 2', 3'. In descending vertically by means of a newly-spun thread, they hang by one of the hind legs ; on ascending the same thread they employ three legs ; the two first on one side, and the first or second on the other ; in running, the second pair of legs is placed in advance of the first, then those of the third be- fore the second, thus giving the feet a greater range of space at each step. The fourth pair, or hind let's, are directed backwards nearly pa- rallel to the line on which the animal is moving ; they seem to be chiefly used to support the posterior segments of the abdomen, but also exercise a limited action in propelling the body forwards. Four legs support the bodv almost, but not quite, simultaneously, as stated by Professor Muller, whilst the other four are raised. The progression of the spider is usually rapid ; it can run upon its web with great facility ; it can leap many times its own length in chace of prey ; it can float during a limited period on water; and the facility with which it can spin and throw a cord across cavities from one fixed point to another, at a considerable distance, endows it with a mode of transit across spaces which is denied to many other animals. Decapoda. — The modes of progression em- ployed by the Decapods are both various and singular. Organized either to swim in rivers or seas, to walk and run on the dry land or at the bottom of water, both fresh and salt, they are furnished with organs of locomotion suitable for these different purposes. The five pairs of legs articulated at the base of the cephalo-thorax have the whole of the joints articulated, and directed to move on solids either laterally or directly backwards. The front legs are generally the most massive and powerful, throwing the centre of gravity for- wards nearly between the axes of their articu- lations. The Brachyurous Decapods, as the Cancer, Maiu, Sfc., present either a quadrilateral or a pyriform figure. They are generally destitute of the great elongations of the abdominal seg- ments and expansion of tail into tins for swim- ming, which we find in the Macrourous De- capods. The consolidated carapace of the de- capod tribe deprives them of lateral flexibility in the thoracic section of the trunk. The land species of Decapods, such as the Cancer cursus, or land crabs, are capable of running with such velocity, that a man on horseback has difficulty in keeping up with them. From their speed they were called by the more ancient natu- ralists etjid. In many species, such as the Inachm thoracicus, the Leptopus longipcs, and the Leptopodia sagittaria, the legs are greatly elongated, and consequently exercise a locomo- tive office resembling that of the tipula amongst insects, differing however from it in the direc- tion of the articulations, by which the pro- gression of these different classes is reversed. Thus in the Leptopus lungipes (fig- 239), the action resulting from the flexion and ex- tension of the legs in g J] g' J' will propel 445 Leptopus longipes. the centre of gravity c backwards in the direction of d e, but by the elongation of one set of legs from /' to h, and subsequent re- traction towards f, and the simultaneous con- traction of the other set from f to h', and subsequent extension towards J'', the centre c will be propelled laterally in the direction of * = r* (24) L — 1+ n Cos I JL (t — a) \ . . (25) h= k (t — 3)2 (26) fl_3-/V 1+fk r (27) I ir 2 r=sJ— (28) In which equations a = arc (Cos = - ). k=z + l)g A+rn^Sin J J-(« -«) j )*-(!- ry- The mass of the trunk is supposed to be con- centrated in a point m at the upper end of the leg, and the mass of the swinging leg in a point »n'°in the leg which is considered as a straight line. , , , , . / is the length of the lander leg at the begin- ning of a step. , , . , , h is the height of m above the horizontal plane at that time. , , ■ j , , p is the distance between the hinder foot and the forward atthat time, or the length ofa step. 8 is the time during which m falls below its ho- rizontal line at the end of the time t. I' is the length of the liinder leg at the end of the time 8 before it is extended or becomes I. t is the time of one step. t is that portion of it during which the leg is swinging. the pendulous movements of the legs a person was placed upon a small block, and by sup- porting himself on one leg, suffered the other, measuring thirty inches, to swing, with relaxed muscles, as a pendulum. A vibratory motion having been communicated by a slight movement of the trunk backwards and forwards, the num- ber of oscillations made in the time of a minute were found to be 84, consequently 60" — = 0'. 714285 = time of one oscillation ; 84 and since the lengths of pendulums at the same place vary inversely as the squares of the numbers of oscillations in a given time, '84* : 60* : : 39£ : I (the length of a pendulum which vibrates synchronously with the leg) ; ■ , 60* X 394 140850 net hence I = _ — _B — = 19.961 842 842 inches. Now as the whole length of the leg was 34 inches, the centre of oscillation must be less than two-thirds of that length from the point of suspension, and consequently less than in a prismatic rod, the length of which is such as will vibrate synchronously with the leg. This accords with the known figure of the leg, the mass of which diminishes as the distance from the axis of motion in- creases. The time of a half oscillation of the freely suspended leg which we have found 0 .714285 _ 0"<3571425j approximates very closely to that found by the Webers, both in the living and the dead subject. The second experiment was made by our engraver, Mr. Vasey. In walking at the rate of four miles per hour he counted 2000 steps 1 5 X 60 every fifteen minutes; then - = 0".45 2000 the time of each step ; now as 2000 steps were taken in one mile of 5280 feet, the length of each r is the ratio of the distance between m and to' to I. g is the accelerating force of gravity = 32.5 feet. it is the number 3.1416. T is the time of an oscillation of a pendulum whose length is rl. y, is the ratio of the mass of the trunk to the mass of the swinging leg. The quantities I' T, fj. must be previously ascertained, and it and g being always the same, there will be nine equations for finding the values of the ten remaining quantities ; if therefore we know any one of these ten, the rest may be found. In regular progression the force communicated by the supporting leg to the trunk must equal that imparted by the trunk to the swinging leg, that is m'(c+rnpJ!L sin | JL (f— a) j V— m'(i— r) 2ca to + m ,2 ( - t , = — r — s v ' from which, by substituting ?i_ for c and /a. for — we get equation (26.) m MOTION. 463 Fig. 251 . Fig. 251 shows the consecutive positions of the leg /luring two successsive steps. To render them more distinct they are divided into two groups. The 1 8 figures o f the Jirst group show all the positions through which the leg passes while the toe rests upon the ground. The 10 of the second show the successive positions during the time the body is carried forward by the swinging leg. The positions from 1 to 4 show that division of time of the Jirst step, when both legs are on the ground ■ the figures 5 to 14 give the portion of time of the first step wfien one leg rests on the ground while the other swings; from 15 to 18, that division of the second step where both legs rest on the ground ; No. 19 to 28 show the portion of time when one leg swings while the other rests on the ground. step must have been £152 = 2.64 feet. 2UOO In thii case also the length of the leg was 34 inches, which gives 19.961 inches for the length of the synchronous pendulum, and for the time of each half oscillation 0".357 ; hence the time of taking each step was longer than the time in which the leg was susceptible of swinging without muscular effort, as a pendulum, by about 0".093. The step is considered as commencing at the instant when the hindmost leg is raised from the ground. Let us then suppose the whole sole of the foot of the right leg, which is in advance of the left, to be in contact with the ground, upon which it acts as a fulcrum; the hip, knee, and ankle-joints to be in a state of partial flexion, and the line from the head of the femur to the ankle-joint to be vertical, as in fig. 251, No. 4. In this position, the right leg- supports the whole weight of the trunk, and the left, being extended obliquely backwards, does not contribute to the support of the burthen. The flexed position of the right leg lowers the centre of gravity, and the effective portion of the force of extension, acting only in a vertical direction, produces no horizontal motion. At this moment, the left leg having previously communicated a slight horizontal impulse to the centre of gravity, and the trunk being inclined forwards, the head of the femur of the right leg is propelled from No. 4 towards No. 18. The leg, instead of being vertical, is now di- rected obliquely forwards and upwards. In order that the head of the femur with its load may be sustained at the same height above the 464 MOTION. Fig. 252. Fig. 252 shows the simultaneous positions of both legs during a step, divided into four groups. The first group, 4 to 7, gives the different positions which the legs simultaneously assume while both are on the ground ; the second group, h to 11, shows the various positions of both leys at the time when the posterior leg is elevated from the ground, but behind the supported one ; the third group, No. 12 to. 14, shows the positions which, the legs assume when the swinging leg overtakes the standing one ; and the fourth group, 1 to 3, the positions during the lime when the swinging leg is propelled in advance of the resting one. plane of motion, whilst it moves forwards with the trunk, from No. 4 to 18, the distance from the head of the femur to the foot must be con- stantly increasing. To accomplish this the mus- cles which extend the hip, knee, and ankle- joints are gradually contracted, and the length of the leg sufficiently increased by its extension to reach from No. 18 to the ball of the foot {fig. 251). In these movements the sole of the foot rotates on the ground, and (independently of the angle formed by the legs) increases the length of the step by the length of the foot from the heel to the ball ; because, when the head of the femur arrives at No. 18, fig. 251, the line from the ankle-joint to the ball is perpendicular to the ground. At the moment that the head of the femur of the left leg arrives at a position vertical to the foot, as No. 4, ■fig. 251, the right leg is lifted from the ground,* and, from its oblique position and weight, swings forward like a pendulum, whose axis of motion is in the hip-joint, Nos. 19 to 28,i/i'g'-251, and having passed by the sup- porting leg it touches the ground, with the ankle-joint in advance of the head of the femur, No. 1, fig. 251. The heel is first placed upon the earth, and by degrees every part of the * Measure of the elevation of the heel and toes in walking, the distance passed through 30 metres. Num- ber of steps. Time. Elevation of the heel. Elevation of the point of the toe. Velocity. metre. metre. 41 17".4 0.178 0.092 1.72 39 12".7 0.173 0.115 2.36 sole, the hollow arch only excepted, is brought into contact with the ground, and the head of the femur is again over the ankle-joint, as before, No. 4, fig. 251. The motion of the left leg al- ternates with that of the right in the same manner.* In the first period of the movement the left leg is seen in the rear of the right leg, No. 8 to 11, Jig. 252. Having overtaken the latter, No. 12 to 14, fig. 252, it advances before it and comes to the ground in sufficient time to receive the weight of the body as soon as the right leg ceases to act, No. 4, fig. 252, so that the instant the weight of the trunk is transferred to it from the right leg bend- ing slightly and returning to its former posi- tion, it acts like a spring, and prevents any sudden concussion arising in consequence of the translation of the burthen from one leg to the other. The weight of the trunk being thus propelled, supported, and transferred from one leg to the other alternately, a constant and uniform movement in a horizontal direction is maintained. The right and left leg having thus swung and supported the body alternately, and having been on the ground simultaneously a short, and separately a long, period, the ho- rizontal path of the centre of gravity, during these two movements, is equal to the length of a double step. In consequence of this inter- change of offices the supporting leg is active, whilst the swinging leg is comparatively pas- * The Webers compare the action of the foot to the rolling of a wheel, with this difference, that the ro- tation of the wheel is uninterrupted, whilst that of the foot is terminated and renewed at every step. In walking on the ball of the foot, or on the toes, the rotation is confined to the distance between the ball of the foot and the point of the toes. MOTION. 465 sive ; that is, it swings forwards by the force of gravity alone, independently of muscular ac- tion. The supporting leg is regarded by the Messrs. Weber as a substitute for the pro- pelling weight of a clock, and the swinging leg as the substitute for the pendulum, both ex- changing their offices alternately. The distance from the point where the ball of the foot of the swinging leg quits to the point where it is again placed on the earth, is equal to the length of a double step. This outline of the action of the legs in walking depends on principles which we shall now proceed to investigate more strictly, in doing which we shall draw largely from the theoretical and experimental researches of the Messrs. Weber, whose labours have con- tributed so extensively to advance our know- ledge in this interesting branch of human phy- siology. The positions of the body in walking at va- rious instants of time have been described both by Borelli and Weber; it is thus represented by the latter. Let Jig. 253 be the vertical, and Jig. 254 the ground plan, on planes in a straight Fig. 253. Fig. 254. horizontal path. In Jig. 253 the simultaneous positions of the two feet are represented at the moment when they reach the ground, also the position of the centre of gravity of the body in the vertical plane. The position of the right leg is shown by the continued lines, and that of the left leg by the dotted lines. The extremity of the right foot is designated by the letter u, that of the left by the letter b, and the centre of gravity by c, the contemporaneous positions of these points being denoted by the numerals annexed to these letters. In the horizontal projection,^'. 254 represents the si- multaneous position of both legs and of the cen- tre of gravity : the letters and figures are the same as in the preceding diagram. At tiie instant when the hinder leg is raised from the ground at the commencement of each step, the extremity of the forward leg and the centre of gravity lie in the normal plane of the line of progression ; for example, at the beginning of the first step, b0 and r0, of the second step rt2 and c2, and of the third step, bt and r4, lie in the normal plane of the direction of progression. In each step the extremity of one leg must VOL. III. be advanced as far before the foot of the other as in the preceding or following steps the other leg was placed before the first, for example: — in the first step, the foot, «, 2 3 4 must ad- vance so far before b0 , 2, as in the second step b3 4 5 0 must advance before a{ 2 3 4. The time of each step, that is, the space of time between the raising of each foot in succes- sion, is subdivided by Borelli and the Webers into two parts, namely, one part in which one leg, and the other when both legs are on the ground : for instance, during the first step, while the centre of gravity advances from c0 to cp one leg, and, while it advances from c, to c2 both are on the ground. In the second step, while the centre moves from r2 to r3, one leg only, but while it advances from c3 to c4 both legs are again on the ground, and so on m succession. But there is no instant in walking in which the body moves freely through the air without either leg touching the ground, as in running. The sum of the squares of the elevation of the centre of the body above the horizontal plane, and the length of the step, is equal to the square of the length of the extended leg.* This pro- position depends on the circumstance that the forward leg stands vertical to the ground at the instant the hinder leg quits it ; and that the two legs, with the horizontal distance between them, form, at this moment, a right-angled tri- angle. According to the Webers, the body, in walking, continues to be affected by the exten- sor power of one leg only, because the expen- diture of the extensor power of the legs to support the body is only just sufficient to sus- tain it; and this expenditure is at a minimum only when the forward leg bears the whole burden during that period in which they are both on the ground, for as the forward leg acts at a less angle than the hinder leg, it is capable of supporting the body at a much greater me- chanical advantage, which is at a maximum when it stands vertically. MM. Weber also find that the body is accelerated whilst one leg, and is retarded whilst both legs are on the ground ; for, in slow walking, the forward leg being placed on the ground in advance of the centre of gravity, it tends for an instant to check the horizontal velocity of the body. We shall now take a brief view of the velo- city in walking, and of the principles on which it depends. MM. Weber have shewn that the velocity in walking varies with the height at which the head of the femur is carried from the ground ; as this height increases, the velo- city decreases.^ The length of each step de- creases as the height of the centre of gravity in- creases ; for the greater the elevation, the less will be the distance to which the leg will ex- tend ; therefore corpulent persons, and porters with heavy burdens on the shoulders, take steps of diminished length. The duration of a step, * Hence we get cq. 23. t The velocity being uniform — _JL therefore increases as h decreases, ■466 MOTION. also, depends on this height. When the centre of gravity is most depressed, the swinging leg must be placed on the ground in the vertical position, instead of being suffered to pass be- yond it, as it does in slow walking. In quick walking the propelling leg acts more obliquely on the trunk, which is more inclined, and forced forwards more rapidly than in slow walking. The time when both legs are on the ground diminishes as the velocity increases, and it vanishes altogether when the velocity is at a maximum. Table 5. Measure of the velocity in quickest walking. Space traversed 47 metres. Number of Steps. Time. 53 17.57 54 18.00 55 18.20 54.5 18.18 55 18.42 54.5 18.00 54 17.92 55 18.10 54 17.77 54 18.05 54.3 18.021 From this table we observe that the velocity in quickest walking is at the rate of 2.608 metres, or about 7.897 feet per second. In conducting their experiments the MM. Weber found that the velocity was constant, whether the power of the muscular system had been renovated by repose, or exhausted by fatigue, and therefore they concluded " that so long as the muscles exert the general force necessary to execute locomotion, the velocity depends on the size of the legs and on external forces, but not on the strength of the muscles." Table 6. Measures of military marching Space traversed 43.43 metres. Number of Steps. Time. Duration of Step. Lengtb. in Metres. Velocity. 49.3 21 .50 6 436 0 831 2.020 52.3 27.17 0.519 0.831 1.598 54.7 32.35 0.592 0.794 1.342 61.7 43.57 0.706 0.704 0.997 68.8 55.08 0.801 0.631 0.789 74.2 64.02 0 863 0 585 0.678 87.1 83.72 0.961 0.499 0.519 100.5 105.16 1.046 0.432 0.413 111.5 124.00 1.112 0.390 0.350 Table 7. Measure of the time of vibration of the leg, and of the shortest time of a step in dif- ferent persons. Duration of Duration of Persons. Swinging. Step. A Am f\ 7 on U. / oU V.OI o R 0.662 0.337 p 0.730 0.372 u. 0.680 0.340 E. 0.696 0.348 F. 0 746 0.341 KJ . A TA{\ V. l 'iV U.ooU H. 0.690 0.370 I. 0.663 0.337 K. 0.678 0.345 L. 0.724 0.362 M. 0.743 0.374 Mean. 0.7068 0.3567 Table 8. Measure of the natural gait in walking with different velocities on the entire sole of the foot. Space traversed 43.43 metres. Number of Steps. Time. Duration of Steps. Length of Steps. Velocity. met. 51 18".12 0.335 0.851 2.397 52 20.48 0.394 0.835 2.110 54 22.55 0.417 0.804 1.928 54 24.83 0.460 0.804 1.748 55 26.38 0.480 0.790 1.646 57 28.90 0.507 0.726 1.503 60 33.70 0.562 0.724 1.288 61 34.92 0.572 0.712 1.245 65 39.27 0.604 0.668 1.166 66 41.60 0.630 0.658 1.044 69 45.72 0.663 0.629 0.949 69 46.07 0.668 0.624 0.942 73 53.02 0.726 0.595 0.819 76 57.72 0.760 0.572 0.753 82 69.40 0.846 0.530 0.627 80 68.78 0.860 0.543 0.631 88 79.67 0.908 0.493 0.545 97 93.67 0 966 0.448 0.464 101 104.08 1030 0.430 0.417 109 114.40 1.050 0.390 0.379 Table 9. Experiments on the time during which the leg rests on the plane of position in various degrees of velocity. Duration Length Time of of of Leg stand- Step. Step. Velocity. ing. met. 0.344 0.790 2.30 0.341 0 376 0.804 2.14 0.400 0.429 0.755 1.76 0.484 0.523 0.657 1.27 0.570 0.742 0.659 0.89 0.817 MOTION. 467' Table 10. In the following table we find the proportion between the duration of the step and the time of the leg resting and swinging during very diversified paces. Duration of Duration of Duration of Step. Standing. Swinging. 0.344 6.341 0.347 0.376 0.400 0 352 0.4-29 0.484 0.374 0.523 0.570 0.476 0.742 0.817 0.667 These experiments prove that the time in which the leg is swinging is least in the quickest pace, and is equal to half the whole time of oscillation of the leg ; that it increases in pro- portion as the step becomes slower; that, con- sequently, that division of time which the swinging leg occupies in describing its entire curve is increased by one-half of the entire portion of time, and more in proportion as the pace becomes slower. This gives rise to an- other range of experiments which have been made by the Messrs. Weber with the same design, of which the following table is the result.'* Table 11. Experiments on the time in which the leg stands on the ground, with various degrees of velocity in walking. Duration Length Duration of of of the Leg Step. Step. Velocity. resting. m. 6.317 0.820 2.587 6.317 0.430 0.741 1.721 0.513 0.463 0.712 1.537 0.504 0.582 0.621 1.067 0.692 0.660 0.562 0 851 0.782 Whence we deduce the following comparison between the duration of the leg standing and that of its swinging. Duration Duration Duration of of of Step. Standing. Swinging. 0.317 0317 6.317 0.430 0.513 0.347 0.463 0 504 0.422 0.582 0.694 0'472 0.660 0.782 0.538 The number of steps which a person can take in a given time in walking depends, first, on the length of the leg, which, governed by the laws of the pendulum, swings from behind * In these experiments the footsteps were tiiken on the ball only. forwards: secondly, on the earlier or later in- terruption which the leg experiences in its arc of oscillation by being placed on the ground. When the hinder leg has quitted the ground, it swings forward by its own gravity, in conse- quence of its freedom of motion in the ilio- femoral articulation and its oblique position ; and, in order that the body may be supported, it must, at least, move so far forwards that the foot may arrive at a position vertically under the head of the femur ; for in that direction the leg not only supports the body with least effort, but it is also in that position that it can most easily avoid any impediment in its path by transferring the point of support to any por- tion of the sole of the foot, particularly if the latter be turned outwards, which gives a greater security than when it is directed parallel to the line of motion. The weight of the swinging leg and the velocity of the trunk serve to give the impulse by which the foot attains a position vertical to the head of the thigh bone ; but as the latter, according to the laws of the pendu- lum, requires, in the quickest walking, a given time to attain that position, or half its entire curve of oscillation, it follows that every person has a certain measure for his steps, and a cer- tain number of steps in a given time which in his natural gait in walking he cannot exceed. We can easily ascertain the time it requires to accomplish the quickest step in walking, which is equal to the half vibration of the leg made with relaxed muscles. In order to make the steps follow each other in much slower succes- sion, the foot is not placed on the ground when it arrives in the perpendicular position, or the half oscillation from behind forwards as in the rapid pace, but we plant it on the ground somewhat later when the foot has described more than half the curve of vibration. From these principles we conclude that the man in fig. 255 walks much faster than that in fig. 256; in fact the former makes steps 27.559 in. in length, whereas in the latter the steps are barely 23.622 in. in length; and whereas the first makes a step in 0".35, the second takes 0".422 for a step, so that the velocity of fig. 255 is nearly double that of fig. 256. These figures are represented as walking on the toes, as if the foot always touched the ground in the same position, and their steps are shorter than when the entire sole is brought into action. Fig. 255 shows the greatest step which it is possible to make with the toes. The steps are shortest in fig. 257, in which the difference of the heights of the centre of gravity, compared with that of fig. 255, may be easily seen.* In figs. 258, 259, and 260, the legs are of * These figures, with the others upon the same plan, reduced to ^th the natural size, are drawn in accordance with the principles on which the theories of walking, running, and leaping are based. They are taken in the various instants of a step as seen through a revolving disc, con- structed upon the principles of the stroboscope in- vented by Dr. Faraday, and modified so as to apply to these purposes by Stamplier.t These t Vide Foggendorff's Ann vol. 22. p. 600. 2 n 2 403 MOTION. Fig. 255 figures serve also to illustrate the following for- mulas. A- + f = P. t T = T COS — /. 1 ('+"): These three equations, which are deduced from the general formulas, are intended to express the principal data upon which the theory of walking is based. If n == v = 1, and fl = o, and we substitute for //. its value as deduced from experi- ment in walking, and let (,u -(- 1 ) g = 34 .66, t T — 0",7 and / = 0.95 met. by substituting these f In this estimate /x — 2.53, g — 9.811 metre. values in the equations above we get the following results which accord very closely with experiment. No. T t h V 0.350 m. m. 1 0.350 0.642 0.700 2 0.414 0.372 0 727 0.611 3 0.422 0.375 0.736 O.600 4 0.432 0.378 0.749 0.585 5 0.446 0.382 0 765 0.564 6 0.465 0.387 0.786 0.533 7 0.494 0 395 0.817 0.484 8 0.542 0.406 0.864 0.395 Nos. 1 and 3 are represented in figs. 255, 256, and Nos. 1, 3, 7, \nfigs. 258, 259, 260. MOTION. 469 equal length, equally extended, and represented at the moment when the previously swinging leg is placed on the ground ; but Jig. 260, which is walking slowly, has the leg advanced for beyond the vertical. Fig. 259, which is walking quicker, has the leg less advanced, whilst jig. 258, which represents the greatest possible celerity, has the foot placed directly in the vertical line, passing through the head of the femur. We observe also that of the paths described by the swinging leg of the three figures, that of Jig. 260 has nearly completed the entire curve, that of Jig. 259 a little more than half, and that of fig. 258 exactly half the curve; and that the dotted line which serves to indicate the path of the leg is least in Jig. 260, greater in Jig. 259, and greatest in fig. 258. The time is greatest in fig. 260, less in fig. 259, and least in fig. 258 ; conse- quently, when the leg swings beyond the Fig. 257. 470 MOTION. Fig. 260. vertical line, not only the time of swinging the leg has increased, but also the time in which both legs are resting on the earth ; for the latter commences at the instant when the forward leg has reached the ground, and termi- nates when the head of the femur has arrived at the vertical line, passing through the point of support of the same foot. The time aug- ments in proportion to the distance which the swinging leg passes beyond the vertical posi- tion, or half oscillation. The time when both legs are resting is greatest in fig. 260, because it must be sufficiently great for the head of the femur, together with the whole trunk, to advance to a position directly over the foot, during which the head of the femur moves very slowly, and by the direction of the for- ward leg its action is to retaid the horizontal advance of the centre of gravity. The time is less in fig. 259, because the head of the femur has to pass through a less space, and the sup- porting leg acts against the trunk at a less angle; but in Jig. 258 the time of both legs resting at the same time, disappears altogether. The two legs complete the least portion possi- ble of the vibrating curve, and the duration of each step amounts only to the time of half an oscillation. In walking very slowly we may suffer the swinging leg to vibrate so long, that it partly returns to its former position before it reaches the ground. We have seen in quick walking that during the time both legs rest on the ground, the ad- vanced leg continually forms a smaller angle with the vertical than the hinder leg ; but in very slow walking the forward leg may form a greater angle with the vertical than the hinder le^; the magnitude of this angle determines the kind of gait the walker acquires. In order to accomplish this, the swinging leg is suffered nearly to complete its curve of oscillation be- fore it is placed on the ground, and during this time the centre of gravity moves so little, that half the length of the step may not be at once described, and the entire duration of the step will be about four times greater than in the quickest pace.* In this case the forward leg really makes a greater angle than the hinder as it reaches the ground, but during the time that both legs are on the ground, the angle of the forward leg diminishes, whilst that of the hinder leg augments, and there is an instant when both legs form equal angles. When the angle of the forward leg becomes zero, or in other words, when it is directed vertically, the hinder leg rises from the earth ; for example, in Jig. 261, where a c represents the right leg, be the left, in the beginning of a step, or the instant the foot a is raised from the ground ; c d" is the magni- tude of the step, or the space which the centre of gravity passes through in the time of a step, c" being the centre of that space. Now, if the foot a, which was raised at the begin- ning of the step, were placed again on the ground at a', at the instant when the centre of gravity reaches the middle point c", then both legs would form equal angles with the vertical ; or, the angle b c" a. = a c" a., in which c" a. is the vertical through c" ; but if the angle of the hinder leg to the vertical be less, when the right leg is set down in a', the centre of gravity will not have arrived at the middle point c", but at c'; however, whilst both legs are on the ground, the centre of gravity is pro- pelled from c'to c", after which the angle b c' ot increases and the angle a' c" a diminishes (where c' a is the vertical through c'); when the centre of gravity is propelled onwards from c'' to c'", the angle a c" a. is less than b c" «, until the termination of the step. In this slow method of walking a very mea- sured pace results, in which the body is carried very erect, and remains for a considerable time in the rear of the forward leg after it first reaches the earth ; consequently the duration of the step will be very considerable, nearly one se- cond and a half, the length of the step very short, and the velocity of the centre of gravity, which is very little at the middle of the step, varies considerably during each step, so that there is an instant in which the body is nearly at rest. This is denominated by Weber the grave or procession step.-] A remarkable difference may be observed in the duration of the steps of two different per- sons, one of whom has long and the other short legs. In quickest walking the duration of * That is, where T represents the entire duration of an oscillation of the leg, the time of a step in the quickest to that in the slowest walking will be as JTto2T, or four times that of quickest walking. t Vide Weber, loc. cit. sect. 139, p. 344. MOTION. their steps will equal the time of oscillation, and the case is nearly the same in a slower pace. We observe, therefore, that when children and grown persons, or tall and little men, are walk- ing together in the pace most easy and natural to them, they move in a different time. It is true the movements of the legs, like those of any other member, may be accelerated by means of the muscular force and made to move quicker than when they are merely impelled by their own gravity in swinging from behind forward, but when so continued an exercise of muscular power is required, such an unnatural pace cannot long be sustained. In the estimate already given of the forces which have an influence in walking, it will be observed that as long as the force of the exten- sion of the legs in a vertical direction upwards, is equal to that of gravity upon the body acting vertically downwards, the centre of gravity will move in a direction perfectly horizontal ; but experience shows that as soon as the force of the extension of the supporting leg ceases, the centre of gravity falls below the horizontal path in which it was previously moving; but the instant the other leg stands perpendicularly it will rise again to its former level. The mathe- matical theory of walking proves that from the figure of the human machine there must of ne- cessity be a sinking of the centre of gravity in order that progression may be accomplished. By varying the time of the sinking of the body at the end of each step, the effect of the resist- ance of the air and other extraneous influences which would disturb the horizontal velocity of the trunk, are compensated. In a favourable wind, when it travels at a greater velocity than the walker, it is necessary he should increase the time of sinking to counteract its effect, and preserve a mean uniform motion. The application of mechanical principles does not accord with slow as it does with that of quick walking, for the former is too much under the control of the will of the walker, and the limbs are not suffered to swing freely by their own gravity as in quick walking, in which this volition diminishes, according to Weber, at least when the slightest exertion is continued for any length of time, and it is in this condition alone that theory and experiment nearly ap- proximate. We must, however, remember that the control exercised by the muscular system over the limbs in slow walking is a new force which animals are enabled to interpose in order to vary the effects which result from the physical laws in operation during locomotion, and by no means refutes the theory of the influence of those forces which affect, not only the locomotion of animals, but the motion of matter universally. Running. — The laws which regulate running in many of the lower animals, such as qua- drupeds and birds, are nearly the same as in Man. It will therefore be necessary to enter into the details of this movement in reference to the latter only. The principles upon which walking and running differ. — In running as in walking it may be considered as a fundamental law that 471 the same motions of the body recur after each double step ; and that both legs exercise equal and alternate actions in these movements. In running the object is to acquire a greater velo- city in progression than can be attained in walking. In order to accomplish this, instead of the body being supported on each leg alter- nately, the action is divided into two periods, during one of which the body is supported on one leg, and during the other it is not sup- ported at all. The latter condition constitutes the principal difference between these two modes of progression. When the body is pro- jected upwards so as to swing freely in the air, the hinder leg must be raised from the ground before the advanced swinging leg has leached the vertical position ; hence, in run- ning, the duration of the step is less than the half-duration of the oscillation of the leg, be- cause, when the advanced leg has reached the vertical position and is again placed on the ground, the hinder leg has already begun to describe a portion of its arc of oscillation. By these means the duration of the step is di- minished, whilst the length is increased, both of which tend to augment the velocity. The length of the step is consequently greater than that side of a right-angled triangle, whose hypotheneuse is the extended leg, and the other side the elevation of the centre of gravity above the ground. In running the step may be divided into two periods; the first, the time t, during which the body is supported on one leg, and the second, the time t — t, during which it is not supported at all. Forces employed in running. —The forces which act in running are the same as in walking; first, extension; secondly, gravity; thirdly, resistance. In running, a horizontal move- ment of the centre of gravity is not practicable as in walking, for although the extensor power might be so regulated that the centre should continue at the same elevation so long as the body poised on one leg, it would evidently fall during the time it was left unsupported. Now, as it is found after the whole time of a step to have neither sunk nor risen, and since no instantaneous elevation of the centre of gravity takes place between the termination of the pre- ceding and the commencement of the following step; it follows that during the time t, it must ascend just as much as it sinks during the time t — t. The effects of gravity and resistance have been sufficiently explained in the theory of walking.* The conditions for regular progression in * By an analysis based on data similar to those for walking, Messrs. Weber have deduced the following equations which express the general laws of running. (h 4- s)! + c* C7 — IK. (29) (/i + s — » g 0-') -+ c- That is, the square of the length of the extended leg is equal to the sum of the squares of the * The line c2d is vertical, and c, rf, horizontal, meeting c2 d in IS Figures designed by Weber, to illustrate the laws of running. and that whilst it moves From these principles it is obvious that n moves from c2 to from c3 to Cr0 ; the latter portion is the duration of the step ; the former the time in which the body swings freely in the air. man in the act of running could possibly be in Fig. 266. a 'rep ' to run, and running, from designs hy F/aj man. In Jig. 265 c A falls behind the advanced foot, so tha ,e posterior leg hears only a small portion of the weight of the body, but is in a position to push the centre "J gravity forwards before quitting the ground. 474 MOTION. the attitude of the annexed design by Flaxman (fig. 266), in which it will be seen that the whole mass of the body lies posterior to the vertical line a c b, passing through the base of support, whereas the preceding theory shews that in quick walking and running the swinging leg never passes beyond the vertical d c, which cuts the head of the femur. This figure has therefore been drawn upon false principles. Table 12. A Table of fifty-six experiments on running with various velocities. Space passed through 43.43 met. — 142 -2501 feet. Number of experiments. Mean Number of Steps. Time. Dura- tion of Step. Length in metres. Velocity. 6 2817 7-56 0-268 1-542 5-753 3 3883 991 0-293 1-284 4-382 6 35-92 10-80 0-301 1-209 4-016 7 3817 11-99 0-314 1-138 3 624 3 42-67 1360 0 319 1-018 3-194 7 46-5 15-173 0-326 0-934 2-865 6 53- 16-81 0-317 0-819 2-583 8 60-5 18-35 0-303 0-718 2-369 5 71-2 21-68 0-304 0-640 2105 4 83-75 25-45 0-304 0-519 1-707 3 104-33 31-84 0305 0-416 1-367 3 137-7 41-49 0-301 0-315 1-046 From this table we see that the length of step increases rapidly, whilst the duration va- ries but very little ; and that the duration is always equal to a half oscillation of a pen- dulum. Duration of spring .. — 0 2618 ~\ nc Duration of half oscil- J _ S l,^^ lation of pendulum S -"^ 3° 0612 Hence we perceive that the duration of the spring is less than the oscillation of the leg as a pendulum by a very small fraction only, which is probably due to muscular action. In quick running the length of step rapidly increases, whilst the duration slowly dimi- nishes; but in slow running the length dimi- nishes rapidly, whilst the time remains nearly the same. The time of a step in quick run- ning, compared to that in quick walking, is nearly as two to three, whilst the lengths of the steps are as two to one, consequently a person can run in a given time three times as fast as he can walk. The velocity in running is usually at the rate of about ten miles in an hour, but there are many persons who for a limited period can exceed this velocity. In the human race, however, the velocity in running varies considerably, depending on a variety of physical conditions, such as age, sex, stature, muscular power, the nature of the surface on which the progression is performed, and the angle of elevation above, or depression below the plane of the horizon. Man is ex- ceeded in speed_by many of the lower animals, owing to differences in the structure of the locomotive organs, and the physical laws which they obey. Leaping or jumping. — This mode of pro- gression is adopted by a great number of animals; some of which resort to it only for the accomplishment of a particular object, others as a regular means of locomotion. In most of the orders of the animal king- dom there are some species which transfer themselves from place to place by a succession of impulses, in air, in water, and on solids : it is to the latter we shall confine our attention, having already briefly mentioned the former in the sections on flying and swimming. In leaping, the object to be attained is to take the greatest length of step without refer- ence to its duration ; and herein it differs from running, in which the greatest steps are taken in the least possible time. The height to which animals of different orders are capable of springing* varies, but, according to Strans-Durckheim, all those in the same order leap to equal elevations. Amongst insects, the Grasshopper and Cricket, and in the order Felis, the Cat, the Leopard, and the Tiger, all rise to the same elevations above the positions of their respective centres of gravity at the instant when their feet quit the ground. This appears at first to be inconsistent with the computations made on the proportion of the force of muscles to the mass of animals of different dimensions. If we select four diffe- rent animals of the same order, in which the dimensions of one kind are as 1, 2, 3, 4, their weights will be as the cubes of these numbers, or, as 1, 8, 27, 64 ; but since the force of a muscle depends on the number of its fibres, and therefore increases in the ratio of its transverse section ; that is, as the square of one of these dimensions, the muscular forces of the animals will be as 1, 4, 9, 16, and the velocities (supposing the muscles to act instantaneously) will be as the forces divided by the weights,'or as 1, \, J, \, and the heights of the leaps being as the squares of the velocities would be as 1, \, ^, Now, as they are all found to arrive at the same height, this may be ex- plained by supposing that the muscles do not act instantaneously, but as constantly accele- rating forces during thecontinuanceof the spring. The force on an unit of mass in the Cat is to that on an unit in the Tiger, as 1 to |; and since the dimensions of the latter are four times those of the former, the tiger passes through four times the space the Cat passes over, reckoned from the beginning to the end of the time the muscles act, until the animal quits the ground, and therefore is elevated to the same height as the cat f From these principles we see the reason why * The spring is that portion of the leap which takes place before the feet quit the ground. t Thus : — Let « — the space passed through during the spring of the cat, / = the muscular force employed in the time t of a spring, then, by equation (3), s = \ft*. Now, as the tiger passes through a space = As, MOTION. 475 Fig. 267. many of the small insects leap a greater dis- tance in proportion to their masses than the larger animals; for example, if the Flea, which can leap two hundred times its own height, were as large as the Cricket, it could only leap as far as it does at present ; but the latter can leap much higher than the former, and there- fore, of these two insects, the Cricket is the best organized for leaping. We shall now pro- ceed to investigate the effect of the extension of the legs of insects in leaping. and the muscular force equals J /, during the time f of its spiing, f, 4s = t'3 (36) (37) and, H = 4t The velocity of the cat will be, v — JWs hence, that of the tiger is, v' = Vl L 4s — \S<2 fs 4 J that is, the tiger and cat have the same velocity, and therefore the same height of spring, reckoned from the positions of their centres ot gravity at the instant of their quitting the ground. Let f g (Jig. 267) be the axis of the body, passing through the centre of gravity o; a b, the tarsus ; b c, the leg ; c d, the thigh, with the trochanter ; and d e, the hip. All these articulations being flexed, the tarsal extremity b of the leg is advanced forwards under the centre of gravity o, which is a little above it. In this state, if the tarsus a b, which is di- rected backwards, become flexed, the angle a b c opens, and as the tarsus rests against the ground, the leg b c begins to move, and raising its crural extremity, draws with it the whole body. Now, as the centre of gravity is placed before the point b, instead of being elevated, it is, on the contrary, urged forwards and downwards, describing an arc of a circle, of which the centre is b, and the action of the flexor muscle of the tarsus continuing during the whole time that the limb is resting against the ground, the direction of the motion which it impresses on the centre of gravity changes at each point of the arc which the latter de- scribes in being always a tangent to this arc. We might thus determine its action for each of these points, but for greater simplicity we shall select only three; namely, the commence- ment, middle, and the end of the motion. During the flexion of the tarsus, the legj expands itself, and tends to open the angle bed; but since it rests with its tarsal extre- mity upon the plane of position, the thigh c d be- comes moveable, and is raised forwards, turning as a radius round itscruro- tibial articulation c, and carrying with it the whole body, in the same manner as in the motion of the leg; the direction of the force produced by the extensor muscle changes at each point of the curve which the centre of gra- vity describes ; but this direction is always a tangent to the curve, and consequently per- pendicular to the radius c o, passing through the cruro-tibial articulation and centre of gravity. The motion produced by the extensor muscle of the trochanter on the thigh c d, opens the angle c d e, tending to depress it at its tibial extremity, but as it rests upon the leg, which by its own elevation resists it, the motion is wholly communicated to the hip d e, which is flexed forward, and carries the body with it ; the direction of the force of this muscle is perpendicular to the radius d o, passing through d, the articulation of the hip with the tro- chanter and the centre of gravity. Lastly, the motion produced by the extension of the hip e d upon the body in a direction opposite to that of the thigh, is perpendicular to e o, and impresses on the centre of gravity an oblique impulse downwards and backwards. The forces resulting from the extension of the tarsus and the hip being very feeble, may be neglected. The muscular force expended in these mo- tions may be thus approximative^ estimated. By the extension of the leg, the centre of gra- vity o will be acted on at the beginning of 476 MOTION. motion by a force o m perpendicular to o c ; by the extension of the thigh at the same time the centre will be also urged by a force o n, perpendicular to the radius ud; the resultant of these two forces is o d, in the direction of which the centre of gravity is raised in the first instant of motion, and the body and foot will be in the position a, b, c,' d,' e,' and making this a maximum, we find u = §V, and V = JV. Therefore the effective work of an animal is a maximum when it is so loaded, that with its whole force in action its velocity amounts to one-third of the greatest velocity which it is capable of exerting without any load at all. In a series of experiments made on men and horses, by drawing a lighter along a canal, and working several days consecutively, the force was measured by the curvature and weight of a track rope, as well as by a spring steel- yard ; and the product of this force multiplied by the velocity per hour was considered as the momentum. By these experiments the forces of men were found very nearly as (V — V')2, and those of horses, loaded so as not to be able to trot, as (V — V')1'? to (V — V')1-8, results which agree very closely with the theory. In the application of these formula? let us suppose a man's power to be 70 pounds, and his utmost speed in walking to be six feet per second, hence

«. 275. Fig. 274. A portion of a tubide of the testis ( Guinea-pit], Co- baya), magnified 300 diameters. a a, basement membrane; a', corpuscle in its sub- stance ; b b, epithelium in situ, consisting of par- ticles of different dimensions, with minute gra- nules in their interstices ; c, cavity of the tubule full of detached epithelium particles, of various size and appearance, and mingled with nume- rous seminal animalcules ', d, one of these semi- nal animalcules. even exceeds that amount, its essential charac- ters, however, remaining the same. In the larger tubes, emerging from the gland, this tunic becomes gradually invested by a delicate fibrous layer, by which the vascular network is attached to it, and which at first sight may Terminal vesicles of the pancreas of the dog, magnified 300 diameters. The basement membrane is seen at a a a, where the epithelium has been a little detached. In the salivary and all the allied glands, the basement membrane admits of being easily demonstrated. A very thin slice of the fresh organ should be torn by needles, gently washed, and inspected under a high power. The termi- nal vesicles of the duct will then be brought into view and their outline seen to be perfectly sharp and linear (fie. 275, a a a). In parts where the epithelium which they contain has been loosened, the basement membrane will be left in relief. It is of extreme delicacy ; and, as in all other situations, its capillary plexus (when well filled with coloured materia!) may be seen ramifying, not in its substance (for its tenuity renders such a disposition impossible), but on its parenchymal surface. I have sought in vain for the basement mem- brane in the lobules of the liver, and I am in- clined to think that it does not exist in this gland, except in the excretory part of the bile ducts. In the air-cells of the lungs the basement membrane assumes a most interesting and re- markable developement, for it constitutes almost the entire thickness of their walls, the epithe- lium being of extreme delicacy. It appears to be here strengthened by interlacing arches of elastic fibrous tissue, but to be itself transpa- rent and homogeneous, as elsewhere. It is on its parenchymal surface that the close vascular web is spread out. (See Ptjlmo.) But this membrane may be also detected in every part of the alimentary tube, which is more characteristically mucous, in that, viz. in- tervening between the cardia and the lower ex- tremity of the canal. Here it deserves an attentive study on account of the apparent com- plexity of its foldings, and because its exist- ence here offers the most unequivocal proof which we possess, of the anatomical identity of the true glands with the membranes usually called mucous. As it is more delicate in this part than any other, and difficult of detection by reason of the enormous preponderance of its epithelial investment, I shall describe the man- ner in which it may be best observed. The specimen should be as fresh and healthy as possible, or should have been immersed in 488 MUCOUS MEMBRANE. alcohol immediately on its removal from the body ; a fragment of the tubes of Lieberkiihn should then be scraped off, pulled to pieces, and examined in a fluid medium under a high power. The margins and rounded extre- mities of the tubes will then be seen to be sharply defined, as in the cases already men- tioned, and to be formed by a structure inde- pendent of the epithelium, which latter forms ^tlis of their thickness. This structure is the basement membrane. When masses of epithe- lium, escaped from the tubes and bearing their form, are met with floating around, their out- line is uniformly irregular, and, as it were, woolly. Sometimes, as in the kidney (fig. 273), the basement membrane is seen up to a certain point only, beyond which it has been detached ; and in less recent specimens a tube of basement membrane is sometimes seen, containing a mass of broken-down epithelium. If the part selected for examination be the stomach, the same precautions should be ob- served, for here this membrane is, if possible, more delicate than below the pylorus, and the epithelial particles are often so large as to bulge the tubes very irregularly, especially towards their blind extremities. It is between these bulges that the basement membrane may be best seen (fig. 276). Nothing is more difficult than to explore, in a satisfactory manner, the internal structure of the intestinal villi. Their thick epithelial caps and their abundant vascular rete are readily demonstrable, but the arrangement of the lac- teals, which undoubtedly exist in them, and of the structure on which the epithelium imme- diately rests, has hitherto almost entirely eluded our research. In vertical sections of the recent small intestine of the Car- nivora, I have several times seen the direct continuity of the epithelium covering the villi, with that lining the tubes which open at their base ; and also a distinct continuity between the inte- rior of the villi, where the vessels are spread out, with the vascular intervals be- tween the tubes, which con- tain the fine capillary web surrounding the tubes, and likewise give passage to the branches to and from the villi. It is then difficult to avoid the belief that the basement membrane of the tubes is continued under the Lower extremity of a epithelium of the villi, to ^tomaeh tubule fro,n support it, and form a part of those remarkable projec- tions. Nevertheless I have not been able to see it in an At^f!i^lb_a^™e°t isolated and distinct form, and do not therefore assert its positive existence; only I believe that the fact that the injected vessels of a villus, when seen in profile at its margin under a high power, and the dog ( Canis fa- miliaris ), magnified, 300 diameters. membrane is seen between b b b, bulging epithelial particles. when the epithelium has been removed, seldom come to the extreme edge, is attributable to the circumstance of the basement membrane still investing them. This membrane, if it really exist here, adheres intimately to the parts within the villus. It might seem at first sight a hopeless task to search in so dense and complicated a struc- ture as the skin, for the analogue of a mem- brane like that I have been describing, which, in no situation where it can be unequivocally brought into view, exceeds the 8000th of an inch in thickness. But as it must exist, if at all, between the epidermis and the vessels and nerves of the cutis, in a position sufficiently determinate, much of the apparent difficulty is removed. The most favourable situations for its detection are those in which the skin is highly developed, presenting, like the small intestine, villi (termed papilla?) on its free sur- face. The close resemblance between these papillae and the villi of mucous membranes has been observed by many anatomists. The dis- tribution of the vessels within both is essentially the same. Here, then, under the epidermic layer, we might expect to find the basement membrane. I have removed with great care the whole of the epidermis from a thin ver- tical section of such a specimen (and it is better to have previously steeped it in solu- tion of carbonate of potass), and have then examined the outline of the bare papillae with a power of 300 diameters. This outline is sharply defined, and appears to be formed by a homogeneous membrane, enclosing the vascular and nervous contents. This mem- brane I believe to be that which I am now describing, though, as in the case of the intes- tinal villi, I have never been able to isolate it, and thus unequivocally prove its presence. This is a part of the skin which has never been noticed by anatomists on account of its tenuity, Fie. 277. Part of the tubule of a sudoriferous gland from the human axilla, magnified 320 diameters. A, transverse section -, B, side view of the interior, obtained by bringing the axis of the tubule into focus ; a a a, basement membrane ; b b b, epi- thelium ; c c, cavity of the tubule ; d, superficial epithelial particles ; e, deep epithelial particles; f, a detached superficial epithelial particle, shewing the nucleus and pigmentary granules ; g, its detached nucleus, with a nucleolus. MUCOUS MEMBRANE. 489 but which is quite distinct from the cuticle, and the great mass of that complicated struc- ture to which the terms 4 cutis ' and ' dermis ' are applied. A very strong reason for believing this mem- brane to be present in the skin, is the fact of its existence in those minute organs, so profusely scattered under the cutaneous surface, the se- baceous and sudoriferous glands. In Jig. 277 I have represented it in a portion of one of the latter, taken from the axilla, where they are very large. These glands are nothing more than involutions of the external tegument, and correspond closely with the labial and allied glands connected with the ordinary mucous membranes. It is impossible to suppose that a structure attaining so marked a developement in those parts, should be wanting in the general superficies, with which they are, at numberless points, directly continuous. In other situations, where a simple expanse of mucous membrane is spread out upon a surface of the body, as in the oesophagus, pharynx, mouth, nose and its sinuses, vagina, bladder, &c. (from all of which, however, there are numerous prolongations called follicles and glands, which shew this structure well,) a basement tissue such as that described has not been shown to exist. Its existence rests at present principally on analogy, and it is difficult to say whether it be not more or less modified. Certain of the peculiarities presented by these several parts depend on a modified form and greatly augmented mass of the epithelial element, but many also on varieties in the areolar and vascular tissues underlying the mucous tissue, and, properly speaking, forming no part of it. These will be treated of under the topographical descrip- tion of the membrane. Oj the epithelium. — A very brief period has elapsed since it was universally held that most mucous membranes wanted epithelium, and their analogy with the skin was only maintained in this particular by a fancied resemblance drawn between epidermis and mucus. One of the principal results of microscopic observation, conducted with the improved modern instru- ments, is that of Ilenle, proving not only that this structure is present throughout the mucous system, but that in most situations it is so abun- dant as to constitute nearly the whole material of the tissue. This fact, as yet so novel, coupled with the discovery announced at the same time of the occurrence of a lining of analogous cha- racter on all internal cavities, makes the study of this structure under its varied forms pecu- liarly interesting and important. It will readily be conceived how wide a field is here opened to view, and how premature it would yet be to attempt to offer a general history of such a structure. The numerous questions piesenting themselves on every side render this impossible; and if it were not so, the scope of the present article would oblige me to confine the descrip- tion to those forms of epithelium met with in the mucous system. In acknowledging the great obligations I am under to Ilenle's admi- rable paper on this subject, I may state that the following account has been written as much as possible from my own observations. By the term epithelium is now meant a layer of particles or modified cells, furnished with nuclei and nucleoli, lining an internal surface of an organized body, and by their apposition and union constituting a kind of pavement. A similar investment to an external surface is styled epidermis. Both these, in their ordinary forms, will be embraced by the following de- scription. Epithelium is an organized structure endowed with vitality. This is shewn by its form, the process of its growth, and the living properties it displays. Of these the most eminent is that of ciliary motion, which in all the higher animals is performed by cilia clothing the free surface of epithelial particles. But in very many situations, if not in all, the processes of nutrition carried on in the epithelial layer of the mucous system differ materially from those of other organic tissues ; the old elements, which in other cases are reconveyed into the blood, being here shed on the free surface of the membrane, and thus becoming at once eliminated from the system. The epithelial particles preserve a greater resemblance to the form of the development cell than most other tissues. In many parts they continue to be truly cells throughout their existence, and in no instance is the nucleus, from which they have proceeded, absorbed. In connection with a wide and varied range of function, these particles present numerous modifications of form, bulk, and texture, the leading features of which have been pourtrayed by Ilenle. The following arrangement, how- ever, differs in several respects from that pro- posed by him,* and is more in accordance with what I have myself observed. Founding it on the anatomical condition of the particles and on their office, I distinguish three varieties, — the lumcUiform or scaly, the prismatic, and the spheroidal. These all run together by imper- ceptible gradations. The particles may be also divided into non-ciliated and ciliated, the scaly being always bald, the prismatic and sphe- roidal in some situations furnished with cilia. Of the lumcUiform or scaly variety. — This consists of broad flattened particles (or scales, properly so called), having an angular outline (caused by their lateral apposition) and a nucleus, which is generally eccentric. These scales form layers of extremely variable thick- ness. They are generally, however, super- imposed in great numbers over one another, as in the mouth, fauces, and oesophagus of the human subject, where they constitute the opaque defensive investment so visible to the eye in those parts. But the best-known example of this form is presented by the cuticle, which from its ex- posed position is thicker and denser than any internal epithelium. This variety, then, is the one which offers the most convincing proof of • He divides it into pavement epithelium (or the scaly), cylinder epithelium (or the prismatic), and ciliated epithelium. See Miiller's Archiv, 1838. 490 MUCOUS MEMBRANE. Fig. 278. Vertical section of the epithelium of the mouth, shew- ing its lamella and the changes of form which the jjarticles successively undergo. a, superficial laminae, consisting of true scales ; b, c, particles in progress of flattening; d, deep layer of particles; a', b', c', d', separate particles in the several stages. Magnified 300 diameters. Fig. 279. A few scales detached from the surface of the tivula. Magnified 300 diameters. the homology of the mucous membranes with the skin. The term ' scales ' is only applicable to these particles in the last of the stages through which they pass. They first appear on the surface of the basement membrane as gra- nular dots, each of which soon becomes in- vested with a cell membrane. Both nucleus and cell increase in size up to a certain point, the cell being then more or less globular, and con- taining a material that appears transparent and almost entirely fluid. By this circumstance, chiefly, it is distinguished from the spheroidal form of particle, presently to be noticed. The cell now begins to flatten, loses its fluid con- tents, and is at the same time the seat of certain changes by which its chemical properties are modified. At length its opposite surfaces unite, except where the nucleus intervenes, and a lamella of extreme tenuity results, which being now arrived at the surface is loosened and shed. It appears to be by the continual pres- sure arising from the growth of newly-formed particles that the peculiar characters of this variety result. Accordingly, the scales are only found constituting the superficial layers of a series (fig. 278, aa). It is met with in those parts only where foreign pressure, or more pro- perly friction, has to be encountered. In such parts a thick coating of epithelium is evidently desirable, and the hard and almost horny qualities which these particles at length assume where most exposed to violence, admirably adapt them for their object. On such parts, moreover, cilia would not be needed, and it would even seem that this variety of epithelium when converted into true scales possesses neither sufficient substance nor vital power to develope and support these exquisite organs. The scaly epithelium is remarkable for the tenacity with which its particles adhere to one another, and to the surface on which they rest. This adhesion is manifest at all the stages through which the particles pass. It is stronger between particles at the same stage than be- tween those at different stages of growth, so that there is always a tendency to a separation into successive lamina on maceration or other- wise. Hence have resulted the divisions of the epidermis into two, three, or more layers, and especially that remarkable fallacy of re- garding the rete mucosum as a distinct structure. How far this adhesion is owing to the presence of an intercellular substance in all instances it is difficult to decide ; but it seems highly probable that, in the deepest layers, where the particlesare small and rounded, such asubslance must exist in considerable abundance, filling up the interstices, and serving as a kind of blastema, in which the nuclei (or cytoblasts) of fresh parti- cles originate. I have lately (Jan. 1842) ascer- tained a very curious fact, giving evidence of this adhesion. This is, that the delicate threads drawn out of the cutis when the cuticle is stripped from a piece of macerated skin, con- sist entirely of the epithelium of the sweat- ducts, the particles of which are so intimately united with one another, and with those of the deeper layers of the epidermis, as to allow of being thus dragged out of their tube of base- ment membrane, often for a length of an eighth of an inch. The scaly epithelium is subdivisible into two forms, the regular and the irregular. In the former, the scales are united edge to edge in a regular manner, as in the skin of the Frog and other reptiles, and on many internal surfaces, especially in the lower animals. In this form, the particles do not become so thin as in the other, and the superficial scales are cast off in laminae consisting of a single series and of uniform thickness. In the latter form, they overlap one another without order, and present no regular figure. This is the ordinary form, and is that presented in the skin and other parts of Mammalia and Birds. Of the prismatic variety.* — In this the par- ticles have the shape of small rods, disposed endwise on the basement membrane, in a single layer, the thicknpss of which depends on their length. These rods are united to one another by their sides, which are flattened for that pur- pose. They are, therefore, prisms and not cylinders, as Henle terms them. They are also almost invariably of very unequal thickness in different parts, being bulged somewhere near the middle by their nucleus, which is oval, with its long axis parallel to that of the particle. Their deep or attached extremity, also, usually tapers to a point, in order, probably, to allow room for new particles to spring up in the in- tervals. This is more decidedly the case where they clothe a convex surface, (as that of the * To this the very appropriate term columnar lias been lately given by Professor Todd. MUCOUS MEMBRANE. 491 intestinal villi,) and their sides tend to assume the direction of radii from a common centre. Hence they are sometimes even triangular in outline. Their opposite or free extremity is much thicker, often as thick as the part bulged by the nucleus, and near this extremity neigh- bouring particles are generally very intimately attached to one another, having often the ap- pearance of being blended into a single mass. The best example of this is on the villi of the small intestine (Jig. 280). The contiguous par- ticles, however, are fitted closely together in the greater portion of their length, and to effect this the bulging nuclei vary in the height at which they are placed. There can be no doubt, that, in certain situations at least, as will be afterwards shown, these particles are being con- tinually shed, and consequently are being per- petually renovated. But it is very difficult to ascertain their early condition and changes, and I am not aware of any satisfactory observations having been made for this end. From the great facility with which they become detached from the surface they invest, it is next to im- possible to examine them in situ on thin verti- ng. 280. Fig. 282. Villus of the intestinum ilium of the Dog, tvith the epithelium partially detached. a a, solitary particles remaining attached ; b, club- shaped extremity of the villus from which the epithelium has been detached ; c c, epithelium at its base. Magnified 150 diameters. d, detached particles, shewing their close union, especially at the surface (at the letter) ; e, other detached particles, shewing their various shape, their nuclei and nucleoli. The letter is placed at their free extremity. Magnified 350 diameters. Fig. 281. a, ciliated epithelial particle from the inner surface of the membrana tym- pani of the human subject ; b, cili- ated epithelial particles from the bronchial mucous membrane of the human subject. All these shew the nuclei and nucleoli. Magnified 300 diameters. Epithelial particles from the cornu uteri of the Cow. The opposite cornu contained a foetus one inch and a half long. a, small particle, apparently in an early stage of development. The nucleus is smaller than in the other specimens ; b, another more advanced — the nucleus and surrounding substance are both larger, especially the latter, which presents a fine granular texture ; c, a particle made angular by pressure against others. It presents two nuclei, as though formed by fission ; d, another of a dif- ferent shape ; e, detached nucleus, showing its transparency and clear outline ; also two excen- tric dots, the nucleoli. Magnified 300 diameters. cal sections. But there is no reason for sup- posing their mode of growth to be originally different from that of the scaly variety- Their nuclei probably appear first on the surface of the basement membrane, and around these a cell is developed (fig- 280, a). But this cell from its earliest period seems to contain an amorphous substance, which under high micro- scopic powers looks finely mottled, but not so definitely so as to allow of being called granu- lar. As the particle advances towards its full size, it loses its cell -membrane, and when com- plete is to be regarded rather as a solid mass of organic substance, surrounding a nucleus, than as a cell. Here, then, is a striking difference between the scale and the prism: maturity being marked in the one by the disappearance of the substance of the cell ; in the other, by that of the cell- membrane. Of the spheroidal variety (see Jigs. 273 to 277). — In this the particles are of a rounded Fig. 283. Three epithelial particles from the human liver. nucleus ; b, nucleolus ; c, fatty particle. Magnified 300 diameters, form, though generally somewhat flattened where they touch. They are always thick, from the substance they contain. It is this variety that constitutes the chief mass of the secreting glands, and hence it might not impro- perly be styled glandular. It corresponds with the prismatic variety, in its usually constitu- ting in the glands a single layer, and in the predominance, from the first, of its substance over its membrane. In the glands, indeed, the membrane can seldom be discerned at all, and the substance surrounding the nucleus, though more bulky, has the same finely mottled cha- racter already noticed in the prisms. In other situations the cell-membrane is persistent, but even then it never flattens into a scale. This variety presents in the different glands nume- rous modifications, which have not yet been studied with the accuracy they merit. It is 492 MUCOUS MEMBRANE. difficult to reject the belief that it is intimately concerned in the glandular function, and varies in correspondence with it. To the preceding summary account of these three principal kinds of epithelium much might be added respecting the intermediate forms. This, however, does not appear to be required in so general a description. The spheroidal and the prismatic are seen blended in the speci- men I have figured from the human membrana tympani (fig. 281). Of the non-ciliated and ciliated epithelium. — The true scaly variety appears never to be clothed with cilia. The prismatic epithelium is that which most commonly bears these vibra- tile organs. They are placed on the free extre- mities of the prisms in the respiratory tract and in the uterus and Fallopian tubes. The true glandular epithelium is always without cilia. This is a general fact, and one of great import- ance. But those varieties which seem interme- diate between the spheroidal and the other two forms are often furnished with cilia ; of which examples maybe seen in the Malpighian bodies of the kidney, in the mucous membrane of the frog's mouth, and in that of the human tympa- num (jig. 281). In all cases the cilia, when Fig. 284. Various particles of epithelium from the frog's mouth. a, b, c, small particles that have not reached the surface. They appear to present three stages or periods, showing a subdivision of the nucleus and a formation of two cells out of one ; d, three fully developed particles, with cilia on their free sur- face; e,f,g, other complete particles, showing cilia on that part only which has formed a portion of the general surface of the membrane. Magnified 400 diameters. they exist, are developed only on that aspect of the particles which forms a portion of the gene- ral surface of the membrane. It is as yet entirely unknown by what pro- cess the cilia are produced and nourished ; whether the particles, with their cilia, are shed from time to time, and are succeeded by others, (as is most probable,) or whether the same organs remain, and merely change their com- ponent elements. (On the subject of Cilia in general the reader is referred to Dr. Sharpey's excellent article.) Of the elementary tissues appended to the mucous system. — The two elementary tissues now described may be considered as the more essential constituents of the mucous system, or as forming the simple mucous membrane. This simple mucous membrane envelopes the rest of the body. It contains within its own substance neither vessels nor nerves, but is, strictly speak- ing, extra-vascular. By modifications, chiefly of the epithelial element, it is in itself capable of presenting great variety of appearance and properties in different situations. But in im- mediate connection with its deep surface, that is, with the basement membrane, there are cer- tain tissues common to almost every part of the frame, but here assuming a peculiar arrange- ment and office, and by their diversities in various localities, occasioning the most compli- cated varieties of outward form, of structure, and of function. These appended tissues are minute blood- vessels, a lymphatic network, nerves, and areo- lar tissue. It has been already stated that in many parts the simple mucous membrane, by its innume- rable minute involutions over an extensive sur- face, is formed into a compound membrane. Into the composition of this (of which a good example is afforded by that of the stomach) the appended tissues enter more or less largely, but they are likewise, in addition, generally spread out in great abundance as a layer underneath the compound membrane. This layer has been commonly termed submucous cellular membrane, (sometimes tunica nervea,) in the case of in- ternal surfaces, and cutis vera or dermis in the case of the skin. Bloodvessels. — These may be said to be universally present under the simple mucous membrane, with the exception perhaps of the cornea, where vessels, in the normal state, have not yet been demonstrated. The capillaries, in their simplest form, appear to be arranged as a plane network, such as that of the rectum of the frog (fig. 285). The interstices of this network vary much in size and shape in diffe- rent localities. The most copious supply of blood distributed to any such membrane is that afforded to the air-cells of the lungs in all ani- mals. Here this plane capillary plexus has areola; scarcely exceeding the diameter of the vessels themselves. Where the membrane they supply is folded, however irregularly, they follow its surface, and hence result many varie- ties in their arrangement and inosculations. It even seems to be for the purpose of gaining a great freedom of inosculation between the ca- pillaries that the extraordinary complexity has been given to many parts of the simple mem- brane, especially in the secreting glands. For many foldings from somewhat distant parts of the membrane are there brought into imme- diate proximity to one another, and are sup- plied by the same or closely connected vessels. This is remarkably exemplified in the testis, kidney, and liver. The capillary system of all these, as well as of other solid glands, may be styled a solid plexus, being extended in every direction, and presenting areola? of nearly equal size in whatever plane a section of it be made. The liver presents the most perfect instance of such a solid plexus, and in it the vessels are of MUCOUS MEMBRANE. 493 Fig. 285. Capillaries on the rectum of the Frog, a, a, arteries ; b, b, veins. unusual dimensions, apparently to allow of the more free transit of the blood, which is here propelled feebly by the vis a tergo acting through the capillaries that form the portal vein. Though it has not been so described, I believe, from injections that I have made, that the whole organ is one such plexus, and that if it were possible to abstract from it all vessels larger than capillaries, and to leave these entire, all the lobules would still be connected together by capillary channels identical with those of which they themselves principally consist. Hence the lobules of the liver are not definitely bounded on all sides by a capsule of any kind, but here and there blend by continuity of sub- stance with those adjoining them. The larger portion of their contour is, however, well de- fined by the ultimate twigs of the portal vein, and of the ducts derived from the lobule, as so clearly proved by Mr. Kiernan in his well- known paper. The size of the capillaries varies much in different parts of the mucous system. In the liver they are very capacious, always one-third wider than the diameter of the blood globule, and sometimes nearly double. In the lungs they are almost equally great. In the intestinal villi also they are of large dimensions. In these organs they form a network on the inner surface of the basement membrane, and are supplied by an artery that ascends in the axis of the villus. The veins from this network are generally two, one on each side. This plexus of the villi is strikingly contrasted by that clothing the tubes that open at their base. In this latter I have observed the diameter to be as small as that of the capillaries of the salivary glands, which do not exceed the width of a blood globule. This disparity is another con- firmation of the opinion that the villi are chiefly absorbing, and the tubes secreting organs. Many other varieties might be enumerated, but these are among the most remarkable. Under most of the compound mucous mem- branes bloodvessels are spread out in great pro- fusion, and especially in certain localities. The arteries and veins respectively form plane ple- xuses, more or less close, more or less intricate, from which emerge branches that pass between the foldings of the simple membrane and com- municate with its capillaries, already described. There may even be a series of these arterial and venous plexuses situated one over another, and successively springing out of one another. The effect of this arrangement of an arterial network on one side of the capillaries and a venous net- work on the other side, is that the blood, be- sides being delayed in their neighbourhood, is most freely and equably distributed in the capillaries themselves : a condition which could scarcely be otherwise accomplished, since, in the case of a villous membrane at least, the capillaries form a series of isolated systems, of which one belongs to each villus. The arrange- ment now spoken of exists in the submucous areolar tissue of the stomach and intestinal canal, and in most parts of the skin. In the solid glands, where the capillaries form one continuous system, such arterial and venous networks are not found. At least such inoscu- lations, when they exist, are few and rare. In the stomach of many fishes there is a plexus of great thickness under the mucous membrane. In the nose also, chiefly on the spongy bones and septum, there is a plexus of very large veins, well known to anatomists, and also a less capacious arterial plexus ; smaller ones are met with in other parts, as the cheeks and lips, the palate and pharynx. The use of these, especially that of the nose, may be to serve as a diverticulum for the blood in cerebral con- gestions. These are the vessels that give way in ordinary epistaxis. Of the lacteal and lymphatic vessels. — The lacteals have their sole origin from a plexus underlying the simple mucous membrane of the alimentary canal, and it is probable that in every part of the skin a close network exists, such as has been described by several anato- mists (see Lymphatic System). Considering the means hitherto at command for ascertaining the precise position of this network, it is not wonderful that disputes should have arisen as to whether it lies in the rete Malpighii, or within the surface of the dermis. I would hazard the opinion that the real situation of this plexus is underneath the basement mem- brane which is everywhere present in the skin. Of the nerves. — These are numerous and varied, as might be expected from the position of the mucous system in regard to the rest of the body. They may all be styled afferent, and are divisible into three kinds, viz. the sensory, the excito-motory, and the sympathetic. The nerves of special sense distributed to this system are those of smell, taste, and touch. The nerves of common sensation and the excito- 494 MUCOUS MEMBRANE motory nerves are almost exclusively found here. The tubules of the sympathetic nerves are chiefly given to the proper mucous mem- branes and to the glands. All these will be considered more at length under other heads, and they are therefore only referred to here. Of the areolar tissue. — Before describing the remarkable varieties presented by this tissue under different parts of the mucous system, I must advert to its constitution in those situations where its ordinary characters are well marked — as in subcutaneous fascia, in muscle, on the exterior of the pharynx, &c. Singular as it may appear, there is no correct account of this structure in any of the works on minute anatomy. It in truth consists of two tissues, distinct from each other, and respec- tively allied to the white and to the yellow fibrous tissues. The while fibrous element of areolar tissue is chiefly in the form of bands of very unequal thickness, in which are to be seen numerous streaks taking the general direc- tion of the whole, but not parallel to the border, nor continuous from end to end. These streaks more resemble the creases of a longitudinal folding than intervals between separate fibrillae, for which they have been mistaken. These bands split up without difficulty in the long direction, whence result fibrils of the most va- ried width, the finest being far too minute for measurement, even with the best instruments.* These bands interlace and cross one another in various directions, and their natural course is wavy. They frequently subdivide and join those near them. Besides these bands, com- monly called fasciculi, there are some finer filaments of the utmost tenuity which seem to take an uncertain course among the rest. The yellow fibrous element is everywhere in the form of solitary fibrillae, which correspond in their essential characters with the tissue of that name. They are disposed to curl, and are truly branched at intervals of variable length ; these branches (which usually retain the size of the fibril from which they spring) becoming continuous with others in the neighbourhood. They have higher refractive properties than the white element, and their borders are conse- quently darker. It is easy to overlook this twofold compo- sition of areolar tissue in specimens examined in water, but their discrimination is made easy by a trifling artifice. This consists in adding a drop of acetic acid, which instantly swells the white bands, and makes them transparent, but produces no change in the yellow fibrils. These effects of the acid may be watched, if the agent be made to spread gradually over the specimen ; and there can scarcely be conceived a more beautiful example of the aid chemistry will afford anatomy than that presented in the course of this interesting process. + The change * The fibrillae of true white fibrous tissue are almost precisely similar, and, as I believe, are only produced by the observer himself in opening out his specimen for inspection. t In the case of the dartos, this procedure de- tects not only what has just been described, but a third element, hitherto in this situation quite con- produced in the white bands is such as to shew very clearly that they are not truly fasciculi, or aggregations of fibrillae. The action of the acid on these two elements is identical with that produced on the two tissues to which I have shewn them to be anatomically allied. To these two elements of areolar tissue are to be attributed physical properties similar to those of white and yellow fibrous tissues, and these will vary greatly in different situations, accord- ing to the proportion and mode of arrangement under which the t*vo elements coexist. 0/ the areolar tissue of glands. — There appears to be a very prevalent misconception with regard to the quantity of this tissue found in the interior of the large glands, as the liver and kidney. It is imagined that it penc- trates into every interstice, mingles with the capillary rete, and envelopes the ultimate secreting tubules. It is, however, impossible in the most recent specimen of these organs to discover anything answering to this descrip- tion. All that can usually be detected is a small quantity accompanying the larger vessels in their course within the organ, and forming septa between its coarse subdivisions. And it would be difficult to suppose a purpose which a more abundant supply could subserve. The ca- pillary network and the secreting tubules by their mutual and intricate interlacement sufficiently sustain one another ; no freedom of motion is required between them ; there is no force tending to separate them. I am far from saying, however, that the ultimate substance of these glands consists only of simple mucous membrane and bloodvessels. in the inter- stices of these there are probably nerves and lymphatics, of the mode of termination of which we know nothing, but which seem much fewer than is commonly supposed. There is also more or less of an interstitial amorphous substance, hereafter to be described. In these glands and in the substance of many compound mucous membranes there are to be seen here and there small bodies not unlike cellular tissue in an early stage of its development. They have a bulging nucleus from which they taper to the extremities; and they are much longer and slenderer than the prismatic epithelium. With their nature and use I am at present quite unacquainted. The lungs seem mainly to owe their extraordi- nary elasticity to the yellow fibrous element of their submucous areolar tissue. This is spread in great abundance under the whole surface, and much predominates over the white. In the trachea and bronchia it is besides largely deve- loped in longitudinal bands visible through the mucous membrane. In the whole of this re- gion its fibrils take a general longitudinal direc- tion, but branch and inosculate at very frequent intervals, enclosing areola of small dimensions. But this element does not cease with the tubes; it is prolonged in the form of branching, arching bands over the basement membrane of the air- cells, which it renders elastic and firmly supports. founded with areolar tissue. This is non-striated muscle, at once known by its being loaded wiih corpuscles, or persistent cell-nuclei. See MUSCLE. 496 MUCOUS MEMBRANE. lying underneath it ; and am come to the con- clusion that the most complicated diversities that are met with, admit, when studied in this manner, of being explained and reconciled to a common type of structure. Peculiarities of the skin, mucous membranes, and glands. Of the skin. — This is chiefly peculiar in its epithelial element and its submucous areolar tissue. The epidermis is composed of a vast number of superimposed lamina of scales, which, in the earlier stages of their develope- ment, and especially in certain races of man- kind, contain minute pigment granules in their interior. The pigment disappears more or less completely as the particles attain the surface. It is continued for some distance down the hair follicles and sweat-ducts, and thus serves to mark the continuity of these parts with the general surface. Hairs, nails, hoofs, and other simi- lar appendages are all composed of modified epithelial particles, and are nearly peculiar to the skin. The sebaceous and perspiratory glands, and the spiral ducts of the latter travers- ing the epidermis, are also among the most characteristic features of this part of the mucous system. The papillae of the skin have their counterpart in the villi of the mucous mem- branes ; the cutis vera, as it is called, has also its analogue in the submucous areolar tissue, but it is so enormously developed that the re- semblance has escaped the notice of anatomists. Its characters have been already briefly de- scribed. It is a striking fact that the cutis, like the submucous areolar tissue, contains no fat, even in the most corpulent subjects. I have repeatedly made this remark. The cutis differs in this respect from the subcutaneous fascia, which is therefore, perhaps, to be regarded as less allied to the submucous areolar tissue. Of the mucous membranes — These hold an intermediate place between the skin and the true glands. They blend insensibly with the former at the different orifices of the body, and may, under favourable conditions, become so modified as to assume the appearance of skin. The change then wrought is nothing more, however, than an increased deposit of epithelial scales, with an absence of the natural moisture; and it may be doubted whether a transforma- tion of this kind could occur in a mucous membrane of which the epithelium was not of the scaly variety. On the other hand certain parts of the membranes usually termed mu- cous are nothing less than real glands arranged in a membranous form. The mouth, pharynx, oesophagus, the vagina and vaginal surface of the uterus, are the parts whose lining membrane most nearly resembles the skin. Their most remarkable feature is the thickness of their covering of epithelial scales, provided for their protection against foreign contact and pressure, and in connection with this the existence of numerous glands opening upon them for the lubrication of their surface. Many of these glands correspond with the sweat-glands of the skin in being similarly scattered under the surface. Such are the buccal and all the small glands allied to them, which, in particular, resemble the largely deve- loped sweat-glands of the axilla. The only difference between them is in the mode of in- volution of the secreting membrane, which in the former is cellulated, in the latter tubular. These portions of the mucous membranes also approach the skin by the denseness of their submucous areolar tissue. In the pharynx it is only that part of the lining membrane below the posterior arches of the palate, or that exposed to friction during deglutition, that has the dermoid characters now described : all above is more delicate, is clothed with ciliated epithelial prisms, and be- longs physiologically to the nasal or respiiatory tract. The lower or buccal surface of the soft palate differs in a similar way from the upper. The lining membrane of the Eustachian tubes and tympana is very delicate, none of the elementary tissues predominating. The epithelium is in a single layer of prisms clothed with cilia. The submucous areolar tissue is in very small quantity, and the vascular network consists of little more than a simple plane ex- pansion. In the nose, the epithelium, accord- ing to Henle, is scaly on the septum and on the aloe for some way within the nostrils. Here also there are hairs — an advance towards the characters of the skin : beyond this it is every- where ciliated, even within the bony sinuses. The membrane covering these sinuses is of extreme tenuity, and presents the elementary tissues all in a simple form. That covering the pendulous parts of the spongy bones, on the contrary, has long been noted for its great thickness — a character due to neither of the elements of the mucous tissue itself, but to the extraordinary size of the submucous vessels. Both arteries and veins are large, but especially the latter, which here form a plexus imme- diately beneath the surface, and not separated from it by any considerable quantity of dense areolar tissue. Hence the facility with which these vessels give way externally when dis- tended with blood. The lining of the nose has been sometimes called a Jibro-mucous mem- brane, from its close connection with the pe- riosteum. The periosteum in the sinuses is extremely delicate, in consequence of the te- nuity of the bony laminae it invests; and it would perhaps be impossible to separate it there from the submucous areolar tissue. The globe and cornea are covered with scaly epithe- lium, of which the particles are smaller towards the folds of the eyelids,* where they gradually become prismatic, and along the tarsal borders clothed with cilia, so small as to be only recog- nizable a short time after death. The conjunc- tiva of the lower lid is very minutely villous. At the pharyngeal orifice of the glottis, the epithelium becomes ciliated and continues so along the trachea and bronchial ramifications as far as the air-cells, but, according to my own observations, the cilia there cease, and the epithelium changes its character to a remark- able variety of the glandular form. In the air- * Henle, loc. cit. MUCOUS MEMBRANE. Where mucous membranes are not destined to move on the parts they cover, the areolar tissue beneath them is very scanty. This is the case in the nasal cavities, even in the por- tions furnished with a great substratum of bloodvessels. But where much motion is re- quired, as where a muscular lamina underlies the mucous, and the enclosed cavity is liable to vary in its dimensions, the areolar tissue is co- pious, and very similar in its elements and in the size of its interstices to the ordinary forms. Examples of this are seen in the whole alimen- tary tract. But it is under the cutaneous part of the mu- cous system that this tissue assumes its highest developement. Elsewhere its object is to pro- mote freedom of movement, or to confer elasti- city. Here it answers both these purposes, and in addition gives a great capacity of resistance against external pressure and violence. The former end is attained by the structure called subcutaneous fascia, which is a large quantity of this tissue in its ordinary form. The two latter are effected by that more condensed part to which the term of cutis has been given. This last is the structure to which the submucous areolar tissue of the intestinal canal mainly cor- responds, as may be shown by an examinatioh of the submucous tissue of the mouth, pharynx, and oesophagus, which holds an intermediate place. To describe its modifications in different situations would be to encroach too much on the province of another article (see Skin), and a lew general remarks must here suffice. The framework of the cutis may be said to consist entirely of a modified form of the areolar tissue. Both elements are enormously deve- loped, but especially the yellow fibrous one. The fibrillae of this are thicker than elsewhere, and branch and inosculate with great freedom, enclosing interstices open on all sides, and giving passage to the wavy bands of the white fibrous element as well as to vessels, nerves, the ducts of the sweat-glands, the sebaceous glands, and the roots of the hairs. These in- terstices are in general very close, but they vary with the size of the parts which occupy them. On the deep surface of the cutis the yellow fibrous element changes gradually into that of the subcutaneous fascia, or that of ordinary areolar tissue. It cannot be doubted that the skm chiefly owes its elasticity and toughness to this remarkable developement of the yellow fibrous element. Topogi'uphiail view of the mucous si/stem in man. — Beferring the reader to the article Skin for a detailed description of that part of the mucous system, and its immediate dependen- cies, I shall now proceed to point out some of the more remarkable varieties of the internal tracts. These tracts have been usually com- prehended under two general divisions, the gastro-pulmonary, and the genito-urinary. The former is continuous with the skin at six points, the two eyelids, the two nostrils, the mouth, and the anus; the latter at a single one, the orifice of the urethra in the male, and the labia pudendi in the female. Besides these, there are two smaller tracts, the mammary, each of 496 which is subdivided into several, which open separately on the skin. The description of the gastro-pulmonari/ tract may be commenced at the lips. It covers their inner surface, the cheeks, gums, tongue, and palate, and extends into the labial, buccal, and larger salivary glands, of which it consti- tutes the chief mass. It passes over the arches of the palate, (where its involutions form the tonsils, )and lines the pharynx, Eustachian tubes, and the cavities of the tympana. Penetrating into the nose by the posterior nares, it lines all the passages and chambers of that organ, and advances along the nasal duetto the lachry- mal sac. Thence it may be traced along the canaliculi to the front of the eye, where it takes the name of tunica conjunctiva; covers the posterior surface of the eyelids, a certain por- tion of the sclerotic, and the cornea, and forms the caruncula, the Meibomian and lachrymal glands. In these complicated portions of its course, the membrane shares more or less in the construction of the five organs of special sense, and is the essential seat of two of them, taste and smell. From the pharynx it spreads in two directions ; first, into the larynx, trachea, tracheal glands, and bronchial ramifications, until it terminates by forming the air-cells of the lungs ; secondly, into the alimentary canal. Here it lines the oesophagus, stomach, and intestinal tube, as far as the anus, and it penetrates along the excreting ducts of the liver and pancreas, into the inmost recesses of those glands, to form their secreting surface. The genito-urinary tract may be traced along the urethra into the bladder, ureters, and pelvis of the kidneys; and thence into the substance of those organs as far as the Malpighian bodies, the extremities of the uriniferous tubules.. In connection with the urethra, processes pass to the glands of Cowper; and, in the male, into the interior of the prostate, the vesicula> seminales, vasa deferentia, and tubules of the testes. In the female, the vagina, uterus, and Fallopian tubes receive a lining from it, which, at the fimbriated extremity of those canals, be- comes continuous with the serous membrane of the abdomen.* The very remarkable differences presented to the eye by different parts of this system have been a source of great difficulty to anatomists, who, on other grounds, believed them to be nearly allied ; and it would appear that hitherto no satisfactory explanation has been given of the anatomical conditions on which this variety depends. This deficiency I shall now endea- vour in some degree to supply. From the ex- aminations I have made, I have been led to consider in a distinct and separate manner the several elementary tissues already mentioned, composing the simple mucous membrane, and * This remarkable exception to a general fact has long attracted attention. As a mere anatomi- cal difficulty, it has lately received curious illustra- tion from He nle's discovery of the existence of an epithelium on serous and other allied surfaces. But its true explanation can probably only be attained by a study of its morphology, joined with that of its final cause. MUCOUS MEMBRANE. 407 passages, as formerly described, the submu- cous areolar tissue presents a remarkable mo- dification, and is closely joined to the peri- chondrium of the inner surface of the cartilages. It is worthy of remark that the glands with which the tracheal portion of the membrane is furnished, are not placed, like the buccal, duodenal, and other similar glands, immedi- ately subjacent to the mucous membrane, but on the posterior surface of the tracheal is muscle, which is pierced by their ducts. This peculiar arrangement would seem to be accounted for by the deviation from the ordinary form which the submucous areolar tissue hete presents, and which renders it ill adapted to give to these irregular-shaped bodies that loose investment which they everywhere possess, and which therefore appears necessary to them. The mucous lining of the whole alimentary canal below the cardia is the largest and best marked example of what I have termed the compound mucous membiane, being com- posed of vertical tubes which are truly glands, opening on the general surface. That of the small intestine presents villi also. This entire membrane is very soft and easily torn, because its chief mass consists of an epithelium, the particles of which adhere but slightly either to one another or to the basement membrane, and are everywhere disposed in a single layer. There is moieover scarcely any areolar tissue between its involutions, which have, therefore, little besides the vascular web to sustain them. The submucous areolar tissue is in considerable abundance between themucousand the muscular coats. (See Stomach and IntestinalCanal.) The lining membrane of the hepatic and pan- creatic ducts is simple, and its epithelium of the prismatic variety. In the gentto-urinary tract, the epithelium presents every variety. The fossa naviculars* is clothed with small, flat, or roundish scales, the rest of the urethra with a single series of prismatic particles. The cells of the prostate are lined with spheroidal epithelium, the vasa deferentia with prisms. In the vesiculae semi- nales there is a pavement of somewhat flat- tened granules, and also in Cowper's glands. In the bladder, ureters, and pelves of the kid- neys, the epithelium is in the form of longish cells intermediate between the spheroidal and the prismatic varieties. The nymph*, clitoris, hymen, and vagina are covered with scaly epi- thelium, and this has been noticed by Henle in cases where the hymen has been entire. Within the neck of the uterus the epithelium becomes prismatic and clothed with cilia, and so con- tinues over the surface of the uterus and Fal- lopian tubes, and even for some distance over the outer surface of their fimbriated extremities. Beyond this it merges gradually into the com- pressed cells of the serous membrane. The lining membrane of the Fallopian tubes, as well as that of the uterus, is of a compound nature, especially during gestation, and consists of tubules arranged vertically to the general sur- face. It is to be observed that the cilia only * Henle, loc. cit. VOE. III. clothe the general surface, and that the epithe- lium lining the tubules is spheroidal, or inter- mediate between that and the prismatic. It is a form of the glandular variety, and bears no cilia. Of the g/am/s.—The varieties apparent in these organs also may be explained by an ex- amination of the modifications and modes of aggregation of the elementary tissues already mentioned. It may be said, in general terms, that the glands are characterized by their solid form, by the great preponderance of their epi- thelial and vascular tissues, and by the small quantity of their areolar tissue. It is rare for this last to invest every individual involution of the mucous surface in the interior of a gland ; but it usually gives a common covering to the whole organ, as well as less complete ores to those subdivisions of it, termed lobes or lo- bules, which result from the mode of distri- bution of the bloodvessels and duct, and are designed for the purposes of package or pro- tection. Such an investment is usually termed the proper coat or capsule of a gland, and seems to correspond most nearly with the submucous areolar tissue of the compound mucous mem- brane, as, for example, that of the intestinal canal. The propriety of these remarks will appear, on a particular application of them. As I be- fore entered somewhat in detail into the internal composition of the liver, it may now be se- lected for illustration. The epithelium, which in the gall-bladder and larger ducts is of the prismatic kind, becomes bulky and of a flat- tened spheroidal form, in the lobules. It there also acquires a peculiar character, viz. nume- rous minute globules of an oily or fatty nature, disseminated within the substance of each par- ticle. The basement tissue seems to cease, and on an examination of a thin section of the lobule under a high power of the microscope, its chief bulk appears to consist of epithelium. There is scarcely a trace of areolar tissue to be anywhere detected. Even the coats of the capacious capillary bloodvessels, in the close meshes of which the ultimate ramifications of the bile ducts are situated, are with difficulty seen, and are of extreme delicacy. The sub- mucous areolar tissue of the hepatic ducts, with which the whole of the contiguous cap- sule of Glisson should be associated, cannot, when arrived at the lobules, be followed into their interior. It can only be distinguished in very slender quantity, giving them a partial in- vestment, on those aspects which share in form- ing the portal and hepatic-venous canals, and where, in the angles of union between three or more lobules, a terminal twig of the portal vein runs up to open on all sides into their capillary plexus. No lobule is isolated from the rest by a complete capsule, but commu- nicates immediately by its capillary network, with those near it. The intralobular vein has a similar want of areolar tissue around it; and thus the main mass of the lobule, and of the whole liver, consists of epithelium and a plexus of capillaries. Those lobules, however, which contribute to form the general surface of the 2 K 498 MUCOUS MEMBRANE. organ have an additional and dense covering of areolar tissue on that surface: a covering, which has the same relation to the mucous element, as that on the portal aspect ; which is continuous with the capsule of Glisson at nu- merous points; and which is here developed as a membrane of support, as a nidus for a lymphatic rete, and as a foundation for the peritoneal tunic, that it sustains. The nerves and lymphatic vessels of the in- terior of the liver, though but little known, are too inconsiderable in point of size to affect the general accuracy of this description. Hence it evidently appears, on what modifications of the elements of the mucous tissue and of those appended to it, the peculiar friability, colour, and other properties of this organ depend. If the " parenchymatous'' areolar tissue abounded in this gland to the extent implied in the de- scriptions of Bichat and some more recent authors, no doubt its toughness would be far greater than it really is. But where an organ is sufficiently screened from injury by its po- sition, where its different parts are so well connected by the continuity of a close network of capillary vessels, and are not required to move on one another, it would be difficult to imagine what purpose a greater development of areolar tissue would serve. In the kidney, the epithelial and vascular elements are in corresponding abundance, the areolar tissue in very small quantity. The general texture, however, is more tough than in the liver, from the universal presence of the basement membrane on the tubes. In the me- dullary portion, the tubes radiate from the apex towards the base of the cones, and are imbedded in a firm, granular substance, not hitherto described, but which resembles a blastema, and is probably composed of cells. In this substance is also imbedded the capil- lary plexus surrounding the tubes, as well as the vessels that convey blood to and from this plexus, and take the same direction as the tubes. Hence the firmness and close texture of this part of the kidney as compared with the other, and the facility with which it tears from the apex to the base of the cones. At the base of the cones, the tubes enter the cortical substance and take a course, in sets, towards the surface. The central tubes of each set reach the surface and then recline inwards and become convoluted. But the others bend down one after another and become convoluted before reaching the surface. All at length terminate in the Malpighian bodies, which lie among the convolutions. The arteries and veins also take a general course from the hilus towards the surface. Hence, on tearing the cortical part of the organ, there is a disposition for the lacera- tion to occur in lines continuous with the radii of the medullary cones, and this disposition is less evident as we approach the surface ; but between these lines the torn surface is very uneven, where it is formed by the contorted tubes. The cortical part has less of the inter- tubular matrix than is met with in the medul- lary cones. In the kidney there is a peculiarity of the highest interest in the relative situation of the vascular and mucous tissues, which seems to have reference to the peculiar function of the gland. There are two systems of capillary vessels, the former of which, or that in con- nection with the renal artery, perforates the mu- cous membrane at the extremity of each tube, and lies on the outer surface of the membrane, that is, bare and loose within the dilated ex- tremities, which thus form the capsules of the Malpighian bodies.* (See Ren.) The common submucous areolar membrane of the kidney, or that forming its capsule, is in most animals chiefly composed of ordinary areolar tissue with close meshes. But where a more resisting covering is required, as in the lion, this areolar tissue is modified; the white fibrous element predominates so much as to give the capsule the glistening aspect of an aponeurosis. This is an admirable example of the transition from areolar tissue into white fibrous tissue, and helps to show the true nature and relations of the tunica albuginea of the testis. The testis, compared with the liver and kid- ney, presents several modifications of the ele- mentary tissues. The basement membrane is much stouter than in the latter gland, the tubes are larger and their convolutions more loosely joined by any intervening substance. There is no appearance of an intertubular substance except towards the corpus Highmorianum, and the principal connecting medium between the tubes seems to be the vessels, which are less nu- merous than in the glands already mentioned, and form a looser network. The secreting tu- bules for these reasons admit of being very easily separated from one another, and un- ravelled to great lengths. The epithelial ele- ment of the testis constitutes a lining of con- siderable thickness, and is highly remarkable (see Jig. 274). Though no seminal animalcules have been hitherto seen in the interior of the particles while still attached to the basement membrane of the tubes, yet from recent re- searches, and especially from those of Wagner, on the phases of their development, it is ren- dered highly probable that these singular moving bodies originate in the epithelial particles, as one of the results of their natural evolution. The loose aggregation of the tu- bules of the testis makes a firm external cap- sule necessary, and where, as in man, this gland is much exposed to injury by its situ- ation, a further protection of this kind is made requisite. Hence the firm and unyielding character of the tunica albuginea in man, the contrast of which with the thin covering of the large but well protected testicle of the por- poise (for example), is well worthy of attention. In many large animals, the tunica albuginea, like the aponeurotic capsule of the lion's kid- ney, is traversed more or less completely by large veins which it thus serves to support. The tunica albuginea consists almost solely of white fibrous tissue, and represents the sub- mucous areolar tissue of the mucous system. The peculiarities of the salivary glands re- * Phil. Trans. 1842, part I. MUCOUS MEMBRANE. 499 suit from the predominance of their epithelial element over the others. The ducts terminate in vesicles, very similar in the figure they assume to those of the lungs, but nearly filled up with epithelial particles* The basement mem- brane is very delicate. The capillary vessels encircle the vesicles, and are comparatively few in number, whence the pale colour of these glands. The areolar tissue forms capsules for those aggregations of vesicles, termed lobules, but does not penetrate between the individual vesicles. The mammary glands derive their extreme denseness and toughness, as well as their white colour, principally from the areolar tissue, in which the proper glandular membrane is en- closed. This tissue penetrates more abundantly between the minuter subdivisions of the gland than is observed in any other instance. It thus affords support, at the same time that it permits and facilitates movement of one part of the organ on another. It is also of such a nature as to readily allow of distension during lactation. General outline of the functions of the mu- cous system. — By its external anatomical posi- tion, this system is subservient to four great functions : the reception of impressions from without, the defence of the body from external injurious influences, the absorption of foreign particles, and the separation of such as are for any reason to be eliminated. It may almost be said to be the peculiar seat of these func- tions, which, however, are distributed in a very unequal manner over its different regions. Reception of external impressions. — The skin and mucous membranes appear everywhere fitted by their nervous supply to receive im- pressions, which, being conveyed to the ner- vous centre, may there excite a reflexion of stimulus along motor nerves, without the in- tervention of consciousness. Common sensa- tion, or that which in its most exalted form becomes touch, exists in all parts of the cuta- neous surface, within the mouth, for some dis- tance within the nostrils, and (with the excep- tion of the pharynx and oesophagus) in general, wherever the epithelium is of the true scaly variety. Where the sense of touch is most perfect, the simple membrane is observed to be involuted into the form of papillae for the pur- pose of crowding a larger number of nervous loops into a given space. Taste and smell, which are nearly allied to touch, are the other special senses of which the mucous system is the seat. The sensations of hunger and thirst seem also referrible to this tissue. Defence from external influences.- — One chief division of the mucous system, viz. the skin, derives its main characteristics from its adap- tation to this function, and those parts of the mucous membranes which are most exposed to the contact of irritating substances approach the most nearly to the skin in their structure. Their epithelium is scaly and in thick laminae, their submucous areolar tissue abundant, dense, and resisting. The nervous endowments of such surfaces, whether excito-motory or sen- sorial, mainly contribute to the protection of the animal. And, on the external tegument, the developement of hairs, nails, &c. in their endless modifications of form, position, and structure, serve, with few exceptions, the same important purpose. In some parts of the mu- cous membrane peculiarly obnoxious to pres- sure, there are special glands for the lubrication of their free surface. Absorption of external material. — Every particle, entering the body from without, is ab- sorbed, in the first instance, through some por- tion or other of the mucous system. What is now known of the nature of this function in general, renders it certain that every part of the mucous system would form an absorbing sur- face, if favourably circumstanced for doing so. But as the extraneous material, to be absorbed, must be brought into contact with the absorb- ing surface, often by some special and com- plicated means, this function is chiefly limited to certain distinct districts of the system. With few exceptions the glands are not suited either by their position or structure to receive the contact of extraneous substances, and even many portions of the mucous membranes are incapacitated in the same manner, as, for ex- ample, most of those lining the excretory pas- sages of the glands. The secretions which, in a healthy state, are the only substances brought into contact with these surfaces, are, it is true, occasionally modified by a partial absorption of their constituents; but, generally speaking, this occurs to a very slight extent. Once formed, they usually traverse the channels, leading to the outlets of the body, unchanged. The simplest condition under which this function presents itself appears to be that ex- hibited by the respiratory surface, which, whe- ther it be arranged as lungs or gills, is con- cerned with aeriform particles, and absorbs and secretes through the self-same structure. The skin also is a very active absorbing surface, and appears, by the best observations, to be provided with a close net-work of lymphatics, which I have already stated to be most probably situated immediately under the basement mem- brane. It does not appear that the existence of the lymphatic pores, described by MM. Breschet and Roussel de Vauzeme as opening on the free surface of the cuticle, has been confirmed by any subsequent anatomist. I have sought in vain for any such system of vessels in the cuticle, and I believe those distinguished ob- servers must have been deceived by the irre- gular lines of union between the epidermic particles. It is true that the thickness and tex- ture of the layers of epidermic scales are little calculated to allow of their being permeated by foreign material, whether fluid or gaseous ; and, therefore, it is not likely that absorption is effected to any great extent either through their substance or interstices. It seems more con- sonant with facts to suppose, that this process, especially in respect to solid matters, is carried on by the simple membrane of the sudoriferous ducts, with which external particles would easily be brought into contact through their open extremities. But as these ducts traverse the thickness of the cuticle, and in that part of 2 k 2 500 MUCOUS MEMBRANE. their course have not (in man) any proper wall, but are bounded only by the edges of the scales between which they pass, it is very probable that the deeper and softer lamina? of epidermic particles may not merely be moistened by the secretion of the ducts, but, under favourable circumstances, may borrow extraneous matters from them, and thus become a part of the ab- sorbing medium. In reference to the question of absorption by the skin, it is interesting to notice the modification of this structure in those lower animals in which this function is mani- fested in much greater activity than in man. A better example cannot, perhaps, be selected for this purpose than that of the frog. Its epi- dermis consists of a single layer of scales, and in consequence they do not overlap, but join edge to edge. These scales are not reduced to mere membrane, but always contain a con- siderable quantity of fluid in their interior. The sweat-pores open here and there in the interstices between three scales, and have true walls, formed out of a pair of modified epi- dermic particles, adapted to one another, and elongated into the subcutaneous texture. They thus" bear a very close resemblance to the stomata of leaves. I lately discovered this singular arrangement in the cast-off cuticle of the animal. It seems undeniable, that, here, absorption is effected by the whole series of epidermic scales, as well as by the pores. But the most remarkable, and at the same time the most recondite form, under which this func- tion is exhibited in the mucous system, is that met with in the alimentary tract. Here, indeed, water and aqueous solutions are imbibed, with great rapidity, into the vascular plexuses of the blood and lacteal systems, as the united testi- mony of many able experimenters abundantly shews. But from this merely physical process of imbibition is to be distinguished the more mysterious and elective function of chylous absorption, which is conducted by the lacteals alone, and is consequently limited to the region supplied with that system of vessels. For an account of the present state of knowledge on the highly important subject of the intimate nature of this function, the reader is referred to Absorption and Lymphatic System, in which he will find the chief of the conflicting statements and opinions of physiologists de- tailed and discussed. It has already been ex- plained in the present article, that the latest observations on the structure of the villi, and apparently the most exact ones, because con- ducted with the most improved lenses, and accordant with other collateral discoveries, make it highly probable that the opinion assigning open" mouths to the lacteals is erroneous In the description of those orifices, furnished by Treviranus, .we may plainly discern his partial acquaintance with characters which we now know to be those of the prismatic epithelium investing the villi ; and the less precise asser- tions of the same kind by several other excel- lent anatomists, we may now, perhaps, fairly consider to have been founded on deceptive appearances which, in their day, did not admit of accurate interpretation. If any such orifices exist, their minuteness must be extreme, and they must lie in the intervals between the prisms of epithelium. But even such attenu- ated pores, the best microscopes fail to detect, and at least it may with certainty be affirmed, that none large enough to admit a chyle-globule exist. The structure of the villi, no less than our knowledge of the absorbent function in general, seems to indicate that the chyle, when first taken up, is strictly a fluid, and only ac- quires its solid particles after it has entered the lacteal plexus. Of the separation of material from the body. — This function appears to be carried on in every part of the mucous system. One great division, that of the glands, is specially des- tined to it, as are likewise those portions of the compound mucous membranes, which have been already described as coming properly under the designation of glands. If, however, the essential nature of the function of secretion be adequately considered, it will scarcely be doubted that even the simplest parts of the mucous membranes, and the whole cutaneous surface (as distinguished from its sebaceous and perspiratory glandular offsets) share largely in this important office. It is true that in the skin this function holds a subordinate place to that of defence and protection, but its existence is only an example of what an attentive survey of nature everywhere discovers; the accom- plishment of various ends by means of the same simple instruments. The notion that a secreted product must be fluid, is one that has arisen out of a partial and imperfect insight into the nature of the secreting process. Those matters which are eliminated in the largest quantities and by the largest glands are for the most part so, in the shape under which they meet the eye, that is, after their separation from the organ in which thev are secerned. But in the case of the lungs the secretion is gaseous as well as fluid, and in numerous instances, which have been recently brought to light, chiefly by the labours of Ilenle, it is found, when minutely scruti- nized, to consist of organic forms entitled to be styled solid. The problem which physiologists have now to resolve, is how far these organic forms, which are more or less altered epithelial par- ticles, are necessarily concerned in the per- formance of the function, for epithelium is all but universal in the mucous system. It would be foreign to the province of this article to enter at length on the general question of secre- tion, and I shall confine myself to a few re- marks tending to show in what direction recent researches point* When the secretion of a sebaceous follicle of the skin is minutely examined, it is found to consist entirely of epithelial particles contain- ing the sebaceous matter, and more or less broken and compressed. These are similar to the particles lining the follicle, and are mani- * Purkinje, Isis 1838, No. 7. Schwann, Froriep's notiz. Feb. 1838. Henle, Mutter's Archiv. 1838, p. 104-8, 1839, p. 45; also Muller's Phys. by Baly, 2nd edit., vol. i., p. 503-4. MUCOUS MEMBRANE. 501 iestly the same structures, detached and matted together. The secretion found in the tubules of the testis is chiefly composed of epithelial particles resembling those attached to the base- ment membrane of the tubules. Some of these are very perfect, others have undergone changes. It has been already staled that the seminal ani- malcules are most probably a developement of some of these particles, not altogether different in its nature from that of the cilia found upon them in other situations. The secretion of an ordinary mucous follicle is likewise made up of epithelial particles resembling those still attached to the membrane. The thick, semi- fluid mucus found in the stomach has been shown by Wasmann* to consist of rounded nucleated particles, which both in size and shape correspond with those of the stomach tubules. This mucus may be even seen pro- jecting from the cells into which these tubules discharge themselves, and no doubt can exist that the proper secretion of this organ is chiefly composed of the bulky epithelium thrown off by the tubules; a view corroborated by the fact,f that this mucous membrane, consisting almost solely of epithelium, when mixed with certain acids naturally existing in the gastric juice, evinces the same powers of dissolving alimentary substances as that wonderful men- struum itself. The same thing may be ob- served in the intestinal canal, where the adhe- sive mucus is little else than the aggregated epithelial caps of the villi, together with that which has escaped from the vertical tubes of the membrane. These facts may be always verified in a healthy animal just killed, and may thus be shewn to be independent of any morbid action. The legitimate conclusion from them seems to be this : that the peculiar prin- ciples of these respective secretions are lodged in the epithelial particles ; having been depo- sited there from the blood, in the natural course of developement. In other words, the process of secretion in these cases consists in an assimilation of the material from the blood by an organized tissue, which, when fully de- veloped, is loosened and shed. This view, so captivating by its simplicity, has certainly much satisfactory evidence in its favour, and it may, at least, be regarded as sufficiently established to constitute a strong presumption in favour of the general position, that all seeretion is primarily assimilation. That the epithelial particles, when their growth is completed, should detach themselves in a more or less entire state, in all cases, from the membrane to which they have adhered, cannot be supposed essential to this general position, and even the total absence of any vestiges of these particles from any particular secretion would scarcely form a valid argument against it. For at present we know of no" reason why the assimilated material should not be gradually given up by a slow disintegration or deliquescence of the particles, or even by a continual separation of it without a concomitant destruction of the particles themselves. But in numerous instances besides those that have been mentioned, there is more or less direct evidence of an actual shedding and con- tinual renovation of the epithelium. The scaly variety of this tissue, whether on skin or mu- cous membranes, is a wide-spread example of this: the particles may be observed to augment in size by the intus-susception of new material from the blood, afterwards to undergo a slow loss of substance, and, finally, to lose their connection with the body altogether. They retain their position till nothing but the nucleus and cell-membrane remain, till they are re- duced, as it were, to a mere skeleton. How the material thus separated from the body is to be distinguished from a secretion, it would not be easy to decide. In the saliva of the mouth, are present, not only detached scales, but globu- lar nucleated particles, of a very delicate aspect and regular character, which seem manifestly to come from the salivary glands. They differ in some respects from tiie epithelium of these organs, but appear most probably to be par- ticles of it altered by endosmose of the water of the secretion through the cell-membrane ; for the ultimate vesicles and ducts of these glands are not merely lined, but filled, with epithelial particles, which, being thrown off from the basement membrane, must in due time escape to make room for the advancing series : and yet none of them in an unaltered state are found in the saliva. I may in this place refer to an opinion recently entertained in Germany, that the secreting membrane of certain glands is arranged in the form of closed vesicles filled with nu- cleated particles, which, from time to time, are discharged, as the secretion, by the bursting of the cell in which they are contained. Ilenle* conceives that this arrangement exists in the mammary, salivary, and lachrymal glands, as well as in almost every mucous membrane, however apparently plain and simple. Was- mann j has described a similar structure in the middle part of the stomach of the pig. This view of the existence of closed vesicles is obviously at variance with the general view before given of the universal continuity of the simple membrane of the mucous system. I am familiar with many of the appearances on which it is founded, and without presuming to pronounce them very decidedly deceptive, I may state that hitherto my observations induce me to agree with Dr. Balyt in his rejection of the interpretation put upon them by the Ger- man anatomists. A thin slice of a mass of the many-lobed terminal vesicles of one of these glands, especially if compressed, very readily assumes the aspect of a congeries of cells, each entirely surrounded by an envelope of base- ment membrane. But I have several times, in favourable sections, observed this membrane passing off into a neck, and becoming coa- * De digestione nonnnlla. Berol. 1839. * Miiller's Archiv. 1839, p. xlv. t Miiller's Archiv. 1836, page 90. Schwann, t Dedigestione nonnulla. Berol. 1839. uber das Wescn des Verdauungs prozesses. % Translation of Miiller's Physiology, p. 50k 502 MUCOUS MEMBRANE. timious with that of the duct. Such observa- tions seem to me in a great measure conclusive on this subject ; and I am strengthened in this view by the fact, that the capsules of the Malpighian bodies of the kidney are now universally considered to be perfectly closed vesicles, whereas they are in reality the ex- panded wall of the duct, as I have lately shown by several kinds of proof.* But what- ever may be the real fact in the matter under dispute, it is admitted by all that the epithelium is formed in enormous quantities, and is being continually thrown off; which is the circum- stance chiefly intended to be insisted on at present. In the healthy bile also, in the urine, and in various other secretions Dr. Henle has met with particles of epithelium detached from the excretory passages, and in different stages of decay. Turning to those two great emunctories, the liver and kidneys, in the secretions of which no trace of the epithelium of the secreting part of the organs can be detected, we might be disposed, on a slight consideration, to conclude the evidence they furnish to be unfavourable to the general position here advanced. We must, indeed, be content for the present to acknow- ledge that it is less plain and direct, and shrouded in our great ignorance concerning the play of chemical affinities in living bodies; but still it is too interesting and important to be passed over in silence. Though the epithe- lium of these organs be not detached entire, as in many other cases, there is much, in each instance, to explain the discrepancy consistently with the theory in question. 1 have described the lobules of the liver as consisting of a solid plexus of capillary blood- vessels, in the meshes of which is a congeries of epithelial particles. We possess no accurate account of the mode of termination of the biliary ducts; but it seems clear, from the small meshes of the vascular plexus being completely filled by the epithelium, that no true ducts, i. e. tubes, penetrate the substance of the lobules: the tubular ducts probably commence on the surface of the lobules. The epithelium of the lobules is doubtless conti- nuous with that of the ducts, but the cavity of the ducts and their basement membrane termi- nate at the surface of each lobule. Though the cavity of the ducts be not continued within the lobule, yet it is very possible that injection urged along the ducts might insinuate itself by the side of the epithelium into the interstices of the vascular plexus, and thus, like the epithelium itself, form a solid plexus within the lobule. This appearance probably led Mr. Kiernan to describe the termination of the ducts as forming a plexus within the lobule, the lobular biliary plexus. And this description must be allowed to be essentially correct; for although the cavity of the duct cease at the surface, the epithelium of the lobule is, in respect of function, its real continuation. I have further observed, that although the epithe- * Phil. Trans. 1842, Pt. I. p. 59. Hum of the lobule has, on the whole, a plexi- form arrangement, yet its particles in some measure afiect a radiating direction from the central axis towards the circumference, perhaps towards certain parts only; and when a lobule is broken up by violence, the resulting frag- ments of epithelium are apt to consist of a linear series of particles. Many of the particles, too, are smaller than the rest, and have all the appearance of having been recently formed and as yet incompletely developed. It is also remarkable that the particles should contain granules of oily matter in their interior; for although chemical analysis has detected diffe- rences between this substance and cholesterine,* yet as the chief peculiar principles of the bile are forms of hydro-carbon, the coincidence cannot be an accidental one. It is not con- tended that the contents of these particles are the finished secretion, but rather that their chemical constitution undergoes some modifi- cations during the disintegrating process. And it is worthy of notice, that in many cases where the decarbonizing function of the lungs is slowly but greatly interfered with, as in phthisis pulmonalis, and where the liver is consequently called into increased activity as a compensating organ, these oily globules exist in such abun- dance and size as to gorge and swell the parti- cles (and therefore the whole viscus) to nearly double their natural bulk.f But this is not all the evidence, that this epithelium is the source of the bile. I am informed by my friend, Dr. W. Budd, that Dr. Henle in his recent edition of Soemmering, of which I have not yet been able to obtain a copy, describes the epithelial particles as appearing yellow or yellowish brown in direct light, and as probably containing bile. He also states that the presence of the fatty globules in the epithelium is inconstant, and corresponds with the varying fatty contents of the bile. He is unable at present to determine in what manner the contents of the particles find their way into the ducts. The foregoing facts, taken together, afford a very strong presumption that the epithelial particles of the lobules are theagent assimilating the secretion from the blood. It would be still more satisfactory if particles could be found undergoing decay. Meanwhile it seems im- possible to assign to them any other office, if it be granted that the sole function of the liver is to secrete bile. For in the case of other glands, the only other use that can with any degree of plausibility be attributed to the epi- thelium is that of its serving to defend the secreting membrane from the contact of the secretion, and to prevent the latter from re- entering the blood. And it cannot exist for that purpose in the liver, because it is itself the only structure besides the bloodvessels, and does not constitute a lining membrane. The peculiarity in the minute structure of the kidneys, which bears on the present ques- tion, is of a kind entirely different from any presented by the liver, and yet tends to establish a similar conclusion. It consists of a special * Kuehn, Kastner's Archiv. xiii. p. 337. t Author in Lancet, Jan. 1842. MUCOUS MEMBRANE. 503 apparatus at the extremity of each secreting tube, apparently designed to furnish a flow of water down the canal.* A large quantity of water is evidently required in this secretion as a menstruum for the salts and proximate prin- ciples it contains; and there is no doubt, from the analogy of other glands, that the walls of the tubes are the membrane secreting these substances. Now the epithelium constitutes at least isths of their thickness, and is the only part of them with which the water can come into contact. It therefore seems highly pro- bable that this fluid is provided in the manner described, in order to dissolve, out of the epithelial particles, the peculiar principles which they have previously assimilated from the blood. In support of this general position it may be observed, further, 1. That the epithelium, which constitutes so large a portion of the true glands, is solid and bulky, usually character- ized by its finely granular texture, and in this respect contrasts strongly with that lining the vascular system, which is of extreme delicacy and transparence. The exceptions to this re- mark confirm its importance. In the air-cells of the lungs, the secretions of which are ga- seous and not solid, the epithelium is of great tenuity, and in the Malpighian capsules of the kidney, which appear to serve principally as receptacles for the aqueous fluid that escapes from the bare capillaries within them, this structure is either wanting or consists of per- fectly transparent particles. In many inter- mediate varieties, too, there appears traceable a correspondence between the bulk of the nu- cleated particles and the activity of the secreting function ; of which the scaly form in general may be mentioned as an instance. 2. That many peculiar substances are secreted into the interior of nucleated cells, although prevented, by the position of those cells, from escaping from the body. Such are various fats and fixed oils, colouring matters, &c. 3. That this func- tion of abstracting somewhat from the blood, and elaborating it, seems the most probable one that can be assigned to the thymus and thyroid bodies, the spleen, and supra-renal capsules, and specially to the nucleated par- ticles forming so large a portion of these several structures. On the whole there seems much weight of evidence in favour of the proposi- tion " that secretion is a function very nearly allied to ordinary growth and nutrition : that whereas these are a combination of two func- tions, assimilation of new particles and rejection of old, the old being reconveyed into the blood, secretion consists in a corresponding assimila- tion and rejection, but the old particles are at once thrown off from the system without re- entering the blood. According to this view, all effete material received into the blood, from the old substance of the various organs, must be reassimilated by an organized tissue, specially designed for the purpose, viz. the epithelium, before it can be eliminated : and all substances * Phil. Trans. Pt. I. 1842, p. 73. Sec also the article Ren. thrown off from the system, but designed for an ulterior purpose, must in like manner be assimilated in order to their separation." It places in a strong light a principle of great im- portance in physiology, the subordination of the bloodvessels and their contents to the tis- sues among which they are distributed. The function of secretion may therefore be considered to be universal over the mucous system, and its different activity in various si- tuations to be dependent on, as it certainly is closely associated with, differences in the ar- rangement and structure of the epithelial ele- ment. The basement membrane, from being absent from the lobules of the liver, seems a tissue of inferior (perhaps of no) importance in respect of this function, and probably is chiefly subservient, wherever it exists, to the mechanical support of the epithelium. There are probably three ways in which the secretions are finally separated from the body : and these three ways appear to have a reference to the chemical qualities of the product, and to their effete or non-effete character. 1. The par- ticles assimilated into the nucleated cell may be thrown off' by virtue of minute chemical changes occurring in it, without the cell itself being altered in form. In this case the nu- cleated cells will be permanent, or only very slowly renewed, and the secretion will be formed, or at least perfected, by the passage of its elements through the cells. 2. The nu- cleated cells, as they arrive at their full size, may undergo a slow change in the arrangement of their elements, and gradually disappear by a kind of solution or deliquescence, thus form- ing the secretion. 3. The nucleated cells, when mature, may be cast off at once, and entire, with their contents. The two last modes are attended with a continual formation of new cells. It would appear that, in general, where the secretion is formed by the rejected chemical elements of the cells (1), or by the destructive solution of the cells (2), it is effete; but that, when formed chiefly by the separation of cells that are mature and contain much organic matter (3), it is destined for ulterior purposes in the (Economy. Of the fust the kidney seems to be an example, of the second the liver, of the third the lining membrane of the stomach. The varieties in the qualities of the products secerned by different portions of the mucous system are only referrible to varieties in the elective powers of the tracts which respectively furnish them, and admit of being most readily exp'aincd by the view of the nature of secre- tion already advanced. It is unnecessary, in this place, to enter on a particular description of the boundaries of these several tracts, and I shall only offer a few observations on the nature and extent of that secretion which has given its name to the structures here treated of. The term mucus, like so many others trans- mitted from an early period, was originally employed to denote an exaggerated and partial condition, was subsequently applied more loosely and widely in a generic sense, and now requires to be reduced to a more definite 504 MUCOUS MEMBRANE. application in accordance with that necessity for precision of thought and expression which characterizes modern science. The exposition contained in the article Mucus will render it superfluous for me to define its present accept- ation. It is denied by Dr. Gruby that the viscid form of mucus is a normal secretion from any membrane whatever, and he considers its existence as a certain mark of diseased ac- tion. This view, if less absolute, would be in a great measure correct, since there is no doubt that in a state of perfect health most mucous surfaces are wholly unprovided with any pro- tection of this kind. If the nasal cavities, the trachea or bronchia, the intestinal or urino- genital tracts, be examined in a healthy animal killed for the purpose, we may search in vain for any slimy covering, such as they are com- monly imagined to possess. But in a state of disease, each of these surfaces will secrete great quantities ; and it is not a little remarkab'e, that, even when healthy, if moistened and allowed to undergo slight putrefaction, they will become coated with a viscid fluid, having the physical characters of mucus. Yet the slimy fluid of the mouth cannot with propriety be considered abnormal. The true saliva is not viscid, as it escapes from the ducts of the glands into the cavity of the mouth : it probably becomes so by dissolving the substance derived from the scales of epithelium lining the mouth, as they advance to the surface and flatten. The fluid of ranula is not merely the accumulation of a natural secretion, but seems gradually to ac- quire its great viscidity by receiving the debris of the epithelium lining the excreting channels, and by the partial reabsorption of its aqueous portion. In the intestinal canal, however, although there is no viscid mucus naturally present, yet there is a large amount of" inspissated mucus" being continually separated from the villi and follicles of Lieberkuhn. This mucus, as already mentioned, is nothing more than the debris of epithelial particles. But chemists have detected, iD most of the secretions, a small proportion of a substance nearly allied to mucus, and probably a form of it. There is good reason to believe this to be the product of the membrane lining the ex- cretory passages, and to represent the old epi- thelium of that membrane. Where the secre- tion of the gland is fluid and in considerable quantity, it seems to be sufficient to convey away this debris from the surface which it tra- verses on its way out of the system, as in the salivary and allied glands, the liver, kidney, &c. But where, from the absence of this means of carrying off the debris of the epithe- lium, it might be supposed to be liable to accumulate and clog the surface, cilia are de- veloped ; of which the best example is fur- nished by the respiratory tract, the nasal ca- vities, and the tympana. That this is the great office of these wonderful organs upon these extensive surfaces appears to be proved by the fact that the currents they produce are uniformly towards an outlet, llenle has ob- served this in several parts, and I have ascer- tained it by experiment in the case of the tm-- clieal and bronchi.il membrane. In this tract no secretion is visible with the naked eye, but with the aid of the microscope I have found, in perfectly recent animals, mi- nute globules of extreme tenuity and of va- rious sizes, which had all the appearance of mucus oozing from the interstices of the epithe- lial particles. It is impossible but that the cilia should move these globules along the sur- face, and discharge them into the pharynx; and it hardly admits of doubt that mucus, morbidly existing on the bronchial membrane, is gradu- ally lifted up by these untiring agents to that region where it excites coughing, and is forcibly expelled by the rush of air. The patient is often conscious of its slow motion upwards, when it is in the form of a pellet and proceeds from an isolated spot. This is remarkably the case too in haemoptysis, and also in that rare disease the bronchial polypus, where branched tubes of lymph are brought up in this manner. This view of the use of cilia in the mucous system of the higher animals appears to me to merit much attention. I had intended to have considered it under a separate head, but it has been introduced here both in corroboration of the general position as to the nature of secre- tion, and in illustration of the nature and extent of the special secretion from the ordinary mu- cous membranes. On the whole I think it may be concluded: 1. That every part of the mucous system, where epithelium exists, secretes. 2. That the secretion differs, in different re- gions, according to the vital properties of their epithelia; and that these vital properties are usually attended with appreciable varieties of structure. That corresponding varieties of che- mical constitution coexist with these is highly i "liable, though only as yet proved in a few cases. 3. That mucus is the least peculiar of the secretions, yet by no means universal from the mucous membranes, but confined to tracts of comparatively limited superficial extent, chiefly the excretory channels of the glands. In the preceding summary account of the structure, relations, and offices of the mucous system, I have not been able (without inter- ruption to the course of the description) to refer sufficiently to the labours of those anato- mists to whom we owe almost all our know- ledge of the subject. This deficiency, of which I am very sensible, I shall endeavour in some degree to supply by a brief review of the re- searches which have led to the more modern and general views on the subject. Passing over the imperfect descriptions of the ancients, we find that when the microscope first became an instrument of anatomical research, the scaly character of the cuticle was recognised by Mal- pighi and Leeuwenhoeck ; and that, the former of these great anatomists had a wonderfully clear insight, considering the period at which he lived, into the close relation that subsists between the glands, mucous membranes, and skin. The labours of the anatomists of the next age were spent with great success upon matters of detail, MUCOUS MEMBRANE. 505 particularly on the distribution of the blood- vessels, which Ruysch and Liebeituhn particu- larly illustrated; and, by the general advance of knowledge, the way was being gradually prepared towards that more philosophical ar- rangement of the tissues of the body, in con- formity with their intimate texture and con- nexions, of which the first example is to be found in the work of Bonn,* already alluded to. He here traces, with great accuracy, the continuity of the skin and mucous membranes at the different orifices of the body, and he clearly recognises their close structural rela- tion, considering the mucous membranes to be productions of the skin. To our countryman, Dr. Carmichael Smith,f we are indebted for the first application of this arrangement to the purposes of pathological classification, and Pinel soon after followed in the same track.J But a new era dates from the remarkable works of Bichat,§ in which he delineated the structure, vital and other properties, and the relations of the different tissues of the body, and arranged them on a basis, which, though faulty in some of its details, has received no essential modification in its princip'es since his time, and entitles him to the praise of rare genius and sagacity. He seems to have clearly perceived the true connexion that exists between the skin, mucous membranes, and glands, al- though he failed to carry out his views into the subdivisions of his system, where he was still fettered by the crude notions of his predeces- sors. One of the most remarkable features in his work, bearing on the present subject, is the analogy he draws between the epidermis of the skin and the mucus of mucous membranes, an analogy which he discovered with the eye of the mind, which has been since often rejected, but which can now be shewn to be real by the eye of sense. Most writers of eminence since the time of Bichat have adopted the principal part of his views, and some have advanced further towards a full recognition of the homology of the skin, mucous membranes, and glands, among whom must be mentioned, in particular, J. Muller, whose classical work on the glands, || published in 1830, placed him at once in the foremost rank among the anatomists of our own clay. Subsequently to that date, the improve- ments in the construction of the microscope and the consequent employment of greater magnifying powers, have added an extraor- dinary stimulus to anatomical and physiolo- gical studies, and directed a host of inquirers into an almost unexplored field, from which the harvests already reaped give the most fa- vourable earnest of future and rapid additions to the stores of knowledge. To the Germans is unequivocally due the merit of having far outstripped all other nations in the honourable * De continuationibus Membranarum. Roterod. 1769. t Medical Communications, vol. ii. London, 1790. t Nosographie Philosophique. Paris, 1798. & Traite des Membranes, 1800. Anatomic Gene- rale, 1801. || De Glandulanim seccrncntium structura peni- tiori. Lipsise, 1830. path thus opened, and in no collateral path of inquiry which has been pursued to the same extent, has so much new, interesting, and im- portant information of an accurate and satis- factory character, been obtained, as in that which it has been my duty to treat of in the present article. The names of Purkinje, Va- lentin, Henle, and Schwann deserve primary honour in this place, and to these may be added those of Ehrenberg, Treviranus, R. Wagner, Boehm, Wasmann, Gruby, and Gerber. Among the French anatomists, MM. Turpin, Mandl, and Donne have contributed much, and our own countrymen have not been be- hind. Dr. Sharpey, Dr. Sprott Boyd, Dr. Todd, Mr. Nasmyth, Dr. Barry, and Mr. Toynbee, are all distinguished in this field of research.* In the present article I have endeavoured to combine with all the authentic information I could obtain from these sources, the results to which I have been brought by a two-years' study of the anatomical characters of the whole mucous system. So rapid, however, are the daily advances of knowledge, that it is possible much has been omitted which is already in some shape before the public, and, on the other hand, that a few years may greatly modify the general views that are here set forth. As the anatomical details, however, have been all sub- stantiated by my own observations, except where otherwise stated, I am enabled to speak with more confidence of their correctness. Bibliography.— (See also the list of works appended to the articles GLAND and SkIV) — Mar- eellus Malpighius, De viscerum structura. Op. omnia, Lond. 1687. Peyer, De gland, intest. Amstel. 1681. J. C, Brimner, De glandulis duodeni, Fran- cofurt. 1715. Lieberkuhn, De fabrica et act. vill. intest. hom. Lugd. Bat. 1744, 4to. Holler, Ele- menta Physiol, lib. xi. Bonn, Specimen Anato- mico-Medicum, &c. extat in Sandifort. Thesauro, vol. ii. Roterodami, 1769, xii. p. 265. Carmichuel Smith, In transactions of a Soc. for promoting Med. Knowl. vol. ii. Lond. 1790. Soemmering, Bane des Menschlichen kbrpers. Frankfurt a M. 1791. R. A. Hedwiy, Disquis. Ampull. Lieber- kiihnii physico-miciosc. Lipsi*, 1797, 4to. Pinel, Nosographie philosophique, Paris, 1798. X. Bi- chat, Traite des Membranes, Paris, 1800; Ana- tomie generale, 1801. K. A. Rudolphi, Piogr.de humani corporis partibus simil. 4to. Grypli. 1809. J. F. Meckel, Handbuch der Menschlichen Ana- tomic, Bd. 1. Halle, 1815. C. Mayer, iiber His- tologic u. eine neue Eintheilung der Gewebe des Menschlichen Kbrpers, 8vo. Bonn, 1818. H. Buerger, Examen Microsc. vill. inlest. Halae, 1819. F. A. "B'eclwri, Elemens d'anatomie generale, 8vo. Paris, 1825. Billard, De la membrane muqueuse gastro-intestinale, &c. 8vo. Paris, 1825. Cra'ujie, Elements of general and pathological anatomy, Edinb. 1828. Due/linger, De vasis sanguiferis qua; villis intestinorum, &c. insunt, Monacliii, 1828. E. H. Weber, Hildebrandt's Anatomie, 1830. J. Mailer, De glandul. secernentium structura peni- tiori, Lipsiae, 1830; and, in English, Mr. Sully's abridged translation. G. Breschet, Ann. des Sciences Nat. 1834. Parkin je & Valentin, Commentatio phy- siolonica de phenom. motus vibratorii continui, &c. 4"to. Wratislav. 1835. Isis, 1838, No. 7. Buehm, * To these must now be added Mr. Goodsir, who, in a paper (of which an abstract has been just pub- lished) read at the Royal Society of Edinburgh on the 30th March, supports the view of secretion here given, with several new proofs. See Lond." and Edin. Monthly Journal of Med. Science, May, 1842. 506 MUSCLE. De Gland, intcst. struct, penitiori, Berol. 1835. Gurlt, Miiller's Archiv. 1835, page 399,-1836, page 263. Sprott Boyd, Inaugural Essay on the structure of the mucous membrane of the stomach, Edinb. 1836. Krause, Muller's Archiv. 1837, p. 8. Henle, Symbol* ad anatomiam villorum intest. imprimis eorum epithelii el vasorum lacteorum, Berol. 1837. Hufeland's Journal, 1838. Muller's Archiv. 1838, p. 103. Ibid. 1839. Heft iii. p. xxxi.— Heft iv. p. xlv. Valentin, Repertor. 1838, p. 310. Was- mann, De digestione nonnulla. Dissert. Inatig. Berol. 1839, and Froriep's Notizen, April, 1839. Muller's Physiology by Baly, London, 1837-41, vol. i. 2d edit. 1839, p. 477-503, et seq. Schwann, Froriep's Notiz. Feb. 1838 : Mikrosk. Unter- suchung. Berol. 1839. R. B. Todd, Lectures on the mucous membrane of the stomach and intes- tinal canal, Med. Gaz. 1839 and 1842. Gerber, General anatomy by Gulliver, Lond. 1841. A. Na- smyth, Three memoirs on the teeth and epithelium, Lond. 1841. Toynbee, On non-vascular animal tissues, Phil. Trans. 1841, part ii. Martin Barry, On the corpuscles of the blood, Phil. Trans, part ii. 1840, parts i. & ii. 1841. Mandl, Anatomie microscopique, Paris, 1839-41. Gruby, Observ. microscopical, Vienna;, 1841. ( W. Bowman.) MUSCLE.— (Syn. MDc, Musculus, Mus- cular or Sarcous tissue ; vu/go, Flesh, Meat.) This term is applied to certain fibrinous con- tractile organs, either elongated and fixed at their two extremities, or hollow and enclosing a cavity, which in all the higher animals are the seat of the power by which locomotion, circulation, the prehension and passage of food, the expulsion of many of the excretions and of the young, as well as other diversified functions, are performed. It is also used to denote the peculiar contractile material or tissue, constituting the principal and essential portion of such organs. This tissue is always arranged in the form of fibres, which in many minute animals occur singly, each serving the purpose of a perfect muscle. But they are usually aggregated in very great numbers, sur- rounded with a network of capillary vessels, and connected to one another by areolar tissue. The nervous tissue is universally associated with the muscular, however small may be the quan- tity of the latter; it is through this that the stimulus to contract is ordinarily transmitted, and, when the mass is great, made to affect simultaneously many contiguous fibres. A muscle is the organ resulting from the* union of these several parts. Muscles are styled voluntary or involuntary, according as they are, or are not, subject to the influence of volition, and they have been usu- ally so classified. But, however convenient these terms may be in the ordinary language of physiology, they cannot be applied, in a strict sense, to the purposes of classification without obvious objections. Many muscles, especially those under the immediate domi- nance of reflex nervous action, (as the respi- ratory and sphincter muscles,) partake of both characters, since volition can interfere only temporarily with their contraction ; and all muscles, even the most confessedly voluntary, are subject to emotional and instinctive influ- ences, in which the will has no share. The attempt to introduce an intermediate or mixed class, which has been generally sanctioned, while it is an acknowledgment of the imper- fection of the arrangement, does not appear to be sufficiently warranted either on anatomical or physiological grounds. If subjection or non-subjection to the influence of the will be made the basis of classification, all muscles should be accounted voluntary on which this can exercise a direct influence either in causing or controlling contraction, even though such influence be but momentary, and capable of being exerted only while the stimulus excitive of involuntary action is in abeyance. The voluntary muscles are generally solid organs, while the involuntary are hollow; and, on recurring to the minute structure of their respective elementary fibres, we detect very striking differences between them, those of the former being striped crosswise with very deli- cate and close parallel lines, which, with some exceptions, are altogether absent from the lat- ter. But these exceptions are of so important a kind as to demonstrate beyond doubt that there is no necessary connexion between the minute conformation of the fibres and their re- lation to the influence of the will. The mus- cular coat of the oesophagus often displays the striped structure as far down as the stomach, though the will has no power whatever over its movements ; and the heart itself is composed of striped fibres. As the structural differences between these two kinds of fibre are constant, well-marked, and therefore easily ascertained, and as they seem, moreover, to be related to varieties in the activity and mode of exercise of their contractile power, they will be employed as the ground of division in the present ar- ticle. I shall first describe the minute anatomy of these two kinds of elementary fibre, and the steps of their development; and, secondly, I shall advert to their mode of aggregation and to the arrangement of the tissues found in con- nection with them. a. Of the striped elementary fibres. — These have received the name of Primitive Fasciculi on the erroneous supposition of their being bundles of finer filaments. They may be sepa- rated from the tissues associated with them in the compound organ by a variety of means, but as they always constitute the principal mass of the organ, they may be examined without any attempt at such separation. It was a favourite plan with the older anatomists to obtain the fibres apart by submitting them to a long boiling, which destroys the texture of the vessels and filamentary tissue, but at the same time considerably modifies the size, shape, and structure of the fibres. It is in general only requisite to take a small portion of a muscle, as fresh as possible, (but after its contractility has departed,) and to tear it, under water, into fine shreds, with needles. By these means the elementary fibres will be separated from one another, and being in parts irregularly broken, and torn, can be submitted to inspection under a high power of the microscope, in such a condi- tion as to exhibit most of the important points in their structure. Many sedulous examinations of specimens from various sources are requisite for the acquirement of a correct idea of their MUSCLE. 507 organization and properties, but that this simple method of procedure is the one most likely to lead to a true insight and conclusion regarding the anatomy, not only of this but of all elemen- tary structures, becomes every day more evi- dent. Various subsidiary means may doubtless be employed with advantage, such as injections and physical and chemical agencies ; but the method which of all others is the least liable to admit of erroneous interpretations by the ad- mixture of artificial elements in which the mind of the inquirer has had a share, is that of em- ploying a power capable of reaching the utmost limits of organization, on examples the most nearly approaching to their natural state during life. There is perhaps no one line of inquiry in the whole range of minute anatomy so beset with difficulties and sources of error, and therefore so much demanding a cautious study and sagacious discrimination between conflict- ing appearances, as this of the structure of the striped fibre. The following description is substantially the same as that published by me in the Philosophical Transactions, 1840, and which all my subsequent observations have tended to confirm. To that paper I would venture to refer those who may desire to enter at greater length upon the grounds of the view here summarily given. 1. Length. — This varies exceedingly in dif- ferent muscles. The sartorius, the longest in the body, often surpasses two feet in length, and the individual fibres are as long, extending in parallel bundles from end to end. In many others they do not exceed a quarter of an inch ; thus their greatest variety is presented in their length. 2. Thickness. — This should be examined in the uncontracted state of the fibre, which for this purpose should be removed from the body after all contractility has departed. I have elsewhere* given a table of numerous compa- rative measurements in various animals, and subjoin the following abstract : — Diameter of the elementary Jibres of striped muscle infractions of an English inch. From to Human s\3 average of males ^ „ females ^ Other Mammalia nos "rk> average SJT Birds fj'og 355? 857 Reptiles i » ,k Flsh 733 „ & Insects ^3 5J5, „ I believe that the average diameter of the fibres in the human female is upwards of a fourth less than in the male, and that the ave- rage of both together is greater than that of other Mammalia; but a more extensive exami- nation is requisite to establish this. Fish have fibres nearly four times thicker than those of Birds, which have the smallest of all animals. Next to Fish come Insects, then Reptiles, then Mammalia. In each of these different classes, however, an extensive range of bulk is observ- able, not only in the different genera, but in the same animal and the same muscle, some fibres being occasionally three, four, or more times * Philosophical Transactions, 1840, p. 460. the width of others. In general the fibres of the heart are smaller than those of other striped muscles. The varieties in the average bulk in different classes have a close connection with differences of nutrition and of their irritability, which will be reverted to. 3. Figure. — This is subject to some variety, depending on their number and manner of package. Sometimes, as in some parts of In- sects, they are flattened ; but when they are isolated, or loosely aggregated, they are more or less cylindrical. In all the cases, however, where many fibres are arranged side by side, as in the Vertebrata, the larger Insects, and Crustacea, they are irregularly polygonal, the contiguous sides being flattened, evidently from the effect of package. Yet some interspaces are always left for the passage of bloodvessels, nerves, and areolar tissue among and be- tween them. Their form may be most readily displayed by a transverse section of a muscle that has been dried en masse, as long ago shown by Leeuwenhoeck (fig. 286). 4. Colour. — The colour of muscle depends partly on the colour of its elementary fibres, partly on the blood contained in its vessels, and there is strong reason to believe that the colouring matter of both is the same, or nearly so. That the fibres have always a colour of their own is at once evident on inspection under the microscope. It is generally more or less of a reddish-brown, but varies much in different animals and in different muscles, and even in the same muscle according to its state of development and activity. In Reptiles and Fish generally, and in Crustacea, the flesh is white, sometimes pinkish, but in some fishes, as the Gurnard, the gill-muscles are red. These varieties of colour are attended with none of struc- ture. In Birds the colour varies much, being often white and deep red in the same animal, but generally the pectoral muscles are very dark. Fig. 286. Transverse sections of striped muscle that had been injected and dried, magnified 70 diameters. A, from the Frog. B, from the Dog. a, a, section of elementary fibres, shewing their angular form and various size. b, b, sections of the injected capillaries, shewing the position they occupy among the fibres. These figures shew th greater vascularity of the muscle with the narrower elementary fibres. 503 MUSCLE. The most deeply coloured muscle I have seen was the great pectoral muscle of the Teal ( Qucrquedula crecca ), killed after migration. In Mammalia the colour is ordinarily red, being deeper in the Carnivora than in the vege- table feeders. Among the dompstic animals many varieties exist, which need not be spe- cially enumerated. A considerable part of the colouring matter is extracted by repeated wash- ing of a muscle, which then becomes pale, but not quite colourless ; some part of the loss of colour here sustained is doubtless owing to the solution of the haematosine of the blood con- tained in it. A muscle, if hypertrophied, grows redder, and vice versa ; and probably the practice of bleeding calves some days before they are killed, makes their flesh more pale and tender, by causing the absorption of a portion of the proper colouring matter of the fibres, as well as by abstracting the blood circulating among them. 5. Internal structure. — Though the elemen- tary fibres of all animals are visible to the naked eye, and in some animals, as the Skate (Kaia Batus), are often as thick as a small pin, nothing of their internal organization can be distinguished without the aid of a powerful lens. There is indeed, in certain lights, a splendid pearly iridescence, resulting from the arrangement of their structure, and quite characteristic among the soft tissues ; but this is not explained till a high power of the micro- scope is brought to bear upon the fibres. They are then seen, when viewed on the side, to be marked by innumerable alternate light and dark lines, whose delicacy and regularity nothing can surpass, and which take a parallel direction across them ; and if the focus be altered so as to penetrate the fibre, they are found to be pre- sent within it just as on its surface, thus differ- ing from those on the tracheae of insects, which exist only at the surface. At the extreme border of the fibre the light lines are sometimes seen to project a trifling degree more than the dark ones, thus giving a slight scallop, or regular indentation, to the edge. If often happens, in tearing the fibres roughly with needles before examination, that they crack across, or give way entirely, along one or several of these dark lines, the line of fracture or cleavage running more or less completely through the fibre in a plane at right angles with its axis; and occasionally two or more "of such complete cleavages will occur close together, the result of which is the separa- tion of so many plates or discs (jig. 287, B), of which the light lines at the surface are the edges, and the corresponding light lines seen within are what may be termed the focal sections. Thus it is evident that there is a tendency in the muss of the fibre to separate, when torn or^ pulled after death, along the transverse planes, of which the dark transverse stripes are the edges. When such a separation takes place, a series of discs result, but to say that the fibre is a mere pile of discs is incorrect, for the discs are only formed by its disintegration. Neverthe- less they are marked out, and their number and form are imprinted, in the very structure of the fibre, in its perfect state. (Figs. 287 and 288.) Fig. 287. A Fragments of striped elementary fibres, shewing a cleavage in op]>osite directions, magnified 300 diam. A, longitudinal cleavage. At a the longitudinal and transverse lines are both seen. Some longitudinal lines are darker and wider than the rest, and are not continuous from end to end. b, primitive nbrillae, separated from one another by violence at the broken end of the fibre, and marked by transverse lines equal in width to those at a. c represents two appearances commonly presented by the separated single fibrillar. On the upper one the borders and transverse lines are all perfectly rectilinear, and the included spaces perfectly rect- angular. In the lower the borders are scalloped, the spaces bead-like. When most distinct and de- finite, the fibrilla presents the former of these ap- pearances. B, transverse cleavage. The longitudinal lines are scarcely visible. a, incomplete fracture following the opposite surfaces of a disc, which stretches across the inter- val and retains the two fragments in connexion. The edge and surface of this disc are seen to he minutely granular, the granules corresponding in size to the thickness of the disc and to the distance between the faint longitudinal lines. b, another disc nearly detached. But again, it always happens that longitu- dinal lines, more or less continuous and pa- rallel, according to the integrity of the fibre and the strength and distinctness of the trans- verse lines, are also to be discerned ; and like the transverse ones, not on the surface only, but throughout the whole of its interior. And it is found that there is a remarkable proneness in the fibre to split in the direction indicated by these lines also; by which splitting it is resolved into a great number of fibrilla. These fibrilla;, like the discs, do not exist as such in the fibre, and to obtain them its structure must be neces- sarily broken up to a certain extent, for the union which naturally subsists between these parts must be destroyed. It is therefore most correct to say that there is an indication in the entire state of the fibre of a longitudinal ar- rangement of its parts, occasioning a cleavage in that direction on the application of violence. (Fig. 287.) " Sometimes the fibre will split into discs only, more often into fibrilla; only, but there are always present in it the transverse and the longitudinal lines which mark the two cleav- ages. It is the most common to find a crack or fracture taking both directions irregularly, running partly in the transverse dark lines, MUSCLE. 509 partly in the longitudinal dark lines, some- times being crosswise on the exterior, more or less lengthwise within. These cracks are often short, even, well defined ; at other times the parts near them are much stretched, or quite disorganized, — differences depending on the brittleness or toughness of the particular fibre, which qualities vary very much in different specimens, according to the state of nutrition, period of examination, and other circumstances. Hence it is clear that the discs and fibrilla consist of the same parts, and merely result from the different direction in which the mass breaks up. To detach a fibrilla entire is to remove a particle from every disc, and to take away a disc is to abstract a particle of every fibrilla. Thus, every disc consists of a particle of every fibrilla, and every fibrilla of a particle of every disc. Therefore every fibrilla of the same fibre has the same number of particles, and every disc in like manner is composed of the same number of particles. If,now, isolated discs and fibrilke be examined under a high magnifying power, they will be found to bear out, in the fullest manner, the description that has been given. The discs are marked on the edge by the fragments of the longitudinal lines, and if regarded On their flat surface, present a finely granular appearance, the granules being equal in diameter with the fibrilla- (fig. 288). In fact, the dark lines be- Fig. 288. Surface of a disc separated from an ele- "5tt«^ mentary Jibre of a Lizard which had J^^&hi lain long in spirit. It displays the §\ -< . \ Jl!" ly tjinnitlur structure spohcu of in ihr ir.ri . Tin- (/ninnies are intended