PRESENTED TO THE UNIVERSITY OF TORON: BY Digitized by the Internet Archive — o. in 2007 with funding from - Microsoft Corporation : “HISTOLOGY i - . 1 =~ 4 le he ny a | } LONDON ! PRINTED BY “BPOTTISWOODE AND CO., NEW-STREET SQUARE AND PARLIAMENT STREET ; F $; LSS. ax. ee eee oP , ang * ISTOLO sift Y DESCRIPTIVE AND PRACTICAL . FOR: THE USE OF STUDENTS S hav Pe = Sel at oy, Gi y) Edward # Noort (B. A. SCHAFER, F.RS. ) JODRELL PROFESSOR OF PHYSIOLOGY IN UNIVERSITY COLLEGE, LONDON EDITOR OF THE HISTOLOGICAL PORTION OF QUAIN’S ‘ANATOMY’ cee 72 ‘- <5 f7 LON DON | EONGMANS GREEN, AND CO. 1885. ty . - ” rs = f ‘ rs 5 3 q < at etl Phe * . ~ ; A _ ‘ ~ at and . Barrie) » e 1 ‘ ? Brien ty)! | 5 iis Bate ; ‘ a is p wee std Hiv. 5 Fi: os + Ps - 7) A 5 i ° " y ROR. Son Velen, » pew exe VER Eg Fe po A aK, . ) aes a a ef tnyictest inta forte iwo acuity ye fm arr st No. POMP ae hia tonya @ A ie i Ai, - : Hie ehieb, the piiparation: 20-10n34 bohetieihd bode 28 peat ts basal ty (A Madont= - A teal PREFACE. — 7. f st » + ' ) fe ‘ rms ¥ few . ; —* -* Nes “ an. A: j Pare ARAB, Biet) Rs PAGE -BLOOD-VESSELS, LYMPHATIC kmaeiniins SEROUS MEMBRANES, . . 92 ATIC GLANDS, TONSIL, tHyMUS - a coe te ee Ma tag a LESSON XXIII. e ‘THE SKIN . i > >. > - © ° . . - re z . 105 = LESSON XXIV. | 5 STRUCTURE Q.meweatee-c + fe ee FSM. ee a _ LESSON XXV. POMR TRAKHEA AND LUNGS -' » - «6 eel eC aa me, - LESSON XXVI. ‘ STRUCTURE OF THE TEETH, THE TONGUE, AND MUCOUS MEMBRANE oF & q MEME ew oes ce OTe we ee 18 | ents. LESSON XXVII. | =z SeeWE SALIVERY, GEANDS fs. eel ek Oe a T LESSON XXVIII. (THE STRUCTURE OF THE STOMACH . - » 3. «© «©... Mt LESSONS XXIX. anp XXX. nie STRUCTURE OF SMALL AND LARGE INTESTINE - . - 2. . 146 LESSON XXXI. MME EIVER-ANDTEANOROAS. . - . B® . ws cosa = .°* > I6g0N XXxr. ‘THE SPLEEN, SUPRARENAL CAPSULE, AND THYROID BODY : as . LESSON XXXIV. eta \ —_— ‘ * STRUCTURE OF THE URETER, BLADDER, AND MALE GENERATIVE ORG. LESSON XXXV. 3 GENERATIVE ORGANS OF THE FEMALE, AND MAMMARY GLANDS se 5 : - i LESSON XXXVI. ie STRUCTURE OF THE SPINAL CORD. 2 : . ae LESSON XXXVIL. ‘ THE MEDULLA OBLONGATA, PONS VAROLII, AND MESENCEPHALON . » 192 LESSON XXXVIII. STRUCTURE OF THE CEREBELLUM AND CEREBRUM . ° . + « 201 LESSONS XXXIX. anp XL. - STRUCTURE OF THE EYELIDS AND OF THE PARTS OF THE EYEBALL . . LS LESSON XLI. > STRUCTURE OF THE OLFACTORY MUCOUS MEMBRANE AND OF THE EXTERNAL | AND MIDDER RAR, . 6.9% ks . LESSON XLII. STRUCTURE OF THE LABYRINTH ree ee ee ; 7 = ; APPENDIX . . . . . . ° + © Eee . * PAC) ‘ 6 Beis Bit y J = ’ § 3 - By: j Pyris -_ = ; & ; ' ~ bil . oe . a@ : : 4 r gn by let 4 F _ i Ay mre : int r 4 ee ete eee ee ee ee ; i ie “THE ESSENTIALS OF HISTOLOGY. INTRODUCTORY. ENUMERATION OF THE TISSUES AND THE GENERAL STRUCTURE OF ANIMAL CELLS. Animal Histology ! is the science which treats of the minute struc- * ture of the tissues and organs of the animal body; it is studied with the aid of the microscope, and is therefore also termed Microscopical Anatomy. Every part or organ of the body, when separated into minute frag- ments, or when examined in thin slices (sections), is found to consist of certain textures or tissues, which differ in their arrangement in different organs, but each of which exhibits characteristic structural features. The following is a list of the principal tissues which compose the body :— 1. Epithelial. . Areolar Fibrous. Elastic 2. Connective + Adipose Lymphoid Cartilage | Bone , Voluntary 8. Muscular + Involuntary or plain Cardiac. f 4. Nervous. _ Some organs are formed of several of the above tissues, others contain only one or two. Tt is convenient to include such fluids as the blood and lymph amongst the tissues, because they are studied in the same manner and contain cellular elements similar to those met with in some of the other tissues. The elements which compose the tissues are of the nature either 1 From fords, a web or texture. B g- THE ESSENTIALS OF HISTOLOGY of fibres or cells. Some tissues are composed almost entirely of fibres with relatively few cells interspersed amongst the fibres; this is the - case with most of the connective tissues. Others are composed entirely of cells, which, however, may in some cases be prolonged so as to form fibres; but these are different, from the fibres of the connective tissues in being formed directly from the cells of the tissue, whereas the fibres of the connective tissues are formed between the cells in an intercellular substance. Tissues which are entirely composed of cells are the epithe- lial tissues, whilst nervous and muscular tissue are formed of cells which are partly or wholly extended so as to form fibres. Cells.—In the early embryo the whole body is an agglomeration * of cells. These are minute portions of living substance or protoplasm, — enclosing a vesicle which is known as the nucleus. The tissues are subsequently formed either by changes which occur in the intercellular — substance, or by changes in the cells themselves; frequently by both these processes combined. The cells which are least altered from their embryonic condition are the white corpuscles of the blood, and these may be regarded therefore as typical cells. The protoplasm of a cell (fig. 1, ») is composed of a soft albuminous substance, which is characterised in typical cells by possessing the property of spontaneous movement. When the cell is unenclosed by a membrane a change in the shape, or even in the position of the cell, may be thereby produced (amcboid movement). The protoplasm often contains granules of various kinds or droplets of watery fluid (vacuoles) ; the latter may be present in sufficient abundance to impart a reticular or sponge-like structure to the protoplasm. In some cells the protoplasm has a striated or fibrillar structure. The nucleus of the cell (fig. 1, 7) is a minute vesicle embedded in the protoplasm. It is bounded by a membrane which encloses a clear substance (nuclear matrix), and the whole of this substance is generally pervaded by an irregular network of fibres, some coarser, others finer (intranuclear network, n'). This intranuclear network often exhibits one or more enlargements, which are known as the nucleoli.. The fibres within the nucleus have been observed to undergo spontaneous changes of form and arrangement, but this Fig. 1—DIAGRAM OF A CELL. beeomes much more evident when the cell Fe ecleas mnuclene with iata. is about to divide. The division of the proto- Tuclear network, m,andnucleo- Hlasm is always preceded by that of the nucleus, and the intranuclear fibres undergo during its division a series of remarkable changes in arrangement and position, which are known collectively by the term karyomitosis (karyokinesis). These changes may best be studied in the division of epithelium-cells (see Lesson VI.), but exactly similar phenomena have been shown to occur in cells belonging to the other tissues. In INTRODUCTION 3 some cases it may be observed that the filaments of the intranuclear network are made up of fine juxtaposed particles, arranged either in a single or a double row. All the embryonic cells are formed from the division of the ovwm or egg-cell, which divides first into two cells, these again into two, and soon until a large number of cells (embryonic cells) are produced. Eventually these resultant cells arrange themselves in the form of a membrane (blastoderm) which is composed of three layers. These layers. are known respectively as the ectoderm or epiblast, the meso- derm or mesoblast, and the entoderm or hypoblast. The ectoderm gives rise to most of the epithelial tissues and the tissues of the nervous system; the entoderm to the epithelium of the alimentary canal (except the mouth), and the glands in connection with it; and the mesoderm to the connective and muscular tissues. The histogenetical relation between the three layers of the blasto- derm and the several tissues and organs of the body is exhibited in the following table :— (The epithelium of the skin or epidermis, and its appendages, viz., the hairs, nails, sebaceous and sweat glands. The epithelium of the mouth, and of the salivary and other glands which open into the mouth. The enamel of the teeth. The gustatory organs. Ectoderm | The epithelium of the nasal passages, and the cavities and glands gga ! which open into them. ' Epiblast The epithelium covering the front of the eye. The crystalline lens. The retina, The epithelium lining the membranous labyrinth of the ear. The epithelium lining the central canal of the spinal cord and the fourth, third, and lateral ventricles of the brain. The tissues of the nervous system. ‘The pituitary body. The pineal gland. (The connective tissues. The blood and lymph corpuscles. The epithelial lining of the heart, blood-vessels, lymphatics, and serous membranes. Mesoderm | The epithelium of the uriniferous tubules (in part). or . The epithelium of the generative organs, and the generative pro- Mesoblast ducts in both sexes. The muscular tissues, voluntary, involuntary and cardiac (except the muscular fibres of the sweat glands, which are epiblastic in origin). \The spleen and other lymphatic and vascular glands. (The epithelium of the alimentary canal (from the pharynx to the lower end of the rectum) and all the glands which open into it (including the liver and pancreas). The epithelium of the Eustachian tube and cavity of the tym- Entoderm panum. or + The epithelium of the larynx, trachea, and bronchi, and of all Hypoblast ross ramifications. The epithelium of the pulmonary veoli. : The epithelium of the thyroid body. Part of the thymus gland. The epithelium of the urinary bladder and ureters, and of part E of the uriniferous tubules. B2 THE ESSENTIALS OF HISTOLOGY LESSON I. USE OF THE MICROSCOPE. EXAMINATION OF COMMON OBJECTS. Tuer requisites for practical Histology are a good compound microscope mag- nifying from about 50 to 400 linear; slips of glass technically known as ‘slides,’ upon which the preparations are made; small pieces of thin glass used as covers for the preparations; a few simple instru- ments, such as a razor, a scalpel, scissors, fine-pointed forceps, and needles mounted in wooden handles; and a set of fluid re- | agents for mounting and staining micro- scopic preparations.' A sketch-book and j pencil are also requisite, and must be con- stantly employed. Examine the microscope (fig. 2). It | consists of a tube (¢ ¢’) having twosystems = of lenses, one at the upper end termed | the ‘ eye-piece’ or ‘ ocular ’ (0c), the other, at the lower end, termed the ‘ objective’ (obj). There should be at least two | objectives—a low power, working at about . 4 inch from the object, and a high power, | ad having a focal distance of about 4 inch. = — The focus is obtained by cautiously bring- SS = ing the tube and lenses down towards the object by the coarse adjustment, which is either a telescopic or a rack-and-pinion O movement (adj), and focussing exactly by adj” the fine adjustment, which is always a finely cut screw (adj’). ae The stage (st) upon which the prepa- rations are placed for examination, the mirror (m) which serves to reflect the light ft up through the central aperture in the stage and along the tube of the instrument, and the diaphragm (d) below the stage which serves to regulate the amount of light thus thrown up, are all parts the employment of which is readily under- stood. : It is convenient to begin the study of Fic. 2—D1acram or MICROSCOPE. histology by the examination of the blood, ' The directions for making the principal fluids used in histological work will s be found in the Appendix. ee : vP a: USE OF THE MICROSCOPE | 5 but before doing this the student should endeavour to familiarise himself with the use of the microscope, and at the same time learn to recognise some of the chief objects which are liable to occur accidentally in microscopic specimens. On this account it has been considered desirable to introduce + # AO ee LT: I ee sR LOT Fig. 3.—ORGANIC MATTERS FREQUENTLY PRESENT IN Dust. (Heitzmann.) __&, fibres of silk; C, of cotton ; Z, of linen; W, of wool; F, feather; S¢, starch-granules; C7, : cork; 0, spores of mildew; 4/, mycelium or threads of mildew; Mc, micrococci; B, bac- - teria; Z/, leptothrix filaments (500 diameters). A . _ directions for the examination of starch-granules, air-bubbles, linen, cotton, nd woollen fibres, and the usual constituents of the dust of a room, into the rst practical lesson, 6 THE ESSENTIALS OF HISTOLOGY 1. Examination of starch-granules. Gently scrape the cut surface of a potato with the point of a knife; shake the starch-granules so obtained into a drop of water upon a clean slide and apply a cover-glass. With the low power the starch-granules look like dark specks differing considerably in size; under the high power they are clear, flat, ovoid particles (fig. 3, St), with a sharp outline when exactly focussed. Notice the change in appearance of the outline as the microscope is focussed up or down. On close examination fine concentric lines are to be seen in the granules arranged around a minute spot which is generally placed eccentrically near the smaller end of the granule. Sketch two or three starch-granules. Notice the appearance of air-bubbles in the water. If comparatively large they are clear in the middle, with a broad dark border due to refraction of the light ; if small they may look entirely dark. 2. Examine fibres of linen and of cotton in water, using a high power. Compare the well-defined, relatively coarse, striated, and slightly twisted linen- with the longer, finer, and more twisted cotton-fibres. Sketch one of each kind. 3. Mount two or three hairs from the head in water and look at them, first with the low, then with the high power. Examine also some fibres from any woollen material and compare them with the hairs. They have the same structure, although the wool is finer and is curled; its structure may be partly obscured by the dye. Draw one or two woollen fibres. 4, Examine some dust of the room in water with a high power. In addition to numerous groups of black particles of carbon (soot) there will probably be seen fibres of linen, cotton, or wool, and shed epithelium-cells derived from the epidermis. 5. Prepare a scale to serve for measuring objects under the microscope. To do this put a stage-micrometer (which is a glass slide ruled in the centre, with the lines ,4, and ;3; millimeter apart) under the microscope in such a manner that the lines run from left to right (the microscope must not be inclined). Focus them exactly. Put a piece of white card on the table at the right of the microscope. Look through the instrument with the left eye, keeping the right eye open. The lines of the micrometer will appear projected upon the paper. Mark their apparent distance with pencil upon the card, and after- wards make a scale of lines in ink the same interval apart. A magnified repre- sentation is thus obtained of the micrometer scale. Mark upon it the number of the eye-piece and of the objective, and the length of the microscope tube. This scale-card will serve for the measurement of any object without the further use of the micrometer. To measure an object, place the scale-card upon the table to the right of the microscope and view the object with the left eye, keeping the right eye open. The object appears’ projected upon the scale, and its size in ; or ;1; of a millimeter can be read off. It is important that the same objective and eye-piece should be employed as were used in making the scale, and that the-microscope tube should be of the same length. LESSON II. STUDY OF THE HUMAN BLOOD-CORPUSCLES. 1. Havine cleaned a slide and cover-glass, prick the finger and mount a small drop of blood quickly, so that it has time neither to dry nor to coagulate. Examine it at once with the high power. Note (a) the coloured corpuscles, mostly in rouleaux and ¢lumps, but some lying apart seen flat or in profile; (b) the colourless corpuscles, easily made out if the cover-glass is touched by a needle, on account of their tendency to stick to the glass, whilst the coloured corpuscles are driven past by the cur- rents set up; (c) in the clear spaces, fibrin filaments and elementary particles or blood-tablets. Sketch a roll of coloured corpuscles and one or two colourless corpuscles. Count the number of colourless corpuscles in a field of the microscope. 2. To be made like 1, but the drop of blood is to be mixed upon the slide with an equal amount of 0°6 per cent. salt solution, so that the red corpuscles tend to be less massed together, and their peculiar shape is better displayed. Sketch a red corpuscle seen on the flat and another in profile (or optical section). Also a crenated corpuscle. ; Measure ten red corpuscles, and from the results ascertain the average diameter of a corpuscle. 3. Make a preparation of blood as in § 1 and put it on one side to coagu- late. After fifteen minutes allow a drop of a solution of borax-carmine! to run under the cover-glass. This decolorises the red corpuscles, but stains the nuclei of the white corpuscles and brings the network of fibrin filaments and the elementary. particles clearly into view (fig. 7). After a drop of gly- cerine has been allowed to diffuse into the fluid the cover-glass may be cemented with gold-size and the preparation labelled and kept. 4. Enumeration of the blood-corpuscles. This is readily effected by the hemacytometer of Gowers. This instrument consists of a glass slide (fig. 4, ¢), the centre of which is ruled into ;4, millimeter squares and surrounded by a glass ring + mm. thick. It is provided with measuring pipettes (A and B), a vessel (D) for mixing the blood with a saline solution (sulphate of soda of sp. gr. 1015), glass stirrer (E) and guarded needle (F). ‘The mode of proceeding is extremely simple. 995 cubic millimeters of the saline solution are placed in the mixing jar; 5 cubic millimeters of blood are then drawn from a puncture in the finger and blown into the solution. _ The two fluids are well mixed by the stirrer and a small drop of this dilution is placed in the centre of the cell, the cover-glass gently laid on (so as to touch the drop, which thus forms a layer } mm. thick between the slide and cover- glass) and pressed down by two brass springs. In a few minutes the cor- te have sunk to the bottom of the layer of fluid and rest on the squares. e number in ten squares is then counted, and this, multiplied by 10,000, gives the number in a cubic millimeter of blood.’ = 1 See Appendix. THE ESSENTIALS OF HISTOLOGY Fig. 5.—HuMAN BLOOD AS SEEN ON THE WARM Fic. 6.—HuUMAN RED CORPUS- staGE. (Magnified about 1,200 diameters.) ' CLES LYING SINGLY AND COL- 7, 7, single red corpuscles seen lying flat ; 7’, 7’, red cor- LECTED INTO ROLLS. (As seen puscles on their edge and viewed in profile ; 7/’, red under an ordinary high power ~ corpuscles arranged in rouleaux ; ¢,c, crenate red cor- of the microscope. ) : puscles; p, a finely granular pale corpuscle; g, a P coarsely granular pale corpuscel Both have two or J a three distinct vacuoles, and were \ndergoing changes of shapeat the moment of observation ; in g, a nucleus , ; 7 " also is visible, ? Poe = op are gene at Big SPA. eh ith Oh Wes ep lye aked eet inn. ; Ee 5 . 7 + fiah 46 7 . i “| - \ . yp Se ‘ w % ’ } ’ . “* 4 a, r f én ; x 1 Poh Sebel r > i- spre ’ . " - ; | ™ ty tt « f-4fe ie - v3 <7 rons t 5 2 ; ‘ 3 r 2 q ed oe f" . a" ‘ < sh poh ay Re : teh). See oa pe ‘ ey b « ‘i + i Lest? PM 5 ves ‘ Set os a 15% a . a s ¥ belie ls te Pi +a 7 STUDY OF THE HUMAN BLOOD-CORPUSCLES 9 The coloured blood-corpuscles.—Under the microscope the blood is seen to consist of a clear fluid (plasma), in which are suspended the blood- corpuscles (fig. 5). The latter are of two kinds: the red or colowred (7, r'), which are by far.the most numerous, and the white, pale, or colourless (p,g), which from their occurrence in the lymph are also known as lymph-corpuscles. When seen singly the coloured corpuscles are not distinctly red, but appear of a reddish-yellow tinge. In the blood of man and of all other mammals, except the Camelide, they are biconcave circular disks. Their central part usually has a slightly shaded aspect, under the-ordinary high power (fig. 6, 1), but this is due to their biconcave shape, not to the presence of a nucleus. They have a strong tendency to become aggregated into rouleaux and clumps when the blood is at rest, but if it is disturbed they readily become separated. If the density of the plasma is increased in any way, as by evapo- ration, many of the red corpuscles become shrunken or crenated (c). The average diameter of the human red corpuscles is 0°077 milli- meter (about 5/5, inch).! There are from four to five millions of coloured corpuscles in a cubic millimeter of blood. The colourless corpuscles of human blood are a little larger than the coloured, measuring 0°01 mm. (s,;)55 inch) in diameter. They are far fewer, numbering not more than ten thousand in a cubic millimeter. Moreover they are specifically lighter, and tend to come to the surface of the prepara- tion. If examined soon after the | blood is drawn, they are usually spheroidal in shape, but they soon become irregular (fig. 5, p, g), and their outline continually alters, owing to the ameba-like changes of form to which they are subject. Some of the colourless corpuscles are very pale and finely granular, !!* GS ee lg a ee: others contain coarser and more A, network of fibrin, shown ee washing away distinct granules in their proto- the corpuscles from B preparation of Blood tliat plasm. The protoplasm may also radiate from smail clumps of blood-tablete, contain clear spaces or vacuoles, ("0% 0uer, Moot-corpuscls, and elemen- and a reticular structure is described Y°™ in it by some histologists. ach pale corpuscle has one. or more nuclei, which are difficult to see without the aid of reagents. - In the clear fluid in which the corpuscles are suspended, a network of fine straight intercrossing filaments (fibrin) soon makes its ap- pearance (fig. 7). There are also to be seen a certain number of 1 The following list gives the diameter in parts of a millimeter of the red blood- _ corpuscles of some of the common domestic animals :—Dog, 0:0073 ; rabbit, 0-0069 ; eat, 0:0065 ; sheep, 0:0050; goat, 0-0041. A - | | { 10 THE ESSENTIALS OF HISTOLOGY minute round colourless discoid particles, either separate or collected into groups or masses, which may be of considerable size. These are the elementary particles or blood-tablets. Their meaning is not known. Fatty particles may also occur in the plasma. Development of blood-corpuscles.—In the embryo, the first- formed coloured blood-corpuscles are amceboid nucleated cells, the protoplasm Fic. 8.—DEVELOPMENT OF BLOOD-VESSELS AND BLOOD-CORPUSCLES IN THE VASCULAR AREA OF THE GUINEA-PIG, v1, b!ood-corpuscles becoming free in the interior of a nucleated protoplasmic mass. of which contains hemoglobin. These embryonic blood-corpuscles are developed within cells of the mesoderm, which unite with one another so as to form a protoplasmic network (fig. 8). The nuclei then multiply, and around some of them there occurs an aggregation of coloured protoplasm. Next the branched cells become hollowed Fic. 9.— BLoop-coRPUSCLES DEVELOPING WITHIN CONNECTIVE-TISSUE CELLS. h, a cell containing diffused hemoglobin; h’, globular masses of coloured substance in the protoplasm, within which also are \numerous vacuoles; A’, a cell filled with coloured globules, \ out by an accumulation of fiuid in their protoplasm so as to form a network of blood-vessels, and then the coloured nucleated portion of protoplasm are set free within them as the seagate blood- corpuscles (fig. 8, Bop t 5 + — 4 ; _ » Wie pede shir Sebi); wees) ole rena yay: ee yiat ae 6G 6 Lithew ite & eet Pern. Pianeta aria 4a Burge Piuhaon | Mig NY) Ge se". > rr. ay fa : at: : Beet: gigi): Cae LAC AS fais ie ' “ a F : ! ‘ . , : A “ , 1 t Zz '] 7 hb . ‘ a mile ~ Seipedt! |. , 3 7 * 7 ; , : . : ‘e Age Sy at © 1 ¢: f BB Aiken, yp at wt tive? Hie 3 ata Ss : ged aa/iit A7): ph. iu . yee Aas idence i , Pela icrit (orto ef : ; : : Awan true Gola, vs . * one a AiG tn te hell suers s Larter they bhostus formed: 32 Ya PRUE tue Tate! niwyeed ad milan) iDaye, pa! v0 a by grcke ae ou. Bhi Shiu Sidvert, ely Rey ett mw ~, } Fic. 15.—SIMpPLE WARMING APPARATUS, COMPLETE, SHOWN IN OPERATION. of the microscope. The preparation, which should be made upon a rather thin slip of glass, is put on to the warm stage and pressed into contact with it by the brass clips. Heat is applied to the copper tongue by a small spirit- lamp flame, and a greater or less amount is conducted to the warm stage and the superjacent preparation according to the point to. which the flame is’ ~ Peed Beis Wek tag TP . 2 a : a AA POT EOE ae a ? f bi - AY: A 4 * 1 . ¥. a * ~ he \ & "eal | - = . i = \ - b> a2 3 . , 7 = G 7 - > = Fi k es ‘ = = ay = ™ ' 4 io \ = J - = " . > ‘ 1 . ¥ ’ 2 7 r ss - 1? * . s ™ - . 7 cee en re A Se: TA or" Ath ste THe: a. a ve —- oT = aan. all AMCBOID PHENOMENA OF COLOURLESS CORPUSCLES 17 applied. To ascertain that the right temperature is got and maintained, put two pieces of paraffin, one melting at 35° C. (95° F.) and another at 88° C. (100° F.), on the slide, one on either side of the preparation. The tempera- ture must be such that the first piece is melted and remains so whilst the second remains solid.' 2. Mount a drop of newt’s blood diluted with an equal amount of salt solution, and examine it in the same manner upon the copper stage; the temperature must, however, be kept below 80° C. Observe the effect of heat in. accelerating the amceboid movements of the pale corpuscles. Sketch one at intervals of a minute (a) in the cold, (6) whilst warmed. 3. Examine some yeast which has been mixed with salt solution. Observe the yeast-cells or torule, some of them budding. Sketch two or three. Now mix a little of the yeast and salt solution with a fresh drop of newt’s blood, oiling the edge of the cover-glass as before. Endeavour to observe the inception of torule by the white corpuscles. Sketch one or two corpuscles containing torule. ; Milk-globules or particles of carbon or of vermilion may also be used for this experiment, but the process of inception is most readily observed with the yeast particles. 4. At the commencement of the lesson collect a drop of newt’s blood into a fine capillary tube, seal the ends of the tube, and mount it in a drop of oil of cloves. Towards the end of the lesson examine it again to see white cor- puscles emigrating from the shrunken clot (see fig. 16). Fic. 16—WHITE CORPUSCLES OF FROGS BLOOD MIGRATED FROM SHRUNKEN : CLOT WITHIN A CAPILLARY TUBE. 1 For exact work, an apparatus somewhat more complex than the above is re- ‘quired. For description of such a onesee A Course of Practical Histology, pp. 22, 23, Cc 18 THE ESSENTIALS OF HISTOLOGY The ameboid phenomena which are exhibited by the protoplasm of the colourless blood-corpuscles consist, in the first place, of spontaneous changes of form, which when active may also produce changes in place or actual locomotion (migration) of the corpuscle ; and, secondly, of a tendency which it presents. to enwrap and take into its substance foreign particles with which it may come in contact, and particles thus incepted may then be conveyed by the corpuscle in its locomotory changes from one place to another. It is probable that particles of organic matter which are taken up by the pale corpuscles may undergo some slow process of intracellular digestion within their protoplasm. The processes of the granular corpuscles are generally quite clear at first, and.the granules afterwards flow into them. The migration of the colourless corpuscles from the blood-vessels into the surrounding tissue, or from a blood-clot into the surrounding serum (fig. 16), is owing to these amceboid properties. The conditions which are most favourable to this ameceboid activity of the white corpuscles are (1) the ee slightly alkaline medium, such as plasma, serum, or lymph, or, failing these, ‘normal saline solution ; (2) the prevention of didecooation: Any increase of density of the medium produces a diminution of amceboid activity, whilst, on the other hand, a slight decrease in its density has the opposite effect ; (3) a certain temperature. In warm-blooded animals the phenomena cease below about 10°C. When gradually warmed they become more and more active up to a certain point, the maximum being a few degrees above the natural temperature of the blood. Above this point they become spheroidal and their protoplasm is coagulated and killed. Acids at once kill the corpuscles and stop the movements. Narcotic gases and vapours, such as carbonic acid gas or chloroform vapour, also arrest the movement, but it reeommences after a time if their action is discontinued. ) \ 4 1 t > Ly ai si = . e p UE ehh): \ Fs. Wee eeeigas «opie hat ‘7 RIV TA ie eo ‘ oe oa Pi ics; bing 5 : * Ret ae: mt el tic: a . FREES > Spey aw, 26 WETS ma “ B ‘ + | 5 hire ath ajget, jane bh ) cummed Vi. £4 fotithe Je ie Pe ha yen : sh a) + F » 5 ‘ : . : ’ the - = ee Ret Le ScpApaece F wo. awe Melettie uate oi 1 hodh Tee thie ate ti 19 LESSON VI. EPITHELIUM. \ 1. Mount a drop of saliva and examine first with a low, afterwards with the high power. Observe the nucleated epithelium-cells, some single, and others still adhering together by overlapping edges. Measure three or four, and also their nuclei. Sketch one or two on the flat and one edgeways. Notice the salivary corpuscles, which are like white blood-corpuscles swollen out by imbibition of water. OR aa eT ay Ve oe ey 2. Put a small shred of human epidermis into a drop of strong caustic potash solution for one or two minutes. Then break it up in water with needles, cover and examine. Observe the now isolated swollen cells. Measure some. ed ; 3. Study the arrangement of the cells in a section through some stratified epithelium, such as that of the mouth, skin, or cornea. The section may be prepared beforehand by the demonstrator; it should be mounted in Canada balsam.' Notice the changes in shape of the cells as they are traced towards the free surface. Measure the thickness of the epithelium. Count the number of layers of cells. y 4, Study the minute structure of epithelium-cells and their nuclei, both at rest and dividing, in the tail of the salamander-tadpole.? This preparation may also advantageously be prepared beforehand by the demonstrator. (The preparation is made as follows: The tail is placed in chromic acid solution (0°1 per cent.) for three days, then thoroughly washed for some hours in water to remove the excess of the acid, then placed in dilute hematoxylin solution for twenty-four hours, or in 1 p. c. safranin solution for a similar time. After having been again rinsed in water it is rapidly dehydrated in absolute alcohol, then transferred to spirits of turpentine, and finally mounted in Canada balsam. | Sketch an epithelium-cell with resting nucleus, and others with nuclei in different phases of karyomitosis. _ An Epithelium is a tissue composed entirely of cells separated by a very small amount of intercellular substance (cement substance), and generally arranged so as to form a membrane covering either an ex- _ ternal or an internal free surface. , _ The structure of epithelium-cells, and the changes which they undergo in cell-division, are best seen in the epidermis of the tail of the salamander-tadpole, in which the cells and nuclei are much larger _ than in mammals. ! The methods of preparing sections are given in the Appendix. 2 If these tadpoles are not obtainable, the structure may be studied in the idermis of the newt, prepared as recommended in Lesson VII. § 1 for the study f columnar epithelium, and also in sections stained with hematoxylin. j c2 20 THE ESSENTIALS OF HISTOLOGY Structure of the cells.—Each cell consists of protoplasm containing a nucleus. The protoplasm may be either clear or granular, or it may have a reticulated appearance. In some kinds of epithelium it is striated. The nucleus is a round or oval vesicle lying in the proto- plasm. Usually there is only one, but there may be two or more in a cell. In the resting condition (7.e. when not undergoing division) the nucleus is composed of a membrane enclosing a clear substance, which - is traversed by a network of filaments (fig. 17, a). There may be one Fic. 17.—EpirHELIUM-CELLS OF SALAMANDER LARVA IN DIFFERENT PHASES OF DIVISION. or more globular enlargements (nucleoli) on this network. The nucleus is stained more easily by dyes than the protoplasm; this staining affects chiefly the nucleoli, nuclear filaments, and membrane. Division of the cells.—The division of a cell is preceded by the division of its nucleus. This, in dividing, passes through a series of remarkable changes (fig. 17), which may thus be briefly summarised :— 1. The network of filaments of the resting nucleus becomes trans- emit G aor B24 ed Oe ant ‘ sas fais ‘ y ; E . \ . 1 , in it ashe by Ke. A PEIN TEL UY >. AM velrsinctay > Oyoe : ah q \\ Me sLotgeer 92 . v = Phas eotls Rehesd the wiviboe axe ale nat Uaioe! r nee Tw The eG ’ _, > “ar Leah ey “ hi e “EPITHELIUM ~ 21 formed into a sort of skein, formed apparently of one long convoluted filament; the nuclear membrane and the nucleoli disappear or are merged into the skein (fig. 17, b, c, d). 2. The skein. becomes arranged in the form of a rosette, the fila- ments looping in and out, to and from the centre (e). 3. The outer loops of the rosette separate, so that the filament breaks into a number of V-shaped fibres arranged like a star (aster, fi, gh.) 4. The V:shaped fibres separate into ne groups, the ends of which ~ for a time are interlocked (i, j, i). 5. The two groups pass to the opposite poles of the now elongated nucleus and form a star-shaped figure (J) at each pole (dyaster). Hach of the stars represents a daughter nucleus. 6, 7, 8. Each star of the dyaster goes through the same changes as the original nucleus, but in the reverse order—viz. rosette (m), skein (x), and network (0, p, q); passing finally into the condition of a typi- cal resting nucleus. The protoplasm of the cell divides soon after the formation of the dyaster (m). Sometimes fine lines may be seen in the protoplasm, during the process of division, radiating from the poles of the nucleus, and others uniting the two daughter nuclei. Classification of epithelia.—Epithelia are classified according to the shape and arrangement of the component cells. Thus we speak of scaly or pavement, cubical, columnar, polyhedral, and spheroidal epithelium. All these are simple epithelia, with the cells only one layer deep. If forming several superposed layers, the epithelium is said to be stratified, and then the shape of the cells differs in the dif- ferent layers. Where there are only three or four layers in a stratified epithelium, it is termed transitional. Stratified Epithelium covers the anterior surface of the cornea, lines the mouth, pharynx (lower part), and gullet, and forms the epi- dermis which covers the skin. In the female it lines the vagina and Fig. 18.—SEcTION OF THE STRATIFIED EP:THELIUM COVERING THE FRONT OF THE CORNEA OF THE EYE, c, lowermost columnar cells ; », polygonal cells above these ; 77, flattened cells near the surface. part of the uterus. The cells nearest the surface are always flattened and scale-like (fig. 18, ff; fig. 19), whereas the deeper cells are more 22 THE ESSENTIALS OF HISTOLOGY rounded or polyhedral, and those of the deepest layer generally some- what columnar in shape (fig. 18, c). Moreover, the deeper cells are soft and protoplasmic, and are separated from one another by a system of intercellular channels, which are bridged across by numerous pro- cesses passing from cell to cell. The deeper cells multiply by division, the newly formed cells tending as they enlarge to push those external to them nearer to the surface, from which they are eventually thrown off. As they approach the surface they become hard and horny, and in the case of the epidermis lose entirely their cellular appearance, which can, however, be in a measure restored by the action of potash ($ 2). The cast-off super- ficial cells of the stratified epithelium of the mouth, which are seen in abundance in the saliva ($ 1), are less altered, and the remains of a nucleus is still visible in them. Fig. 19.—EPitieLiuM-sCALES FROM THE FiaG, 20,— PAVEMENT-EPITHELIUM FROM INSIDE OF THE MOUTH. (Magnified 260 A SEROUS MEMBRANE. (Magnified-410 diameters.) diameters. ) a, cell; 6, nucleus ; c, nucleoli, Simple scaly or pavement epithelium is found in the saccules of the lungs, in those of the mammary gland when inactive, in the kidney (in the tubes of Henle), and also lining the cavities of serous mem- branes (fig. 20), and the heart, blood-vessels, and lymphatics. When occurring on internal surfaces, such as those of the serous membranes, blood-vessels, and lymphatics, it is often spoken of as endothelium. Polyhedral or spheroidal epithelium is characteristic of many secreting glands; columnar and ciliated epithelium are for the most part found covering the inner surface of mucous membranes, which are membranes lining passages in communication with the exterior, such as the alimentary canal and the respiratory and generative passages. The detailed study of most of these may be reserved until the organs in which they occur are respectively dealt with. The hairs and nails and the enamel of the teeth are modified epithelial tissues. a ik > 5% =a a, vr" "i oA i oes edi im : a eae : Gelgmiiag peter le re : \ ’ Mchie e CuE : r t. u pa Thorn: te ead torarie the are 1 L ve @ Threksinete:: H Gétaod wt av Srak he+s y Pak : ag wae ti hs + £ M4 Sten Jn lis 7, ae dliteier eet Te, slyis - a ee wits Bre te ; : L a. ES \ Bb cay eh antphay hs Lpdiend gh dau, tf ae 2 ally e« , ‘ wine a) ie at ~ a ac (Wb. ee r men bh DiiGa, 2 23 LESSON VII. COLUMNAR AND CILIATED EPITHELIUM, AND \ i TRANSITIONAL EPITHELIUM. 1. Take a piece of rabbit’s intestine which has been two days in chromic acid solution (1 part chromic acid to 2,000 normal salt solution). Scrape the inner surface with a scalpel, break up the scrapings in a drop of water on a slide. Add a small piece of hair to avoid crushing, and cover the preparation. Sketch one or two columnar cells and also a row of cells. Measure two or three cells and their nuclei. To keep this preparation, add a drop of dilute hematoxylin (1 drop of the ordinary solution to half a watch-glass-ful of distilled water) at one edge of the cover-glass. When the hematoxylin has passed in and has stained the cell- nuclei, place a drop of glycerine at the same edge, and allow it slowly to diffuse under the cover-glass. Cement this another day.' 2. Break up in glycerine a shred of epithelium from a piece of frog’s intestine that has been treated with osmic acid, and has subsequently macerated in water for a few days. The cells easily separate on tapping the cover-glass. They are larger than those of the rabbit and exhibit certain points of structure better. Measure and sketch one or two cells. The cover-glass may be at once fixed by gold size. 3. Prepare the ciliated epithelium from a trachea that has been in bichromate of potash solution (4 per cent.) for two days, in the same way as in § 1. Measure in one or two of the cells (a) the length of the cell, (6) the ‘ length of the cilia, (c) the size of the nucleus. Sketch two or three cells. ‘This preparation is to be stained and preserved as in § 1. 4. Make a similar teased preparation of the epithelium of the urinary bladder. Observe the large flat superficial cells, and the pear-shaped cells of the second layer. Measure and sketch one or two of each kind. Stain and preserve as in §§ 1 and 3. Columnar epithelium.—The cells of a columnar epithelium (fig. 21) are prismatic columns, which are set closely side by side, so that when seen from the surface a mosaic appearance is produced. ‘They often _ taper somewhat towards their attached end, which is generally trun- cated, and set upon a basement membrane. Their free surface is covered by a thick striated border (fig. 22, str), which may some- times become detached in teased preparations. The protoplasm of the cell is highly vacuolated or reticular, and fine longitudinal strize may be seen in it, which appear continuous with the strie of the 4 Gentian-violet solution (see Appendix) may be employed instead of hema- toxylin. AA 24 THE ESSENTIALS OF HISTOLOGY : é free border. The nucleus (mv) is oval and reticular. The lateral borders of the cells are often somewhat irregular or jagged, the result of the pressure of amceboid lymph-cells, which are generally found between the columnar cells, at least in the intestine. After a Fic. 21—A Row OF COLUMNAR CELLS FROM THE INTESTINE OF THE RABBIT. Smaller cells are seen between the epithelium-cells, probably of the nature of white blood or lymph corpuscles, meal containing much fat the cells may be filled with fat-globules, which become stained black in the osmic preparation. Some of the columnar cells contain mucigen, which may greatly distend the part of the cell nearest the striated border. When the Fic. 22.—CoLUMNAR EPITHELIUM-CELLS OF THE RABBIT’S INTESTINE, The cells have been isolated after maceration in very weak chromic acid. The cells are much vacuolated, and one of them has a fat-globule near its attached end; the striated border (sf7") is well seen, and the bright disk separating it from the cell-protoplasm ; m, nucleus with intranuclear network ; a, a thinned-out wing-like projection of the cell which probably fitted between two adjacent cells, mucigen is extruded as mucus, this border is thrown off, and the cell takes the form of an open cup or chalice (goblet-cell, fig. 23). Columnar epithelium-cells are found lining the whole of the interior of the stomach and intestines: they are also present in the ducts of most glands, and sometimes. also in their secreting saccules. The epi- thelium which covers the ovary also has a modified columnar shape, but cells having all the structural peculiarities indicated above are found only in the alimentary canal and in its diverticula. Ciliated epithelium.—The cells of a ciliated epithelium are also usually columnar in shape (fig. 24), but in place of the striated border the cell is surmounted by a bunch of fine tapering filaments which, Paiste vd ae igh Sher kin fine es its 2 sles. ay i 63. riies Glue F The th : t ‘ c Erin i af: ips he 2 doi ‘ ¥, ONtes Ri 14a a . : M > sania ha ae a Blows + Barsaghycurl, typ inthe wash 08 - Gi we tah nS ba ef at Te Tena ee pth sf a 5 ‘ 4 . SEM) 2.4 - \ ~a =| 7 f : Or Sie i v 4 arte : a! - iit ua & i ued GE ga: . ee ale i Ti. We 7, 0@ 44 by ed wales ¥¢ it ey , wit ; eee Peon he: calle heviee Q: Wie Str pcs pe + gh ee NjHivt Puipiiethe ae TOSAY Gah iy 2 = COLUMNAR, CILIATED, AND TRANSITIONAL EPITHELIUM 25 - désng life, move spontaneously to and fro, and serve to produce a $ current of fluid over the surface which they cover. | The cilia are to be regarded as active prolongations of the cell- protoplasm. The border upon which they are set is bright, and appears formed of little juxtaposed -knobs, to each of which a cilium is attached. In the large ciliated cells which line the alimentary canal of some molluscs (fig. 25) the knob may be observed to be prolonged into the protoplasm of the cell as a fine varicose filament, termed the rootlet of.the'cilium. These filaments may represent. the longitudinal _ strie often seen in the protoplasm of the columnar cell, the bunch of cilia being homologous with the striated border. The protoplasm and nucleus have a similar vacuolated or reticular structure in both kinds of cell. Goblet cells may also occur in ciliated epithelia. Fig, 23.—GonLEr CELL. Fic. 24.—CoLUMNAR coed Fig. 25.—CILIATED CELL, ATED EPITHELIUM-CELLS. PRO. THe? SATueTTeE OF A MOLLUSC, Ciliated epithelium is found throughout the whole extent of the air-passages and their prolongations (but not the part of the nostrils fica by the olfactory nerves, nor in the lower part of the pharynx) ; in the Fallopian tubes and the greater part of the uterus; in some of the efferent duets of the testicle (where the cilia are much longer than a eS ee oF 26 THE ESSENTIALS OF HISTOLOGY elsewhere in the body) ; in the ventricles of the brain, and the central canal of the spinal cord; and in the convoluted tubules of the kidney. Transitional epithelium is a stratified epithelium consisting of only two or three layers of cells. It occurs in the urinary bladder, the ureter, and the pelvis of the kidney. The superficial cells (fig. 26, a) are large and flattened; they often have two nuclei. On their i Fie. 26.—EpituELIAL CELLS FROM THE BLADDER OF THE RABBIT. (Magnified 500 diameters. ) a, large flattened cell from the superficial layer, with two nuclei and with strongly marked ridges and intervening depressions on its under surface; 6, pear-shaped cell of the second layer adapted to a depression on one of the superficial cells. under surface they exhibit depressions, into which fit the larger ends of pyriform cells, which form the next layer (fig. 26, b). Between the tapered ends of the pyriform cells one or two layers of smaller polyhedral cells are found. 1 epee i-F LESSON VIII. \, STUDY OF CILIA IN ACTION. 1. Mount in sea-water one or two bars of the gill of the marine mussel (fig. 27). Study the action of the large cilia. Now place the preparation upon the copper warm stage (see Lesson V.) and observe the effect of raising the temperature. i) Fic. 27.—VALVE OF MUSSEL (MYTILUS EDULIS) SHOWING br, br, THE EXPANDED GILLS OR BRANCHIA, WHICH, OWING TO THE LITTLE BARS OF WHICH THEY ARE COMPOSED, PRESENT A STRIATED ASPECT. mi, mantle ; m, cut adductor muscle ; 7, mass of viscera; the dark projection just above is the foot. ’ i 3 5 Keep this preparation until the end of the lesson, by which time many of the cilia will have become languid. When this is the case pass a drop of dilute potash solution (1 part KHO to 1,000 of sea-water) under the cover-glass and observe the effect. 2. Cement with sealing-wax a piece of small glass tubing toa slide so that Fic. 28.—Moist CHAMBER ADAPTED FOR PASSING A GAS OR VAPOUR TO A ‘ PREPARATION UNDER THE MICROSCOPE. one end of the tube comes nearly to the centre of the slide. On this put a ring of putty or modelling wax half an inch in diameter so as to include the - ae . ae ~~ a i , , . ' . ‘ 28 ' THE ESSENTIALS OF HISTOLOGY end of the tube, and make a deep notch in the ring opposite the tube. Place a small drop of water within the ring (fig. 28). Put a bar from the gill upon a cover-glass in the least possible quantity of sea-water ; invert the cover-glass over the putty ring, and press it gently down. The preparation hangs in a moist chamber within which it can be studied through the cover-glass, and into which gases or vapours can be passed and their effects observed. Pass CO, through the chamber, and after observing the effect replace it by air (see fig. 29). Repeat with chloroform vapour instead of CO,,. The Movement of Cilia.—When in motion a cilium is bent quickly over in one direction with a lashing whip-like movement, immediately recovering itself. When vigorous the action is so rapid, and the - rhythm so frequent, that it is impossible to follow the motion with the eye. All the cilia upon a ciliated surface are not in action at the same Fic. 29.—_MrETHOD OF SUBJECTING A PREPARATION TO A STREAM OF CARBONIC ANHYDRIDE. b, bottle containing marble and hydrochloric acid ; 6’ wash-bottle, connected by indiarubber tube, ¢, with the moist chamber, s. instant, but the movement travels in waves over the surface. If a cell is detached from the general surface, its cilia continue to act for a while, but at once cease if they are detached from the cell. The rhythm is“slowed by cold, quickened by warmth, but heat beyond a certain point kills the cells. The movement will continue for some time in water deprived of oxygen. Both CO, gas and chloro- form vapour arrest the action, but it reeommences on restoring air. Dilute alkaline solutions quicken the activity of cilia, or may even restore it shortly after it has ceased. i % S ‘ by Hy .- % = ; s : i n : : ba 4 Ss ayvars Peanic 3 be Sip t ful ; Sis Whose t : vl ie tie Guat vA J . ae Fae rBint +, ae =: r - j J om at 1% a PEM ee tiene ido i ‘ i Lwigise “a WO6, FAL Buh spice dora bi rege ey ata iienaooplond muh Paynes " ie , Le 2 latin dooms ol Saat iia ; ie any aes uae, tehive 23 . fl Hin 6 hea be’ ,, ? Fi : ¥ - t . ] iy eee : ap’ “oe yee Toh A, LESSON IX. THE CONNECTIVE TISSUES. AREOLAR AND ADIPOSE TISSUE. 1. Take a little of the subcutancous tissue or of the intermuscular connective tissue of a rabbit or guinea-pig and spread it out with needles on a dry slide into a large thin film. Keep the centre moist by occasionally breathing on it, but allow the edges to dry to the slide. Before commencing put a drop of salt solution on a cover-glass, and now invert this over the film. Ex- amine with a high power. Sketch one or two bundles of white fibres and also one or two elastic fibres, distinguishable from the former by their sharp outline, isolated course, and by their branching. Sketch also one or _ more connective-tissue corpuscles, if any such are visible in the clear inter- spaces. Look also for migratory cells (lymph-corpuscles). Next carefully remove the cover-glass and replace the salt solution by dilute acetic acid. Watch its effect in swelling the white fibres and bringing more clearly into view the elastic fibres and corpuscles. Look for constricted bundles of white fibres. 2. Make another film in the same way, but mount in dilute magenta solution ! instead of saline solution. The elastic fibres are deeply stained by the dye; the cells are also well shown. When the staining is completed pass dilute glycerine under the cover-glass and cement this at once with gold size. 8. Prepare another film of the subcutaneous tissue, including a little adipose tissue. Mount in glycerine and water, coloured by magenta, with a piece of hair under the cover-glass to keep this from pressing unduly upon the fat-cells. Cement at once with gold size. Examine first with a low and after- wards with a high power. The nucleus and envelope of the fat-cell are well brought out by the magenta, and if from a young animal, fat-cells will be found in process of formation. Measure and sketch two or three of the cells. 4, Spread out another large film of connective tissue, letting its edges dry to the slide. Place on its centre a large drop of nitrate of silver solution (1 per cent.). After ten minutes wash this away with distilled water, mount in Farrant', and expose to the sunlight until stained brown. Sketch the out- lines of two or three of the cell-spaces. The connective tissues include areolar tissue, adipose tissue, elastic tissue, fibrous tissue, retiform and lymphoid tissue, cartilage and bone. All these tissues agree in certain microscopical and chemical charac- ters. They, for the most part, have a large amount of intercellular substance in which fibres are developed, and these fibres are of two ' See Appendix. 30 THE ESSENTIALS OF HISTOLOGY kinds—white and yellow or elastic. Moreover, there are many points of similarity between the cells which occur in these several tissues ; they are also developed from the same embryonic formation, and they tend to pass imperceptibly the one into the other. Besides this, their use is everywhere similar; they serve to connect and support the other tissues, performing thus a passive mechanical function. They may therefore be grouped together, although differing consider- ably in external characters. Of these connective tissues, however, there are three which are so intimately allied as to be naturally con-— sidered together, being composed of exactly the same elements, although differing in the relative development of those elements; these are the areolar, elastic, and fibrous tissues (adipose tissue may be looked upon as a special modification of areolar tissue). Areolar tissue being the commonest and, in one sense, the most typical, its structure may be considered first. Areolar tissue.—The areolar tissue presents to the naked eye an appearance of fine transparent threads and lamine which intercross in every direction with one another, leaving intercommunicating meshes, or areole, between them. When examined with the microscope, these threads and fibres are seen to be principally made up of wavy bundles of exquisitely fine transparent fibres (white fibres, fig. 30). The bun- dles run in different directions, and may branch and intercommuni- cate with one another; but the individual fibres, although they pass - from one bundle to another, never branch or join other fibres. The Fic. 31.—GROUND SUBSTANCE OF CONNECTIVE TISSUE STAINED BY sILvER. (The cell-spaces are left white.) °F THE WHITE FIBRES OF ARTLY UNRAVELLED. Fic. 380.—BuNDLE AREOLAR TISSU fibres are cemented ther into the bundles by a clear substance containing mucin, and tlh, ~me clear material forms also the basis or ground-substance of the ti in which the bundles themselves course, and in which also the corpuSéles of the tissue lie embedded. This 7 Pa PC. = eit ae eat Tiaras: ili = PAA lh acer"! CS is vel ~ harearn Sees Sok RDUIAL PS) in " Tae, f 4 biexree y het ~ ay > eracaa-yY.)- - j ~ c- fs ‘ * » ‘ " % + 1 3 = ~ = = & ; ; * ) . pe e . ’ | i ' 7 oh = * e = ‘ ay ¢ pe Bre . nes ‘ : : ' Tw a) 3 ; mY ai 4 ele SECcer. 4) iy Ty vo : Ee SSIES Soho aa rr) Wiest TERT Ts) Ae Se 7 fd ie. Paya su hia ie x HA ster perv wes ASS PP Yon ayraalt ~- x : 3 fe r s, APoet Wee & . ‘ > wlerron geil ee Tesi? 2Q4 P| “oF patent . oer ‘ + oo) see >! EN > 35 t THE CONNECTIVE TISSUES (continued). LESSON X. ELASTIC TISSUE, FIBROUS TISSUE, SPECIAL VARIETIES, DEVELOPMENT OF CONNECTIVE TISSUE. 1. TEAsE out as finely as possible a small shred of elastic tissue (ligamentum nuche of the ox or ligamenta subflava of man) in Farrant’s solution’ and cover the preparation. Note the large well-defined fibres constantly branching _ and uniting with one another. Look for transverse markings on the fibres. Measure three or four. Sketch a small part of the network. Note the existence of bundles of white fibres amongst the elastic fibres. 2. Mount in Farrant a thin transverse section of ligamentum nuche _which has been hardened in 2 per cent. solution of bichromate of potash. Observe the grouping of the fibres and their angular shape. Sketch one or two groups. ; 3. Pinch off the end of the tail of a dead mouse or rat, draw out the long silk-like tendons and put them into saline solution. Take two of the longest _ threads and stretch them along a slide, letting the ends dry firmly to the slide but keeping the middle part moist. Put a piece of hair between them and cover in saline solution. Observe with a high power the fine wavy fibrillation of the tendon. Draw. Now run dilute acetic acid under the cover-glass, watch the tendons where they are becoming swollen by the acetic acid. - Notice. the oblong nucleated cells coming into view between the tendon bundles. Sketch three or four cells in a row. Lastly, lift the cover-glass, wash away the acid with distilled water, place a drop of hematoxylin solution on the tendons, and leave the preparation for fifteen minutes or more; then wash away the logwood and mount the preparation in acidulated glycerine. _ Cement the cover-glass with gold size. 4, Immerse one or two other pieces of tendon in nitrate of silver solution ‘ ‘(1 per cent.) for ten minutes, then wash them in distilled water, stretch them upon a slide, mount in Farrant, and expose to the sunlight. 5. Stain with magenta solution! a thin section of a tendon which has been hardened in alcohol. Mount in dilute glycerine and cement the cover- _ glass at once. Sketch a portion of the section under a low power. Elastic tissue is a variety of connective tissue in which the elastic fibres preponderate. It is found most characteristically in the liga- mentum nuche of quadrupeds and the ligamenta subflava of the vertebre, but the connective tissue of other parts may also have a con- oo dr. / 1 See Appendix. p2 36 THE ESSENTIALS OF HISTOLOGY siderable development of elastic fibres. It occurs also in an almost pure form in the walls of the air-tubes, and uniting the cartilages of the larynx. It also enters largely into the formation of the walls of the blood-vessels, especially the arteries. In the ligamentum nuche the fibres are very large and angular _ (fig. 88); they often exhibit cross-markings or even transverse clefts. When dragged asunder, they break sharply across; they constantly branch and unite, so as to form a close network. In transverse section they are seen to be separated into small groups (fig. 39) by. intervening white bundles of connective tissue. Fic. 39.—CrRoss-SECTION OF ELASTIC FIBRES FROM THE LIGAMENTUM NUCH. OF THE OX. Fic. 38.—ELASTIC FIBRES FROM THE LIGA- MENTUM NUCHA OF THE OX, SHOWING TRANSVERSE MARKINGS ON THE FIBRES, Elastic tissue does not always take the form of fibres, but may occur as membranes (as in the blood-vessels). Sometimes the fibres are very small, but their microscopical and chemical characters are always very well marked (see p. 31). Fibrous tissue is almost wholly made up of bundles of white fibres running in a determinate direction. These again are collected into larger bundles, which give the fibrous appearance to the tissue. The bundles are constantly uniting with one another in their course, sitbecge ; their component fibres remain perfectly distinct. The interspaces between the larger bundles are occupied by scoala tissue (fig. 40) in which the blood-vessels and lymphatics of the fibrous _ i ee We eee 8 y * = = ‘ rok ¥ahi ~ en A ee - s > 4 es oh a Goreme bn cyt a 8 a - . oat 4 c an ru > * r bubdieo, whiny gfe the (haw iaaeii “ACG goa bes iey ule othe! e | - dl Corns obey — go eee ; --BIBROUS’ TISSUE ‘ Fie. 40.—PArtT OF A LARGE TENDON IN TRANSVERSE SECTION. a, areolar sheath of the tendon, with the fibres for the most part running transversely, but with two or three longitudinal bundles, 6; 7, lymphatic cleft in the sheath; immediately over it a blood-vessel is seen cut across, and on the other side of the figure a small artery is shown cut longitudinally ; ¢, large septum of areolar tissue; d, smaller septum ; ¢, still smaller septum. The irregularly stellate bodies are the tendon cells in section. _. Fig, 41—TEnpon OF MOUSE’S TAIL, STAINED WITH LOGWOOD ; SHOWING CHAINS OF CELLS BETWEEN THE TENDON-BUNDLES. (175 diameters.) A ; <= . ‘Fie. 42.—TRANSVERSE SECTION OF TENDON OF MOUSE’S TAIL, STAINED. . é . >. (175 diameters.) e : right angles from the body of the cell, flattened processes of the tendon-cells appear in section as lines, frequently coming off at ee | 38 THE ESSENTIALS OF HISTOLOGY ae tissue are conveyed. The interstices between the smallest bundles. are occupied by rows of connective-tissue corpuscles (tendon-cells), which from being squeezed up between three or more bundles become flattened out in two or three directions. In transverse section-the cells appear somewhat stellate (figs. 40, 42), but when seen on the flat they appear lamellar (fig. 41), and from this aspect their general shape is square or oblong. They lie, as before said, in rows between the tendon-bundles, and the nuclei of adjacent cells are placed opposite Fic. 48.—EIGHT CELLS FROM THE SAME TENDON AS REPRESENTED IN FIG. 41. (425 diameters. ) The nuclei, with their numerous nucleoli, are coloured by the logwood. The dark lines on the surface of the cells are the optical sections of lamellar extensions directed towards or away from the observer. one another in pairs (fig. 43), The cell-spaces correspond in general figure and arrangement to the cells which occupy them (fig. 44). Fic. 44.—CELL-SPACES OF TENDON OF MOUSE’S TAIL, BROUGHT INTO VIEW BY TREATMENT WITH NITRATE OF SILVER. (175 diameters.) Fibrous tissue forms the tendons and ligaments, and also certain membranes, such as the dura mater, the fibrous pericardium, the fascize of the limbs, the fibrous covering of certain organs, &c. It is found — wherever great strength combined with flexibility is concerned. It receives a few blood-vessels, disposed longitudinally for the most part, and contains many lymphatics. Tendons and ligaments also receive nerve-fibres, which, in some cases, end in small localised ramifications like the end-plates of muscle, while others terminate in end-bulbs or in _ simple Pacinian corpuscles. Retiform or reticular tissue is a variety of connective tissue in which the intercellular or ground substance has mostly disappeared or is replaced by fluid, very few or no fibres having been developed in it ; and these, when present, are enwrapped by the cells. The tissueis — composed almost entirely of the cells, which are ramified and united Bt 597 Fa ae ven all tree sere d tate tie AT > ei Agr ys itd wrk apie = my She Wats ake fi tere Gt aife® Sire Will iy ux way desta ; Bek BOehectire-tiss ‘ ge ied Haye ities OR ieee , (jeg ait ie pedi bate der foe Auth Ve Maka, She imaisty cn buketiey by @ wiped tartan, sein. | gv Let Mie pet oneal} ' ~- y * ; . Relviara trey qlee Kuske Oe Wiurd Ptiplercea aX ; { ch rs i ! | fe LCi. pe Pee oe ee | ee ee ’ esd, eee NC eo tice at" ; - -VARINTIES OF CONNECTIVE TISSUE 39 a Z with one another into a network or sponge-work by their processes } in some cases, the cell-nuclei have disappeared (as at 0), fig. 45), Fic. 45.—THIN SECTION FROM THE CORTICAL PART OF A LYMPHATIC GLAND, MAGNIFIED, A network of fine trabecule formed by retiform tissue, from the meshes of which the lymph-corpuscles have been washed out, except at c, where they are left. Lymphoid or adenoid tissue is retiform tissue in which the meshes of the network are largely occupied by lymph-corpuscles. This is by far the most common condition of a retiform tissue, and is met with in the lymphatic glands and allied structures (see Lesson XXII.), and also in the tissue of the alimentary mucous membrane, and in some other situations. ‘7 Basement membranes (membrane proprie) are homogeneous-look- ing membranes, which are found forming the surface-layers of con- nective-tissue expansions in many parts, especially where there is a covering of epithelium, as on mucous membranes, in secreting glands, and elsewhere. They are generally formed of flattened connective- tissue cells joined together to form a membrane; but, in some cases, they are evidently formed not of cells, but of condensed ground- substance, and in others they are of an elastic nature. _ Jelly-like connective tissue, although occurring largely in the em-. bryo, is found only in one situation in the adult—viz. forming the _ vitreous humour of the eye. It seems to be composed entirely of soft ound-substance, with cells scattered here and there through it, and ‘with very few fibres, or none at all.. These several varieties of con- nective tissue will be more fully described in connection with the - organs where they occur. Development of connective tissue. Connective tissue is always | developed in the mesoblast or mesoderm of the embryo. In those _ parts of this layer which are to form connective tissue, the embryonic _ cells become separated from one another by a muco-albuminous semi- - fluid intercellular substance (ground-substance), but the cells generally remain connected by their processes. The connective-tissue fibres, A ' 40 THE ESSENTIALS OF HISTOLOGY a: | both white and elastic, are deposited in this ground-substance, - the | elastic substance usually in the form of granules (fig. 47, g), which Fic. 46.—JELLY OF WHARTON. 7, ramified cells intercommunicating by their branches ; 7, a row of lymph-cells ; J, fibres developing in the ground-substance. i | subsequently become connected together into elastic fibres or lamine, _ as the case may be, the white fibres appearing at first in the form of | very fine bundles, which afterwards become gradually larger ; so that | in fibrous tissue the whole ground-substance is eventually pervaded by Fic. 47.—DEVELOPMENT OF ELASTIC TISSUE BY DEPOSITION OF FINE GRANULES, g, fibres being formed of rows of ‘elastin’ granules ; p, flat platelike expansion of elastic substance formed by the fusion of ‘elastin’ granules, them, and the cells of the tissue become squeezed up into the intervals between them. Before any considerable development of fibres has taken place, the embryonic connective tissue has a jelly-like appear- ance; in this form it occurs in the umbilical cord, where it is known as the jelly of Wharton (fig. 46). em ‘ ‘ = al 4 * j . aiee + ‘ ; . 7 ! ; % ? ) = a . + “tear * eas = -le -F = ‘ it ; a ‘ a Pariiace 5) Eee eee watt ; : - = yi Lo Sein os ra et RA end 3 eo tat “| ee arity Worm, of :¢ sheter 4 f “3 Diesel Meiveby by coro J bikes : | t= ea Be Murane, whisk ks ' re ines 8 U | til th CAT, Wikre [ree Frye er ae ites A pilird-rer 1h! $e tetris: |, oT hale perce Sines, Fhatiathcs : so te Wale. Sees i ae cae they are uboaig a) ; wat ' ey a Ss : fr ; Ps Sie aire » as “a0 ' é zs ae? y r Tab 7 > a aoc * nag er, : ve me te i ce Saree fF (dates ee 5 - a * iF ; : ‘ Se ediers, soul Ga’ felts of fed Ge ome Yatuce: them, <3) miote LESSON XI. THE CONNECTIVE TISSUES (continued). / ARTICULAR CARTILAGE, 1, Cur two or three very thin tangential slices of the fresh cartilage of a joint, mount them in saline solution and examine with a high power. Observe care- fully the form and grouping of the cells. Look at the thin edge of the section for spaces from which the cells have dropped out. Measure two or three cells and their nuclei, and sketch one or two groups. Now replace the saline solution by water and set the preparation aside for a little while. On again examining it, many of the cartilage-cells will be found to have shrunk away from their containing capsules. 2. Make other sections of the cartilage (1) from near the middle, (2) from near the edge. Mount in magenta solution, and when stained add dilute glycerine and cement the cover-glass. In (2) look for branched cartilage-cells. Draw one or two. 3. Make vertical sections of articular cartilage from a bone which has been for several days in } per cent. chromic acid solution, and mount the sections in Farrant. Sketch the arrangement of the cells in the different layers. 4. Wash a fresh joint with distilled water; drop 1 per cent. nitrate of silver solution over it; after ten minutes wash away the nitrate of silver and expose in water to the light. When browned, cut thin sections from the surface and mount in Farrant. The cells and cell-spaces show white in the brown ground-substance. Draw. Cartilage or gristle is a translucent bluish-white tissue, firm, and at the same time elastic, and for the most part found in connection with bones of the skeleton, most of which are in the embryo at first represented entirely by cartilage. Two chief varieties of cartilage are distinguished. In the one, which is termed hyaline, the matrix or ground-substance is clear, and free from obvious fibres; in the other, which is termed fibro-cartilage, the matrix is everywhere pervaded by connective-tissue fibres. When these are of the white variety, the tissue is white fibro-cartilage ; when they are elastic fibres, it is yellow or elastic fibro-cartilage. Hyaline cartilage occurs principally in two situations—namely (1) covering the ends of the bones in the joints, where it is known as articular cartilage; and (2) forming the rib-cartilages, where it is _ known as costal cartilage. It also forms the cartilages of the nose, the 42 ‘THE ESSENTIALS OF HISTOLOGY external auditory meatus, the larynx, and the windpipe; in these places it serves to maintain the shape and patency of the orifices and tubes. Articular cartilage. The cells of articular cartilage are mostly scattered in groups of two or four throughout the matrix (fig. 48). The latter is free from fibres, except at the extreme edge of the Er AWS AN SY ° TON A AN ANS \ ‘ ALUKA AS XN Wes’ “ Fic, 48.—ARTICULAR CARTILAGE FROM HEAD OF METATARSAL BONE OF MAN (OSMIC ACID PREPARATION). THE CELL-BODIES ENTIRELY FILL THE SPACES IN THE MATRIX. (340 diameters.) a, group of two cells; }, group of four cells; #, protoplasm of cell, with g, fatty granules; n, nucleus. Ss cartilage, where the connective-tissue fibres from the synovial mem- brane extend into it; and here also the cartilage-cells are often branched, and offer transitions to the branched connective-tissue cor- puscles of that membrane (transitional cartilage, fig. 49). By long maceration, however, some observers have obtained evidence of a fibrous structure even in the matrix of true hyaline cartilage. The matrix immediately around the cartilage-cells is often marked off from the rest by a concentric line or lines, this part being known as the capsule of the cell. The cells are bluntly angular in form, the sides opposite to one another in the groups being generally flattened. The protoplasm is very clear, but it may contain droplets of fat; and with a high power fine interlacing filaments and granules have been observed in it (fig. 50). During life the protoplasm entirely fills the Ea Say pety] hers ec wv, ¥) ts rr a é aa & avy sy {RG . + F BE! Tr tvasswwritns: ca ra £ “ Pus hay rf poet ™~ ~) a 1 . col a ae | . 3 ~ ~ @ ¥ ’ 4 : ; ‘ is 2 : ~ 7 i] } < - s r — c , Pe Me Seiad hace <7 bb te bal asta, Nigh. BH eines ; eo ee ner Sey th. of: Divetena ary Serv 44 fy ee 2 y 1, sonnts |. Oee_ee “he, sania «ti chute ou ule obes J ae cs FIBRO-CARTILAGE white fibro-cartilage looks very like fibrous tissue, but its cells are car- tilage-, not tendon-, cells (fig. 57). They are rounded or bluntly angular : Fig. 57.— Wu rE FIBRO-CARTILAGE FROM AN INTERVERTEBRAL DISK, HUMAN. ; ; (Highly magnified.) The concentric lines around the cells indicate the limits of deposit of successive capsules. One of the cells has a forked process which extends beyond the hyaline area surrounding the cell, amongst the fibres of the genera! matrix. and surrounded by a concentrically striated area of clear cartilage- matrix. In some parts of the intervertebral disk many of the cells are branched, and may be looked upon as transitional forms to connective- tissue corpuscles. 48 _ THE ESSENTIALS OF HISTOLOGY | LESSON XIII. BONE AND MARROW. 1. In thin sections of hard bone made by grinding, observe the Haversian canals, lamelle, lacune,; canaliculi, &e. Make a sketch first under a low and afterwards under a high power. 2. With fine forceps strip off a thin shred from a bone which has been decalcified in nitric acid and afterwards kept for some time in dilute alcohol. Mount the shred in water. Observe the fibrous structure of the lamelle. Look for perforating fibres or the holes from which they have been dragged out. Sketch a small piece of the thin edge of a lamella. 3. Stain with dilute magenta very thin sections of compact bone which has been decalcified in chromic or picric acid, and mount in dilute glycerine, cementing at once. Look for fibres of Sharpey piercing the circumferential lamella. The elastic perforating fibres are more darkly stained than the others. Notice the stained nuclei of the bone-corpuscles in the lacune. In the thinnest parts of the sections try to make out the blood-vessels and- other structures in the Haversian canals. 4, Mount in Canada balsam sections of marrow (from a long bone) stained with hematoxylin or borax-carmine.' Observe the fat-cells, the reticular tissue supporting them, the proper marrow-cells in this tissue, &c. 5. Tease in saline solution some of the red marrow from the rib of a recently killed animal. Observe and sketch the proper marrow-cells and look for myeloplaxes and nucleated coloured blood-corpuscles. If examined carefully, amceboid movements may be detected in the latter and in the marrow-cells. . Bone is a connective tissue in which the ground-substance is im- pregnated with salts of lime, chiefly phosphate, these salts constituting ~ about two-thirds of the weight of the bone. When bones are macerated this earthy matter prevents the putrefaction of the animal matter. When bones are calcined they lose one-third of their weight, owing to the destruction of the animal matter; when steeped in acid the earthy salts are dissolved and only the animal matter is left. This, like areolar and fibrous tissue, is converted into gelatine by boiling. Bony tissue is either compact or cancellated. Compact bone is dense like ivory ; cancellated is spongy with obvious interstices. The outer layers of all bones are compact, and the inner part is generally cancellated, but the shaft of a long bone is almost entirely made up of 1 See Appendix. ” - ‘Fas i lt eon by 9 = hoy a 4 lay: a. ne ; , 7 . “a MAP % * 5 . = - MM MG Sebet ist gl wehbe ak 0 ~~ 4 7 as a; ‘ ‘ Bente a. has teenally boot a atin , Pasar Airco pus nsory ; 2 “1h: . : arn 44 fe Ty is Oo a ms Bear’ ur : iS he . I ' i ‘ ra a : , J be ‘ : r _ : s 7 Ca ti 7 Mi) : = F 7 he! a } 4 ‘ wt 1 { . ‘ -_ ; t \e . 5 ny Vetere UP a4 peer . : af nd, dete * it f ' we Ps “ho wae : is ony er se ey ms po cet ot tei ein ' oA: ety ety es Det mails > ean ae " bei. Tit. \ ik ttn mW ge recame Ars tere.) sal Mad © SpanEy ah i ep 08s stagors ai oht\ oe, wh ON Cre: pas, ae BONE . ta - compact substance except along the centre, which is hollow and filled with marrow. The interstices of cancellated bone are also occupied by marrow. Externally bones are covered except at the joints by a vascular fibrous membrane, the periosteum. True bone is always made up of lamelle, and these again are com- posed of fine fibres lying in a calcified ground-substance. Between the lamelle are branched cells, the bone-corpuscles, which lie in cell- spaces or lacune. The ramified passages which contain the cell-pro- cesses are termed canaliculi. In cancellated bone the blood-vessels run in the interstices supported by the marrow. In compact bone they are contained in little canals— the Haversian canals—which everywhere pervade the bone. These canals are about 0°05 mm. (,3, inch) in diameter, but some are -smaller, others larger than this. Their general direction is longitudinal, 4.e. parallel to the long axis of the bone, but they are constantly united by transversely and obliquely running passages. In a section across nee ey je ee “RN SSS * ES “ SS 3) KS SEQE = ai: SSN criti N SS ees SSS na Ss Whee ‘4, “- QS ~. = ee yy \¥ SONAR “cal SE iid TA Fic. 58.—TRANSVERSE SECTION OF A BONE (ULNA). (Magnified 20 diameters.) The openings of the Haversian canals are seen encircled by concentriclamella, Other lamelle run parallel with the surface (@). the shaft of a long bone they are seen as small rounded or irregular holes (fig. 58). When the section has been made by grinding, the _ holes get filled up with air and débris, and they then look black by — : ' E 50 THE ESSENTIALS OF HISTOLOGY transmitted light, as do also the lacune and canaliculi (fig. 59). Most of the lamelle in compact bone are disposed concentrically around the Haversian canals; they are known as the Haversian lamelle, and with Fig. 59.—TRANSVERSE SECTION OF COMPACT TISSUE (OF HUMERUS). (Magnified about 150 diameters.) Three of the Haversian canals are seen, with their concentric rings; also the lacune, with the canaliculi extending from them across the direction of the lamellae. The Haversian apertures had become filled with air and débris in grinding down the section, and therefore appear black in the figure, which represents the object as viewed with transmitted light. the included canal form what is known as a Haversian system. The lacune of a Haversian system communicate with one another and with the Haversian canal, but not as a rule with the lacune of other Haversian systems. The angular interstices between the Haversian systems are generally occupied by bony substance, which.is fibrous but not distinctly lamellar. Besides the lamelle of the Haversian systems there is a certain thickness of bone at the surface, immediately under- neath the periosteum, which is composed of lamelle arranged parallel with the surface; these are the circumferential or periosteal lamelle (fig. 58, a). They are pierced here and there by canals for blood- vessels, which are proceeding from the periosteum to join the system of Haversian canals, and also by calcified bundles of white fibres and by elastic fibres which may also be prolonged from the periosteum. These are the perforating fibres of Sharpey (fig. 60). The lamelle of bone are fibrous in structure. This may be seen in shreds torn off from the superficial layers of a decalcified bone (fig. 61). The fibres often cross one another in adjacent lamelle, and in the Haversian systems they run in some lamelle concentrically, in others parallel with the Haversian canal. In shreds of lamelle which have been peeled off from the surface the perforating fibres may some- times be seen projecting from the surface of the shred, having been peer gers. A oe OTR, Mireili? & i WBsk boca ep aa Ode aio paw WF PS Sieh, amin ine Ove * Sets * Hivk a ape A tell ata ve ee eid — aigity Tux, NOT. . Tel Aare gruel Ata end / ‘. 4 4 , mT oT (Foo bd _ wit* at aon -— Loiolyere 1S ae : sacolw aul "sat _—: Ds if : Te. i © bavi iA vie . ' 1. # Mihm to ee ilk She hate aero eee | Lincoln 97m (ae ey fob Tete ay 6 ee Oty UN lavas ‘ me TA — sy c' ~~ ins 5] Fic. 60.—TRANSVERSE SECTION OF DECALCIFIED HUMAN TIBIA, FROM NEAR THE ; SURFACE OF THE SHAFT. \ i, H, Haversian canals, with their systems of concentric lamelle ; in all the rest of the figure the lamelle are circumferential; s, ordinary perforating fibres of Sharpey; e, e, elastic perforating fibres. Drawn under a power of about 150 diameters. ba y yz Y S245 ~~ ies Cie, YY Zo CE o% KES = Se SSSA SOS RRS KV Fic. 61.—LAMELL”& TORN OFF FROM A DECALCIFIED HUMAN PARIETAL BONE AT SOME DEPTH FROM THE SURi'ACE, a, lamelle, showing decussating fibres ; b, }, thicker part, where several lamelle are super- 3 ¢, ¢, perforating fibres: the fibrils which compose them are not shown in the ; - Apertures through which perforating fibres had passed are seen, especially in the &, ns ckcbe anes a, of the figure. Magnitude as seen under a power of 200, but not drawn to. E2 eR eS aS ES eS SX RAE SS So Wy D, fh SS — ~ SS YE Wf hilt); : SS? Yu dl 52 THE ESSENTIALS OF HISTOLOGY torn out of the deeper lamell (fig. 61 ¢, c). Where tendons or liga-— ments are inserted into bone, their bundles of white fibres are prolonged into the bone as perforating fibres. The lacune are occupied by nucleated corpuscles, which send branches along the canaliculi. The Haversian canals contain one or two blood-capillaries and nervous filaments, besides a little connective tissue; and the larger ones may also contain a few marrow-cells. There are also cleft-like lymphatic spaces running parallel with the vessels and connected by ~ means of canaliculi with neighbouring lacune in the osseous substance - (fig. 62). “uazese Cs aad a Fic. 62.—SEcTION OF A HAVERSIAN CANAL, SHOWING ITS CONTENTS. (Highly magnified.) a, small arterial capillary vessel; v, large venous capillary; , pale nerve-fibres cut across ; 1, cleft-like lymphatic vessel: one of the cells forming its wall communicates by fine branches with the branches of a bone-corpuscle. The substance in which the vessels run is connective tissue with ramified cells ; its finely granular appearance is probably due to the cross-section of fine fibrils. The canal is surrounded by several concentric lamelle. The periosteum, which is best studied in sections from a bone which | has been decalcified in chromic or picric acid, is a fibrous membrane composed of two layers, the inner of which contains many elastic . fibres. In the outer layer numerous blood-vessels ramify and send from it branches to the Haversian canals of the bone. The periosteum ministers to the nutrition of the bone, partly on account of the blood- vessels it contains, partly, especially in young animals, on account of the existence between it and the bone of a layer of osteoblasts or bone- forming cells, a remainder of those which originally produced the bone. The marrow of bone is of a yellow colour in the shafts of the long bones, and is there largely composed of adipose tissue, but in the can- cellated tissue it is red, the colour being partly due to the large amount : of blood in its vessels. This red marrow is chiefly composed of round nucleated cells—the marrow-cells (fig. 68, e+)—which resemble large lymph-corpuscles, and, like these, are ameeboid. There are also to be seen mingled with them a number of corpuscles somewhat smaller in size, but nucleated and ameeboid, and of a reddish tint (fig. 68, j-t) ; these are believed to be cells in process of development into coloured — : ‘Co Bs var t 0 ol} yas an dhuahodagShe—All ae % a : Trad cxit pial Ant. hike ule - — awicncia ames Ui, ° ae AT Fz MARROW 53 blood-corpuscles (hematoblasts). Lastly the marrow contains a certain number of very large cells with multiple nuclei, the myeloplazes (fig. 68, a, b, c, d). These are especially numerous wherever bone is becoming absorbed. The marrow is very vascular, the capillaries and veins being large and thin-walled ; indeed, according to some authorities, j k 1 m Tl OS OE et e QOSHSGSVO*SS Ome Fic. 63.—CELLS OF THE RED MARROW OF THE GUINEA-PIG. (Highly magnified.) a, a large cell, the nucleus of which appears to be partly divided into three by constrictions ; b, a cell the enlarged nucleus of which shows an appearance of being constricted into a number of smaller nuclei; c, a so-called giant-cell or myeloplaxe with many nuclei; d,a smaller myeloplaxe with three nuclei; e-d, proper cells of the marrow ; j-¢, various forms of coloured nucleated cells, some in process of division, the walls of the capillaries are imperfect, so that there is an open com- munication between them and the interstices of the tissue, and in this way it is supposed that the coloured blood-disks, which are believed to be produced from the coloured nucleated cells of the marrow, may get into the circulation. 54 THE ESSENTIALS OF HISTOLOGY LESSON XIV. DEVELOPMENT OF BONE. 1. Mount in Canada balsam a section of the lower jaw of a foetus which has been stained in bulk with magenta or hematoxylin and embedded in paraffin.' Find the part where the lower jaw-bone is becoming ossified, and carefully study the appearances which it presents. The bone is prolonged in the form of osteogenic fibres which are covered with osteoblasts. 2. Intramembranous ossification may also be studied in the parietal bone of a foetus which has been preserved in Miiller’s fluid. :?. oY BA We I ti hig rey t ‘ f ; 24 Ameritas, pied Nive ’ sri AIF Oh ; ‘ oes ‘ ¥ hog “= “he a . 4 i i ‘ } x ' _ + o) > ars as ‘ 4) - S qa er ee que. icee : a bees! hee onc Ves Sl, tin terhy S/N ey, herent ‘ett: 4 i ' ea rowe CLV 8 hie OA Ale ude Be BE Mhyerww basi - yy t eal Ate tp tayov : icnpdeng | 4 an tay Gate ¥is BOWE OF beoyse eeu) ini doe erate of \ lige Bhaleas, i wh that pr? hore. Re 4 7 2 < si) - > . o> a 6 4 te - . wae ie 64, L Gam expats §, 0% Wc BS. ff DEVELOPMENT OF BONE ~ 55 periosteum deposit a layer or layers of fibrous lamelle upon the surface of the cartilage, and these; lamellae also become calcified (fig. 64, im). As they are formed some of the osteoblasts (0) are included between them and become bone-corpuscles. ‘ A ee fo? §2 uw = Besta > se 9 ‘o' a 10 ove BOSS & Ses ~ ESE Rene) ook Vora et Sy oo, “3 oS Z ¢ eae ; ae : eS x Zoe ote at RBS SPR? S 8 © ie SSeS = = gees eineat LO tr eo et eer 5 .. eS! Bap ies ark a Cr thee 26 m® Oo. e £279 Op09379 08 Sones pera fuk 7g, x 3 its 9 Raaese = m Eas - 4 000 G Fic. 64.—SECTION OF PHALANGEAL BONE OF HUMAN FQ@TUS, AT THE TIME OF COMMENCING OSSIFICATION. (Magnified about 75 diameters.) The cartilage-cells in the centre are enlarged and separated from one another by dark-looking calcified matrix; im, layer of bone deposited underneath the periosteum ; 0, layer of osteoblasts by which this layer has been formed. Some of the osteoblasts are already ‘em- bedded in the new bone as lacune. The cartilage-cells are becoming enlarged and flattened and arranged in rows above and below the calcified centre. At the ends of the cartilage the cells are small and the groups are irregularly arranged; the fibrous periosteum is not sharply marked off from the cartilage, In the second stage some of the subperiosteal tissue eats its way through the newly formed layer of bone and into the centre of the cal- cified cartilage (fig. 65, ir). This is freely absorbed before it, so that _ large spaces are produced which are filled with osteoblasts and contain 56 THE ESSENTIALS OF HISTOLOGY numerous blood-vessels which have grown in at the same time. The spaces are termed medullary spaces, and this second stage may be termed the stage of irruption. lia. 65.—-SECTION OF PART OF ONE OF THE LIMB-BONES OF A F@TAL CAT, AT A MORE ADVANCED STAGE OF OSSIFI- CATION THAN IS REPRE- SENTED IN FIG. 64, AND SOMEWHAT MORE HIGHLY MAGNIFIED. ae Ais gat w 90th Ge oL_9 eS The calcification of the cartilage- matrix has advanced from the centre, and is extending between the groups of cartilage-cells which are arranged in character- istic rows. The _ subperiosteal bony deposit (im) has extended part passu with the calcification of the cartilage-matrix. The cartilage-cells ‘in the primary areole are mostly shrunken and stellate ; in some cases they have dropped out of the space. At i” and in two other places an irrup- tion of the subperiosteal tissue, composed of ramified cells with osteoblasts and growing blood- vessels, has penetrated the sub- periosteal bony crust, and has begun to excavate the secondary areole or medullary spaces; p, fibrous layer of the periosteum ; 0, layer of osteoblasts, some of them are embedded in the osseous layer as bone-corpuscles in la- cune ; bl, blood-vessels occupied by blood-corpuscles. Beyond the line of ossific advance the perios- 1 eb teum may be noticed to be dis- 5 il } tinctly incurved. This incurva- ANIA » tion is gradually moved on, the Ni cartilage expanding behind it il i until the head of the bone is HM | } reached, when it forms the peri- Hl i ' ' — “ = Se mars ata o gal = 0 ies osteal notch or groove represented i in fig. 66, p. 57. In the third stage of endochondral ossification there is a gradual advance of the ossification towards the extremities of the cartilage, and at the same time a gradual deposition of fresh bony lamelle and spicules on the walls of the medullary spaces, and on the surface of the new bone under the periosteum. -The advance into the cartilage always takes place by a repetition of the same changes, the cartilage- cells first enlarging and becoming arranged in rows, the matrix between the rows becoming calcified, dnd then the calcified cartilage becoming excavated from behind by the osteoblastic tissue so as to form new medullary spaces (fig. 67). The walls of these are at first formed Pia ay yf he ; r. 4 ~ p . : a ie Dep eitecaus cart Bie > Wd ee em haw oe ina te mee, hy PAR aA) Ad fi Ce eS. abe ee? facig : {tle 4), ge vs : , sor VTieeet + hoe wer » a ‘ “ 4 2 TEES ALY Cm. / -wivert:) g PRD Corsa rts to wali Pawling’ bn oe eG > Pere ee? pa mathe =) ° Lea ati: ’ 4 tear he is ate ets en oe : *, Pe. i; Re he Habe va oh mM Clase deposited by the osteoblasts, and between which bone-corpuscles become included, as in the case of the subperiosteal bone. The latter 58 THE ESSENTIALS OF HISTOLOGY “7 advances pari passu with the endochondral calcification, but beyond — this the uncalcified cartilage grows both in length and breadth, so that the ossification is always advancing into larger and larger portions of cartilage ; hence the endochondral bone as it forms assumes the shape of an hour-glass, the cylindrical shape of the whole bone being main- Fic. 67.—PART OF A LONGI- TUDINAL SECTION OF THE DEVELOPING FEMUR OF THE (eV 3 RABBIT. (Drawn under a | magnifying power of 3850 { diameters. ) a, rows of flattened cartilage-cells ; b, greatly enlarged cartilage- cells close to the advancing bone, the matrix between is partly calcified; c, d, already formed bone, the osseous trabecule being covered with osteoblasts (e), except here and_ there, where an osteoclast (7) is seen, eroding parts of the trabecule 5 gy, h, cartilage-cells which have become shrunken and irregular in shape. From the middle of the figure downwards the dark trabecule, which are formed of calcified cartilage-matrix, are be- coming covered with secondary osseous substance deposited by the osteoblasts. The vascular loops at the extreme limit of the bone are well shown, as well as the abrupt disappearance of the cartilage-cells, aN 7XOLE YO = i) Te i , . aay “33 wal aie WOR iSfeia: -» QU Sat ated apo tar ne ehh | WO Si tee fad Wiad bis: oeetcee rz eal Bagley iicen soa meliliat ry Ed a hae aes Ors | SY ie aa t e rly Ra | ‘ \ \e ’ ‘d x .— . * y ’ : ' f =" 4 = . . t er Tose Bo og Tide ot ae Ae a a STRUCTURE OF MUSCLE ° 65 dark, an apparent reversal being thereby produced in the striz. This reversal is due to the enlargement of the rows of dark dots, and the formation by their juxtaposition and blending of dark disks, whilst the muscular substance between these disks has by contrast a bright appearance. . Thé‘wing-muscles of insects are easily broken up into .very fine fibres or fibrils, which also show alternate dark and light strie. The number and relative thickness of these differ, however, considerably, _ according to the amount of stretching of the fibres (ftg. 75). Muscle- ___ rods are not seen in these fibres. e ‘ eS rH a. \*. Fic. 75.—FIBRES OF THE WING-MUSCLES\OF AN INSECT. = The fibres are in different conditions of extension, from A least extended, to D most ex- 4 tended. e, ¢, chief substance of the fibre; m, m, intermediate lines or disks; the light Fd bands, be, on either side of these only come to view when the fibre is sufficiently stretched K (C); with further extension (D), the middle of the dark band appears lighter, h. es + In muscular tissue which has been hardened in alcohol and certain other reagents, the structural appearances are a good deal altered from those of the living muscle, although the cross-strie are still very obvious. There is also a considerable tendency for the fibres to split up longi- ~ tudinally into fibrils, and by some authorities the finest of such fibrils are regarded as the ultimate elements of the fibre. Certain other reagents, such as dilute hydrochloric acid, cause a transverse splitting of the fibres into disks, and these effects of reagents led Bowman to form the opinion that the muscular substance may be in reality composed of minute prismatic particles set side by side in rows or planes to form the disks, and adhering end to end longitudinally to form the fibrils. _ To these constituent particles of the muscular substance he gave the name of ‘ sarcous elements.’ When living muscular fibres are examined by polarised light, the | _ whole of the muscular substance except the muscle-rods is seen to be doubly refracting, looking bright in the dark field produced by. crossing _ the axes of the Nichol’s prisms. Contracted muscle and dead muscle _ _ show, however, alternate bands of dark and light under those circum- stances. | ; ae Ending of muscle in tendon.—A small tendon-bundle passes to ™” “ely re 66 THE ESSENTIALS OF HISTOLOGY each muscular fibre and becomes firmly united with the sarcolemma, — which extends over the end of the fibre (fig. 76). Further, the areolar tissue between the tendon-bundles is continuous with that which lies between the muscular fibres, so that the connection of a muscle to its tendon is very firm. ee iaiaceeenit = ii EEE | BEE EEL El Bee wu i m & ic a wi z EI ane Fic. 76.—TERMINATION OF A MUS- CULAR FIBRE IN TENDON. m, sarcolemma ; 8s, the same membrane: passing over the end of the fibre; p, Fie. 77.—CAPILLARY VESSELS OF extremity of muscular substance, c¢, MUSCLE retracted from the lower end of the ? sarcolemma-tube; ¢, tendon-bundle passing to be fixed to the sarcolemma, Blood-vessels of muscle.—The capillaries of the muscular tissue are very numerous. They run, for the most, part, longitudinally, with transverse branches, so as to form long oblong meshes (fig. 77). In the red muscles of the rabbit and hare, the transverse eapillaries have small dilatations upon them. No blood-vessels ever a the sarcolemma. Lymphatic vessels, although present in the connective-tissue siedtinil (perimysium) of a muscle, do not penetrate between its cornea ij fibres. The nerves of voluntary muscles pierce the sarcolemma and. ter -minate in a ramified expansion known as an sed -plate Ses Les XIX. \. ~ an oe eet hacia 47 = waewet of A BSaele we tng ae uayue is cena in «ae 4 is near A> rie init i La deuay 22 al Gk to ea md . Me CYL La ed et i * 4 at eee hos "STRUCTURE OF MUSCLE 67 Voluntary Nesatinta fibres are developed from embryonic cells of the: mesoderm, which become elongated, and the nuclei of which become q multiplied, so as to produce long multi-nucleated fusiform or cylindrical fibres. These become cross-striated at first along one side, the change gradually extending around the fibre and also towards the centre ; but the middle of the fibre, to which the nuclei are at first confined, remains for some time unaltered (fig. 78). Eventually the change in structure extends to this also, and the nuclei pass gradually to occupy their ordinary position under the sarcolemma, which by this time has become formed. poor ARMA, CoF aTATE Ay sma BINT rere EP. ms oy eo ny Fic. 78.—DEVELOPING MUSCULAR FIBRE, FROM F@TUS OF 2. MONTHS. p, central protoplasm with several nuclei, n, scat- tered in it; s, commen- cing sarcolemma, with striated muscular sub- - stance developing im- mediately beneath it. - Fic. 79.—MUuUsCULAR FIBRE-CELLS FROM THE MUSCU- | LAR COAT OF THE SMALL INTESTINE, HIGHLY MAG- NIFIED. A. A complete cell, showing the nucleus with imtra-nuclear network, and the longitudinal fibrillation of the cell-sub- ‘stance, with finely vacuolated protoplasm between the fibrils. B. A cell broken in the process of isolation ; the delicate enveloping membrane projects at the proken end a little _ beyond the substance of the cell. : Involuntary or plain muscular tissue is composed of long, some- at flattened, fusiform cells (fig. 79), which vary much in length, but pasoally. not more than ;}5 inch long. Hach cell has an oval or : ¥2 68 THE ESSENTIALS OF HISTOLOGY rod-shaped nucleus, which shows the usual intra-nuclear network and ; commonly one or two nucleoli. The cell-substance is longitudinally striated, but does not exhibit cross-strie like those of voluntary muscle. There appears to be a delicate sheath to each cell. There is a little intercellular cementing substance uniting the cells together, and which can be stained by nitrate of silver. The fibres are collected into fas- cicull. Plain muscular tissue is found chiefly in the walls of hollow viscera ; thus it forms the muscular coat of the whole of the alimentary canal below the esophagus, and occurs abundantly in the muscular coat of that tube also, although it is here intermixed with cross-striated muscle; it is found also in the mucous membrane of the alimentary canal; in the trachea and its ramifications; in the urinary bladder and ureters; in the uterus, Fallopian tubes, and ovary; in the pro- state, the spleen, and muscle of Miller in the orbit, and in the ciliary muscle, and iris. The walls of gland-ducts also contain it, and the middle coat of the arteries, veins, and lymphatics is largely composed of this tissue. It occurs also in the skin, both in the secreting part of the sweat-glands, and in small bundles attached to the hair-follicles ; in the scrotum it is found abundantly in the subcutaneous tissue (dartos). The muscular tissue of the heart constitutes a special variety of involuntary muscular tissue (cardiac), and will be described along with that organ. - q a. is ad TRY — a“ night = Peli ror Wrysai | Lard - 4 aes. ? : mS a” oe y - ’ ‘i ' 7 ri ° ‘ H % - . ' . J - i T ran en re % " ‘ o -_ : ie ' 4B Fic. 82.—A SMALL PART OF A MEDUL- LATED FIBRE, HIGHLY MAGNIFIED. The fibre looks in optical section like a tube— hence the term tubular, formerly applied to these fibres. Two partial breaches of con- tinuity are seen in the medullary sheath, which at these places exhibits a tendency to split into lamine. The primitive sheath is here and there apparent outside the medul- lary sheath, and the delicate strize which are visible in the middle of the fibre pro- bably indicate the fibrillated axis-cylinder. Fic. 84.—Two porrioNs OF MEDULLATED NERYVE-FIBRES, AFTER WITH OSMIC ACID, SHOWING THE AXIS- CYLINDER, AND THE MEDULLARY AND PRIMITIVE SHEATHS, A. Node of Ranvier. B. Middle of an inter- node with nucleus, ¢, axis-cylinder, pro- jecting ; p, primitive sheath, within which the medullary sheath, which is stained dark ~~ by the osmie acid, is somewhat retracted. TREATMENT > Fic. , course of the peri- pheral nerve-fibres, the axis-cylinder at these places being encompassed only by the,primitive sheath. Hence the primitive sheath appears at these spots to pro- duce a constriction in the nerve-fibre, and the interruptions of the medullary sheath are accord- ingly known as the constrictions or nodes of Ranvier (fig. 81, R, R; fig. 83, L), the term nodes being ap- plied from the resem- blance which they bear to the nodes of a bamboo. The length of nerve be- tween two successive nodes may be termed an internode; in the middle of each inter- node is one of the nuclei of Schwann’s sheath. Besides these interruptions the medullary sheath shows a_ variable number of oblique clefts (fig. 83) which subdivide it into irregular portions, which have been termed medullary segments, but there is reason to believe that the. clefts are artificially produced. Osmic acid stains the 83.— NervE- medullary sheath FIBRE STAINED black. WITH OSMIC ACID. 72 ‘ THE ESSENTIALS OF HISTOLOGY The agis-cylinder, which runs along the middle of the nerve-fibre, is a soft transparent thread which is continuous from end to end of the nerve. On account of the peculiar refractive power of the medullary sheath Fie. 85. — AXIS- CYLINDER, HIGHLY MAGNIFIED, SHOW- ING THE FIBRILS COMPOSING IT. Fic. 87.—A SMALL BUNDLE OF Fic. 86.— PorTION OF THE paatipglidir va ete: bar NETWORK OF FIBRES OF oo , : REMAK FROM THE PNEUMO- The bundle is composed of _ nerve-fibres, with the exception CAE OF ee QO of the fibre m,m, which is en- n, nucleus; p, protoplasm sur- closed here and there by a thin rounding it; b, striation caused medullary sheath; m, n, nuclei by fibrils. of pale fibres. it is difficult to see the axis-cylinder in the fresh nerve except at the nodes, where it may be observed stretching across the interruptions in the medullary sheath, and it may also sometimes be seen projecting from a broken end of a nerve-fibre. It is longitudinally striated, being really made up of exceedingly fine fibrils (ultimate fibrils, fig. 85), which are darkly stained by chloride of gold, Staining with nitrate. PI Gds [ho waitin Burr har PORE RS ie V+ ewellcher An =, AP LGARN ’ 06 awe ? : : I ‘ i a { ney f , . 7 i ’ i - “= ™ eu . { a ‘ ? ' .- € 1 A * = } ‘ ” ’ - <> j z Fh, SS! nll ser Th At , 3 X Os See ee i , 2 baat ae Sea A ete =r , Yet even Or ENG OS sli 4 We cys = ; “ae ¢Martectrhied Watigiraias arore, & & ow ind rib oe Joey LAG ley rv * fom : - ’ . 1 ON - i Wg eiecereuy ies yf ij Sent oe ee , te 1 . - “pba it gbais ; Shisha, hi. bed ALG ass uct BS tiproee Vee wf ties ¥/ Ses is. itis nit v) RO = = a -ay der ) vise ye re ak 1SRP- AY srepereedl 6 ; es Por ace hayes wad zh ; .” + vy m4 - 4 tod ae eo Chih diaaion ails Neill at 2 iia a coaliniads = . @ a . 4 - «STRUCTURE OF NERVE-FIBRES 73 of silver produces a curious transversely striated appearance in the axis- cylinder, but it is not known if this indicates a pre-existent structure. Intermingled with the medullated fibres there may always, even in the cerebro-spinal nerves, be found a certain number of pale fibres devoid of the dark double contour which is characteristic of the presence of a medullary sheath. There are the non-medullated fibres, also called, after their discoverer, fibres of Remak (fig. 86). They frequently branch, which the medullated fibres never do except near their termination, and they are beset with numerous nuclei which perhaps belong to a delicate sheath. The sympathetic nerve is in many animals chiefly made up of fibres of this nature, but in some animals, on the other hand, most of the fibres of the sympathetic possess some small amount of medullary sheath (fig. 87). Fic. 88.—SEcTION OF THE SAPHENOUS NERVE (HUMAN), MADE AFTER BEING STAINED IN OSMIC ACID AND SUBSEQUENTLY HARDENED IN AI.COHOL. (Drawn as seen under a very low magnifying power.) ep, epineurium, or general sheath of the nerve, consisting of connective-tissue bundles of variable size separated by,cleft-like areole, which appear as a network of clear lines with fur tm here and -there fat-cell Ai plood-vessels : #®%>funiculi enclosed in their lamellated connective-tissue sheaths (perineurium, p); end, interior of funiculus, showing the cut = § § ends of the medullated nerve-fibres, which are embedded in the connective tissue within the funiculus (endoneurium). The fat-cells and the nerve-fibres are darkly stained by the osmic acid, but the connective tissue of the nerve is only slightly stained. Structure of the nerve-trunks.—In their course through the body the nerve-fibres are gathered up into bundles or fuwniculi, and the funiculi may again be united together to form the nerves which we meet with in dissection. The connective tissue which unites the 74 THE ESSENTIALS OF HISTOLOGY funiculi and invests the whole nerve, connecting it to neighbouring parts and conveying to it blood-vessels, lymphatics, and even nerve- | fibres destined for its coats, is termed the epinewriwm (fig. 88, ep). That which ensheaths the funiculi is known as the perinewriwm (fig. 88, per). It has a distinctly lamellar structure (fig. 89, p), the lamella Fic. 89.—PART OF A SECTION OF ONE OF THE FUNICULI OF THE SCIATIC NERVE OF MAN. (Magnified.) P, perineurium, consisting of a number of closely arranged lamelle. Zn, processes from the perineurium, passing into the interior of the funiculus, and becoming continuous with the endoneurium, or delicate connective tissue between the nerve-fibres. The connective- tissue fibrils of the endoneurium are seen cut across as fine points, often appearing to en- sheath the nerve-fibres with a circle of minute dots (fibril-sheath of Key,and Retzius). Numerous nuclei of connective-tissue cells are embedded in the endoneurium ; v, section of a blood-vessel. being composed of connective tissue and covered on both surfaces by “ flattened epithelioid cells (fig. 90). Between the lamelle are clefts for the conveyance of lymph to the lymphatics of the epimeurium. The delicate connective tissue which lies between the nerve-fibres of the C funiculus is the endonewrium (fig. 88, end; fig. 89, Hn). It assists in ; Fic. 90. — NERVE-FUNICULUS STAINED WITH NITRATE OF SIL- VER, SHOWING THE OUTLINES OF EPITHELIOID CELLS OF THE PERINEURIUM, The dark crosses on the nerve-fibres at the nodes of Ranvier are due to the staining of the axis-cylinder and of a band of intercellular substance which encircles the axis-cylinder at the node (constricting band of Ran- vier). supporting the longitudinally arranged meshwork of blood-capillaries, and its interstices communicate with the lymphatic clefts of the perineurium. i , “cgi: eb The nerve-trunks themselves receive nerve-fibres (nervi nervorum) which ramify chiefly in the epineurium and terminate in this in end- — bulbs. 2 q 4 ; ‘ \ 4 { 4 : ea games 54 ‘t : v >»: st Doster igre roste : . me: Mae erapuni WePTVER, Le Pa Pal) w koe P=. ie ; wee enipac.dy cate ete ed eed, ; i hie Mp : | hae Fie 7. LESSON XVIII. STRUCTURE OF NERVE-CELLS. 1. Tease in Farrant’s solution or in dilute glycerine a small piece of a spinal ganglion that has been: preserved with osmic acid. Notice the spheroidal ganglion-cells; their large nuclei and distinct nucleoli. Look for cells which still retain the axis-cylinder process and for T-shaped junctions of nerve- fibres with this. 2. Prepare a piece of sympathetic ganglion in the same way. Cells may be found with three or more axis-cylinder processes. If from a rabbit observe that the cells are bi-nucleated. 8. Mount stained sections of ganglia in Canada balsam. These will serve to show the arrangement of the cells and fibres in a ganglion and the nucleated sheaths around the nerve-cells. 4, Tease out a portion of the grey matter from a piece of spinal cord that has been a day or two in dilute chromic acid (4; per cent.). Before covering, look for the nerve-cells with a low power, and if possible get out one or two clear of the surrounding substance. Mount in water with a thick hair under the cover-glass. Notice the large branching cells some with a mass of pig- ment near the nucleus. Observe the fibrillation of the cell-processes. Notice also the reticular character of the tissue in which the cells are embedded. Many axis-cylinders will be seen in this preparation deprived wholly or partially of their medullary sheath, and their fibrillar structure can then also be well seen. Carefully sketch these appearances. To keep this preparation run very dilute logwood solution or osmic acid under the cover-glass, and when the cells are stained allow a drop of glycerine to pass in by diffusion. Measure two or three cells in each of the above preparations. Nerve-cells only occur in the grey matter of the nerve-centres, and in little groups on the course of certain of the peripheral nerves, these groups often causing nodular enlargements of the nerves, which are ‘known as ganglia. The most important ganglia are those which are found upon the posterior roots of the spinal nerves, upon the reots of some of the cranial nerves, and upon the trunk and principal branches of the sympathetic nerve. Minute ganglia are also found very nume- rously in connection with the nerves which are supplied to involuntary muscular tissue, as in the heart, alimentary canal, bladder, uterus, &e. _ Nerve-cells vary much in size and shape; they are mostly large, - some being amongst the largest cells met with in the body, but others are quite small. The nucleus is generally large, clear, and 76 "THE ESSENTIALS OF HISTOLOGY spherical, with a single large and distinct nucleolus. The shape depends a good deal on the number of processes, and the manner in which they come off from the cell. If there is but one process, the cell is generally spherical. This is the case with the cells of the Fic. 91.—CELL FROM A SPINAL GANGLION. sh, nucleated sheath of the cell; 7, n’, the nerve-fibre which the single process of the cell, after a number of coils, joins. Fig 92.—GANGLION-CELL OF A Fic. 938. A GANGLION-CELL WITHIN ITS FROG, HIGHLY MAGNIFIED, SHEATH ; FROM THK HUMAN SYMPATHETIC, a, a, straight fibre; b, b, coiled fibre; (Highly magnified.) c, smaller one joining it. : spinal ganglia (fig. 91); in these the single process, after a short course, joins one of the nerve-fibres which is traversing the ganglion. When there are two processes, they often go off in opposite directions al ve \ eppoas i Ger We ney caatior ~~ A eich i - Shirt ry 4 pry it whi at, Peat a : = meee) OULIA FPG \t = ay tal aw > mn Whet ghere ar Lace man ie A. r * a ‘ Pr — f ‘ vg a ; - a } ’ = 1 ‘ tnt z| vUl er bs ris = e ‘ -- eek Peace ART ait wir . oa pce ge wht i bands nh i inn omit polar, ove Oru geist) aly “Kiet Gtrils twat t ier s 7 v ul Mr Age moe i — ¢ A o laa ‘ol ibe e Re eM sai v.61 * - bn if vi~tk by re at ot Oxy Tai! fy ” ' {hive i wild 7) a Cibeliido t Wills Jive der bly are: iv Donk nine Pagheuk x ie) oi * - nee) ’ KOSTA *» STRUCTURE. ‘OF NERVE- CELLS 77 from the cell, which is thus rendered somewhat spindle-shaped, but occasionally they emerge at the same part, and the cell, being tapered in their direction, becomes pyriform (fig. 92). In these cases one fibre - often coils spirally round the other (fig. 92, b) before they separate to proceed in opposite directions as the axis-cylinders of nerve-fibres. When there are three or more processes, the cell becomes irregularly angular or stellate. Sometimes, as in the sympathetic ganglia (fig. 93), all the processes appear to become nerve-fibres, but in other instances, as in the large cells of the grey matter of the spinal cord, only one Tt Gan Fig. 94.—NERVE-CELL FROM SPINAL CORD OF OX, ISOLATED AFTER MACERATION IN VERY DILUTE CHROMIC AcID. (Magnified 175 diameters.) The cell has a well-defined, clear, round nucleus, and a bright nucleolus. The cell processes are seen to be finely fibrillated, the fibrils passing from one process into another through the body of the cell. a, axis-cylinder process broken a short distance from the cell. process becomes the axis-cylinder of a nerve-fibre (process of Deiters), the others dividing and subdividing in a ramified manner until their further course can no longer be traced. Their ultimate branches appear to lose themselves in a network which pervades the whole of the grey matter. According to the number of ihdie processes, nerve-cells are termed uni-, bi-, or multi-polar. Many nerve-cells, and notably those of the spinal cord, have a finely | fibrillar structure. The fibrils can be traced into the branches of the cells and into the axis-cylinders of nerve-fibres which are connected with the cells (fig. 95). Otherwise the cells have a finely granular appearance ; often with a clump of black, brown, or yellow pigment- - granules placed at one side of the nucleus. 78 THE ESSENTIALS OF HISTOLOGY. In the ganglia the nerve-cells have a nucleated sheath (figs. 91- 93) which is continuous with the primitive sheath of the nerve-fibres | with which they are connected. In the spinal ganglia, and in many of the ganglia at the roots of the cranial nerves, the cells are unipolar, “s 4 Fic. 95.—AXIs-CYLINDER PROCESS OF NERVE- CELL. x, ™&, portion of nerve- cell; «a, axis-cylinder process; «, medullary sheath. Highly magni- fied, and the cell-process joins a traversing nerve-fibre by a T-shaped junction (fig. 91). In the sympathetic ganglia they are multipolar. — The cells are disposed in aggregations of different size, separated by — the bundles of nerve-fibres which are traversing the ganglion (fig. 96). _ LJ ae. + ote d F ; ; ceaewie, — . o- + ; re ity STi ae » fins ; a iy avi 4% | # + The! bal tw 4 th AN) tL) - we R Kos tT oT ” — e ~ -. \ f 7 : = - ‘ t - Dice 7 e 7 < a ; ¥ STRUCTURE OF NERVE- CELLS. : 79 “The sarislion if large i is enclosed by an investing capsule of connective tissue which is continuous with the epi- and peri-neurium of the - entering and issuing nerve-trunks, The structure of the nerve-centres and the arrangement of: the cells and fibres in them are given in Lessons XXXVI. to XXXIX. Fig. 96.—LONGITUDINAL SECTION THROUGH THE MIDDLE OF A GANGLION ON THE POSTERIOR ROOT OF ONE OF THE SACRAL NERVES OF THE DOG, AS SEEN UNDER A LOW MAGNIFYING POWER. nerve ; c, connective -tissue coat of the ganglion ; d, principal group of nerve-cells, with fibres passing down from amongst the cells, probably to unite with the longitudinally coursing nerve-fibres by T-shaped junctions, | _ @, nerve-root entering the ganglion ; }, fibres leaving the ganglion to join the mixed spinal ; : : Development.—The cells and fibres of the nervous tissue are developed from cells derived from the ectoderm or epiblast of the embryo. . The nerve-fibres are at first developed as pale fibres like the fibres : of Remak ; it is uncertain whether they are formed by the coalescence of a number of cells, or whether they grow out as the processes of nerve-cells. The medullary sheath is subsequently added. When a nerve is cut, the fibres beyond the section as far as their terminations undergo a process of degeneration, the medullary sheath being broken up and the axis-cylinder interrupted and eventually _._ absorbed. New nerve-fibres are at length produced by a growth of the axis-cylinders in the proximal end of the nerve. 80 THE ESSENTIALS OF HISTOLOGY LESSON XIX. MODES OF TERMINATION OF NERVE-FIBRES. 1. SHELL out a Pacinian corpuscle from a piece of cat’s mesentery which has been kept for two or three days in +, per cent. chromic acid, and clear it as much as possible of adhering fat, aye be careful not to prick or otherwise injure the corpuscle itself. Mount in water with a thick hair to prevent crushing with the cover-glass. Sketch the corpuscle under a low power, and afterwards draw under a high power the part of the core where the nerve enters and the part where it ‘terminates. Notice the fibrous structure of the lamellar tunics of the corpuscle and the oval nuclei belonging to flattened epithelioid cells which cover the tunics. The distinct lines which when seen in the fresh corpuscle are generally taken for the tunics, are really the optical sections of these flattened cells. 2. Mount in Farrant one or more sections of a rabbit’s cornea which has been stained with chloride of gold. Notice the arrangement in plexuses of the darkly stained nerve- fibres and fibrils, (1) in the ‘connective-tissue sub- stance, (2) under the epithelium and (3) between the epithelial cells. Make one or two sketches showing the arrangement of the fibrils. 3. Spread out a small piece of muscle which has been stained with chloride of gold by Léwit’s method, and examine it with a low power to find the nerve-fibres crossing the muscular fibres and distributed to them. Try and separate those parts of the muscular fibres to which nerves appear to go, and mount them in glycerine. Search thoroughly for the close terminal ramifications (end-plates) of the axis-cylinders immediately within the sarcolemma. It is rather difficult to dissociate the fibres, and much patience is some- times required in searching for the nerve-terminations, but when they are ~ found the trouble is amply repaid. : Modes of ending of sensory nerve-fibres.—Nerve-fibres which are distributed to sensory parts end either in special organs or in terminal ramifications or plexuses. There are three chief kinds of special organs, termed respectively Pacinian corpuscles, tactile corpuscles, and end-bulbs. In the tactile corpuscles and end-bulbs the connective- tissue sheath of a medullated fibre expands to form a somewhat solid bulbous enlargement, which is either cylindrical or spheroidal in the end-bulbs and ellipsoidal in the tactile corpuscles. In both kinds of end- organ there is a capsule of connective tissue within which is generally a sort of core containing numerous nucleated cells. As the nerve-fibre enters the corpuscle (which in the tactile corpuscle only happens after it has reached the distal part of the corpuscle having wound spirally — 7 ! For methods of staining with chloride of gold see Appendix. Te . ps " / \ Z..? * 7 y . « a = a. ‘ win ‘ ’ ™ \ | ‘se i ‘ ‘c » H o «\ ,a ; a . turk 4 baa eh: Cee he weasel fia whe! Ageia Ben af, aT) TF. wr ‘ Med beme Mead Leo ~ MODES OF TERMINATION OF NERVE-FIBRES 81 once or twice round it) it loses its sheaths and is prolonged as an axis- _ eylinder only, which terminates after either a straight or a convoluted course within the organ (see figs. 98 to 101). ‘Tactile corpuscles occur an A ra “T. 5 ‘See si (Me \ | iy nl | i ao ee I Me Ns Fic. 97.—SECTION OF SKIN SHOWING TWO PAPILLA AND DEEPER LAYERS OF EPIDERMIS. a, vascular papilla with capillary loop passing from subjacent vessel, c; b, nerve- papilla with tactile corpuscle, ¢. The latter exhibits transverse fibrous markings ; 3 d, nerve passing up to it; Pei e sections of spirally winding nerve-fibres. Fie.98.—TacriLE CORPUSCLE Fic. 99.—SImMPLe TACTILE Fic. 100.—CyLINnDRICAL _ WITHIN A PAPILLA OF THE END-ORGANS FROM THE END-BULB FROM THE SKIN OF THE HAND, STAINED _ CLITORIS OF THE RABBIT. CONJUNCTIVA OF THE WITH CHLORIDE OF GOLD. CALF. _ The conyolutions of the nerve- ; within the corpuscle are oe AP: epidermis. Fig. 101.—ENp-BULB FROM THE HUMAN Fig. 102.—TAcTILE CORPUSCLES FROM THE CONJUNCTIVA. DUCK’S TONGUE, uw, nucleated capsule ; 5, core, the outlines of | A, composed of three cells, with two interposed its cells are not seen; c, entering fibre, disks, into which the axis-cylinder of the nerve, branching, and its two divisions passing to n, is observed to pass; in B there is but one terminate in the core at d. tactile disk enclosed between two tactile cells. AN Hi A SS = eS Fic, 104.—Parr oF PACINIAN BODY, SHOWING THE NERVE-FIBRES ENTERING THE CORE, FROM AN OSMIC ACID PREPARATION. ms, entering nerve-fibre, the medullary sheath of which is stained darkly, and ends abruptly at the Fic. 103.—MAGNIFIED VIEW OF A ‘core ; ps, prolongation of primitive sheath, PACINIAN BODY FROM THE CAT’S towards the outer part of the core; c.f, axis-cylin- der passing through the core of the central fibre ; MESENTERY. , e, some “< bat ae of the corpuscle, - ai nerve-fibre passing to the where they abut aga the canal through whicl ss mova d rey a pt to capiatien are the nerve-fibre passes—the dots within them are also seen issuing from it between the sections of the fibres of. which they are composed ;— tunics, n, nuclei of the tunics; n’/, nuclei of the endo- singing continued by others in the outer part of the core, ‘ he St he ee P a, 7 TN Ls ae fete nes: eyelet a 7 « . 3 MP na pea athe heli Ar ed band sees bs wiay ‘ey Pe a -s ' fe lt ule = ’ yr . is j Pitie. 1c : thes ly torr it Hg! ; ; a eS . & le Jase t s x . ‘ 7 - \ « J ! . 7 t i 2 - Xr) 7 ’ é IN mere Pe" Tee) . bie. plies > ie gma. 4, a — : i ter - , “7 > ete Cs eee PyeiMdey hein al ; oy ne RS } 5 yt oj | =e * ve dh rubght ; : a oe bee lek 0 a} ie! : Am ei >, EM ay hace Wap Sima 8 Bite d : ~ Sow Ae A A wishe mer’ s (LS Lee 5 eat ‘ie Ney ; Fe@erenl:, AT IAs ain wey: iv | '# Pr yt ME Pasirsicn secs Arad spandl la a ipteli a) : irs oy i ees » ically: i Le » eae wa : ig beer: A = | a ee ‘ . : av { Q bet 98 a r - tay Se EATON, a \ - fen lve ‘ bs ; \ ve ¢ ’ ' ’ it ~- 4 a Paty us, 6c nay os a oe ee wn Pe eo vo he Phe eA ey A ag * & «> ve , yt 5 pescve Gea Poey 77 ae || toh MODES OF TERMINATION OF NERVE-FIBRES 83 in some of the papille of the skin of the hand and foot, in sections of which they may be afterwards studied (see Lesson XXIII.) End-bulbs are found in the conjunctiva of the eye, where in most animals they have a cylindrical or oblong shape (fig. 100), but in man are spheroidal (fig. 101). They have also been found in papille of the lips and tongue, and in the epineurium of the nerve-trunks, and somewhat similar Sensory end-organs also occur in the integument of the external genital « organs of both sexes (fig. 99). In the skin covering the bill, and in thé tongue of certain birds (e.g. duck), a simple form of end- organ occurs, consisting of two or more cells arranged 1 in rows within a capsule, with the axis-cylinder terminating in flattened expansions between the cells (corpuscles of Grandry, fig. 102). The Pacinian corpuscles are larger, and have a more complex structure, than the tactile corpuscles and. end-bulbs (fig. 103). They are composed of a number of concentric coats arranged like the layers of an onion, and enclosing the prolonged end of a nerve-fibre. A single medullated nerve-fibre goes to each Pacinian corpuscle encircled by a prolongation of perineurium, and within this by endoneurium ; when it reaches the corpuscle, of which it appears to form the stalk, the lamelle of the perineurium expand to form some of the tunics of the corpuscle. The nerve passes on, piercing the other tunics, and still provided with medullary sheath, and surrounded by endoneurium, to reach the centre of the corpuscle. Here the endoneurium is prolonged to form a sort of soft cylindrical core, along the middle.of which the nerve-fibre, now deprived of its medullary and primitive sheaths, passes in a straight course as a simple axis-cylinder (fig. 104, c. f.) to termi- nate at the farther end of the core in a bulbous enlargement. Occa- sionally the fibre is branched. The tunics of the corpuscle are composed of connective tissue, the fibres of which for the most part run circularly. They are covered on both surfaces with a layer of flattened epithelioid cells, and here and there cleft-like lymph-spaces can be seen between them like those between the layers of the perineurium (see p. 74). When sensory nerve-fibres terminate in plexuses, they generally branch once or twice on nearing their termination. The sheaths of the fibres then successively become lost, first the connective tissue or peri- neural sheath, then the medullary sheath, and lastly the primitive sheath, the axis-cylinder being alone continued as a bundle of primitive fibrils (fig. 105, n). This branches and joins with the ramifications of the axis-cylinders of neighbouring nerve-fibres to form a primary plexus. From the primary plexus smaller branches (a) come off, and these form a secondary plexus (e) nearer the surface, generally imme- diately under the epithelium if the ending is in a membrane covered by that tissue. Finally, from the secondary plexus nerve-fibrils proceed and form a terminal plexus or ramification amongst the epithelium- cells (fig. 106, p), the actual ending of the fibrils being generally in _ little knob-like enlargements (b). Such a mode of ending in terminal G2 84 THE ESSENTIALS OF HISTOLOGY Fig. 105.—Sus-EPITrHELIAL PLEXUS OF THE CORNEA TREATED WITH CHLORIDE OF GOLD. (Ranvier.) n, branch of primary plexus; a, small branch passing to join the sub-epithelial plexus, e. Fic, 106.—VERTICAL SECTION OF CORNEA STAINED WITH CHLORIDE OF GOLD. < (Ranvier. ) n, 7, primary plexus in connective tissue of cornea; a, branch passing to sub-epithelial plexus, s ; 3 Pp, intra-epithelial plexus ; 0, terminations of fibrils, tp ib CRiarmctive! tina lir ateny dy ia. mHAN Be hrouz |. ve K% pies or Win” aa ‘ . J De tithes tis lees ut ‘ * a } na) 0 \ 4 , ; : . ; ; = ! aa * 2 Es * ae he =) ae tn" ; 4 ee 5 ‘ ‘ 7" ’ —? ie Sa 2 Pe v : a ae h ; : of inter Ce ee pint. th bdr Paey Kt organ ry “wth meee re a> af OS hg. inyoline: mitienk 4 Lior, fe ps ata, ~ Wadd) 2) QUOC sie ete tes oe, WIL force sro day Hesse aati ue. vou e_Shh ’ “ Die Piece i Marine hw eat eal 2 MODES OF “TERMINATION ‘OF NERVE-FIBRES 85 plexuses is most characteristically seen in the cornea of the eye. The nerve-fibrils may be brought distinctly into view by staining with chloride of gold, and then the fibrillar structure of the ramifications of the axis-cylinders also becomes’ very apparent. Fia. 107.—NERVE-ENDING IN MUSCULAR FIBRE OF A LIZARD (Lacerta viridis). . a, end-plate seen edgeways; 6, from the surface; s, s, sarcolemma; p, p, expansion of axis- cylinder, In } the expansion of the axis-cylinder appears as a clear network branching from the divisions of the medullated fibres, Fic. 108 —TERMINAL RAMIFICATIONS OF THE AXIS-CYLINDER IN END-PLATES : OF MUSCLE, STAINED WITH CHLORIDE OF GOLD. (Ranvier.) Ending of motor nerves.—Lastly the nerves to muscles also ter- minate either in special organs or in plexuses. The latter is the case with the nerves going to involuntary muscle, and here the primary plexuses are generally furnished with ganglion-cells in abundance. From these other nerve-fibres pass which form secondary plexuses and _ terminal ramifications amongst the contractile fibre-cells. These nerves will be more fully studied in connection with the intestine (see _ Lesson XXIX.) . . 86 | ‘THE ESSENTIALS OF HISTOLOGY ~ = In voluntary muscle the nerves, which are always medullated, ter- minate in special organs, the so-called end-plates. A medullated fibre will branch two or three times before terminating, and then each ~ branch passes straight to a muscular fibre. Having reached this, the primitive sheath of the nerve-fibre is continued into the sarcolemma of the muscle, the medullary sheath stops short, and the axis-cylinder ends ina close terminal ramification with varicosities upon its branches (figs. 107, 108). This ramification is embedded in a granular nucleated protoplasmic mass which lies between the sarcolemma and the cross-— striated muscular substance. In some cases the ramification is restricted to a small portion of the muscular fibre, and forms with the granular bed a slight prominence (eminence of Doyére). This is the case in mammals. In the lizard the ramification is rather more extended than in mammals, whilst in the frog it is spread over a considerable length of the fibre. 2 y } 1 =? \ ” Y \ 4 ft dc / as x l= Ai actengiie. vs | At , says v ap Bi i P “ Next Delite baba ven sing] ve Pe. i phi yt Vib Par emein-dimn' = PoUnte ig Sie. Shur 3 xt =. o iA lesa ile el bidy,: ““Dhesaaieen aes] Hell of veo prin Ayers the janet one as a or | A pil A sl epeians oe as Mie egidothalnurr at gased 3 br te ap pond Be ayia ' | , mole | “On 87 LESSON XX. : "STRUCTURE OF THE LARGER BLOOD-VESSELS. 1. Sections of a medium-sized peripheral artery and vein. In this pre- paration the limits of the vascular coats can be well seen and also the differ- : ences which they present in the arteries and veins respectively. The sections . may either be stained with hematoxylin and mounted in Canada balsam, or they may be stained in dilute magenta and mounted in glycerine and water. 2. Mount in Canada balsam a thin slice cut from the inner surface of an artery which, after having been cut open longitudinally and washed with * distilled water, has been treated with nitrate of silver solution and exposed to the light in spirit. This preparation will show the outlines of the epithelioid cells which line the vessel. t 3. A piece of an artery which has been macerated for two or three days ; in 380 per cent. alcohol (1 part rectified spirit to two parts water) is to be teased so as to isolate some of the muscular cells of the middle coat and portions of the elastic layers (networks and fenestrated membranes) of the inner and middle coats.. The tissue may be stained cautiously with dilute logwood solution, and glycerine afterwards added. The muscular cells are recognisable by their irregular outline and long rod-shaped nucleus. Sketch one or two and also a piece of fenestrated membrane. 4, Transverse section of aorta. Notice the differences in structure between this and the section of the smaller artery. : 5. Transverse section of vena cava inferior. Notice the comparatively thin layer of circular muscle, and outside this the thick layer of longitudinal muscular bundles. Make sketches from 1, 4, and 5, under a low power, from 2 and 3 under a high power. An artery is usually described as being composed of three coats, an inner or elastic, a middle or muscular, and an external or areolar - (fig. sty. ad). - It would, however, be more correct to describe the wall of aii artery as being composed of muscular and elastic tissue lined internally by a pavement-epithelium and strengthened externally by a layer of connective tissue. For the present, however, we may adhere to the generally received mode of description. The inner coat of an artery is composed of two principal layers. The inner one is a thin layer of pavement-epitheliwm (often spoken of as the endothelium), the cells of which are somewhat elongated in the direction of the axis of the vessel (fig. 110), and form a smooth lining to the tube. After death they become conily detached. Next to this comes an elastic 88 "THT. ESSENTIALS OF HISTOLOGY layer in the form either of elastic networks or of a fenestrated mem- brane. In some arteries there is a layer of fine connective tissue im- tervening between the epithelium and the fenestrated membrane (swb-_ epithelial layer). Fic. 109.—TRANSVERSE SECTION OF PART OF THE WALL OF THE POSTERIOR TIBIAL ARTERY. (75 diameters.) a, epithelial and sub. epithelial layers of inner coat ; b, elastic layer (fenestrated membrane) of inner coat, appearing as a bright line in section ; c, muscular. layer (middle coat); d, outer coat, consisting of connective-tissue bundles. ‘In the interstices of the bundles are some connective-tissue nuclei, and, especially near the muscular coat, a number of elastic fibres cut across ‘ Fie. 110.—EPITHELIAL LAYER LINING Fic. 111.—PorTION OF FENESTRA- THE POSTERIOR TIBIAL ARTERY, TED MEMBRANE FROM AN ARTERY, (250 diameters.) (Toldt.) «, b, ¢, perforations, The middle coat consists mainly of circularly disposed plain mus- cular fibres, but it is also pervaded in most arteries by a network of elastic fibres which are connected with the fenestrated membrane of the inner coat and are sometimes almost as much developed as the muscular tissue itself. This is especially the case with the larger arteries such as the carotid and its immediate branches, but in the smaller arteries of the limbs the middle coat is almost purely COP esea _ of muscular tissue. , me Pria ol fot _amety, 4 % (ig a Ls Wives, cere y TeeEsS O94) Fajr. , ee RES ee oe ee ee ' ‘ * ioe * " 3 4 9 q MW - *. - wr 5 a . A é ‘ 1 3 ri ‘ Wart”) ar , as ret ' i x f fae Dim ty - < “ 2 & \ Fe es i f 2 ie ‘ = oe = enn ~ -< Sl) ee Lk te ae oe Ed cana 1) fren’ wal, OM ieee i Pinty ‘ » 7 yfots bes ’ ar pe Sree / 92 oingisty aeecaly if ciesnlatie + tne Gulae Sheers, ‘bull te ic iad PREV 9h Fa ta eartonie : See Shree wh cht dee connect witha me inner cobeca, at aks songtiads nite covey ar Eacat Aaah This ta. < Spooks * = ; 2 - eae __—-s- STRUCTURE OF THE LARGER BLOOD-VESSELS 89 - The outer coat is formed of connective tissue with a good many elastic fibres, especially next the middle coat. The strength of an artery depends largely upon this coat; it is far less easily cut or torn than the other coats, and it serves to resist undue expansion of the .. “ dl . - vs , ~ ie Lf : ’> : Fig. 112.—ELasric NET- Fig. 113.—MUvscuL aR FIBRE-CELLS FROM : WORK OF ARTERY. SUPERIOR THYROID ARTERY. (540 (Toldt.) diameters. ) ns al —— 4 Fic. 114.—SEcTIoN OF THORACIC AOKTA AS SEEN UNDER A LOW POWER. (Toldt.) a, the inner coat consisting of three layers, viz.: 1. Epithelium seen asa fine line. 2. Sub- epithelial. 3, Elastic layers. In the part of the inner coat, at its junction with the middle, a layer of longitudinal muscular fibres is represented as cut across. b, middle coat with its elastic membranes; c, outer coat with two vasa vasorum, vessel. Its outer limit is not sharply marked, for it tends to blend with the surrounding connective tissue (hence it has been termed tunica adventitia). | + Variations in structuwre.—The aorta (fig. 114) differs in some 90 THE ESSENTIALS OF HISTOLOGY respects in structure from an ordinary artery. Its inner coat contains — a considerable thickness of sub-epithelial connective tissue, but its’ elastic layers are chiefly composed of fine fibres, and are not especially marked off from those of the middle coat, so that the inner and middle coats appear almost blended with one another. On the other hand, there is a very great development of elastic tissue in the middle coat, this tissue forming membranous layers which alternate with layers of the mus- cular tissue. A good deal of connective tissue also takes part in the formation of the middle coat, so that the wall is unusually strong. The inner and middle coats constitute almost the entire thickness of the wall, the outer coat being relatively thin. The other variations which occur in the arterial system chiefly have reference to the development and arrangement of the muscular tissue. Thus in many of the larger arteries there are longitudinal muscular fibres at the inner boundary of the middle coat, and in some arteries amongst the circular fibres of the middle coat. This is the case in the aorta. In some parts of the umbilical arteries there is a com- plete layer of longitudinal fibres internal to the circular fibres and another external to them, whilst the amount of elastic tissue is very small. Longitudinal fibres are also present in some other arteries (iliac, superior mesenteric, splenic, renal, &c.), external to the circular fibres, and therefore in the outer coat of the artery. The larger arteries themselves receive blood-vessels, vasa vasorum, which ramify chiefly in the external coat. Nerves, derived for the most part from the sympathetic system, are distributed to the muscular tissue of the middle coat. The veins (fig. 115) on the whole resemble the arteries in structure, but they present certain differences. In the internal coat the same “£ ~&% Fic. 115.—TRANSVERSE SECTION OF PART OF THE WALL OF ONE OF THE POSTERIOR TIBIAL VEINS (MAN), a, epithelial and sub-epithelial layers of inner coat; b, elastic layers of inner coat ; c, middle coat consisting of irregular layers of muscular tissue, alternating with connective tissue, and passing somewhat gradually into the outer connective tissue and elastic coat, d, layers may be present, but the elastic tissue is less developed and seldom takes the form of a complete membrane. The epithelium-cells are less elongated than those of the arteries. The middle coat (c) contains less elastic tissue and also less muscular tissue, being partly occupied by bundles of white connective-tissue fibres. These are derived — i- fhe =) f= rr wa - % i . : ‘ a = ’ i 4 1 y 6 Ae t ih ks iZ : . : - — ‘ ne 4 nae a J Pane sreseyiics moet, w | .- - Wy ane VAte oe ihe eye wr i< pron itt ue hye wiantir tise & « ee vf. we wong. = haa mye ’ Be 4 - ‘STRUCTURE OF THE LARGER BLOOD-VESSELS 91 from the external coat, which is relatively better developed in the veins than in the arteries, so that, although thinner, their walls are often stronger. Many of the veins are provided with valves, which are semilunar folds of the internal coat strengthened by a little fibrous tissue: a few muscular fibres may be found in the valve near its attachment. The layer of the inner coat is rather thicker, and the epithelium-cells are more elongated on the side which is subject to friction from the current of blood than on that which is turned towards the wall of the vessel. Variations in different veins.—The veins vary in structure more than do the arteries. In many veins longitudinal muscular fibres are found in the inner part of the middle coat, as in the iliac, femoral, umbilical, &e. ; in others they occur external to the circularly disposed fibres, and are described as belonging to the outer coat. This is the case in the inferior vena cava and also in the hepatic veins and in the portal vein and its tributaries. In the superior and in the upper part of the inferior vena cava the circular fibres of the middle coat are almost entirely absent. The veins of the following parts have no muscular tissue, viz. pia mater, brain and spinal cord, retina, bones, and the venous sinuses of the dura mater and placenta. It is only the larger veins and especially those of the limbs that possess valves. They are wanting in most of the veins of the viscera, in those within the cranium and vertebral canal, in the veins of the bones, and in the umbilical vein. 92 THE ESSENTIALS OF HISTOLOGY LESSON XXI. SMALLER BLOOD-VESSELS. LYMPHATIC SYSTEM. : 1. TakE a piece of pia mater which has been stained with logwood, and separate from it some of the small blood-vessels of which it is chiefly composed. Mount the shreds in Farrant. The structure of the small arteries can be studied in this preparation, the nuclei of the epithelium and of the muscular coat being brought distinctly into view by the logwood. The veins, however, possess no muscular tissue. Capillary vessels which have been dragged out from the brain in removing the pia mater may also be seen in this preparation. Sketch two small arteries of different sizes, 4 giving also their measurements. 2. Mount in Canada balsam a piece of the omentum of the rabbit stained with silver nitrate. The membrane should be stretched over a cork ora plate of glass, rmsed with distilled water, treated for five minutes with 1 per cent. nitrate of silver solution, again washed and exposed to the light in spirit. When stained brown the spirit is replaced by oil of cloves. Pieces may now be cut off from the membrane and mounted, as directed, in Canada balsam ; they should include one or more blood-vessels. This preparation is intended to show the epithelium of the smaller blood- vessels and accompanying lymphatics and also the epithelium of the serous membrane. Sketch a small piece showing the epithelium of the vessels. 3. Mount in Canada balsam a piece of the central tendon of the rabbit’s diaphragm which has been similarly prepared (except that the pleural surface . has first been brushed to remove the superficial epithelium so as to enable . the nitrate of silver more readily to penetrate to the network of lymphatic vessels underlying that surface). Observe the lymphatic plexus under a low power ; sketch a portion of the network. If the peritoneal surface is focussed, the epithelium which covers that surface will be seen, and opposite the clefts between the radially disposed tendon-bundles stomata may be looked for in this epithelium. . 4. Carefully study the circulation of the blood either in the web of the frog’s foot or in the mesentery or tongue of the frog or toad, or in the tail of the tadpole. The coats of the smaller arteries and veins are much simpler in structure than those of the larger vessels, but they contain at first all the same elements. Thus there is a lining epithelium and an elastic layer forming an inner coat, a middle coat of circularly disposed plain muscular tissue, and a thin owter coat. The same differences also are found between the arteries and veins, the walls of the veins being. thinner and containing far less muscular tissue (fig. 116), and the lining epithelium-cells, much elongated in both vessels, are far longer ee , ayes] : y ad sels Meee lv a a cd SW io: De welt silbevios tad SO the ce i ee « aa : —s aS Ble aha Ue ew > zp ie tr Cie Wes, et : ; tes L ba 3) De s = ’ i : js ’ > f rr AY ‘ ; 3) : : < = l E —_ ’ \ i t ~< ‘ + “3 ; an ee i ) FT —— cae? Re Py, ; | Shee, Pet Aa rer | E Play. an errutiutel oc Her; * bl ipepsin nEeres ; the rarieh) a: SI oe a pabirbli tam csi = ae em sings less roar bi usr Teapoiy site erat When Pept tlisir Mninbiest he eciee, tied Pyehaally sre wc te te pantinned: dnt a iy val capileri 2. ~The Pallere® shese tien ptetsr- nen (is 1 Ly eceyhte gous with Pootade hc E be ext isiod hy ie \ re ae oe ee ~ o i i ré = hy ‘i = | La : ister yee ; ‘ t the : . % 11 PAI) Ge vn ut tad yeina ere pigs any «le, dus Weer egharlanlel eh Piguemin+ Losey, ud 4 fas i! wet lie 2 2 SMALLER BLOOD-VESSELS. 93 and narrower in the small arteries than in the corresponding veins -(fig. 117). In the smallest vessels it will be found that the elastic layer has dis- appeared in the veins, and the muscular tissue is considerably reduced in thickness in both kinds of vessels. Indeed, it is soon represented by but a single layer of contractile cells, and even these no longer form a complete layer. By this time also, the outer coat and the elastic layer of the inner coat have entirely disappeared both from arteries and veins. The vessels are reduced, therefore, to the condition of a tube formed of pavement-epithelium cells, with a partial covering of circularly disposed muscular cells. Even in the smallest vessels, which are not capillaries, the differ- a b B SSE | | Spero ie ae | | Ffimineuaptes | | i oY i Ger ‘ eS eel ed OO Cres U) 0.0) { tO) “() } v 03 We ade He 0 || a = feds? | ty Y( 0 va SS | | Hs "== H Roan) hoe Fic. 116.—A SMALL ARTERY, A, WITH A CORRESPONDING VEIN, B, TREATED WITH ACETIC ACID. (Magnified 350 diameters.) a, external coat with elongated nuclei; 6, nuclei of the transverse muscular tissue of the middle coat (when seen endwise, as at the sides of the vessel, their outline is circular) ; c, nuclei of the epithelium-cells ; d, elastic layers of the inner coat. ences between arteries and veins are still manifested. These differences may be enumerated as follows :—The veins are larger than the corre- sponding arteries; they branch at less acute angles; their muscular cells are fewer, and their epithelium-cells less elongated ; the elastic layer of the inner coat is always less marked, and sooner disappears. Capillary vessels.—When traced to their smallest branches, the arteries and veins eventually are seen to be continued into a network _of the smallest blood-vessels or capillaries. The walls of these are composed only of flattened epithelium-cells (fig. 118) continuous with those that line the arteries and veins; these cells can be exhibited by staining a tissue with nitrate of silver. The capillaries vary somewhat _ in size and in the closeness of their meshes; their arrangement in + ot THE ESSENTIALS OF HISTOLOGY different parts, which is mainly determined by the disposition of the tissue-elements, may best be studied when the structure of the several organs is considered. In the transparent parts of animals, the blood may be seen flowing | through the capillary network from the arteries into the veins. The Fic. 117.—A SMALL ARTERY, A, AND VEIN, V, FROM THE SUBCUTANEOUS CONNECTIVE ‘ TISSUE OF THE RAT, TREATED WITH NITRATE OF SILVER. (17d diameters.) a, a, epitheloid cells with b, b, their nuclei; m, m, transverse markings due to staining of substance between the muscular fibre-cells; c, c, nuclei of connective-tissue corpuscles attached to exterior of vessel. current is very rapid in the small arteries, somewhat less so in the veins, and comparatively slow in the capillaries. The current is fastest in the centre of the vessel, slowest near the wall (inert layer), and with care it may be observed-—especially where there is any commen- __ cing inflammation of the part, as in the mesentery in consequence of _ ay gi r 4 . gaat Reedy << nis gut = ipkcign “hedged Sel eps rtiee i "Wing “nites me te bs nah aaa, % : 4 | - " rn ’ .} / . F ; ‘ \ ~ | \ ? 7 : Fee. e i o, ae F ’ . ‘ 2 >) an al 4 Aft . Fi~ - py - > = : * fot ehxiestwi a ; ‘ i Deas TOMS Hea Meares Se bet alld the heer Abee-ton ee ie ‘ 7 ie 7 Bethe bagi ata c ein ot -scmne acthor . ee : 7 ips Sbeho Betcha. Vonner> tae rpytyd| : di Ly = mistiiar Giros, 1): the wes yecneds tobe Bel os ae rit ea Ligwiyer Bis. cera rat atin hee Father duet | " | Sebati teenage Wire the opitiuliinen pertake nie. pfesaqu it t)s arb Spa} ehuTipaled LD) ae Gh ouden wary voliiva ie Bi. mie w ps ssiere ig a - | wash Laas ve. 4 9. t ] fate cca het OR cee imme ~ Set. bran CAPILLARY BLOOD-VESSELS AND LYMPHATICS © 95 exposure—that the white blood-corpuscles, which always tend to pass into the inert layer, and to adhere occasionally to the inner sur- Fic. 118.—CAPILLARY VESSELS FROM Fic. 119.—CAPILLARY BLOUD- THE BLADDER OF THE CAT, MAG- VESSELS IN THE WEB OF A NIFIED. FROG’S FOOT, AS, SEEN WITH ae . F THE MICROSCOPE, The outlines of the cells are stained by nitrate of silver. The arrows indicate the course of the blood, face of the blood-vessels, here and there pass through the coats of the small. vessels, and appear as migratory cells in the surrounding connective tissue. LYMPHATIC SYSTEM. To the lymphatic system belong not only the lymphatic vessels and lymphatic glands, but also the cavities of the serous membranes, which are moistened with lymph and are in open communication with the lymphatic vessels in their parietes. The larger lymphatic vessels somewhat resemble the veins in structure, except that their coats are much thinner and their valves much more numerous. In lymphatics of somewhat smaller size, the wall of the vessel is formed, first, by a lining of pavement-epithelium cells (endothelium of some authors), which are elongated in the direc- tion of the axis of the vessel; and, secondly, by a layer of circularly and obliquely disposed muscular fibres. In the smallest vessels (lymphatic capillaries), which, however, are generally considerably larger than the blood-capillaries, there is nothing but the epithelium remaining, and the cells of this are frequently not more elongated in one direction than in another, but have a characteristic wavy outline (fig. 121). Lymphatics begin in two ways—either in the form of plexuses, as in membranes (fig. 120), or as lacunar interstices, as is the case in some of the viscera. . 96 THE ESSENTIALS OF HISTOLOGY In order to show the lymphatic vessels, it is generally necessary to stain a tissue with nitrate of silver; but they may easily be in- jected by sticking the nozzle of an injecting canula into any tissue which contains them, and forcing coloured fluid under gentle pressure into the interstices of the tissue. SA Hh AH i | ) | | WUT UMN) \ I) Wh Hy Fic. 120.—LyYMPHATIC PLEXUS OF CENTRAL TENDON OF DIAPHRAGM OF RABBIT, PLEURAL SIDE, a, larger vessels with lanceolate cells and numerous valves; 0, c, lymphatic capillaries with wavy-bordered cells. In silvered preparations it may be observed that the lymphatics always appear in the form of clear channels in the stained ground-sub 4 F re Opt Geran tel preys... -, ie tt 2 4 - . ‘ ’ - ~— 7 ‘ on 0 ct ee . \ l / DL wiry + fy “gegen is Fick} _. le Oe aie apelin wt Ot he Poem Derciirme =m, . Pct a lie el ter ia . “ ‘ ‘ } ce wher i & cr ' ya SB OS , “J . a, _ SEROUS AND SYNOVIAL MEMBRANES 09 passing to which they form folds, within which blood-vessels, lymphatics, and nerves pass to the viscera. The inner surface is lined by a continuous layer of pavement- Shelia (fig. 122), which is very distinct in nitrate of silver prepa- rations. In some places there are apertures in the epithelium which lead direct into subjacent lymphatic vessels. These apertures are called stomata, and are surrounded by small protoplasmic cells (fig. 122, s, s). They are most numerous upon the peritoneal surface of the diaphragm, but are present in all serous membranes, and they serve to prevent any undue accumulation of lymph within the serous cavity during health, The pavement- epithelium rests upon a homogeneous basement-mem- . brane, which is especially well marked in the serous membranes of , man. ‘The rest of the thickness of the membrane is composed of con- : nective tissue, with a network of fine elastic fibres near the inner surface. ; The cavities of the serous membranes are originally formed in the -. embryo as a cleft in the mesoblast (pleuro-peritoneal split) which becomes lined with “epithelium, and its wall eventually becomes dif- ferentiated into the serous membrane. The synovial membranes, which are often compared with the serous membranes, and are indeed, like the latter, connective-tissue membranes which bound closed cavities moistened with fluid, are not so intimately connected with the lymphatic system, nor is the fluid - (synovia) which moistens them of the nature of lymph. Moreover, it is only here and there that there is a lining of epithelium-like cells, in place of the continuous lining of epithelium which we find in the _ serous membranes. Curious villus-like projections occur in many parts ; they are covered by small rounded cells, and probably serve:to extend the surface for the secretion of synovia. The blood-vessels of 7 synovial membranes are numerous, and approach close to the inner | surface of the membrane. — * . 1 H 2 100 THE ESSENTIALS OF HISTOLOGY LESSON XXII. LYMPHATIC GLANDS, TONSIL, THYMUS. 1. Sections of a lymphatic gland which has been stained in bulk with magenta and embedded in paraffin.' Notice (1) the fibrous and muscular capsule, with trabeculie extending inwards from it through the cortex and anastomosing with one another in the medulla, (2) the dense lymphoid tissue (adenoid tissue of authors) forming large masses in the cortex (cortical nodules) and rounded cords in the medulla (medullary cords). Notice also the clearer channel or lymph-sinus which everywhere intervenes between the fibrous tissue and the lymphoid tissue. Observe the fine fibres and branched cells which bridge across this channel. Make a general sketch under a low power of a portion of the cortex together with the adjoining part of the medulla, and under a high power drawings of small portions of cortex and medulla. 2. In sections of tonsil prepared similarly to those of the lymphatic gland, notice the large amount of lymphoid tissue only imperfectly collected into nodules. Observe also that the stratified epithelium, which covers the mucous membrane here as elsewhere in the mouth, is infiltrated with lymph-cor- puscles. Here and there pit-like recesses may be met with glands opening into the pits. 3. A similar preparation of the thymus gland of an infant. Notice that the masses of lymphoid tissue which form the lobules of the gland are separated by septa of connective tissue, and that they show a distinction into two parts, cortical and medullary. Observe the differences of structure of these two parts, and especially notice the concentric corpuscles in the medullary part. Make a sketch of one of the lobules under a low power and of a small part of the medulla under a high power, including one or two concentric corpuscles. Measure the latter. Structure of a lymphatic gland.—A lymphatic gland is composed of a fibrous and muscular framework, which encloses and supports the proper glandular substance, but is everywhere separated from it by a narrow channel, bridged across by cells and fibres, which is known as the lymph-channel. The framework consists of an envelope or capsule (fig. 124, c),-and of trabecule (tr), which pass at intervals inwards from the capsule, and after traversing the cortex of the gland divide and reunite with one another so as to form a network of fibrous bands. At one part of the gland there is usually a depression (hilus), and at the bottom of this the medulla comes to the surface and its fibrous bands are directly continuous with the capsule. i ndi Uy TUN TES) i- Ei * *s fst ee é ‘ \ . - te 4 oH Ped ' . t¥ si- 4 : Leper’ te ST - 101 rc GLAND. a, 1, afferent, e. 1. efferent lymphatics; C, cortical substance; M, reticulating cords of medullary substance ; /.s. lymph-sinus ; ¢, fibrous coat sending trabecule, /7, into the substance of the ¢land. eee foxes = BWeee S % PB. a) 3 © oy (2 Ac LP. AGRA ‘a Fic. 125.—Sncrion OF THE MEDULLARY SUBSTANCE OF A LYMPHATIC GLAND (0x), (800 diameters. ) a, , 4, lymphoid cords ; ¢, lymph-sinus ; 6, b, trabecule; d, d, capillary blood-vessels, 7 = oh ee a Be va oN os . . BAY vs sie 2 _ 102 THE ESSENTIALS OF HISTOLOGY The proper glandular substance (1. h.) is composed of lymphoid tissue, i.e. a fine reticulam with the meshes thickly oecupied by lymph- corpuscles. It occupies all the interstices of the gland, forming com- paratively large rounded masses in the cortex (lymphoid nodules, C) between the trabeculae, and smaller reticulating cord-like masses (lymphoid cords, M/) in the medulla. The cells which bridge across the lymph-channel in the medulla — (fig. 125, c) are branching nucleated cells which often contain pigment, so that this part of the gland has a dark colour. The lymph-channel~ is bridged across not only by these, but also by fibres derived from the capsule and trabecule, which pass to the lymphoid tissue and become ~ lost in its reticulum. But these fibres are often covered and concealed. by the branched cells. Lymphatic vessels (fig. 124, a. J.) enter the lymph-channels after passing through the capsule, and the lymph is conveyed slowly along the channels of the cortical and medullary part towards the hilus, taking up many lymph-corpuscles in its passage. At the hilus it is gathered up by an efferent vessel or vessels (e. /.) which take origin in the lymph-sinuses of the medulla. An artery passes into each gland at the hilus; its branches are’ conveyed at first along the fibrous cords, but soon pass into the lymphoid tissue, where they break up into capillaries: (fig. 125, d): The blood is returned by small veins, which are conducted along the fibrous trabecule to the hilus again. tr 4 3 d ; j Fie. 126.—A LOBULE OF THE THYMUS OF A CHILD AS SEEN UNDER A LOW POWER. C, cortex ; M, medulla ; c, concentric corpuscles ; b, blood-vessels; ¢7', trabeculae. The thymus gland is a lymphoid organ which is found only in the . embryo and during infancy. It is composed of a number of larger and — smaller lobules (fig. 126), which are separated from one another by = eet Vea: st ibe ws M4 *; tly walt ’ "7a we: i} tle: ” a AS is, | : with Ces Sav : ‘ " reas Wesel he, , » * ‘ tA ‘ , ‘ E> - “ = i 1 P -~ } “TK Al \ . ae, \ - ay! 4 = - } 1 3 ~ ss * ) ’ ; eu . 4 ’ oa mot, ne tip be : pas? 4 i iste Blige itts 5, ve \ \ i ’ ‘eo er ea“ bid! Pe vtic be ‘ vik hi. yee be } Tole Pe Pipa ca) tite. ( oo HOA, his hho sasypraiydi< TA ies : ! toi. viel a LNs : - Bible, peri beriatet “iw Cy tages eae aa. we seal 3: Me ibe nels i 34 ad-leey cated ln an co THYMUS GLAND 3 103 iepta of connective tissue, aloke which the blood-vessels and lymphatics pass to and from the lobules. Hach lobule shows plainly, when examined with the low power, a distinction into an outer cortical and ~ an inner medullary portion. The cortical part of the lobule is imper- fectly divided into nodules by trabecule of connective tissue, and is very similar in structure to the lymphoid tissue of the lymphatic glands | and tonsils, but the medulla is more open in its texture, and ‘the reticulum is composed of larger, more transparent, flattened cells, and contains fewer lymph-corpuscles. Moreover, there are found in Fic. 127.—ELEMENTS OF THE THYMUS. (300 diameters.) (Cadiat.) a, lymph-corpuscles ; b, concentric corpuscle. the medulla peculiar concentrically striated bodies (the concentric cor- puscles, fig. 127), which are usually composed of a number of flattened cells arranged concentrically around one or more central cells. Some- times these corpuscles are compound, two or three being grouped together and similarly enclosed by flattened cells. The lymphoid tissue is abundantly supplied with capillary blood-vessels, and large - lymphatic vessels issue from the organ, but in what way the latter are connected with the lobules has not been ascertained. Lymphoid tissue occurs in many other parts of the body in addition to the lymphatic glands, tonsils, and thymus gland, although it may not, as in these structures, constitute the bulk of the organ. Thus itis found in many mucous membranes, such as those of the intestine and of the respiratory tract, both in a diffuse form and also collected into nodular masses which are like the cortical nodules of a lymphatic ‘gland, and may, like those, be partially surrounded by a lymph-sinus. In the spleen also a large amount of lymphoid tissue is found sheathing the smaller arteries, and also expanded into nodular masses (Malpighian corpuscles of the spleen). In these organs it will, however, be studied in subsequent Lessons. Lymphoid tissue also occurs in considerable amount in: the serous membranes, especially in young animals; in the adult it is often trans- - formed into adipose tissue. The tissue is generally developed in con- nection with lymphatic vessels, an accumulation of retiform tissue and _ lymph-cells taking place either external to and around the lymphatic THE ESSENTIALS OF HISTOLOGY = -(perilymphatic nodule) ; or the lymphatic is dilated into a sina a oe 4 ‘ - Fic. 128.—DEVELOPING LYMPHATIC NODULES, FROM THE OMENTUM OF A GUINEA- ¢ PIG. | A, perilymphatie nodule; a, lymphatic vessel ; c, part of its epithelial wall, seen in optical = section ; e, lymph-corpuscles within the vessel ; b, lymphoid tissue of the nodule; d, blood- z capillaries ; B, endolymphatic nodule; a, vein; 6, artery ; c, capillaries; d, a lymphatic z vessel, in which this whole system of blood-vessels is enclosed ; e, lymphoid tissue within af: the lymphatic vessel ; , wall of the lymphatic in optical section. ¢ the formation of lymphoid tissue occurs within it (endolymphatic 4 nodule) (see fig. 128). = ‘ es oe i txt | : . a, = > Pre? , © ’ 7 a a we - ‘ = 2 , is - , 7,7 ot an i ittivnit Pe ts, i 7 Si Harrs +i Sra: | en me poy bis +) 95 eee, J wr ‘ +4, feats - , iF ray : ; hi. Heeates 3a PRY: shy a4 re EAs UE, ai ary Ve ESAS 105 ; LESSON XXIII. THE SKIN. 1. Sections of skin from the palmar surface of the fingers. The sections are to be made vertical to the surface, and should extend down as far as the subcutaneous tissue. They may be stained with logwood or picro-carmine and mounted in Canada balsam. In these sections notice the layers of the epidermis and their different behaviour to the staining fluid. Notice also the papille projecting from the corium into the epidermis, and look for tactile corpuscles within them. In very thin parts of the sections the fine inter-. cellular channels in the deeper parts of the epithelium (see Lesson VI. p. 22) may be seen with a high power. The convoluted tubes of the sweat-glands will be seen here and there in the deeper parts of the corium, and in thick sections the corkscrew-like channels by which the sweat is conducted through the epidermis may also be observed. Make a sketch showing the general structure under a low power, and other sketches to exhibit the most important ~ details under a high power. Measure the thickness of the epidermis and the = length of the papille. 2. Sections of the skin of the scalp, vertical to the surface and parallel to the slope of the hair-follicles, and others parallel to the surface, and therefore across the hair-follicles. Stain and mount in the same way as in the last preparation. Examine also the structure of the hairs. — In these preparations the details of structure of the hairs and hair-follicles together with the sebaceous glands and the little muscles of the hair-follicles are to be made out. 8. Vertical sections across the nail and nail-bed, cut with a strong scalpel or razor. The sections are stained with hematoxylin or picro-carmine. Notice the ridges (not papille) of the corium projecting into the epidermis. Observe also the distinction of the epidermis into Malpighian dager and nail proper. 4. Mount in Canada balsam a section from a portion of skin of which the blood-vessels have been injected, and notice the distribution of the capillaries - to the sweat-glands, to the hair-follicles, and to the papillary surface of the corium. The skin is composed of two parts, epidermis and cutis vera. The epidermis, or scarf skin, is a stratified epithelium (fig. 129). It is composed of a number of layers of cells, the deeper of which are soft and protoplasmic, and form the rete mucoswm of Malpighi, whilst the superficial layers are hard and horny; this horny portion some- times constituting the greater part of the thickness of the epidermis. The deepest cells of the rete mucosum, which are set on the surface of % the cutis vera, are columnar (fig. 129, c) in shape. In the coloured _ Above this comes the main part of the horny layer. It is composed of — 106 THE ESSENTIALS OF HISTOLOGY — races of mankind these cells contain pigment-granules. In as layers immediately above them the cells are polyhedral (fig. 129, p). Between __ all these cells of the rete mucosum there are fine intercellular clefts ; which separate the cells from one another, but’ are bridged across by ; fine fibres, which pass from cell to cell. The intercellular channels serve for the. passage of lymph, and within them occasional lymph- corpuscles may be found, often having a stellate figure from compres- : sion. The most superficial layer of the rete mucosum is formed of somewhat flattened granular cells (stratwm granulosum, s.gr). Im- — Fic. 129.—SrcrioN OF EPIDERMIS. oe H, horny layer, consisting of s, superficial horny scales ; sw, swollen-out horny cells; s.2. stratum lucidum; M, rete mucosum or Malpighian layer, consisting of p, prickle-cells, several rows deep ; ¢, elongated cells forming a single stratum near the corium ; and s.g7. stratum granulosum of Langerhans, just below the stratum lucidum; n, part of a plexus of nerve-fibres in the superficial layer of the cutis vera. From this plexus fine varicose nerve-fibrils may be traced passing up between the epithelium-cells of the Malpighian layer. mediately above this layer, the horny part of the epidermis reeanign as a layer of clear compressed cells several deep (stratum lucidum, s.l.). a number of layers of somewhat swollen cells (sw.), the nuclei of which are no longer visible. These cells become flatter as they — approach the surface, where they eventually become detached in the = gy form of thin horny scales (s). s a The growth of the epidermis takes place by a multiplication of a Fe this resis Pern . A itzish 2) t 4 1 i/ \ st ee te at Fir yet ; ge J 5 F i. ' é } y ) 7 ‘ 3 4 4 . - 2 ‘4 s = U 1 } ; f i , a, / - Z x he i =) " t rs . LAAs _ewi cen: 7) Tb ¢ - ; . of you bey at ied ti ies! me wr ey & Wie pe = é ‘ } aly LAO ys Lt be rey ap aL ati, ns st ut Wak fhoapey prasduaeg Bh hae ely Awe Engen a My 1) iw “eo A ; ‘ ite °@ —— 4 : : 107 cells of the deeper layers. The newly formed cells, as they grow, push towards the surface those which were previously formed, and in their progress the latter undergo a chemical transformation, which converts their protoplasm into horny material. This change seems to occur at the stratum granulosum (see fig. 1380) ; the granules which occupy the cells of that layer being composed of a substance termed eleidin, which is transformed into keratin. No blood-vessels pass into the epidermis, but it receives nerves which ramify between the cells of the rete mucosum in the form of fine varicose fibrils (fig. 129). Fic, 130.—PorTION OF EPIDERMIS FROM A SECTION OF THE SKIN OF THE , FINGER, COLOURED WITH PICROCARMINATE OF AMMONIA. (Ranvier.) _ a, stratum corneum; 6, stratum lucidum with diffused flakes of eleidin; c, stratum granu- losum, the cells filled with drops of eleidin; d, prickle-cells; e, dentate projections by which the deepest cells of the epidermis are fixed to the cutis vera. The cutis vera or corium is composed of dense connective tissue, which becomes more open and reticular in its texture in its deeper part, where it merges into the subcutaneous tissue. The superficial or vascular layer of the corium bears minute papilie, which project up into the epidermis, which is moulded over them. These papille for the most part contain looped capillary vessels (fig. 137), but some, especially those of the palmar surface of the hand and fingers, and the corresponding part of the foot, contain tactile corpuscles, to which medullated nerve-fibres pass (fig. 97, b). “In some parts of the body (scrotum, penis, nipple, and areola), involuntary muscular tissue occurs in the deeper portions of the cutis vera, and in addition, wherever hairs occur, small bundles of this _ tissue’ are attached to the hair-follicles. The blood-vessels of the skin are distributed almost entirely to the _ surface, where they form a close capillary network, sending up loops part of the nail-bed from which the root of the nail grows being known as the nail-groove. The distal part of the nail forms the free 108 THE ESSENTIALS OF HISTOLOGY into the papille. Special branches are also distributed to the various appendages of the skin, viz. the sweat-glands and hair-follicles, with their sebaceous glands and little muscles, as well as to the little masses of adipose tissue which may be found in the deeper parts of the cutis. 1¢ lymphatics originate near the surface in a network of vessels, which is placed a little deeper than the blood-capillary network. They receive branches from the papille, and pass into larger vessels, which are valved, and which run in the deeper or reticular part of the corium, From these the lymph is carried away by still larger vessels, which =~ course in the subcutaneous tissue. The appendages of the skin are the nazis, the hairs, with their ici gle aa Whe Hadi alan de They are all developed as thickenings and downgrowths of the Malpighian layer of the epi- . dermis. f i WA rh Ns i Om Fie, 181.—Srcrion ACROSS THE NAIL AND NAIL-BED, (100 diameters.) (Heitzmann.) P ridges with blood-vessels ; B, rete mucosum ; J, nail. The nails are thickenings of the stratum lucidum of the epidermis, which are developed over a specially modified portion of the corium, which is known as the bed of the nail, the depression at the posterior border, and is the thickest part.of the body of the nail. The horny substance of the nail (fig. 181, N) is composed of clear horny cells, each containing the remains of a nucleus; it rests immediately upon a Malpighian layer (B) similar to that which is found in the epidermis - “rs i . sid tg OLD < eeietibs liioh ata Bre. eo nu afb (oa) Apel ‘ ' . Lyie ‘ - ‘ y f ‘ : > P / 7 ‘ - bat a igs} a ' yt | ’ 4 a7 . . ’ . tet AA * * ; P ’ u | 53 Te eek ae ae ; ? ai oo — permgeid #002 | Lies ; : _ ' e @ abe fil: My ‘ f - a =i H - ae chan, Ub Ted Sosy ye | ait of aT ralte = ee ve Pimalewunll pedicle hd aig: Lith Usied—thp Diet perital : bs a ate a he et hn , i ' : cl * Rites os < Wen ; LAE ‘ . Sh See ~ Be eis . : \ .™ ini FRR Oras 2 ” r te tO Awia Sriirs ona] ‘ I ‘2 eet S Ps. a3 : CW hel ee Rete em A aes batt, Geir iid 5 | “ AS Prt a - ‘ 3 ‘ ‘ | . } e- 7 ‘ penal t - vs é tie he \e 3 t . . , $3 = Vv i] i » 2 hen ~ oN ‘ nai" 32 a “ ’ } 22 + Fi i ; = . hae . a 27 . ’ Y a er : m 4 P : x ' ¢ 4 i + - ; e 4 as na <= : Bai sia’ Fae . : y : Lon $ _ a - be 440 i ae a Raise? 457/ ah pre? Ih Marc Bp sri Sibi toes: ies 4 Wak hop v Oo thee i iefok. = oy] ee tie al 5 Wi THE SKIN of the cutis vera. Its fibres and cells have a regular circular arrangement around the follicle, the cells being flattened against the hyaline layer. Externally the dermic coat of the follicle has @ more open texture, corresponding to the reti- _ cular part of the cutis, and containing the larger branches of the arteries and veins. In the large tactile hairs of animals, the veins near the bottom of the follicle are dilated into sinuses, SO as to pro- duce a kind of erectile structure. The hair grows from the bottom of the follicle by multiplication of the soft cells which cover the papilla, these cells becoming elongated to form the fibres of the fibrous substance, and otherwise modi- fied to produce the medulla and cuticle. When a hair is eradicated, a new hair is pro- duced from these cells. It is not uncommon to find hair-follicles in which the whole of the lower part has degenerated in such a way that the vascular papilla, and the soft, growing cells which cover it, may have entirely disappeared. The hair then ceases to grow, and eventually becomes lost, but its place may be again supplied by a new hair, which becomes formed in a downgrowth from either the bottom or the side of the hair-follicle, a new papilla first becoming formed at the extremity of the downgrowth (fig. 135). If not previously detached, the old hair’may be pushed from out the follicle by the one which replaces it. The hairs are originally developed in the embryo in the form of small solid downgrowths from the Malpighian layer of the epidermis (fig. 136, A). The hair-rudiment, as it is called, is at first com- posed entirely of soft, growing cells ; but presently those in the centre become diiron tinted, so as to produce a minute hair invested by inner root- sheath, and its base resting upon a papilla which has grown up into the extremity of the hair-rudi- ment from the corium (fig. 136, B). As the minute hair grows, it pushes its way through the superficial layers of the epidermis, which it finally __ perforates (C). The hair-rudiments commence at the third or fourth month of fetal life; their growth is completed about the fifth or sixth _ month, and they form a complete hairy covering 111 ij -yroot-sheath by a basement-membrane termed the hyaline layer of the follicle. This inner vascular layer corresponds to the superficial layer Fie. 135.—ComMEN- CING REPLACEMENT OF OLD BY NEW HAIR. (Toldt.) a, outer root-sheath; 3}, dermic coat of follicle ; J, downgrowth of epi- thelium to form new hair-follicle ; p, papilla. of new hair commen- cing ; j, root of old hair ; t, duct of pabaceous gland, fm 4 = 112 ‘THE ESSENTIALS OF HISTOLOGY termed the lanwyo. This is entirely shed within a few months of birth, the new hairs being formed in downgrowths from the old hair-follicles _ in the manner already mentioned. * Hairs grow at the rate of half an inch per month. They ai are found — all over the body except on the palms of the hands and the soles of the feet, and on the distal phalanges of the fingers and toes. They — Fic. 156, A. Hair-rudiment from an embryo of six weeks. «, horny, and b, mucous or Malpighian layer of cuticle ; i, basement- membrane ; m, cells, some of which are assuming an oblong figure, which chiefly form the future hair. B. Hair-rudiment, with the young hair formed - but not yet risen through thecuticle. a, horny, }, Malpighian layer of epidermis ; c, outer, d, inner, root-sheath ; e, hair-knob: 7, stem, and g, point of the hair; , hair-papilla ; n, n, commencing sebaceous follicles, C. Hair- follicle with the hair just protruded, usually slant, and in the negro the hair-follicles are even considerably curved. On the scalp they are set in groups, as is well seen in a hori- zontal section. The hairs of animals are often curiously marked by the arrange- ment of their medulla, the markings being often characteristic of the particular species. Muscles of the hairs.—A bundle of plain muscular tissue is attached to each hair-follicle ; passing from the superficial part of the corium, on the side to which the hair slopes, obliquely downwards, to be attached near the bottom of the follicle (arrector pili, fig. 183, n). When the muscle contracts, the hair becomes erected, and the follicle is dragged — upwards so as to cause a prominence on the general surface of the skin; whilst the part of the corium from which the little muscle arises — is correspondingly depressed; the roughened condition known as * goose skin’ being in this way produced. The sebaceous glands (fig. 133, ¢) are small saccular glands, the. wy. : os “ ‘ a ee Lied ae Em Paw WEEE Z be *S “ay L- ~ : = 7 7+ ‘ . 1¢ > ’ * +. ; : N + _ ‘ , } 3 , , 5 } nd ’ zal ( ’ ; ‘ A ’ = » . bd = , s ba ~ P iz - ~ - *, re i ot é « a . 4 pas ; } : 92.5 i os & ; j ad. fang 7 : ; ‘ ° sg abe Rew |: tide (Ene Fuels ie My _ 7 Hg ve epadioc hh » me wWts. a U tt ® bet 4" i > ee pp Biers bh tren lar Layee, Ey reheaay: st ae Ni acne idbiel re eh a RS a 2 ¢ : : ' a. of Yi Y A. ‘ se i, \ i) ) ei tie pod a Poa meintely, | Sy THE SKIN 113 ducts from which open into the mouths of the hair-follicles. Both the duct and the saccules are lined by epithelium, which becomes charged with fatty matter. This sebaceous matter is discharged into the cavity of the saccule, probably owing to the disintegration of the cells within which it is formed. There may be two or more sebaceous glands attached to each follicle. The sebaceous glands are developed as outgrowths from the outer root-sheath. ‘The sweat-glands are abundant over the whole skin, but they are most numerous on the palm of the hand and on the sole of the foot. They are composed of coiled tubes, which lie in the deeper part of the integument and send their ducts up through the cutis to open on the surface by corkscrew-like channels which pierce the epidermis (fig. 187). Fie. 137.—Duct oF A SWEAT-GLAND PASSING THROUGH THE EPIDERMIS. (Magnified 200 diameters.) (Heitzmann.) BP, papillze with blood-vessels injected ; V, rete mucosum between the papille; Z, stratum corneum ; PL, stratum granulosum ; J, duct, opening on the surface at P. The glandular or secreting tube is a convoluted tube composed of a basement-membrane lined by a single layer of cubical or columnar epithelium-cells, and with a layer of longitudinally disposed plain muscular fibres between the epithelium and basement-membrane. It is considerably larger than the efferent tube or duct, which begins within the gland and usually makes several convolutions before leaving this to traverse the cutis vera. The efferent tube has an epithelium consisting of two or three layers of cells, within which is a well- marked cuticular lining, but there is no muscular layer. The passage _ through the epidermis has no proper wall, but is merely a channel excavated between the epithelium-cells. _ The ceruminous glands of the ear are modified sweat-glands, I The sweat-glands are developed; like the hairs, from downgeewiiaal a of the Malpighian layer of the epidermis into the corium, the rudi- Fic. 188.—Srcrion OF A SWEAT-GLAND IN THE SKIN OF MAN. a, a, secreting tubes in section ; b, a tube seen from above; ec, c, efferent tubes ; d, inter- - tubular connective tissue with blood-vessels. 1, basement membrane; 2, "muscular fibres cut across ; 3, secreting epithelium of a tubule. ments which are thus formed becoming eventually coiled up at their extremities and converted into hollow tubes. The sweat-glands receive nerve-fibres, and each gland has a special cluster of capillary blood-vessels. ‘ 4 1 Pmt , 2 ] $ 4 cai } 4 les Ee wet S 7 7 a ry, ¥ ee q fix - . * } - 4) tT Nols a fled 4 th Beasties baye mo appoter, ao . eFiren. an ah a iw“ > f aS ee @ Apel Ae ici : Py Biren nd, as cossnapcc lite amaze ine : ol Ueda, aos iiwy eens be oe te —tes¥ LESSON XXIV. STRUCTURE OF THE HEART. 1. In a section through the wall of the auricle which has been stained with magenta and mounted in glycerine, notice the relative thickness of the epicardium, myocardium, and endocardium. Observe the blood-vessels and nerve-fibres under the epicardium, often embedded in fat; here and there a ganglion may be seen under this membrane. Notice also the elastic networks under both the pericardium and endocardium. Make a general sketch from this section. 2. Section through the wall of the ventricle, stained with logwood and mounted in Canada balsam. The muscular fibres are variously cut. In those cut longitudinally, notice the branching of the fibres and their union into a network. Notice also that although the fibres are cross-striated this is less distinct than in voluntary muscle, and the nuclei lie in the centre of each -fibre. Transverse markings may also be seen passing across the fibres between the nuclei and indicating a division into cells. The endocardium is very thin, especially over the columne carne. 3. The lymphatics of the heart are easily injected with Berlin blue by sticking the nozzle of the injecting syringe into the muscular substance, in the interstices of which the lymphatics arise. These commencing lymphatics lead to efferent vessels which pass to the base of the heart under the epi- cardium. 4, Section through one of the valves of the heart, stained and mounted as preparation 2. 5. The epithelium which covers the epicardium, and that which lines the endocardium, may be studied in preparations of the fresh organ which have been treated with nitrate of silver and subsequently exposed to the light and hardened in alcohol. The muscular substance of the heart (myocardiwm) is composed of transversely striated muscular fibres (fig. 139), which differ from those of voluntary muscle in the following particulars: their striations are less distinct ; they have no sarcolemma; they branch and unite with neighbouring fibres, and their nuclei lie in the centre of the fibres. Moreover, the fibres are composed of a series of short cylindrical cells (fig. 140) joined together end to end, each corresponding to one of the nuclei. The lines of junction of these cells may sometimes be seen in longitudinal sections stained with hematoxylin or magenta ; but they - come much more distinctly into view in sections of the fresh tissue _ stained with nitrate of silver. ' 12 3 . “= : 7 ee: 116 THE ESSENTIALS OF HISTOLOGY In the interstices of the muscular tissue there is a little areolar tissue in which run the very numerous blood-capillaries and the lacunar lymphatics. —— tom lta tun passa ———— 4 ot 10 es iii Fic. 189.—MuscuLaR FIBRES FROM THE Fig. 140.—S1x MUSCULAR FIBRE-CELLS HEART, MAGNIFIED, SHOWING THEIR FROM THE HEART. (Magnified 425 CROSS-STRLE, DIVISIONS, AND JUNC- diameters. ) TIONS. a, line of junction between two cells; 8, ¢, The nuclei and cell-junctions are only repre- branching of cells. sented on the right-hand side of the figure. Ss 6 eas a)= FS Fe Fic. 141.—SrEcTION OF THE EPICARDIUM OF THE RIGHT AURICLE. a, serous epithelium in section; b, connective-tissue layer; ¢, elastic network ; d, subserous areolar tissue; ¢, fat; jf, section of a blood-vessel; g, a small ganglion; #, muscular fibres of the myocardium ; 7, intermuscular areolar tissue, a The myocardium is covered externally by a layer of serous mem- brane—the epicardium (cardiac pericardium, fig. 141)—composed, like other serous membranes, of connective tissue and elastic fibres, the F ae ; Tite TVA Km. hie pS Ltrs ers uF: Ting 44 Jia Bites. on 444? iP glia, Tey ts MarVvedi*rin a if A M5 - v at Tee it] 2 iS > eet ‘ ~ Mi ‘. ¢ s : = . \ ' + i i. re a 2 i } 4 { ‘ + t ¥ - “NN Tay A } 5 { > ~ : ’ a & . -" -* . * vt a 2% As WAL 8 . é * oe ne ning Sa sae MO ik: rele sere en T) 0s Je) Mp me! de Tel) OCP AEs oy iy ha ey fy . diye portst ia Upon Pal %, “4 hs erga Ma Sty donc fF ; Bi Me re a a es FS , _ - STRUCTURE OF THE HEART 117 latter being most numerous in its deeper parts. Underneath the epicardium run the blood-vessels, nerves, and lymphatic vessels of the heart, embedded in areolar and adipose tissue; this tissue being con- tinuous with that which lies between the muscular bundles. | The endocardium (fig. 142) has a structure not very unlike the pericardium. It is lined by a pavement-epithelium, like the epithelium of a serous membrane, and consists of connective tissue with elastic fibres in its deeper part, between which there may, in some parts, be Fie. 142.—SEcrION OF THE ENDOCAR- DIUM OF THE RIGHT AURICLE. a, lining epithelium ; 6, connective tissue with fine elastic fibres; c, layer with coarser elastic fibres ; d, sub-endocardial connective tissue continuous with the intermuscular tissue of the myocardium; A, muscular fibres of the myocardium ; m, plain muscu- lar tissue in the endocardium. - Fic. 142.—SrcrioN THROUGH ONE OF THE FLAPS OF THE AORTIC VALVE, AND PART OF THE CORRESPONDING SINUS OF VALSALVA, WITH THE AD- JOINING PART OF THE VENTRICULAR WALL. sub-endocardial tissue; c¢, fibrous tissue of the valve, thickened at c’ near the free edge ; d, section of the lunula; e, section of the fibrous ring ; 7, muscular fibres of the ven- tricle attached to it; g, loose areolar tissue at the base of the ventricle; s. V. sinus Valsalve ; 1, 2, 3, inner, middle, and outer coats of the aorta. a, endocardium, prolonged over the valve; b, ' found a few plain muscular fibres. Fat is sometimes met with under the endocardium. In some animals, e.g. the sheep, and sometimes also in man, large beaded fibres are found under the endocardium. These are formed of large clear cells joined end to end, and generally containing in their centre two nuclei, whilst the peripheral part of the cell is formed of cross- striated muscular tissue ; they are known as the fibres of Purkinje. The valves of the heart are formed of folds of the endocardium strengthened by fibrous tissue (fig. 143). This tissue forms a thicken- ing near the free edge of the valve (c’). At jie bale ventricular valves a little of the muscular tissue of yk a found passing a short distance into the valve. are connected at intervals with small pee (fig. 141, a branches pass to the muscular substance, but their mode of tion has not been ascertained. Ee eae ithn, We AF akae adaieiige ooh sauna 4, 5 eran Bhs deft mi? k tS Pi ' ye eee a7 ‘he 3 rs & otra : LESSON XXV. THE TRACHEA AND JLUNGS. 1, In sections of trachea, stained with logwood or borax-carmine, and mounted in Canada balsam, notice the ciliated epithelium, the basement-membrane (of some thickness in the human trachea), the lymphoid tissue of the mucous membrane, the elastic tissue external to this, and lastly the fibrous membrane containing the cartilages. In the mucous membrane and submucous areolar tissue look for sections of mucous glands, ducts of which may be seen opening on the surface. At the back of the trachea notice the plain muscular fibres transversely arranged; there may be larger mucous glands external to these. 2. In sections of lung similarly prepared, notice the sections of the alveoli ‘collected into groups (infundibula). Find sections of bronchial tubes, some cut longitudinally and passing at their extremities into the infundibula, others cut across; the latter show the structure of the tubes best. In each tube notice the ciliated epithelium internally. Next to this the mucous membrane containing numerous elastic fibres and often thrown into folds ; then the layer of circular muscular fibres, and outside this, loose fibrous tissue in which in larger bronchial tubes the pieces of cartilage may be seen embedded. Small mucous glands may also be observed in the fibrous tissue sending their ducts through the other layers to open on the inner surface. Notice always accompanying a section of a bronchial tube the section of a branch of the pulmonary artery. In the sections of the alveoli observe the capillary vessels passing from one side to the other of the interv ening septa; and in places where the thin wall of an alveolus is to be seen in the section, try and make out the net- work of blood-capillaries upon it. Notice within the alveoli nucleated cor- puscles which very frequently contain dark particles in their protoplasm. They appear to be amceboid cells which have migrated from the blood-vessels and have taken in inhaled particles of carbon. They seem to pass back into the lung tissue, for similar cells may be seen in this. Make a sketch of part of the wall of a bronchial tube and of one or two of the alveoli. 3. Mount in Canada balsam a section of lung in which the pulmonary vessels have been injected. Study the general arrangement of the vessels with a low power, and the network of capillaries of the alveoli with a high power. Observe that the veins run apart from the arteries.- Sketch the capillary network of one or two adjoining alveoli. The trachea or windpipe is a fibrous and muscular tube, the wall of which is rendered somewhat rigid by G-shaped hoops of cartilage which are embedded in the fibrous tissue. The muscular tissue, which is of the plain variety, forms a flat band, the fibres of which run trans- versely at the back of the tube. The trachea is lined by a mucous ~ ae 8 7 nm eee ey eee : | ee Se 120 |. THE ESSENTIALS OF HISTOLOGY = membrane (fig. 144, a-c), which has a ciliated epithelium upon its inner surface. The epithelium-cells have been already described : (Lesson VII.); they rest upon a thick basement-membrane.- The mucous membrane proper consists of areolar and lymphoid tissue, and contains numerous blood-vessels and lymphatics. In its deepest part | is a well-marked layer of longitudinal elastic fibres (d). Many small / glands for the secretion of mucus are found in the wall of the trachea. » They may lie either within the mucous membrane or in the submucous tL 6 SERA y CTY Bis ds ON Piss, oS Fic. 144,—LONGITUDINAL SECTION OF THE HUMAN TRACHEA, INCLUDING PORTIONS OF TWO CARTILAGINOUS RINGS. (Moderately magnified.) a, ciliated epithelium ; 6, basement-membrane ; ¢, superficial part of the mucous membrane, containing the sections of numerous capillary blood-vessels and much lymphoid tissue; d, deeper part of the mucous membrane, consisting mainly of elastic fibres; e, submucous areolar tissue, containing the larger blood-vessels, small mucous glands (their ducts and alveoli are seen in section), fat, &c. ; /, fibrous tissue investing and uniting the cartilages ; g, & small mass of adipose tissue in the fibrous layer; h, cartilage. areolar tissue (e), or, lastly, at the back of the trachea, outside the transverse muscular fibres. ; The two divisions of the trachea, the bronchi, are precisely similar in structure. \ ; ! The larynx is also very like the trachea so far as the structure of | the mucous membrane is concerned, but over the true vocal cords and — upon the epiglottis, as well as here and there in the part above the — glottis, stratified epithelium is found, and taste-buds (see Lesson — XXVI.) may occur in this epithelium, except over the vocal cords. a _ ar. e.9) t ‘ , _— ¢ 7 J - THE TRACHEA AND LUNGS 121 The lymphoid tissue is especially abundant in the mucous mem- brane of the ventricle of Morgagni, and a large number of mucous glands open into this cavity and into that of the sacculus. q The true vocal cords are composed of fine elastic fibres. The cartilages of the trachea and larynx are hyaline, except the } epiglottis and the cartilages of Santorini and of Wrisberg, which are . composed of elastic fibro-cartilage. Fic: 145.—DIAGRAMMATIC REPRESENTATION OF THE ENDING OF A BRONCHIAL TUBE IN SACCULATED INFUNDIBULA, The lungs are formed by the ramifications of the bronchial tubes and their terminal expansions, which form groups of sacculated dila- tations. (infundibula), beset everywhere with small hemispherical bulgings, known as the air-cells or pulmonary alveoli. . - RE WES ‘ XK w = z - The lymphatics of the lung form two sets of vessels, ‘one set accompanying the bronchial tubes, and another set forming a network _ in the interstitial connective tissue, and in the subserous tissue. Both _ sets of lymphatics tend towards the hilus and enter lymphatic glands _ at the root of the lung. Those in the subserous tissue communion aay hy ps So ee a ‘i ym + obiizatin vamyiviat Mpeg ee Eis LESSON XXVI. STRUCTURE OF THE TEETH, THE TONGUE, AND MUCOUS MEMBRANE OF THE MOUTH. Ge a a : ‘ 7 he iy 1. Srupy first with the low power and afterwards with the high power a longitudinal section of a human tooth which has been prepared by grinding. It is better to purchase this specimen, for the process of preparation is difficult and tedious without the aid of special apparatus. Examine carefully the enamel, the dentine, and the cement. The dark appearance of the dentinal tubules is due to their containing air in the dried specimen. Measure ; the diameter of the enamel prisms and of some of the dentinal tubules. ; Make sketches from each of the tissues. 2. Mount in Canada balsam a section of a tooth in sitw, which has been decalcified in chromic or picric acid and stained with logwood or borax- carmine. In this section the mode of implantation of a tooth, as well as the structure of the pulp, can be made out. Make a general sketch under a low power, and under a high power draw a small piece of the pulp showing the processes of the odontoblasts extending into the dentinal tubules. ; 3. The development of the teeth and the formation of their tissues are ; studied in sections made across the snout and lower jaw of foetal animals. The preparation should be stained in bulk with alcoholic magenta, borax- carmine, or hematoxylin, and embedded in paraffin, and the sections mounted by the shellac-creosote process (see Appendix). | 4. Section across the whole tongue of a small mammal; stain with log- , wood, and mount in Canada balsam. In these sections the arrangement of the muscular fibres and the structure of the papille of the mucous mem- brane may be studied; and if the organ have been previously injected, the arrangement of the blood-vessels in the muscular tissue and in the mucous membrane will also be well seen. THE TEETH. A tooth consists of three calcified tissues : the enamel, which is of epithelial origin, the dentine, and the cement, or crusta petrosa. The dentine forms the main substance of a tooth, the enamel covers the crown, and the cement is a layer of bone which invests the root (fig. 150). The enamel is formed of elongated hexagonal prisms (fig. 151), which are set vertically, or with a slight curvature upon the surface of the dentine. They are marked at tolerably regular intervals with slight transverse shadings producing an indistinct cross-striated ap- pearance. Sometimes coloured lines run through the enamel across the direction of its fibres. The dentine is composed of a hard dense substance like bone, but — containing no Haversian canals or lacune. It is pierced everywhere, however, by fine canaliculi (dentinal tubules, figs. 152, 158), which radiate outwards from a central cavity which, during life, contains the pulp. The tubules branch at acute angles as they pass outwards; their branches become gradually finer towards the periphery of the Fic. 150.— VERTICAL SECTION OF A TOOTH in situ. (15 diame- ters.) is placed in the pulp- cavity, opposite the cervix or neck of the tooth; the part above is the crown, that below is the root (fang). 1, enamel with radial and concentric markings; 2, dentine with tubules and incremental lines ; 3, cement or crusta pe- trosa,with bone corpus- cles; 4, dental perios- teum ; 5, bone of lower jaw. = dentine. The tubules have a proper wall of their own, which can be isolated by steeping a section of tooth in strong hydrochloric acid. In the living tooth they are occupied by protoplasmic fibres, which are pro- - longed from the superficial nt the pulp. : The intertubular substance ts for the most part homogeneous, but here and there indications can be seen of its deposition in the form of — globules. This is especially the case near the surface of the dentine, — ~ > j . 4 = . - b } = ! f : “a = - = * — a? — J : ~ t ~ ‘ ‘ a > - ‘ * / - ‘ . ei « : ‘4 ‘4s i Bi. \ . | ban ar ye’ “ay paw 4 bias, rye, “ cre pk “on eet bat a+) See vs . ™ 4 oy 5 “ita 0 we tis fee cone oe: Bas Xan ; a i SAND! “i yaya ls a S3 -" ss STRUCTURE OF THE TEETIL 127 ~ @) =) a | Fic. 151—ENAMEL PRisMs. (350 diameters.) A, fragments and single fibres of the enamel, isolated by the action of hydrochloric acid. B, surface of a small fragment of enamel, showing the hexagonal ends of the fibres, Fic. 152.—SrcTIoN oF FANG, PA- RALLEL TO THE DENTINAL TU- BULES. (Magnified 300 diameters. ) 1, cement, with large bone-lacune and indications of lamellze; 2, granular layer of Purkinje (interglobular spaces); 3, dentinal tubules. Fia. 153.—SEcrions or DENTINAL TUBULES. a, cut across ; b, cut obliquely. (About 300 diameters.) ‘where the globular deposit and the interglobular spaces may produce granular appearance (granular layer, fig. 152, 2), and also in the 123 THE ESSENTIALS OF HISTOLOGY course of certain lines or clefts which are seen traversing che dentine across the direction of the tubules (incremental lines, fig. 150, shown magnified in fig. 154). : i q Fic. 154.—A SMALL PORTION OF THE DENTINE WITH INTERGLOBULAR SPACES. (350 diameters. ) c, portion of incremental line formed by the interglobular spaces, which are here filled up by a transparent material. The pulp consists of a soft, somewhat jelly-like, connective tissue, containing many branched cells, a network of blood-vessels, and some nerve fibres which pass into the pulp-cavity along with the blood- vessels by a minute canal at the apex of the fang. The superficial cells of the pulp form an almost continuous layer, like an epithelium. They are known as odontoblasts, from having been concerned in the formation of the dentine. The crusta petrosa (fig. 152, 1) is a layer of lamellated bone in- cluding lacune and canaliculi, but without Haversian canals, at least normally in the human teeth. It is covered with periosteum (dental periostewm), which also lines the socket, and serves to fix the tooth securely. \ Formation of the teeth.—The teeth are developed in the same manner as the hairs. A thickening of the epithelium occurs along the line of the gums, and grows into the corium of the mucous membrane (common enamel-germ, fig. 155, A). At regular intervals there is yet a. further thickening and growth from the common enamel-germ into the tissue of the mucous membrane, each of these special rudiments swelling out below into a flask-shaped mass of cells, the special enamel-germ, fig. 155, B). A vascular papilla grows up from the corium into the bottom of the special enamel-germ (fig. 155, C, D) ; this papilla has the shape of the crown of the future tooth. Each special enamel- germ, with its included papilla, presently becomes cut off from the epithelium of the mouth, and surrounded by a vascular membrane— the dental sac. The papilla becomes transformed into the dentine of the future tooth, and the enamel is deposited upon its surface by the epithelial cells of the enamel-germ. ‘The root of the tooth, with its covering of cement, is formed at a later period, when the tooth is | — } = : > - * 5 i . t =i Ph ; Zi 7 “ ‘ i f ‘ 3 . ‘a ¥ —_ | - DP) FH AMET bees oe on “ wel Dives < 7, wor hss ‘* ‘ Le Su 7 1 <4 PAPELRG iF Phy, _ . Ti fete 49 Le de toh 490% o ahi » wads orn on al yeten et ext ' { is =) i el BM xD & + Te ie Se ae ee | ONE A OL “ 24 nt. “it 7 4 * - ae . ' Fie. 155. A. SECTION ACROSS THE UPPER JAW OF A FG@TAL SHEEP. (3 centimeters long.) 1, common enamel-germ dipping down into the mucous membrane where it is half surrounded by a semilunar-shaped more dense-looking tissue, the germ of the dentine and dental sac ; 2, palatine process of the maxilla, B. SECTION SIMILAR TO THAT SHOWN IN THE PREVIOUS FIGURE, BUT PASSING . THROUGH ONE OF THE SPECIAL ENAMEL-GERMS HERE BECOMING FLASK-SHAPED, c, ce’, epithelium of mouth; /, neck ; /”, body of special enamel-germ. ~C anpd D. SeEcrions AT LATER STAGES THAN A AND B, THE PAPILLA HAVING BE- COME FORMED AND INDENTED THE ENAMEL-GERM, WHICH HAS AT THE SAME TIME GROWN PARTLY ROUND IT. , ¢, epithelium of gum, sketched in outline; 7, neck of enamel-germ ; 7’, enamel-organ ; ¢, its deeper columnar cells; e’, projections into the corium ; p, papilla; s, dental sac forming. In D, the enamel-germ (fp) of the corresponding permanent tooth has become formed. K 130 THE ESSENTIALS OF HISTOLOGY beginning to grow up through the gum, by a gradual elongation of the base of the papilla. ¥ 4 Previously to the deposition of the enamel, the enamel-germ under- goes a peculiar transformation of its previously rounded epithelium- Fic. 156.— A sECTION THROUGH THE ENAMEL-ORGAN AND DENTAL SAC FROM THE TOOTH OF A CHILD AT BIRTH, (250 diameters.) a, outer dense layer of the dental sac; 6, inner looser texture of the same with capillary blood- vessels and a somewhat denser layer towards the enamel organ ; c, spongy substance; d, inner cells; and e, outer cellular layer of the enamel- organ. Fie. 157.— PART OF SECTION OF DEVELOP- ING TOOTH OF YOUNG RAT, SHOWING THE MODE OF DEPOSITION OF THE DEN- TINE. (Highly magnified.) a, outer layer of fully calcified dentine; 6, un- calcified matrix, with a few nodules of calca- reous matter; c, odontoblasts with processes extending into the dentine; d, pulp. The sec- tion is stained with carmine, which colours the unealcified matrix, but not the calcified part. cells into three layers of modified cells. One of these is a layer of columnar cells (fig. 156, d), which immediately covers the surface of the dentine. These columnar cells form the enamel-prisms either by a deposition of calcareous salts external to them, or by a direct caicification of their protoplasm. The cells next to the dental sac , form a single layer of cubical epithelium (e), all the other cells of the ies “s ee WE ION ae) he: jo aoe , PNRM herrea Ink iv vedi 2 PS oe TVG ys ; A. = r ¢ —. = Saye 8 cy fie > . ‘ z 4 hag. 2 . % te ’ a ’ e.# is ; . a ¥ i * “ , ~ { 3 ri os eet . +4 a y ; ' peas i +. i Fe " y 7 fe A 2 cd ’ 4 ° ’ — f + oa ; ‘ ‘ At. iy : 5 - r | o | » . 2 . - a, lS c a ns Bh F ‘ os - > ‘ sli) MR? aa Peas ‘ ae Py vlan es : epi} Goin AL whieh ; aie :" a dl Hie aond uot iepls BCP scop. pecs Oe bea oa pees GREG, Pa WD ek eae of thus ie paiiel giv Te ee mappa a ue, 4 fay é- ty | 4 iit ty Ares Rp AA, hh saan th ; i ry r '. Seip THE TONGUE: 131 enamel-germ become transformed into branching corpuscles (c) com- municating by their processes, and thus forming a continuous net- work. The enamel-germ, after it is thus modified, is known as the enamel-organ. The dentine of the tooth is formed by dlehesies of the surface of the papilla. At this surface there is a well-marked layer of odonto- blasts (fig. 157), and these produce a layer of dentinal matrix which forms a sort of cap to the papilla, and which soon becomes calcified by the deposition of globules of calcareous matter. Processes of the odontoblasts remain in the dentine as it is forming, and thus the dentinal tubules are produced. Subsequently other layers of dentine are formed within the first by a repetition of the same process, and in this way the papilla gradually becomes calcified. A part, however, remains unaltered in the centre of the tooth, and with its covering of odontoblasts forms the pulp. The ten milk-teeth are formed in each jaw in this manner. These, however, become lost within a few years after birth, and are replaced by permanent teeth in much the same way that a new succes- sion of hairs occurs. A small outgrowth takes place at an early period from the enamel-germ of each of the milk-teeth (fig. 155, D, f p), and this eventually becomes the germ of the corresponding permanent tooth. It gradually enlarges, acquires a papilla, forms an enamel- organ, in short, passes through the same phases of development as its parent germ, and when the milk-tooth drops out of the jaw in conse- quence of the absorption of its roots (by osteoclasts) the permanent tooth grows up into its place. But there are six permanent teeth in each jaw which do not suc- ceed milk-teeth ; these are the permanent molars. They are developed from an extension backwards of the original epithelial thickening (common enamel-germ)and the downgrowth from this into the corium of three successive special enamel-germs at comparatively long intervals of time. Within these the tissues of the permanent molars become . formed in a manner exactly similar to that in which the milk-teeth are _ developed. THE TONGUE. The tongue is mainly composed of striated muscular fibres, running, some longitudinally, and others transversely. It is covered by a mucous membrane, the epithelium of which, like that of the rest of the mouth, is thick and stratified, and conceals microscopic papille (fig..158) like _ those of the skin. Besides these, the upper surface of the organ is covered with larger papille, which give it arough appearance. These, which are termed the lingual papille, are of three kinds: (1) About - twelve or thirteen comparatively large circular projections, each of which is surrounded by a narrow groove (fossa), external to which the mucous K 2 === saQ NY 7 NN ‘= SANA mM) i) => = —_ Se Fic. 158.—SrEcrion or MUCOUS MEMBRANE OF MOUTH, SHOWING THREE MICROSCOPIC Fic. 159.—SrecrioN OF CIRCUMVALLATE PAPILLA, PAPILLAE AND STRA- HUMAN. THE FIGURE INCLUDES ONE SIDE OF THE TIFIED — EPITHE- PAPILLA AND THE ADJOINING PART OF THE LIuM. THE BLOOD- VALLUM. (Magnified 150 diameters.) (Heitzmann.) VESSELS HAVE BEEN E, epithelium ; G, taste-bud ; C, corium with injected blood- INJECTED. (Toldt.) vessels ; Af, gland with duct. Fic. 160.—SEcrION OF FUNGIFORM Fic. 161.—Srcrion OF TWO. . ‘PAPILLA, HUMAN. (Heitzmann.) FILIFORM PAPILLA, HUMAN. A. E, epithelium ; C, corium; Z, lymphoid tissue ; (Heitzmann.) (Letters as in ; ‘M, muscular fibres of tongue. previous figure.) _ i 3 iam 4 ee Risin. whe , re | . Soca : v5 4 A : eTesW iby _ a> te : un COP IS . ¥e Lis F , - i> dhe ES ae : \" “ i? : “1 ; ‘ 5? i ; \ a s- F _ ‘ é : - Peis t, = y é + avs tf le * .: ‘ 3 - fant : —~ * , é FiAh 4 1 r ‘ a r - Z \ ral ‘ } } "i = , « — 5 = L, ihe tech a bet bont ‘ ’ Shiites . Be eile Bulges. oe a ; cen Ae sOePe lias ger ig + iutes ; dy i BLP ae E ae eis YW abyiph. shi algeh holt hie: arias ies Beta efiipers ih fui blip na, os A btn ie a Fy Th oy ith ss wie SPM ASH: Heap purist Be oweshtos 8 are vee a eS 4 7! “1S9ii vg Y fa 7 , - - ft AM “eee, Seed ™ © =. - © Uy lias ' rs a > > - hae Ss ak % ate Tir} n = aw J * eee eee ee ee Sao 7 , : as free, eee al" Fie ~ s THE GUSTATORY ORGANS ~~ 138 - membrane is raised above the general level (vallum) (fig. 159). These ql papille form a V-shaped line towards the back of the tongue; they - _ receive filaments of the glosso-pharyngeal nerve, and have taste-buds in the epithelium which covers their sides, and in that of the side of the vallum. They are known as the circwmvallate papilla. (2) All the rest of the papillary surface of the tongue is covered by conical papilla, so named from the conical pointed cap of epithelium which is borne by each ; sometimes this cap is fringed with fine epithelial filaments, when they are termed filiform (fig. 161). (3) Scattered here and there amongst the conical papille are other larger papille, the fungiform (fig. 160). These are very vascular, and lie partly embedded in little depressions of the mucous membrane. Small tubular glands may be seen between the superficial muscular fibres sending their ducts to the surface. Most of them secrete mucus, but those which open into the trenches of the circumyallate papille, and a few others elsewhere, yield a serous secretion. The mucous membrane at the back of the tongue contains a large amount of lymphoid tissue. The taste-buds.—The minute gustatory organs which are known as taste-buds may be seen in sections which pass through the papille vallatze or the papille fungiformes; they are also present here and there in the epithelium of the general mucous membrane of the tongue, especially at the back and sides, and occur also upon the under surface of the soft palate, and on the epiglottis. But they are most easily studied in the papille foliate of the rabbit, two small oval areas lying Fic. 162.—ToNGUE OF RABBIT, SHOWING THE SITUATION OF THE PAPILLA FOLIATA, p. on either side of the back of the tongue and marked transversely with a number of small ridges or lamine with intervening furrows (see figs. 162 and 163). Sections across the ridges show numerous taste-buds embedded in the thick epithelium which clothes their sides. The taste-buds are ovoid clusters of epithelium-cells which lie in ‘cavities in the stratified epithelium (fig. 164). The base of the taste- bud rests upon the corium of the mucous membrane, and receives a branch of the glosso-pharyngeal nerve ; the apex is narrow and com- 134 ‘THE ESSENTIALS OF HISTOLOGY municates with the cavity of the mouth by a small pore in the super- ficial epithelium (gustatory pore, fig. 164, p). fish iho SIR S\ Soa i Fic. 163,—VERTICAL SECTION OF PAPILLA FOLIATA OF THE RABBIT, PASSING ACROSS THE FOLL&. (Ranvier.) p, central lamina of the corium; v, section across a vein, which traverses the whole length of the folia; p’, lateral lamina in which the nerve-fibres run ; g, taste-bud; », sections of nerve-bundles; @, serous gland. Ms i o} ag Leer Fic. 164.—Srcrion THROUGH THE MIDDLE OF A TASTE-BUD. (Ranvier.) i p, gustatory pore; s, gustatory cell; 7, sustentacular cell; m, lymph-cell, containing fatty granules ; e, superficial cells of the stratified epithelium ; , nerve-fibres. The cells which compose the taste-bud are of two kinds, viz. : 1. The gustatory cells (fig. 165, a), which are delicate fusiform or — al pane « re hina oa wih ee cells ae of the cell- body or Bectosied enlargement, and ¥ of two processes, one distal, the other proximal. The distal process is nearly straight, and passes towards the apex of the taste-bud, where it % iarainates in a small, highly refracting cilium-like appendage, which projects into the pore above mentioned. The proximal process is more delicate than the other, and is often branched and varicose ; it is Kia. 165—VARtouS CELLS FROM TASTE-BUD OF RABBIT. (600 diameters.) —." sB “a four gustatory cells from central part ; 6, two sustentacular cells, and one gustatory cell, in , connection ; ¢, three sustentacular cells. believed to be directly connected with an entering nerve-fibre. 2. The sustentacular cells (fig. 165, c). These are elongated cells, mostly flattened, and pointed at their ends; they he between the gustatory cells, which they thus appear to support, and in addition they form a sort of envelope or covering to the taste-bud. Between the cells of the taste- bud lymph-corpuscles are often seen, having probably wander ed here . from the subjacent mucous membrane. 136 ._ THE ESSENTIALS OF HISTOLOGY LESSON XXVII. THE SALIVARY GLANDS. 1. Stupy carefully sections of the submaxillary gland of a dog. The gland should have been hardened in alcohol and stained with logwood. Notice the acini filled with clear cells, the nuclei of which usually lie near the basement-membrane. Notice here and there, outside the clear cells, demi- lunes or crescents of small darkly stained granular-looking cells. Observe also the sections of the ducts with their striated columnar epithelium. Try and find a place where one of the ducts is passing into the alveoli. Sketch under a high power. 2. Study sections of the parotid gland prepared in a similar way. 3. Examine small pieces of both submaxillary and parotid gland fresh in saline solution. In the submaxillary gland notice that the alveolar cells are swollen out with clear mucigen, but that those of the parotid are filled with granules (zymogen).'_ Make a sketch from each preparation under a high power. 4, Prepare a transverse section of the cesophagus. Notice the thick muscular coat partly containing cross-striated fibres and the mucous mem- brane with its papille and stratified epithelium. Look for mucous glands in the areolar coat. Sketch under a low power. The salivary glands may be looked upon as typical of secreting glands in general. They are composed of a number of lobules bound together loosely by connective tissue. Each small lobule is formed of a group of saccular or somewhat tubular alveoli or acini (fig. 166) from which a duct passes, and this, after uniting with other ducts to form larger and larger tubes, eventually leaves the gland to open upon the surface of the mucous membrane of the mouth. The alveoli are enclosed by a basement-membrane, which is reticular (fig. 167). This basement-membrane is continued along the ducts. Within it is the epithelium, which in the alveoli is composed of polyhedral cells (fig. 168, a), but in the ducts is regularly columnar, except in that part of the duct which immediately opens into the ' To study the changes which the alveolar cells undergo during secretion, pilo- carpine is injected subcutaneously into an animal in sufficient amount to produce copious salivation ; after which the animal is killed and its salivary glands are examined as in preparation 3. The granules are not seen in preparations that. have been in alcohol, but osmic acid preserves them ; they are best seen, however, in the fresh tissue, os stk: Lin a el =i i atlas a y ; ae Ae Wad, (ytd SRL deka ey . See fan ™- ’ . md , *, - “THE SALIVARY GLANDS) 847 Fic. 166.—D1AGRAM OF THE CONSTRUCTION OF A LOBULE OF A TUBULO-RACEMOSE (ACINO-TUBULAR) MUCOUS GLAND. a, duct ; 6, a branch of the duct ; ¢, alveoli as they lie together in the gland ; d, the same separated, showing their connection as an irregular tube. ie . . : ; Fria. 167.—MEMBRANA PROPRIA OF TWO ALVEOLI ISOLATED. ———eE oe oe The preparation is taken from the orbital gland of the dog, which is similar in structure to a mucous salivary gland. —————s- —- - =F ‘ Fie. 168.—SrcrioN OF THE SUBMAXILLARY GLAND OF THE DOG, SHOWING THE : _ COMMENCEMENT OF A DUCT IN THE ALVEOLI, (Magnified 425 diameters.) a, one of the alveoli, several of which are in the section shown grouped around the _ commencement of the duct, d’; a’, an alveolus, not opened by the section ; 6, basement- membrane in section ; ¢, interstitial connective tissue of the gland ; d, section of a duct which has passed away from the alveoli, and is now lined with characteristically striated columnar cells ; s, waniiauar group of darkly stained cells at the periphery of an alveolus, 138 Fic. 169.—SEcTION OF DOG’S SUBMAXILLARY, STAINED. a, duct ; b, alveolus; ¢, crescent. Fic. 170.—SEcriON OF PART OF THE HUMAN SUBMAXILLARY GLAND. To the right of the figure is a group of mucous alveoli, to the left a group of serous alveoli, Fic. 171.—ALVEOLI OF A SEROUS GLAND. A, AT Rest. B, AFTER A SHORT PERIOD OF ACTIVITY. C, AFTER A PROLONGED PERIOD OF ACTIVITY. In A and B the nuclei are obscured by the granules of zymogen, wl: aye ay 1 MF RaAfrnyd = Ete rhidiped. ea lim thls al aan alr eae ny ie, ar ety ay Sahin, acasy? 1. , + hail : ; ier. teh ae , rie 4 en Tg arene me ae MAEM Bein ee : ts. t mits v8 t i! ™ = - 1 ) ole . ‘ ? . a - a rf ‘ > . : 7 4 ' t ‘ ‘ . hy ew ; hed : 5 : : ’ Phe : 2 4 a : * ZX ‘ ‘ ee Ih ee A Shine weed ie ” Pie die. tpanl MAREE ae br nd. fede uel i pee 25. iD ca i 4h ’ Pima al be dake iA i eh ms mm asic ty ei i ey ii Vins Rmpre glenid open: ox dy porkey ao BW Vi" Pye! ane F wae fcerg ta BES WH, OL ay flr ow) Wondetog [a hid oteline » ea Sapa ns Wea ras Bae i rh sy. a O or ; feds ire gia | ‘Re A GP ee -THE SALIVARY GLANDS — 139 alveoli; in this it is flattened (d’).. The columnar epithelium of the ducts is peculiar, in that the cells show a distinction into two unequal zones, an outer, larger, striated zone, and an inner, smaller, granular one (fig. 168, d). The cells of the alveoli differ according to the substance they secrete. In alveoli which secrete mucus, such as all the alveoli of the . dog’s submaxillary, and some of the alveoli of the same gland in man (fig. 170), the cells are clear and swollen out with mucigen, which is discharged into the ducts when the gland is stimulated to activity. But in each alveolus there are some smaller cells which do not contain mucigen, and these generally form crescentic groups which lie next to _ the basement-membrane (fig. 169, c). These are the so-called crescents of Gianuzzi ; their constituent cells are also known as marginal cells. - In alveoli, on the other hand, which do not secrete mucus, but watery or serous saliva, such as the parotid in all animals, and some of the alveoli - of the human submaxillary, the cells are filled with’ granules when the gland is at rest, although the outer part of each cell may become clear after a long period of secretion (fig. 171). The largest ducts have a wall of connective tissue outside the base- ment-membrane, and also a few plain muscular cells. The blood-vessels of the salivary gland form a capillary network around each alveolus. The lymphatics commence in the form of lacunar vessels encircling the alveoli. The nerve-fibres, which are derived both from the cerebro- spinal nerves and from the sympathetic, have not been satisfactorily traced to their termination, but they probably become connected with the alveolar cells. THE PHARYNX AND CGSOPHAGUS. The pharynx is composed of a fibrous membrane, which is encircled by striated muscles, the constrictors, and lined by mucous membrane. The mucous membrane is lined in the upper part of the pharynx and on the upper surface of the soft palate with ciliated epithelium, which is continuous with that of the nostrils, and through the Eustachian tube with that of the tympanum. Below the level of the soft palate the epithelium is stratified like that of the mouth and gullet, into which it passes. In certain parts the mucous membrane contains a large amount of lymphoid tissue, especially at the back, where it forms a projection which is sometimes termed the pharyngeal tonsil, and there are numerous mucous glands opening on its surface. The esophagus or gullet, which passes from the pharynx to the stomach, consists, like the pharynx, of a fibrous covering, a muscular coat, a lining mucous membrane, and intervening connective tissue (areolar coat) (fig. 172). The muscular coat is much more regularly arranged than that of the pharynx, and is composed of striated muscle in about its upper third only, the rest being of the plain variety. There 140 ‘THE ESSENTIALS OF HISTOLOGY are two layers of the muscular coat, an outer layer, in which the fibres run longitudinally, and an inner, in which they course circularly. The mucous membrane is lined by a stratified epithelium, into which micro- scopic papille from the corium project. The corium is formed of areolar tissue, and its limits are marked externally by a narrow layer of longi- Fic. 172.—SEcTION OF THE HUMAN ESOPHAGUS. The section is transverse, and from near the middle of the gullet. a, fibrous covering ; b, divided fibres of the longitudinal muscular coat ; c, transverse muscular fibres; d, sub- mucous or areolar layer; e, muscularis mucose ; /, papillae of mucous membrane ; g, lami- nated epithelial lining ; A, mucous gland; i, gland duct. tudinally disposed plain muscular fibres, the muscularis mucose. This is separated from the proper muscular coat by the areolar coat, which 1 contains the larger branches of the blood-vessels and lymphatics, and also most of the mucous glands of the membrane. Se REA wade) iri SSP: Hy jak i) Str een, Bx! o. si a iS Anvousg cugt , ay ih ES ere g The nal.) laboaaee ent is by at , Bape gba teh hl WEEP ti : . : ie.) grcrGninsly Btrd aby Die 6 * ¥ it itywalar Out ‘Bee isooiie , aes , } : y nelly Gigi: ito Hie dred’ hey, Jasirs > ip , Mt +. apr. bated mad irae ay add sta ' “be i ig oe L IW, ol 3 141 LESSON XXVIII. THE STRUCTURE OF THE STOMACH. 1. Sections of the cardiac region of the dog’s stomach, cut perpendicularly to the surface of the mucous membrane. The tissue is to be stained with log- wood or borax-carmine, and the sections are to be mounted in Canada balsam. In these sections the general arrangement of the coats of the stomach is to be studied and sketches are to be made under a low power illustrating this arrangement, and others under a high power showing the structure of the glands of the mucous membrane. Measure the whole thickness of the mucous membrane, the thickness of the muscular coat, the size of the columnar epithelium-cells of the surface, and that of the cells in the deeper parts of the glands. 2. Sections of. the mucous membrane of the same region, cut parallel to the surface. These sections will show better than the others the arrangement of the cells in the glands. 3. Vertical sections of the mucous membrane from the pyloric region of the dog’s stomach. Make a sketch under a low power of one of the glands in its whole length, filling up some of the details with the high power. 4. Study the arrangement of the blood-vessels of the stomach in vertical sections: of the wall of an organ the vessels of which have been injected. The wall of the stomach consists of four coats, which, enumerated from without in, are as follows, viz.: serous, muscular, areolar or sub- mucous, and mucous membrane. The serous coat is a layer which is derived from the peritoneum. It is deficient only along the lines of the lesser and greater curvatures. The muscular coat consists of three layers of plain muscular fibres. Of these the bundles of the outer layer run longitudinally, those of the middle layer circularly, and those of the inner layer obliquely. The longitudinal and circular bundles become thicker and stronger towards the pylorus, at which they pass into the corresponding layers of the small intestine; at the pylorus itself the circular layer is greatly thickened to form the sphincter muscle. The oblique fibres are only present in the left or cardiac part of the stomach. ‘The areolar or swhnvucous coat is a layer of areolar tissue, which serves to unite the mucous membrane loosely to the muscular coat ; in it ramify the larger branches of the blood-vessels and lymphatics. THE ESSENTIALS OF HISTOLOGY 142 DR POsCOGudsG: AGEL ERX aL San ic acid prepara- SIMPLE FORM, FROM THE BAT’S stomAcH. (Osm Fic. 174.—A CARDIAC GLAND OF tion.) JO Oise) ; 76) @lieal 5 ay =e pei ©) 0) 3 ee n, neck of the gland with central and parietal cells ; 7, base or fundus, occupied only by principal or cen- tral cells, which exhibit the granules accumulated towards the lumen of ec, columnar epithelium of the surface ; the gland, ’s sromAcH. (Highly magnified.) _ d, duct or mouth of the gland ; }, base or fundus of one of its tubules. Fic. 178.—A CARDIAC GLAND FROM THE DOG On the right the base — of a tubule more highly magnified ; ¢, central cell; p, parietal cell. _ epee Barger: f © Sat tet Fp Spy ser end) vu vhs "aa i. 3 ion” aS oi str eh a! 2d iy a raemn Bee: ca37 St he yeh tynk vee WR 1 Pee vot gf wy’ Si - . 4 5 ah | Salhi ; SP ipot 6 ’ . : . ; %e* y 23 , P , — . P ~~ a ; 3 : : + af ~ * 7 * ; : } My s L i r 4 ~ , _ - \ ‘ . S \ J : va "9 -. he 7 5", ic ees - Ree okt ’ ; “ ~ ? rag! ist q i é 4 é ¢ - s-/ is }: \ j Ae # Ww Lt i re . - 2 Bo) Ro eh “a AG — iy ; thi ‘ ms? val Mausnde wh Wie é tf VEr pate L ts ‘oe _ aaa Oem diss i bps (anne baal Sr Aas (Es nf ’ f fz $70) oy Figs jhureghins, psa THE STRUCTURE OF THE STOMACH 143 The mucous membrane is a soft, thick layer, generally somewhat corrugated in the empty condition of the organ. Its thickness is mainly due to the fact that it is made up of long tubular glands, which open upon the inner surface. Between the glands the mucous mem- brane is formed of areolar with much lymphoid tissue. Externally it is bounded by the muscularis mucose, which consists of an external longitudinal and an inner circular layer of plain muscular fibres. The glands are formed of a basement-membrane lined with epithelium. Each gland consists of three or four secreting tubules, which open towards the surface into a larger common tube, the duct of the gland. The duct is in all cases lined by columnar epithelium of the same character as that which covers the inner surface of the mucous mem- brane, but the epithelium of the secreting tubules is somewhat different from this, and, moreover, differs somewhat in the glands of the cardiac -and pyloric regions of the organ. In the cardiac glands (fig. 173) the secreting tubules are long, and the duct short. The epithelium of the tubules is composed of two kinds of cells. Those of the one kind, which form a continuous lining to the tubule, are somewhat polyhedral in shape, and in stained sections look clearer and smaller than the others, but in the fresh glands, and in osmic preparations, they appear filled with granules (fig. 174).!_ These cells are believed to secrete the pepsin of the gastric juice, and are termed the chief cells of the cardiac glands, or, from their relative position in the tubule immediately surrounding the lumen, the central cells. Seat- tered along the tubule, and lying between the chief cells and the base- ment membrane, are a number of other spheroidal or ovoidal cells, which become stained by logwood and other reagents more darkly than the central cells. These are the swperadded or parietal cells (oxyntic ? cells of Langley). In the pyloric glands (fig. 175) the ducts are much longer than in the cardiac glands, and the secreting tubules possess cells of only one kind. These correspond to the chief cells of the cardiac glands. They are of a columnar or cubical shape, and in the fresh condition of a granular appearance, and quite unlike the columnar epithelium-cells of the surface, which are long tapering cells, the outer part of which is filled with mucus. At the pylorus itself the pyloric glands become considerably lengthened, and are continued into the submucous tissue, the muscularis mucose being here absent ; they thus present transi- tions to the glands of Brunner, which lie in the submucous tissue of the duodenum, and send their ducts through the mucous membrane - to the inner surface. The blood-vessels of the stomach (fig. 176) are very numerous, and 1 The granules are most numerous at the inner part of the cell, a small outer - zone being left clear. After prolonged activity this outer zone increases in size while the granules diminish in number as in the analogous cases of the pancreas and parotid glands. ft. Ee called because they produce the acid of the gastric secretion. 144 THE ESSENTIALS OF HISTOLOGY pass to the organ along its curvatures. The arteries pass through the muscular coat, giving off branches to the capillary networks of the muscular tissue, and ramify in the areolar coat. From this, small arteries pierce the muscularis mucose, and break up into capillaries near the bases of the glands. ‘The capillary network extends between the glands to the surface, close to which it terminates in a plexus of a ARH ee =e a 1 Weeg, ee ae ye see Fic. 176.—PLAN OF THE BLOOD- VESSELS OF THE STOMACH. a, small arteries passing to break up into the fine capillary network, d, between the glands; 0, coarser capillary network around the mouths of the glands; c¢, c, veins passing vertically downwards from the superficial network; e, larger vessels in the submucosa, Fic. 175.—A PYLORIC GLAND, FROM A SECTION OF THE DOG’S STOMACH. m, mouth; n, neck ; 7, a deep por- tion of a tubule cut transversely. relatively large venous capillaries which encircle the mouths of the glands. From this plexus straight venous radicles pass through the mucous membrane, pierce the muscularis mucosz, and join a plexus-of veins in the submucous tissue. From these veins blood is carried ‘ away from the stomach by efferent veins, which accompany the enter- ing arteries. The lymphatics (fig. 177) arise in the mucous membrane by a ye ba S_ ny 2 - i aa bet ch ry ae oberen= feesels |x: 4 - - \ * <= a - t } ’ : Ss ’ ‘ “y Aros Se THE STRUCTURE OF THE STOMACH 145 plexus of large vessels dilated at intervals, and looking in sections like clefts in the interglandular tissue. From this plexus the lymph is carried into larger valved vessels in the submucous coat, and from these, efferent vessels pass through the muscular coat to reach the Fic. 177.—LYMPHATICS OF THE HUMAN GASTRIC MUCOUS MEMBRANE, INJECTED, The tubules are only faintly indicated ; a, muscularis mucose ; b, plexus of fine vessels at base of glands ; c, plexus of larger valved lymphatics in submucosa, serous membrane, underneath which they pass away from the organ. The muscular coat has its own network of lymphatic vessels. These lie between the two principal layers, and their lymph is poured into the efferent lymphatics of the organ. The nerves have the same arrangement and mode of distribution as those of the small intestine (see next Lesson). 146 ‘THE ESSENTIALS OF HISTOLOGY LESSONS XXIX. anp XXX. STRUCTURE OF THE INTESTINE. LESSON XXIX. 1. Sections of the duodenum or jejunum vertical to the surface. The tissue is to be stained with logwood or borax-carmine and the sections mounted in Canada balsam. The general arrangement and structure of the intestinal wall is to be studied in these sections. Make a general sketch under the low power and carefully sketch part of a villus under the high power. 2. From the same portion of the intestine, sections parallel to the surface, and therefore across the long axis of the villi and glands of the mucous membrane. In order to keep the sections of the villi together so that they are not lost in the mounting, it will be necessary to employ the creosote- shellac method of mounting the sections (see Appendix). In this preparation sketch the transverse section of a villus. 3. Transverse vertical sections of the ileum passing through a Peyer’s patch. Observe the nodules of lymphoid tissue which constitute the patch and which extend into the submucous tissue. Notice also the sinus-like lym- phatic or lacteal vessel which encircles the base of each nodule. Make a general sketch under a low power. 4. To study the process of fat-absorption, kill a rat three or four hours after feeding it with fat meat. Put a very small piece of the mucous mem- brane of the intestine into osmic acid (0°5 per cent.) and another piece into chromic acid (0°2 per cent.) containing a few drops of osmic acid solution. After forty-eight hours teased preparations may be made from the osmic acid ; preparation, in the same manner as directed in Lesson VII. § 2; the rest may be then placed in alcohol. The piece in chromic and osmic ‘acid may also after two or three days be placed in alcohol. When hardened and de- hydrated in this, the pieces of tissue are embedded in paraffin, and sections are made and mounted by the shellac-creosote process. LESSON XXX. 1. Sections of small intestine the blood-vessels of which have been injected. Notice the arrangement of the vessels in the several layers. Sketch carefully the vascular network of a villus. G 2. From a piece of intestine which has been stained with chloride of gold tear off broad strips of the longitudinal muscular coat, and mount them in Farrant’s solution. It will generally be found that portions of the nervous __ plexus of Auerbach remain adherent to the strips, and it can in this way easily be studied. From the Pemaaipaek of the piece of intestine tear off with forceps the — PF tha ieresine TaN LAr Tear : j bide cnt ‘7 30 Ahn Oiler Stn so HS fey Waves aie ctw wntheawenn res j Ti? sty read ix’ iwi hea 2 oa ied seecthy : - Z * 55 Aves tae live: ta a! | - my ' es tie if : 9 . * - 2 = i .. - bf i 5 eek _ = Pa = » »? ' ; i “ ° i ¥ as eg < . . ; Dy, = = ) : 22 i .< 2 ; “4 vt ' ‘ Mey : -~- - 2 au Ab Whom, REP AOR vria ts 5 " we. “TE VAT Wy sie Te Prete ieee, AC buat. i, - - ic ci. | LM. seis of amie ise: WG. r md dg cn, Sie: \ ah ieake ye SEP, a! he tec ey a Sas sive a £4 Aim +> enti. Ni al eet; * i Oah \ + at cast # hie fil athe, . it ‘ei & - racuni) als y i iy Weealys tf oy 7 _ STRUCTURE OF THE INTESTINE 147 fibres of the circular muscular layer on the one side, and the mucous mem- brane on the other side so as to leave only the submucous tissue and the muscularis mucose. This tissue is also to be mounted flat in Farrant’s solution : it contains the plexus of Meissner. Sketch a small portion of each plexus under a high power. 8. Sections of the large intestine, perpendicular to the surface. These will show the general structure and arrangement of the coats. Sketch under a a low power. “4. Sections of the mucous membrane of the large intestine pavalle? to the surface, and therefore across the glands. Sketch some of the glands and the interglandular tissue under a high power. 5. The arrangement of the blood-vessels of the large intestine may be studied in sections of the injected organ. THE SMALL INTESTINE. The wall of the small intestine consists, like the BrominOM; of four coats. The serous coat is complete except over part of the asda, SE OER 7 y~ f- —_— — — =e ee / ie es | STE { } aoa Pm) \ | mage ewe eae a me me ——~ —— — 4 nS em ! tS araaree Fil / / = Wh / it Fie..178 -—PLEXUS or AUERBACH, BETWEEN THE TWO LAYERS OF THE MUSCULAR COAT OF THE INTESTINE. (Cadiat.) The muscular coat is composed of two layers of muscular tissue, an outer longitudinal and an inner circular. Between them lies a net- work of lymphatic vessels and also the close gangliated plexus of non. L2 » 148 THE ESSENTIALS OF HISTOLOGY medullated nerve-fibres known as the plexus myentericus of Auerbach. The ganglia of this plexus may usually be seen in vertical sections of the intestinal wall, but the plexus, like the one in the submucous coat immediately to be described, can only be properly displayed in prepara- tions made with chloride of gold (fig. 178). The submucous coat is like that of the stomach; in it the blood- vessels and lymphatics ramify before entering or after leaving the mucous membrane, and it contains a gangliated plexus of nerve-fibres— Fic. 179.—PLExus oF MEISSNER FROM THE SUBMUCOUS COAT OF. THE INTESTINE. | - (Cadiat.) the plexus of Meissner—which is finer than that of Auerbach and has fewer ganglion-cells (fig. 179). Its branches are chiefly supplied to the muscular fibres of the mucous membrane. The mucous membrane is bounded next to the sabmdsous coat by a double layer of plain muscular fibres (muscularis mucose). Bundles from this pass inwards through the membrane towards its inner sur-— face and penetrate also into the villi. The mucous membrane proper is pervaded with simple tubular glands—the crypts of Lieberkiihn— which are lined throughout by a columnar epithelium like that which covers the surface and the villi. The mucous membrane between these _ a : 7 <3 i £ t a f y > / sae sl ete lente ¥ra; sila tN Lon ge Wiha ore ie “cae . oh ate ied ung " ua Lap = Snipesad ) Lyin bhand seao DRA rRou Splid nest) Fs the Sa-oal fist gOTS he f LAY) ans Le +4. of f; wad i 4 Pia tok aay DS wasily Aterueg hs He eet * ; ‘ tp apeateghe plus fects the Tat : awe oe a ek ae ‘wwh pot ied r STRUCTURE OF THE INTESTINE 149 glands is mainly composed of lymphoid tissue, which is aggregated at intervals into more solid nodules (fig. 181) constituting when they occur | singly the so-called solitary glands of the intestine, and when aggregated Fie. 180.—Cross-SECTION OF A SMALL FRAGMENT OF THE MUCOUS MEMBRANE OF THE INTESTINE, INCLUDING ONE ENTIRE CRYPT OF LIEBERKUHN AND : PARTS OF THREE OTHERS, (Magnified 400 diameters.) a, cavity of the tubular glands or crypts; 6, one of the lining epithelial cells; c, the inter- glandular tissue ; d, lymph-cells, Were 2: Fig, 181—Sxcrion OF THE ILEUM THROUGH A LYMPHOID NODULE. (Cadiat.) a, middle of the nodule with the lymphoid tissue partly fallen away from the section; b, epithelium of the intestine; c, villi: their epithelium is partly broken away ; d, crypts of Lieberkiihn. : together form the agnvinated glands or patches of Peyer. The latter occur chiefly in the ileum. | - The villi with which the whole of the inner surface of the small - : ' : i 2 150 THE ESSENTIALS OF HISTOLOGY — intestine is closely beset are clavate or finger-shaped projections of the mucous membrane, and are composed, like that, of lymphoid tissue and covered with columnar epithelium (fig. 182). The characters of this have been already described (Lesson VII.). Between and at the base of the epithelium-cells many lymph-corpuscles occur. The epithelium rests upon a basement-membrane formed of flattened cells. In the middle of the villus is a lacteal vessel (c. 1) which is somewhat enlarged near its commencement. Surrounding this vessel are small EY, Sy Fire ‘ re CE aa LOMITA ey / - . Fic. 182.—Cross-SECTION OF A VILLUS OF THE CAT’S INTESTINE, e, columnar epithelium ; g, goblet cell, its mucus is seen partly exuded ; 2, lymph-corpuscles between the epithelium-cells; 6, basement-membrane; c, blood-capillaries ; m, section of plain muscular fibres; ¢. 1, central lacteal. Fic. 183.—MAGNIFIED VIEW OF THE BLOOD-VESSELS OF THE INTESTINAL VILLI. The drawing was taken from a preparation injected by Lieberkiihn, and shows, belonging to . each villus, a small artery and vein with the intermediate capillary network, bundles of plain muscular tissue prolonged from the muscularis mucose. The network of blood-capillaries (fig. 183) lies for the most part near the surface within the basement-membrane ; it is supplied with blood — by a small artery which joins the capillary network at the base of the villus ; the corresponding vein generally arises nearer the extremity. _ The lymphatics (lacteals) of the mucous membrane (fig. 184), after NE Leeda pay Peay ST Pee is s at (are Llcteale uF Ai 4-i 0m the TESST Titieberite: Fick wey Oe + fate valved, iymoumties Wines he hy Hie sds Wendt c cial Sem dots anges tee lin cm tha J ‘letaa ‘igtrita —< Oe Bic <7) 1% \ Pays >) rt r ‘ S 4 Fels ; ; me A m% . ba t P; ‘ - ace) ~s =) “i 7 i e? | a = he & ate ra Sas ee ’ i ae i by) faa} rps Bepearest Dos Cir yens we ok é Bees esi atid tilicthe < shhes ap prea i mabe HP Blie vesinvtay © NE wi? 7 ‘ert eg: aaa wehetr eri ppt? } Mags i tua bieshond fron tL metin 78M ithsity Else ‘ead - nase i Legs aise Gis are im ofewe ateux iy aaneatvinkidy fete Theee Facts it per seapante phy’ af. Peg esas , ‘ . A De t \ J 4 4 ‘ q ; ’ ; « ; 1 * il - te? AA ee P r be Le ih ™ > Wee wine ia : he r elk Orie = k ol Boa 4 ag ao \ te STRUCTURE OF THE INTESTINE 161 receiving the central lacteals of the villi, pour their contents into a plexus of large valved lymphatics which lie in the submucous tissue and form sinuses around the bases of the lymphoid nodules. From the submucous tissue efferent vessels pass through the muscular coat, receiving the lymph from an intramuscular plexus of lymphatics, and are conveyed away between the layers of the mesentery. Fig. 184.—VERTICAL SECTION OF A PORTION OF A PATCH OF PEYER’S GLANDS, WITH THE LACTEAL VESSELS INJECTED. (82 diameters.) (Frey.) The specimen is from the lower part of the ileum: a, villi, with their lacteals left white ; b, some of the tubular glands; c, the muscular layer of the mucous membrane; d, cupola or projecting part of the nodule; e, central part; 7, the reticulated lacteal vessels occu- pying the lymphoid tissue between the nodules, joined above by the lacteals from the ’ yilli and mucous surface, and passing below into g, the sinus-like lacteals under the nodules, which again pass into the large efferent lacteals, g’; i, part of the muscular coat. Absorption of fat.—The lymph-corpuscles of the villi are the chief agents in effecting the passage of fat-particles into the lacteals. In | order to study this process of transference, it is convenient to stain y the fat-particles with osmic acid, which colours them black. It can then be observed that in animals which have been fed with fat these particles are present (1) in the columnar epithelium-cells ; (2) in the lymph-cells ; and (3) in the central lacteal of the villus. The lymph- cells are present not only in the reticular tissue of the villus, but also in considerable number between the epithelium-cells; and they can also be seen in thin sections from osmic preparations within the com- mencing lacteal; but in the last situation they are in every stage of disintegration. Since the lymph-cells are amceboid, it is probable from ‘these facts that the mechanism of fat-absorption consists of the following pro- cesses—viz. (1) absorption of fat into the columnar epithelium-cells of the surface ; (2) inception of fat by the lymph-corpuscles in the epi- thelium, partly from the epithelium-cells, and partly, perhaps, directly 152 THE ESSENTIALS OF HISTOLOGY from the intestinal contents; (8) migration of the lymph-corpuscles carrying the incepted fat-particles by their ameeboid movements through the tissue of the villus and into the central lacteal; (4) disintegration and solution of the immigrated lymph-corpuscles, and setting free both of their fatty contents and also of the proteid matters of which they are themselves composed. . Vic. 185, AA—SEcCYTION OF THE VILLUS OF A RAT KILLED DURING FAT-ABSORPTION. ' ep, epithelium ; s¢7, striated border; c, lymph-cells; c/, lymph-cells in the epithelium ; 1, central lacteal containing disintegrating lymph-corpuscles, Fic. 185, B—Mucovus MEMBRANE OF FROG’S INTESTINE DURING FAT-ABSORPTION, “ep, epithelium ; st”, striated border ; ¢, lymph-corpuscles ; J, lacteal. This migration of the lymph-corpuscles into the lacteals of the villi is not a special feature of fat-absorption alone, but occurs even when absorption of other matters is proceeding; so that the transfer- ence of fat-particles is merely a part of a more general phenomenon accompanying absorption. THE LARGE INTESTINE. The large intestine has the usual four coats, except near its ter- mination, where the serous coat is absent. The mscular coat is pecu- liar in the fact that along the cecum and colon the longitudinal muscular fibres are gathered up into three thickened bands which pro- duce puckerings in the wall of the gut, ia "a - , ee t fia yale Spiro be laeere, Inher ; glans BOLE trea. § Pee nt Huds? , ; , iitextane, ‘yor 3 Behe pine Mri Bue of #53 hat ie aed POL : ; ‘ : Metab fey Pa eve” . * > res 131 Hine “er . be % / \ ’ . ° a - ‘ . y . 1 ‘ he ‘ ~ 2 A * - . ‘ by = = - = ‘ = "I * Pi ( t = a \ % a j ‘ - : - Z ° * i ' ° j } : +. Fi Pas a ie ' A ae!) %3,' (aie meet Sheiicotie wey 3 > ’ ; ae ie! [iL - me Gio) Chu. 5 mg 4 : Bul héqouws Sriisecnee w Nebleubiike 4 ~ apni eae aN EE hs. piuii iiviegud olay tthe Pr “s tn . ‘ . ’ | * Os . ’ ‘ * ' . a | rine as if ae . : iywcag F hire b alt , 2 rere. 9 . F . -aree in teatis,- sL4 % oe INDE cae i: we, Sere Lis Gd wits AE a yeaa b tar be ‘Sag fret Wak song ie peed ‘STRUCTURE OF THE INTESTINE 153 The mucous membrane of the large intestine is beset with simple tubular glands somewhat resembling the crypts of Lieberkiihn of the small intestine, and lined by columnar epithelium similar to that of the inner surface of the gut, but containing many more mucus- secreting or goblet cells (fig. 186). The extremity of each gland is usually slightly dilated. ‘The interglandular tissue is like that of the Fic. 186.— A GLAND OF THE LARGE INTESTINE OF THE DOG, (From Heidenhain and Klose.) b, in longitudinal, ¢, in transverse section, stomach, as is also the arrangement of the blood-vessels and lymphatics in it. The nerves of the large intestine also resemble those of the small intestine and stomach in their arrangement. At the lower end of the rectum the circular muscular fibres of the gut become thickened a little above the anus so as to form the internal sphincter muscle. In this region also there are a number of compound racemose mucous glands opening on to the surface of the mucous membrane. 154 . THE ESSENTIALS OF HISTOLOGY LESSON XXXI. STRUCTURE OF THE LIVER AND PANCREAS. 1. Make sections of liver and study them carefully with a low and high power. Sketch the general arrangement of the cells in a lobule under the low power and under the high power. Make very careful drawings of some of the hepatic cells and also of a portal canal. 2. Study, first of all with the low and afterwards with a high power, a section of the liver in which both the blood-vessels and the bile-ducts have been injected. Make a general sketch of a lobule under the low power and draw a small part of the network of bile-canaliculi under the high power. 3. Tease a piece of fresh liver in salt solution for the study of the appear- ance of the hepatic cells in the recent living condition. 4, Prepare sections of the pancreas from a gland which has been hardened in aleohol. The sections are stained with borax-carmine and mounted in the usual way in Canada balsam. Make a sketch under the low power. 5. Tease a small piece of fresh pancreas in salt solution. Notice the granules in the alveolar cells, chiefly accumulated in the half of the cell which is nearest the lumen of the alveolus, leaving the outer zone of the cell clear. Sketch a small portion of an alveolus under a high power. THE LIVER. The liver is a solid glandular mass, made up of the hepatic lobules. These are polyhedral masses (about 1mm. in diameter) of cells, separated from one another by connective tissue. In some animals, as in the pig, this separation is complete, and each lobule is isolated, but in man it is incomplete. There is also a layer of con- — nective tissue underneath the serous covering of the liver, and forming the so-called capsule of the organ. The blood-vessels of the liver (portal vein and hepatic artery) enter it on its under surface, where also the bile-duct passes away from the gland. The branches of these three vessels accompany one another in their course through the organ, and are enclosed by loose connec- tive tissue (capsule of Gilisson), in which are lymphatic vessels, the whole being termed a portal canal (fig. 187). The smallest branches of the vessels penetrate to the intervals between the hepatic lobules, and are known as the interlobular branches. ‘The blood leaves the liver at the back of the organ by the hepatic veins: the branches of these run through the gland unaccompanied by other vessels (except — aes Pend rs phe De specter) Ely the paws + ’ ny af- a Penile We Srstrbl Werciesli Cine wty) ive ein ¥ SPavelt ure eds, he fabele Gri) overs diptotl? ort ibirited 7 shri) Fig ts: $c sj . + 7" y ‘ : t ‘ a fon . A , ‘ os f 3 4 ; be - . L s } - ; . > a” em _ ‘ y ye ca 7 i Z _ - { =). “f y: i > me aay re = Ss } ; ; a 9 + oxy Oe zx si ‘ ei . F ? a. P *, b 2. ip ” fea Pt Tit vie Vig. Wades ae fr: 4 oonicater eee fe ‘ Yeates Sort : : elt 4 on cpio Bs He pays Z C ~ t F ue vs cre ol, ewes wile piped wrary chek WAL Nae i), wie) Anat We Lean anf isn {ek univer b ae pe che ol Be, a Tabane Poa al J yo. “nt alive ~ . vada abi . i ele "ge esol imiiiige Ariane Ae 4 a m “is Whtheet pieaeee away pee bi ‘ > ’ 4 + ere arena teat - a ee * ew. 1 ae eel cage ook > oe. 7 , ae wi Caen h lip " Wiehe | wLuicd wf Re vedsate ye whtale » gk at wt ale. & a hye ; | ae STRUCTURE OF THE LIVER _ 155 lymphatics) and can also be traced to the lobules, from each of which they receive a minute branch (intralobular vein) which passes from the centre of the lobule, and opens directly into the (sublobular) branch of the hepatic vein. Wf {{ Wz i TEX ee Fig. 187.—SECTION OF A PORTAL CANAL. a, branch of hepatic artery ; v, branch of portal vein; d, bile-duct ; 1,7, lymphatics in the areolar tissue of Glisson’s capsule which encloses the vessels. Fic, 188.—DIAGRAMMATIC REPRESENTATION OF TWO HEPATIC LOBULES, The left-hand lobule is represented with the intralobular vein cut across; in the right-hand one the section takes the course of the intralobular vein. p, interlobular branches of the portal vein; A intralobular branches of the hepatic veins; s, sublobular vein; ¢, capil- laries of the lobules. The arrows indicate the direction of the course of the blood, The liver-cells are only represented in one part of each lobule. Each lobule is a mass of hepatic cells pierced everywhere with a network of blood-capillaries (fig. 188), which arise at the periphery of the lobule, there receiving blood from the interlobular branches of the portal vein (y), and converge to the centre of the lobule, where they ‘unite to form the intralobular branch of the hepatic vein. The inter- 156 ‘THE ESSENTIALS OF HISTOLOGY lobular branches of the hepatic arteries join this capillary network a short distance from the periphery of the lobule. The hepatic cells (fig. 189), which everywhere lie between and sur- round the capillaries, are polyhedral, somewhat granular-looking cells, Fic. 189.—SECTION OF RABBIT’S LIVER WITH THE INTERCELLULAR NETWORK OF BILE-CANALICULI INJECTED. (Highly magnified.) (Hering.) Two or three layers of cells are represented ; b, b, blood-capillaries, each containing a spherical nucleus. After a meal, the cells in the outer part of the lobule may become filled with fat, and masses of glycogen can also frequently be seen within the cells. The bile-ducts commence between the hepatic cells in the form of fine canaliculi, which lie between the adjacent sides of two cells, and form a close network, the meshes of which correspond in size to the cells (fig. 189). At the periphery of the lobule these fine canaliculi pass into the interlobular bile-ducts (fig. 190), the columnar epithe- lium-cells of which become, by a gradual transition, changed into cubical and polyhedral cells, which join those of the hepatic lobules. The bile-ducts are lined by clear columnar epithelium (fig. 187, d). Outside this is a basement-membrane, and in the larger ducts some fibrous and plain muscular tissue. Many of the larger ducts are beset with small cecal diverticula. The gall-bladder is in its general structure similar to the larger bile- ducts. It is lined by columnar epithelium, and its wall is formed of © fibrous and muscular tissue. The lymphatics of the liver are said to commence as perivascular lymphatic spaces enclosing the capillaries of the lobules. Efferent lymphatics pass away from the organ in the connective tissue which invests the portal and hepatic veins. — z é Ej 3 4 berg ¥ 3 ea : ~_ ¥ 4 : , f ° -% ‘ j ; i : FTL YES & ' EVN mW if ; Ait bile oki BS tihya le ru: eapRRing vi gions. falta ie peters) 2: < ay) is ary LT Wert > tia Faw Beegliy if 1 Ag , 7 ibSbyiae pA Ghareeiery D1: Graetye oy ac? ron mA ml in ‘golnwr hint Lan hie ‘ ¢ ' } » OL, "Oe vas . ai pila ike Wht. 3 ie Ve * fab if woth it'd Wass PM Pe a vedeodis » bite fue hicay de | ahkiiy, 4, va Woy ie tithe Of tite omit a : Mi si rd Oy , » poo tvs Apeia® > ‘s A ‘i . a ” - ‘ \ \ . ‘ 4 “ ; i? 7% wire ti “ « if 2 : $ i. sO ba wo. ‘ie, Pay ' Pe sha vet Une 0 v. _" ‘ pobt : | 2s \s* ieee tots ao ’ " a Lhe u , ‘ a2 ( aetare. elie igs Lie - i? Oe ee eee eee Tt ee Lar Loh, ; Mee lata Gh Ui Ms wre Sivc} coun ‘ —— Fic. 190.—LoBULE OF RABBIT’S LIVER, VESSELS AND BILE-DUCTS INJECTED. (Cadiat.) a, central vein ; }, 6, peripheral or interlobular veins; c, interlobular bile-duct. THE PANCREAS. - The pancreas is a tubulo-racemose gland, resembling the salivary glands, so far as its general structure is concerned, but differing from them in the fact that the alveoli, in place of being saccular, are longer and more tubular in character (fig. 191). Moreover, the connective tissue of the gland is somewhat looser, and there occur in it at intervals small groups of epithelium-like cells, which are supplied with a close network of convoluted capillary vessels; their function is unknown, but their presence is very characteristic of the pancreas. The cells which line the alveoli are columnar or polyhedral in shape. When examined in the fresh condition, or in osmic prepara- 158 THE ESSENTIALS OF HISTOLOGY tions, their protoplasm is filled in the inner two-thirds with small i granules, but the outer third is left clear (fig. 192, 4). After a period of 2 C55 a CE Ra capes ates eS. CS = Ip CLD week Kh) 5) J&3 of 5 Has) Fi Ge Fic. 191.—SECTION OF THE PANCREAS OF THE DOG. d, termination of a duct in the tubular alveoli, alv. Fic. 192.—PART OF AN ALVEOLUS OF THE RABBIT’S PANCREAS, A, AT REST; B, A¥TER ACTIVE SECRETION. (Foster, after Kiihne and Lea.) a, the inner granular zone, which in A is larger and more closely studded with fine granu'es than in B,in which the granules are fewer and coarser; }, the outer transparent zone, small in A, larger in B, and in the latter marked with faint striw; c, the lumen, very pile in B, but indistinct in A; d, an indentation at the junction of two cells, only seen in B, activity the clear part of the cell becomes larger, and the granular J part smaller (B). In stained sections the outer part is coloured more , deeply than the inner. ‘ ; In the centre of each acinus there may generally be seen some spindle-shaped cells, the nature of which (whether epithelial or con- nective tissue) has not been determined (centro-acinar cells of Lan- gerhans). "» aes x . ene ’ “ ke 5 ‘ a = . Ty + - \ =] ¢ 4 ai} - ; + : st ‘ . . ie ths ealy2 ap ti.: y aa WA A: ihe dy, ited [hp ‘ t + Gor Uhihehs ficco:ines: i (hae Fieger! , ies): By Sree lls pri indthess 3 vais iW ied eh yivelr.: pheearpanidl eG rl’. Sat pe 7 bts tab Pitre tes Wife: bh se ith Wins eye hated ‘e\3 34) rates exer asy large ation) good a4 Mk eae, ie wiMTilaa ital aphe. Dest ail Bi ec) HP aiden Oi Ce el palin of eh #3) fee cid tnt Pe ah ge ue if; 7“ arate cg | ’ . : y ! | rn vo tbeds We eT), AP ee ’ e ~ { i / PY \ = ‘ ’ . / \ i a ‘ = : ~ - v . wv tr. oF : s t Te . ao th 4 . ‘ ioe : : Se wpally pe seat * ee ATS ee ’ 3 ay ow a Ow oie ry) whe \'« j t : Asie 1 ceo LESSON XXXII. \ SFRUCTURE OF THE SPLEEN, SUPRARENAL CAPSULE, AND THYROID BODY. 1. Sections of the spleen stained with logwood. Notice the trabecule extend- ing into the substance of the organ from the capsule. Notice also that the glandular substance is of two kinds, (1) lymphoid tissue accumulated round the small arteries and here and there massed to form lymphoid nodules—the Malpighian corpuscles of the spleen—and, (2) a tissue consisting of a reticulum of branched and flattened cells containing blood in its interstices and pervaded by capillaries and venous radicles. Sketch part of a section under a low power and a small portion of the reticulum under a high power. 2. Sections across a suprarenal capsule. Examine first with a low power, noticing the general arrangement and extent of the cortical and medullary parts of the organ, making a general sketch which shall include both. Afterwards sketch carefully under the high power a group of cells from each part of the organ. 8. Sections of the thyroid body stained with logwood. Notice the vesicles lined with cubical epithelium and filled with a ‘ colloid’ substance which be- comes stained by the logwood. Notice also in some parts of the sections a peculiar highly vascular retiform tissue. Sketch a part of this tissue and also one or two vesicles. Measure several vesicles. THE SPLEEN. The spleen is the largest of the so-called ductless glands. It appears to be connected in some way with the elaboration of the blood, white blood-corpuscles being certainly formed and the coloured blood- corpuscles being probably submitted to destruction within it. Like the lymphatic glands, the spleen is invested with a fibrous and muscular capsule (fig. 193, A), and this again has a covering derived from the serous membrane. The capsule sends fibrous bands or tra- becule (b) into the organ, and these join with a network of similar trabecule which pass into the gland at the hilus along with the blood- vessels. In the interstices of the fibrous framework thus constituted lies a soft pulpy substance containing a large amount of blood, and therefore of a deep red colour, dotted within which are here and there to be seen small whitish specks, the Malpighian corpuscles of the spleen (c, c). These are composed of lymphoid tissue which is gathered up into masses which surround the smaller arteries, whilst the red pulp which everywhere surrounds them and which forms the bulk of the 160 THE ESSENTIALS OF HISTOLOGY - organ is composed of a close network or spongework of flattened and branched cells like connective-tissue corpuscles. Coursing through the — pulp and communicating with its interstices are capillary blood-vessels Fic. 193.—VERTICAL SECTION OF A SMALL SUPERFICIAL PORTION OF THE HUMAN SPLEEN, AS SEEN WITH A LOW POWER. A, peritoneal and fibrous covering ; b, trabecule ; c, c, Malpighian corpuscles, in one of which an artery is seen cut transversely, in the other longitudinally ; d, injected arterial twigs ; é, spleen-pulp. Fic. 194.—TrIn SECTION OF SPLEEN-PULP, HIGHLY MAGNIFIED, SHOWING THE MODE OF ORIGIN OF A SMALL VEIN IN THE INTERSTICES OF THE PULP, v, the vein, filled with blood-corpuscles, which are in continuity with others, 8/, filling up the interstices of the\retiform tissue of the pulp; w, wall of the vein. The shaded bodies amongst the red blood-corpuscles are pale corpuscles. which are connected with the terminations of the arteries; whilst in other parts venous channels arise from the pulp, and bring the blood which has passed into its interstices from the arterial capillaries — . : EF ir at slat ie | i? ‘os - rei ee Porgete peewilly deus Vhs To ir , J - \ <4 a 3 « rs 4 Hi » - ‘ = . sai Mona ' tk - ; == = : : ; Vv ¥ aa yi a ¥. t ree ? bal a. * * 7 e”™ - 2 we, aa ; ‘ . ‘ ‘ ‘ oat F > F is a 3 ‘i ‘ 4 ' ie i i» 1 . " —_ {Eke 22) wy ier Ve ea riRreS, SMPMCLE Re. yyy ier) RA Ave t A, A ee Phas, ma rf ahval i yiaalitk ae: FY * eee dion Wir \ oar ee fhe Creer. while) bh eon 3 Spree ao eeey at uw fe) sy iby ae “eM - AONE. | ia “Reise edeindh he bein wed An's WIN v TA TEAL» of eT X tonne’ . \ ~ ’ ' Ss. T a BP Se ~ . = - ‘ ' , . Ch { Po | x x tr ~ - = soa i i ras . -, ¢; tin ‘> ake ’ ri u « P i ‘ " : ; ‘veo tr) Os wipe 9 en See ee no oe : \ ; . / . =_ ‘wily Shh oe tel, , , ; , ee Pig Origa es Rew g. STRUCTURE OF THE SUPRARENAL CAPSULES 161 - towards the larger veins of the organ, which run in the trabecule, and are by them conducted to the hilus. The arteries, which are also at first conducted from the hilus along the trabecule into the interior of the organ, presently leave the trabecule, and their external coat becomes converted into a thick sheath of lymphoid tissue which invests : them in the remainder of their course, and in places becomes swollen into the Malpighian corpuscles already mentioned. These small arteries distribute a few capillaries to the Malpighian corpuscles, and then break up into pencils of small vessels which open iuto the pulp in the manner already mentioned. The cellular elements of the spleen-pulp are of sie kinds, viz. ~ large, amceboid, connective-tissue cells, also called splenic cells, lymph- corpuscles, and the branched, flattened cells which form the sponge- work. The first-named are frequently found to contain coloured blood-corpuscles in their interior in various stages of transformation ; into pigment. - The lymphatics of the spleen run partly in the trabecule and cap- | sule, and partly in the lymphoid tissue ensheathing the arteries. They join to form larger vessels which emerge together at the hilus. THE SUPRARENAL CAPSULES. The suprarenal capsules belong to the class of bodies known as duct- less glands, but they are entirely different in structure from the spleen and lymphatic glands. A section through the fresh organ (fig. 195) Fic. 195.—A VERTICAL SECTION OF THE SUPRARENAL BODY OF A FGTUS, TWICE THE NATURAL SIZE, SHOWING THE DISTINCTION BETWEEN THE MEDULLARY AND CORTICAL SUBSTANCE. v, issuing vein ; 7, sammit of kidney. shows a cortical zone which is striated vertically to the surface, and of a yellowish colour, and a medulla which is soft and highly vascular, and of a brownish-red colour. The whole organ is invested by a fibrous capsule which sends fibrous septa inwards to the cortical substance _ (fig. 196), subdividing this for the most part into columnar groups of cells (zona fasciculata, c). Immediately underneath the capsule, however, M 162 THE ESSENTIALS OF HISTOLOGY ~- the groups are more rounded (zona glomerulosa, b), whilst next to the medulla they have aclosely reticular arrangement (zona reticularis, d), and a similar disposition both of the cells and the connective tissue is noticeable throughout the medulla. The cells which form the rounded groups and columns of the cortical substance are polyhedral in form (fig. 197) ; each contains a clear round nucleus, and there are often yellowish oil-globules in their protoplasm. Fic. 197—CELLS AND CELL-GROUPS FROM THE OUTERMOST LAYER OF THE CORTICAL SUBSTANCE OF THE SUPRARENAL BODY. ni 9 £ Po >) 1, 998,28 0998 19 aa Nice Mees ve SEN Fie. 196.—VERTICAL SECTION OF SUPRA- RENAL BoDY. (Magnified.) 1, cortical substance ; 2, medullary substance ; * a, capsule; b, zona glomerulosa; ¢, zona Fic. 198.—A SMALL PORTION OF THE fasciculata; d, zona reticularis; e, groups MEDULLARY PART OF THE SUPRA~ of medullary cells ; 7, section of a large vein. RENAL CAPSULE OF THE OX, No blood-vessels penetrate between these cells, both the blood-vessels and lymphatics of the cortex running in the fibrous septa between the columns; the lymphatics have been stated to communicate with fine spaces which run between the cells of the columns. pe The cells of the medulla (fig. 198) are more irregular in shape, and are often branched. Their protoplasm is either clear, or it may in some animals contain a brownish pigment, but in man the dark red colour of rz x y ; feiatin's 3 qae Ww bead Wa a he Ve) are oh 2 . sane > : ow as = ~ =i a tur bya; ge .F l Le peti lead ig , 7 > Fie diols ‘rere | ee Bub lite rite ra tien tlaavieser- a tie’, 2 ; Fe sve: vie ng. Pigtyth: SS ae a ral beats pte Suen eri th | ‘ os be SISA OF abs estiryn » Baabctaspalgiicad tow Soiled Avent utile ayt miuvoe LAS tae? ant uEny ot a ; Act Dur mea Lana tte wth’ dbuat af fe birsed ap" baile Kaa, seth syiaibuelly i ey t | ee STRUCTURE OF THE THYROID BODY 163 the medulla is largely due to the blood contained in the large venous spaces by which it is pervaded, and which receive the blood after it has traversed the capillaries of the cortex. Investing the larger veins are bundles of plain muscular fibres ; and numerous nerves, after traversing the cortical substance, are distributed throughout the medulla, where they form a close plexus provided with ganglion-cells. ‘ THE THYROID BODY, The thyroid body consists of a framework of connective tissue en- closing numerous spherical or oval vesicles (fig. 199) which are lined with cubical epithelium. The cavities of the vesicles are filled with a peculiar viscid liquid which is coagulated by alcohol and which then becomes stained by hematoxylin. A similar material has been found Fic. 199.—SEcTION OF THE THYROID GLAND OF A CHILD. Two complete vesicles and portions of others are represented. The vesicles are filled with colloid, which also occupies the interstitial spaces. In the middle of one of the spaces a blood-vessel is seen cut obliquely, and close to it is a plasma-cell. Between the cubical epithelium-cells, smaller cells like lymph-corpuscles are here and there seen. in the lymphatics of the gland, and may sometimes be detected also in the interstices of the connective tissue. The blood-vessels of the thyroid are exceedingly numerous, and the capillaries form close plexuses round the vesicles. Some of the blood- vessels are distributed to a peculiar highly vascular retiform tissue which occurs in patches here and there in the organ. Disease of the thyroid or its extirpation is accompanied by remark- able changes in the chemical composition of the blood and many of the tissues, resulting chiefly in the accumulation within them of a large amount of mucin; a condition of general myxcedema, and eventually of cretinism, being produced. he 164 THE ESSENTIALS OF HISTOLOGY LESSON XXXIII. STRUCTURE OF THE KIDNEY. 1. SecTIoNS passing through the whole kidney of a small mammal, such as a mouse or rat. These sections will show the general arrangement of the organ and the disposition of the tubules and of the Malpighian corpuscles. A general sketch should be made of one of these sections under a low power. 2. Thin sections of the kidney of a larger mammal, such as the dog, may next be studied. In some the direction of the section should be parallel. with the tubules of the medulla, and in others across the direction of those tubules. The characters of the epithelium of the several parts of the uriniferous tubules are to be made out in these sections. 3. Separate portions of the urmiferous tubules may be studied in teased preparations from a kidney which has been subjected to some process which renders it possible to unravel the uriniferous tubules for a certain distence.' 4. Sections of a kidney in which the blood-vessels have been injected. Examine these with a low power of the microscope. Try and follow the course of the arteries—those to the cortex sending their branches to the glomeruli, those to the medulla rapidly dividing into pencils of fine vessels which run between the straight uriniferous tubules of that part. Notice also the efferent vessels from the glomeruli breaking up into the capillaries which are distributed to the tubules of the cortical substance. Make sketches showing these points. The kidney is a compound tubular gland. To the naked eye it ap- pears formed of two portions—a cortical and a medullary—the latter being subdivided into a number of pyramidal portions (pyramids of Malpighi), the base of each being surrounded by cortical substance, while the apex projects in the form of a papilla into the dilated commence- ment of the ureter (pelvis of the kidney).2 Both cortex and medulla are composed entirely of tubules—the wriniferous twbules—which have a straight direction in the medulla and a contorted arrangement in the cortex; but groups of straight tubules also pass from the medulla through the thickness of the cortex (medullary rays). The uriniferous tubules begin in the cortical part of the organ in dilatations, each enclosing a tuft or glomerulus of convoluted capillary ' For a method which may be employed for this purpose, see Course of Prac- tical Histology, p. 209. 1 Os * In many animals the whole kidney is formed of only a single pyramid, but in man there are about twelve. a aS bie to 1 oe AoW obs, flie Mhitoll Poameornennant OE Mpe ainsi see B = > > > aa | : a urpostlan tte SKY |. Sie Dy terl Tet ey See eee Cas - be : : ; 2 “ + ing ‘ * van) =~ . , . 1d . j 2 ‘ { 4) a 2 ss — ; 5 a ie aliah iby pial Ones es r : pies hours) jute tive coprnllip aisemn ts | < > 7 +48 “ia ts = soa Ke : . hy ; : uot ‘ i Oe CT ORAS ral Ej a \ ? ’ } { i . « - dD) whe ‘ < ea ee — STRUCTURE. OF THE KIDNEY 165 Pesca: vessels, the dilated eomniencement of the tubule eh known as the capsule (fig. 200, 1). The tubule leaves the capsule by a nar- row neck (2); it is at first convoluted (first convoluted tubule, 3), but Go “ ane: 8 4 7 6 18 H | { f Cc Fic, 200.—DIAGRAM OF THE COURSE OF TWO URINIFEROUS TUBULES. "2 A, cortex; B, boundary zone; c¢, papillary zone of the medulla ; a, a’, superficial and deep layers of cortex, free from glomeruli. For the explanation of the numerals, see the text. _ goon becomes nearly straight or slightly spiral only (spiral tubule, 4), and then, rapidly narrowing, passes down into the medulla towards the ~ dilated commencement of the ureter as the descending tubule of Henle = ™ ‘Tt does not at ana however: oe into the ners of” the kidney, Beri dt: 166 THE ESSENTIALS OF HISTOLOGY but before reaching the end of the papilla it turns round in the form of a loop (loop of Henle, 6) and passes upwards again towards the cortex, - parallel to its former course and somewhat larger than before (ascend- ing tubule of Henle, 7, 8,9). Arrived at the cortex, it at first becomes irregularly zigzag (zigzag tubule, 10), and then again convoluted as at first (second convoluted tubule, 11), eventually, however, narrowing into a vessel (ywnctional tubule, 12) which joins a straight or collecting tubule (13). This now passes straight through the medullary substance of the kidney (14) to open at the apex of the papilla as one of the ducts of Bellini (15). The tubules are throughout bounded by a basement-membrane, Fic. 201.—TUBULES FROM A SECTION OF THE DOG’S KIDNEY. a, Capsule, enclosing the glomerulus; n, neck of the capsule; ¢, c, convoluted tubules; b, irregular tubules; d, collecting tube; ¢, e, spiral’ tubes; 7, part of the ascending limb of Henle’s loop, here (in the medullary ray) narrow. which is lined by epithelium, but the characters of the epithelium-cells vary in the different parts of a tubule. In the capsule the epithelium is flattened and is reflected over the glomerulus (fig. 201, a). In the first convoluted and spiral tubules it is thick, and the cells show a marked fibrillar structure (figs. 202, 203). Moreover, they interlock laterally and are difficult of isolation ; in many animals they have been shown to be ciliated. In the narrow descending limb of the looped tubule (fig. 204, c), and in the loop itself, the cells are clear and flat- tened and leave a considerable lumen; in the ascending limb they again acquire the striated structure and nearly fill the lumen. The fibrillations of the cells are still more marked in the zigzag tubules (fig. 201, b), and a similar structure is present also in the seco | hats yo week " Prk SP Se - ‘ +4 gtd? rr iy “ie i toric ha \ 7 | » \ bekiracte ; wy *. r 4 mn } * ae % wa F -,* ’ ’ J ’ ; \ ; . r én ~ - y r Fic, 202.—SrrucrurE OF THE EPITHELIUM OF THE CONVOLUTED TUBULES. d, section of a convoluted tubule from the rat, showing the unaltered proto- plasm occupying a circular area around the nucleus of each cell; a, 6, ¢, isolated cells from the convoluted tubules of the rat; e, isolated cells from the dog’s kidney, viewed from the inner surface, and showing the irregular contour of the protoplasm; 7, isolated cells from the newt, showing the rods and the homogeneous cuticular layer, Fic, 203.—Parr orf A con- VOLUTED TUBULE FROM THE DOG’S KIDNEY, Fie. 204,—PortTIoNs OF TUBULES, ISOLATED, Cadiat.) 4% a, large collecting tubule; b, loop of Henle; c, descending : , tubule of Henle, | STRUCTURE OF THE KIDNEY 167 wi a “a - * ~. = "4 - _ aie, etl 168 THE ESSENTIALS OF HISTOLOGY convoluted tubules, into which these pass. On the other hand, the junctional tubule has a large lumen and is lined by clear flattened cells, and the collecting tubes have also a very distinct lumen and are lined by a clear cubical or columnar epithelium (figs. 201, d; 204, a). Fic. 205.—SEcTION ACKOSS A PAPILLA OF THE KIDNEY. (Cadiat.) a, large collecting tubes (ducts of Bellini); 0, c, d, tubules of Henle; e, 7, blood-capillaries., The following gives a tabular view of the parts which compose a uriniferous tubule, and the nature of the epithelium in each part : Portion of tubule Nature of epithelium Position of tubule Capsule First convoluted tube Spiral tube Small or descend- ing tube of Henle Loop of Henle Larger or ascend- ing tube of Henle Zigzag tube Second _ eonvo- luted tube Junctional tube . Straight or col- lecting tube Duct of Bellini . . Cubical, fibrillated (like the last) . | Flattened, reflected over glomerulus . Cubical, fibrillated, ciliated, the cells interlocking Clear, flattened cells . Like the last Cubical, fibrillated, sometimes imbri- cated .| Cells strongly fibrillated ; varying in height ; lumen small Similar to first convoluted tube, but cells are. longer, with larger nuclei, and they\-have a more refractive aspect Clear flattened.and cubical cells Clear, cubical and columnar cells Clear, columnar cells. . | - | Papillary -|Opens at apex Labyrinth of cortex Labyrinth of cortex .| Medullary ray of cor- tex -|Boundary zone and partly papillary zone of medulla zone of medulla Medulla, and mednl- lary ray of cortex Labyrinth of cortex Labyrinth of cortex .| Labyrinth passing to medullary ray Medullary ray and med papilla of St sritneblig =the cies Bee ele Lhe caetaee ne 1% eee elit Miteotryait sas 4 eet: aa MR St eo Tuie Axe ove Hr i, é + ie ‘ se ~ yy . ‘ : f 7 she . y t ; - | 1 eal = A oe if ie Fat ' voy efit eierheget ortags > ; . mea te fein | nhpreaptot ¢ i ” th wo denen, seit lates an: & Ve Pai 2 . s r yy eee a Mae rolemetl ae. Re AN (Clea eal - STRUCTURE OF THE KIDNEY ~ 169° ' Blood-vessels.—The artery of the kidney divides into branches on entering the organ, and these branches pass towards the cortex, ‘forming incomplete arches between the cortex and the medulla (fig. 206, a). The branches of the renal vein form similar but more com- plete arches (7). From the arterial arches vessels pass through the co ‘ 7 ee N «2 | | a \ ) ae 2 Fic. 206.—VaAscuLAR SUPPLY OF KIDNEY. (Cadiat.) ' a, part of arterial arch; 6, interlobular artery; c, glomerulus; d, efferent vessel passing to medulla as false art. rect. ; e, capillaries of cortex ; 7, capillaries of medulla; g, venous arch ; A, straight veins of medulla; j, vena stellula; i, interlobular vein. cortex (interlobular arteries, b), and give off at intervals small arteri- oles (afferent vessels of the glomeruli), each of which enters the dilated commencement of a uriniferous tubule, within which it forms a _ glomerulus. From the glomerulus a somewhat smaller efferent vessel passes out, and this at once again breaks up into capillaries, which ’ 170 THE ESSENTIALS OF HISTOLOGY ‘are distributed amongst the tubules of the cortex (e); their blood is collected by veins which accompany the arteries and join the venous arches between the cortex and the medulla, receiving in their course ~ certain other veins which arise by radicles which have a somewhat stellate arrangement near the capsule (vene stellule, J). The medulla derives its blood-supply from special offsets of the ~ arterial arches, which almost immediately break up into pencils of fine straight arterioles running in groups between the straight tubules - of the medulla. These arterioles gradually break up into a capillary © network with elongated meshes which pervades the medulla (fig. 206, /), and which terminates in a plexus of somewhat larger venous capillaries in the papille. From these and from the other capillaries the veins Fic. 207.—SrcrioN THROUGH PART OF THE DOG’s KIDNEY. P, papillary, and g, boundary zones of the medulla; ec, cortical layer ; h, bundles of tubules in the boundary layer, separated by spaces, b, containing bunches of vessels (not here represented), and prolonged into the cortex as the medullary rays, m;c, intervals of cortex, composed chiefly of convoluted tubules, with irregular rows of glomeruli, between the medullary rays. collect the blood, and pass, accompanying the straight arterioles, into the venous arches between the cortex and medulla. The groups of small arteries and veins (vasa recta) in the part of the medulla nearest — the cortex alternate with groups of the uriniferous tubules, and this arrangement confers a striated aspect upon this portion of the medulla (boundary zone, see fig. 207). - The efferent vessels of those glomeruli which are situated nearest to the medulla may also break up into pencils of fine vessels (false arteri@ recte) and join the capillary network of the medulla (fig. 198, d). Between the uriniferous tubules, and supporting the blood-vessels, is a certain amount of connective tissue (fig. 205), within which are cleft-like spaces from which the lymphatics of the organ originate. — “ee Fes ther + wie jon Se 171 LESSON XXXIV. - STRUCTURE OF THE URETER, BLADDER, AND MALE GENERATIVE ORGANS. 1. Section across the ureter. 2. Section of the urinary bladder vertical to the surface. In the sections of the ureter and of the urinary bladder, notice the transitional epithelium resting on a mucous membrane, which is composed ' chiefly of areolar tissue without glands, and the muscular coat outside this. In the ureter there is some fibrous tissue outside the muscular coat, and at the upper part of the bladder there is a layer of serous membrane covering » the muscular tissue. Sketch a section of the ureter under a low power, and the epithelium of the bladder under the high power. 3. Section across the penis. The blood-vessels of the organ should have been injected so as the better to exhibit the arrangement of the venous spaces which constitute the erectile tissue. Notice the large venous sinuses of the corpora cavernosa and the smaller spaces of the corpus spongiosum, in the middle of which is seen the tube of the urethra. 4, Section across the testis and epididymis. The sections are best made from a rat’s testis which has been hardened in alcohol and pieces of which have been stained in bulk in dilute logwood. In these sections notice the strong capsule surrounding the gland, the substance of which consists of tubules which are variously cut, and the epithelium in which is in different conditions of development in the different tubules. Observe the strands of polyhedral interstitial cells lying in the loose tissue between the tubules and the lymphatic clefts in that tissue. Notice also in sections through the epididymis the ciliated epithelium of that tube. Sketch carefully under a high power the contents of some of the semini- ferous tubules so as to illustrate the mode of formation of the spermatozoa. 5. Examination of spermatozoa. The spermatozoa are to be obtained fresh from the testis or seminal vesicles of a recently killed animal and ex- amined in saline solution. Their movements may be studied on the warm stage; to display their structure a very high power of the microscope is necessary. Measure and sketch three or four spermatozoa. The ureter is a muscular tube lined by mucous membrane. The muscular coat consists of three layers of plain muscular tissue, an outer and inner longitudinal and a middle circular. Outside the mus- cular coat is a layer of fibrous tissue in which the blood-vessels and nerves ramify before entering the muscular layer. The mucous membrane is composed of areolar tissue end is lined by transitional epithelium. 172 THE ESSENTIALS OF HISTOLOGY The urinary bladder has a muscular wall lined by a strong mucous membrane and covered in part by a serous coat. The muscular coat consists of three layers, but the innermost is incomplete. The principal fibres run longitudinally and circularly, and the circular fibres are collected into a layer of some thickness which immediately surrounds the commencement of the urethra, form- ing the sphincter vesice. The mucous membrane is lined by a transi- * tional stratified epithelium like that of the ureter. The shape and structure of the cells have already been studied. ; The penis is mainly composed of cavernous tissue which is collected into two principal tracts—the corpora cavernosa, one on each side, and the corpus spongiosum in the middle line inferiorly. All these are bounded by a strong capsule of fibrous and muscular tissue, containing also many elastic fibres and sending in strong septa or trabecule, 1 1 ‘ ; Vic. 208.—SEcTION OF ERECTILE TISSUE. (Cadiat.) a, trabecule of connective tissue, with elastic fibres, and bundles of plain muscular tissue (c); b, Venous spaces. which form the boundaries of the cavernous spaces of the erectile tissue (fig. 208). The arteries of the tissue run in these trabecule, and their capillaries open into the cavernous spaces. On the other hand, the — spaces are connected with efferent veins. The arteries of the cavernous tissue may often in injected specimens be observed to form looped or twisted projections into the cavernous spaces (helicine arteries of Miller). Urethra. The: cross-section of the urethra appears in the middle of the corpus spongiosum in the form of a transverse slit. It is lined by columnar epithelium, except near its orifice, where the epithelium is stratified, The epithelium rests upon, a vascular mucous membrane, PeeeAh ia ainpered oy Santivg of tyro few: a Dhow Sihteedlay fires Le! gag Far ei itt 4 Piya. (Fa sat! >iile, Wc. 1 2 ; _+" me ay ! = ¥ ; = ‘~ Dae avieted WILLS sro? pay lee seid | ; ‘ 1 tt P c : Wet - yi 3 : . . ‘s y ‘ 7 ‘ ‘ e 3 . é 4 ‘ ’ r . i is . r 4 Z . f 3 ; é “a { os ee ‘ ; 4 P ne : » . . ‘ e J] ; ” es . : = oa ‘wee see Ve we fe Satertis 26 UO-_: ” . Boledic To ~ . , 5,-6 ae ‘heat i & ; bie is’ | ea ness.) cone - te - . eS ‘le } rhe P * ’ t Lierdég tile é iG 0 | oe we Sewbk, ADE Af 4 . S, ‘ he the wlitr tim La & a : ' at wierd of: 7 ; ; ; i oh A L hm , : as Wa ub td ‘Dba A30 tae ~~ ~. ' 7 : - t rer 4) | ‘ Lele ey Garvey mete( HE af phy ni ah a es 10 are y MALE GENERATIVE ORGANS 178 and this again is supported by a coating of submucous tissue, con- taining two layers of plain muscular fibres—an inner longitudinal and an outer circular. Outside this again is a close plexus of small veins which are connected with, and may be said to form part of, the corpus spongiosum. The mucous membrane of the urethra is beset with small mucous glands, simple and compound (glands of Lnttré). There are also a number’ of oblique recesses termed lacune. Besides these small glands and glandular recesses, two compound racemose glands open into the bulbous portion of the urethra (Cowper’s glands). Their acini are lined by clear columnar cells which secrete mucus. The prostate, which surrounds the commencement of the urethra, is a muscular and glandular mass, the glands of which are composed ‘of tubular alveoli, lined by columnar epithelium, with smaller cells lying between them and the basement-membrane. Their ducts open upon the floor of the urethra. The integument of the penis contains numerous special nerve end- organs of the nature of end-bulbs, and Pacinian bodies have also been Fic. 210.—PLAN OF A VER- Fic. 209.—TRANSVERSE SEC-~ TION THROUGH THE RIGHT TICAL SECTION OF THE TESTICLE AND THE TUNICA TESTICLE, SHOWING THE VAGINALIS. ARRANGEMENT OF THE ‘a, connective tissue enveloping DUCTS. the parietal layer of the tunica The true length and diameter of vaginalis; 6, this layer itself ; the ducts have been disre- ce, cavity of the tunica vagi- garded. a, a, tubuli seminiferi nalis; d, reflected or visceral layer adhering to e, the tunica albuginea; 7, covering of epi- didymis (yg); /, mediastinum testis ; i, branches of the sper- matic artery; 4, spermatic vein ; 7, vas deferens ; m, small artery of the vas deferens ; n, 0, septa or processes from the mediastinum to the surface. coiled up in the separate lobes ; b, vasa recta; c, rete vascu- losum; d, vasa efferentia end- ing in the coni vasculosi ; J, e, g, convoluted canal of the epi- didymis; 4, vas deferens; /, section of the back part of the tunica albuginea; i, i, fibrous plocesses running between the lobes ; 7 to s, mediastinum. found upon the nerves. Lymphatic vessels are numerous in the in- tegument of the organ and also in the submucous tissue of the urethra. 174 THE ESSENTIALS OF HISTOLOGY The testicle is enclosed by a strong fibrous capsule, the tunica al- | q buginea (fig. 209, e). This is covered externally with a layer of serous epithelium reflected from the tunica vaginalis. From its inner surface there proceed fibrous processes or trabecule, which imperfectly sub- divide the organ into lobules, and posteriorly the capsule is prolonged into the interior of the gland in the form of a mass of fibrous tissue, which is known as the mediastinum (fig. 209, h). Attached to the pos- terior margin of the body of the gland is a mass (epididymis) which when investigated is found to consist of a single convoluted tube, receiy- Fic. 211.—PaAssaGE OF CONVOLUTED SEMINIFEROUS TUBULES INTO STRAIGHT TUBULES AND OF THESE INTO THE RETE TESTIS. a, seminiferous tubules; 6, fibrous stroma continued from the mediastinum testis ; c, rete testis. ing at its upper end the efferent ducts of the testis and prolonged at its lower end into a thick-walled muscular tube, the vas deferens, which conducts the secretion to the urethra. The glandular substance of the testicle is wholly made up of convo- luted tubules, which when unravelled are of very considerable length. F Each commences near the tunica albuginea, and after many windings © terminates, usually after joining one or two others, in a straight tubule (fig. 211), which passes into the mediastinum, and there forms, by ~ oe aie te Shae» 1 Dertisvrou aa thee | vm piucber ERP ik trek tlds uct teehee sy Ge . sab Gin Aue a ie epideives . Smarmnturk of tie tabaler -- lin + Beis Pb ees Figs yy. ALT sh ' Heats (aye | = “Hi ’ & i ‘ ’ . ¢ ‘ ' ’ - : , a \ R \ ! _— \ hs | he { cad rie SA) We! & VO ReAS a he t WW, Troe it Sion tipber nat pacenai 2! Mepall qyiditsyplud 1. 4 » peti?” bigest ty) fb : » atious Ke i thal? a ; bi ; “if i bay, Hsae. ° . LM) ae rea ed. babeaen: Ahem £7 % at hint) OER WR ; cme oe aereye oes ‘onpdih emayntok ‘as NS a iy ts a heespibg wag) ; patently vat ~ are a i. 7 At, ;* “7 be * « . ah og ‘ ‘ ss i ‘ bce Get é wer 3 tia a ‘ etal, a 4g ot bined i ‘lnger aig ite (oneal - tai apes ethyl * cece te hala f Becta ay) r Bi 4 ; aud f ; Je (226 Delp pad yee | Y : . : > “ees : i} i! a He Arent > ia gis we thas rnp Ser Of ta, bor tinla wh oH, re Wie, eovaghe wid Leah pi, tae + ae Mit ~ > aber pears ss : } = STRUCTURE. OF THE TESTICLE 175 -uniting with the other straight tubules, a network. of intercom- municating vessels, which is known as the rete testis. From the rete a certain number of efferent tubules arise, and after a few convolutions pass into the tube of the epididymis. Structure of the tubules—The seminiferous tubules are formed of a basement-membrane, and contain several layers of epithelium-cells. Of these layers, the one next the basement-membrane is a uniform layer of clear cubical cells (lining epithelium), the nuclei of which, for the most part, exhibit the irregular network which is characteristic of 2] ie AS BiXo) Fig. 212.— SECTION OF PARTS OF THREE SEMINIFEROUS TUBULES OF THE RAT. a, with the spermatozoa least advanced in development; 6, more advanced; ¢, containing fully developed spermatozoa, Between the tubules are seen strands of interstitial cells with blood-vessels and lymph-spaces. the resting condition. Here and there these epithelium-cells appear enlarged and to project between the more internal layers. Next to this layer of cubical epithelium there is seen a layer of larger cells (spermatogenic cells), the nuclei of which have the skein- like aspect which is typical of commencing division ; these cells may be two, three, or more deep (as in the tubule a, fig. 212). Next to them, and most internal, are to be seen in some tubules (6 and c) a large number of small protoplasmic corpuscles with simple circular nuclei (spermatoblasts). In other tubules these corpuscles are elongated, and the nucleus is at one end, and in others again these elongated cells are converted into evident spermatozoa, which lie in groups with. their heads projecting between the deeper cells and connected with one of the enlarged cells‘of the lining epithelium, and their tails emerging into the lumen of the tubule (fig. 212, b). As they become matured they gradually pass altogether towards the lumen, where they eventually become free (c). During the time that this crop of spermatozoa has -been forming, another set of spermatoblasts has been produced by the mm 176 THE ESSENTIALS OF HISTOLOGY division of the spermatogenic cells, and on the discharge of the sperma- ‘tozoa the process is repeated as before. The straight tubules which lead from the convoluted serainiteriwe tubes into the rete testis (fig. 211) are lined only by a single layer ~ of clear flattened or cubical epithelium. The tubules of the rete also have a simple epithelial lining, but the basement-membrane is here absent, the epithelium being supported directly by the connective ‘tissue of the mediastinum. The efferent tubules which pass from the rete to the epididymis, and the twhe of the epididymis itself, are lined by columnar ciliated epithelium, the cilia being very long ; these tubes have a considerable amount of plain muscular tissue in their wall. Fic. 213.—SEcCTION ACROSS THE COMMENCEMENT OF THE VAS DEFERENS, a, epithelium ; 6, mucous membrane; ¢, d, e, inner, middle, and outer layers of the muscular coat ; 7, bundles of the internal cremaster muscles ; g, section of a blood-vessel. The vas deferens (fig. 213) isa thick tube, the wall of which is formed of an outer thick layer of longitudinal bundles of plain muscular tissue ; within this an equally thick layer of circular bundles of the same tissue, and within this again a thin layer of longitudinal muscle. The tube is lined by a mucous membrane, the inner surface of. wih is -covered by columnar non-ciliated epithelium. The connective tissue between the tubules of the testis is of "very Aare “v ? | 5 et. : A240 few oT : = > - Pad ; ps 4 “ “ £ é ‘ ' ! ‘ , ir 6 ‘ =: Z - ot - * — ‘ ) 2 ss - . \ . + - } * = iz ‘ r ; * V3 Mi : r J _ ‘ 7 . ' “_ 7 , ve } r =} rs ae ee SO biv\c Bi E tak ONrnu na Ba Wits ' tn iy : : Delia Akh eae se 2ikey idk yai | ’ Sh 5 OaAye ns es She vt lyeriet 4 : 7 is " = . wn a fijvads fp, fpr. 2 5 afea +i tig! a ig tyes idee es an! hh TBH OS et eee oe Syncs»: beret iho see ‘he. Mea aad ater oaal hi | i mae f. dyes 3 - viva ‘ , Lr ae © getthyyes ets iat Eve me iz | a ash spe iy Palas V Es 7 STRUCTURE OF THE SPERMATOZOA. 177 loose texture, and contains numerous lymphatic clefts, which form an - intercommunicating system of commencing lymphatic vessels. Lying in this intertubular tissue are strands of polyhedral epithelium-like cells (interstitial cells) of a yellowish colour; they are much more _ abundant in some species of animals (cat, boar) than in others. They accompany the blood-vessels before these break up to form the capillary networks which cover the walls of the seminiferous tubules. Fig. 214.—HuMAN SPERMATOZOA. 1, in profile ; 2, viewed on the flat : b, head ; c, middle-piece ; d, tail; e, end-piece of the tail. The spermatozoa.—Each spermatozoon consists of three parts, a head, a middle part or body, and a long tapering and vibratile tazl. In man (fig. 214) the head is of a flattened oval shape, somewhat more flattened and pointed anteriorly; and the middle-piece is short and cylindrical, and appears to have a spiral fibre passing round it ; but in different animals the shape of the head and the extent of the middle- piece vary greatly. In the rat the head is long, and is recurved ante- riorly ; it is set obliquely on the middle-piece, which is also of con- siderable extent, and has a closely wound spiral filament encircling it in its whole length. The tail is the longest part of the spermatozoon, and during life is in continual vibratile motion, the action resembling - that of the cilia of a ciliated epithelium-cell. The spermatozoa are developed from the small cells or spermato- blasts which form the innermost strata of the seminal epithelium, and are themselves produced by the division of the large cells of the second layer. The nucleus of the spermatoblast forms the head of the sperma- tozoon, while the protoplasm forms first the middle-piece and subse- quently the tail; but a portion of the protoplasm of each spermato- blast containing a number of small darkly staining particles (seminal granules) appears always to become detached and disintegrated before the spermatozoon is fully mature. E . N 178 THE ESSENTIALS LESSON XXXV. GENERATIVE ORGANS OF THE FEMALE, AND MAMMARY GLANDS. 1. Sections of the ovary of the rabbit. Study the sections with the low power, observing the small and large Graafian vesicles, each enclosing an ovum, scattered through the stroma. Measure some Graafian vesicles of different sizes; make a general sketch of a section under the low power. Then sketch carefully two or more of the Graafian vesicles with their contents. 2. Sectionsacross the Fallopian tube. Sketch a section under the low power. 3. Section across the body of the uterus. Observe with the naked eye the thickness of the muscular and mucous coats respectively. Notice the ciliated columnar epithelium lining the organ and extending into the glands of the mucous membrane. Draw a part of the section under the low power. 4. Sections of the mammary gland from an animal killed during lactation. Notice the fat-globules in the alveoli and also in the alveolar cells. Draw an alveolus under the high power. The ovary is a small solid organ, composed of a stroma of fibrous tissue, with many spindle-shaped cells, and also containing, especially near its attachment to the broad ligament, a large number of plain Fie. dis Sncow OF THE OVARY OF THE CAT. ¢ 1, outer covering and free border of the ovary; 1’, attached border ; 2, the central ovarian stroma, presenting a fibrous and vascular structure; 3, peripheral stroma; 4, blood- vessels ; 5, Graafian follicles in their earliest stages lying near the surface ; 6, 7, 8, more advanced follicles which are embedded more deeply in the stroma ; 9, an almost mature follicle containing the ovum in its deepest part; 9’, a follicle from which the ovum has accidentally escaped ; 10, corpus luteum. ‘ - rites. tet i Oa, Wiel “e fs YS ie pti fits bape < ~ ‘ »! t i Pidi'c wes Bix as. Mi: tthe a Theerial Bet 4 ate ¥ * . i 2 x / * 2 - i] bo - ' P fashiiass S dedeniaael ee - GENERATIVE ORGANS OF THE FEMALE 179 = muscular fibres. It is covered by a layer of small columnar epithelium- cells (germinal epithelium, fig. 216, a), between which are here and there to be seen a few larger spheroidal cells, with large round nuclei (primitive ova, fig. 218, c). In the young subject the epithelium may occasionally dip down into the subjacent stroma. The stroma is beset with vesicles of different sizes, the smallest a oe ey ae ey i a Gq Fic, 216.—SEcrION OF THE OVARY OF AN ADULT BITCH. ¥° u, germ-epithelium ; b, egg-tubes ; ¢, c, small follicles ; d, more advanced follicle; e, discus pro- ligerus and ovum ; 7, second ovum in the same follicle (this occurs but rarely); g, outer tunic of the follicle; A, inner tunic; i, membrana granulosa; 4, collapsed retrograded follicle ; 7, blood-vessels ; m, m, longitudinal and transverse sections of tubes of the paro- varium ; y,involuted portion of the germ-epithelium of the surface ; z, place of the transi- tion from peritoneal to germinal or ovarian epithelium. : being near the surface of the organ, the larger ones placed more deeply in the stroma, although, as they increase in size, they may again tend to approach the surface. ‘These vesicles are the Graafian follicles. Each Graafian follicle N2 180 THE ESSENTIALS OF HISTOLOGY has a proper wall of basement-membrane, strengthened by a layer derived from the stroma, and contains an ovwm, surrounded by a number of epithelium-cells. In the smallest follicles the ovum is small, and the epithelium of the follicle is formed of a single layer of cells, which are flattened against the ovum. In somewhat larger follicles the epithelium-cells are in two layers, and these are columnar in shape. In still larger ones, each of these two layers is formed of several strata of cells, and fluid has begun to collect between the layers at one part. Of the two layers, the one which lines the cavity ~ of the follicle is termed the membrana granulosa, while the mass of cells which more immediately surrounds the ovum is known as the discus proligerus. In the largest follicles the fluid has much increased in amount, so that the follicle has become gradually larger and more tense. Finally it reaches the surface of the ovary, and projects from that surface, where it eventually bursts, and the liquor folliculi, with its contained ovum, is set free. This event occurs at about the time of menstrua- tion.! Fic. 217.—SEMI-DIAGRAMMATIC REPRESENTATION OF A MAMMALIAN OVUM. (Highly magnified.) zp, zona pellucida ; vi, vitellus ; gv, germinal vesicle; gs, germinal spot, The ovayare large spheroidal cells (fig. 217). When mature, as in the largest Graafian follicles, each ovum is surrounded by a thick transparent striated membrane (zona pellucida). Within this is the protoplasm of the cell (vitellus), filled with fatty and albuminous granules. Lying in the vitellus, generally eccentrically, is the large clear round nucleus (germinal vesicle), which contains an intranuclear network, and usually one well-marked nucleolus (germinal spot). Both > the ova and the epithelium of the Graafian follicles are developed ' Some of the Graafian follicles do not burst, but, after attaining a certain stage of maturity, undergo a process of retrograde metamorphosis and eyentually _ disappear. s he he ae - Remi he Sen ifica! ay Ain abs + Fy Mie-ek He liver, coreieny. Lite Riyoud 4 ipeOuits Atls Batts wt opting sun -oelio.§ ! arts : ti igh Pe, rine onrnaa Pics of bie er’ Mane a ; , ‘ Lewd pi titre re i in me ft : ] t; pear ' (? ‘ al 4 ; . P \ 4 _ 4 = -. . = 7, f a . s ¥ - - \ = . ‘ ‘ fet A - = 7 7 ‘ he ‘ ‘ ‘ * - : . tes a - ‘ a ti _ x5) Hive io. erties if Be ~ 15a 1 rh pik os : - a Yeas ae | ty = ‘ : \ ‘a aa fs bipcagr i : : de rae Shs (Oslo. Whi en . tab Grunhia d 7 fae pee Lay bagotigooras 521 ' ot cola f Frag ateke, w iti bei pt? sit + Vas Le ' iié ytyeg ee roe ye t HR AMILE GD’ « bia eae vee 1 ; ee A apiate a Seton elit (Er HOt a. SAYGRa af tii Peron otto “Pini coll geu dachis fod Ss ai \seddats erie aa! S i yp takin be euodhy os biel fs | ohne, senethonet awa Th, eoteiid ‘hoywrk_ Vines ag > . = uv \ tue : iwnied ’ , > := z ’ Ul ‘ — ’ * os . ~~ ‘ ’ . he \ \ . « wie om wy. 2, Wis . " fe! 2 } tibia’ Or ts ee 1 tha eorsivet: Sits GENERATIVE ORGANS OF THE FEMALE 181 . originally from the germinal epithelium. In the embryo, this forms a thick layer, covering the fibrous and vascular stroma. After a time solid cords of epithelium-cells, which in some animals are partly tubular (ovarian tubes of Pfliiger), grow down into the stroma, whilst this at the same time grows into the epithelium. The cords presently become broken up by the ingrowths of stroma into small isolated nests of epithelium-cells, each of which may represent a Graafian follicle. To form the ova, some of the germinal epithelium-cells become en- larged, and usually there is one such enlarged cell in each of the isolated nests. The remaining cells form the epithelium of the follicle (see fig. 218). Fic. 218.—SEcTION OF THE OVARY OF A NEWLY BORN CHILD. (Highly magnified.) a, ovarian or germinal epithelium ; 6, formation of an ovarian tube ; ¢, c, primordial ova lying in the germ-epithelium; d,d, longer tube becoming constricted so as to form nests of cells; e, e, larger nests; 7, distinctly formed follicle with ovum and epithelium; g, g, blood-vessels, The stroma of the ovary contains, besides the spindle-shaped con- nective-tissue cells and plain muscular fibres already mentioned, a number of epithelium-like interstitial cells, like those found in the intertubular tissue of the testis. They are most abundant near the hilus. Corpora lutea may also be seen in the stroma. These are large yellow nodules, which are developed out of the Graafian follicles _ after the ovum has become extruded. They consist of columns of large yellowish cells, with intervening vascular fibrous tissue, which converge to a central strand of connective tissue occupying the axis of the nodule. The columns of yellow cells are not unlike those of the cortex of the suprarenal capsule. The cells are derived from the membrana granulosa of the follicle, which becomes thickened and folded ; between the folds connective tissue and blood-vessels grow in ‘towards the centre, and in this way the corpus luteum becomes 182 THE ESSENTIALS OF HISTOLOGY developed. After persisting for a time it gradually shrinks and iota = pears, but it becomes larger and remains longer persistent in the event of pregnancy supervening. The Fallopian tubes are chiefly composed of plain muscular tissue disposed circularly. They are lined by a mucous membrane which is covered with ciliated epithelium. Externally they are covered by a serous coat, within which is a thin layer of longitudinal muscular fibres overlying the circular fibres. The uterus is usually described as composed of two parts, the body and cervix. The wall of the uterus is formed of the following layers: 1. A serous layer, derived from the peritoneum, which covers the greater part of the fundus. 2. A muscular layer, which is of considerable thickness and is composed of plain muscular fibres disposed in two imperfectly separated strata, Of these the outer is much the thinner, and its fibres are dis- posed partly longitudinally, partly circularly. The inner muscular _layer, on the other hand, is very thick; its fibres run in different direc- tions, and it is prolonged internally into the deeper part of the mucous membrane, the extremities of the uterine glands extending between and amongst its fibres. It is imperfectly separated from the thinner external layer by the ramifications of the larger blood-vessels, and probably represents a much-hypertrophied muscularis mucose. 3. A mucous membrane, which is very thick and is composed of soft connective tissue containing a large number of spindle-shaped cells. It contains long, simple, tubular glands (fig. 219), which take a curved or convoluted course in passing through the membrane. They are lined by ciliated epithelium continuous with that which covers the inner ~ surface of the mucous membrane. In the cervix the mucous membrane is marked by longitudinal and oblique ridges, and the glands are shorter than those of the body of the uterus. Near the os uteri the epithelium becomes stratified and overlies vascular papille of the corium. The mucous membrane is exceedingly vascular, and it also contains a large number of lymphatic vessels. At each menstrual period the greater part of the mucous membrane of the body undergoes a process of disintegration accompanied by an escape of blood from the capillaries of the membrane. This is suc- ceeded by a rapid renewal of the membrane. Should gestation super- vene, the process of renewal results in the formation of a greatly thickened mucous membrane, with long convoluted glands, which is then known as the decidua. The mammary glands are compound racemose glands which open by numerous ducts upon the apex of the nipple. The ducts are dilated into small reservoirs just before reaching the nipple. If traced back- wards, they are found as in other compound racemose glands to com- mence in groups of saceularalveoli. The walls of the ducts and alveoli ~ are formed of a basement-membrane lined by a simple layer of flattened epithelium (fig. 220, A). But during lactation, when the gland is in ar . 4 " e : . { \ \ . a - 4 | A / i 4 . « Apotnk zee lass é ott ies ern uel ont | y : Sis ‘ I i ‘ ‘ si) ‘ Ue | 77 api Ty ci *doirdd or ot mse ee Erie o, ge Nt hae ee = fe i a ; < ’ : E “Yy exc i : ' , | GENERATIVE ORGANS OF THE FEMALE 188 rs ‘i au ee, : 7 A rm _ *, J - fy) . ‘ ] " fi ) MOG , WINS : mi, ‘ . : Fic. 219.—SEcTION OF - THE MUCOUS MEM- BRANE OF THE UTE- RUS FROM NEAR , a THE FUNDUS. 5 a, epithelium of inner surface; 0, b/, uterine glands; c,interglandular connective tissue; d, muscular tissue, ke Te oss ees we 154 ‘ P y H i l L/ V MN Tp hy HA Mah i Wwe DAs 4 coal | 184 THE ESSENTIALS OF HISTOLOGY activity, the cells of the alveoli become much enlarged and of a columnar shape, and fatty globules become formed within them (B).’ These fatty globules appear to become set free by the breaking down of the inner part : of the cell, the protoplasm of the cells becoming partially dissolved and - Fic, 220.—ALVEOLI OF THE MAMMARY GLAND OF THE BITCH UNDER DIFFERENT - CONDITIONS OF ACTIVITY. - A, section through the middle of two alveoli at the commencement of lactation, the epithelium-cells being seen in profile; B, an alveolus in full secretory activity. forming the proteid substances of the milk. According to some authors, ly nph-corpuscles may also carry fat into the alveoli and there become disintegrated. At the commencement of lactation this disintegration is imperfect, so that numerous cells containing fat-particles appear in the secretion (colostrum corpuscles). \ ia ¥ Tw. Rite ar : PIAL Zi ie 2 = = faced | 4 a ives Wr FF Beit heh: . ee Saha: i. rie wes eo. ee ay G alinost oh aif Wry bars , . resiead ‘Pen 4 aaa | . POH Ate y pera 185 LESSON XXXVI. STRUCTURE OF THE SPINAL CORD. 1. Sections of the spinal cord from the cervical, dorsal, and lumbar regions. [The spinal cord is hardened by being immersed for about a month in bichromate of ammonia solution (2 per cent.) ; the sections are made with a freezing microtome and are stained with aniline blue black.'] Notice the relative extent of the grey as compared with the white matter in the different regions of the cord. In the white matter the stained dots are sections of the axis-cylinders of the longitudinally disposed medul'ated nerve-fibres; the tissue between the nerve-fibres is neuroglia. In the grey matter the branched nerve-cells are conspicuous, lying in a reticular sub- stance which is formed of neuroglia together with an interlacement of nerve- ' fibres and cell-processes. Sketch a section from each region under a low power. Sketch also a small portion of the white substance, two or three nerve-cells, and the central canal with its lining epithelium and surrounding neuroglia under the high ower. - Measure the diameter of some of the nerve-fibres in the anterior columns, in the lateral columns, and in the posterior columns. The spinal cord is composed of grey matter in the centre and of white matter externally. It is closely invested by a layer of connective tissue containing numerous blood-vessels (pia mater), and less closely by two other membranes. One of these is an areolar membrane, re- sembling a serous membrane in general structure, but non-vascular and more delicate in texture (arachnoid). The other, which lines the vertebral canal, is a strong fibrous membrane known as the dura mater. At the middle of the anterior and posterior surfaces the pia mater dips into the substance of the cord in the anterior and posterior median fis- sures, 80 as to divide it almost completely into two lateral halves. These are, however, united by an isthmus or bridge, which is composed anteriorly of transversely crossing white fibres (white commissure), posteriorly of grey matter (grey commissure), in the middle of which is a minute canal lined by ciliated epithelium (central canal, fig. 221, e). Kach lateral half of the spinal cord contains a crescent of grey matter, which is joined to the corresponding crescent of the opposite side by the grey commissure. Of the two cornua of the crescent the - ' See Appendix. 186 ‘THE ESSENTIALS OF HISTOLOGY oe posterior is the narrower and comes near the surface of the cord; opposite to it the bundles of the posterior nerve-roots enter the cord. The bundles of the anterior nerve-roots enter the anterior cornu. ,, The white matter of each half of the cord is subdivided by the passage of the nerve-roots into the cornua into three principal columns —anterior, lateral, and posterior. It is composed of longitudinally — coursing medullated nerve-fibres, which in stained sections appear as clear circular areas with a stained dot, the axis-cylinder, near the- middle (fig. 222). Fic, 221.—SEcCTION OF THE SPINAL CORD IN THE LOWER DORSAL REGION, (Cadiat.) A, B, C, anterior, lateral, and posterior columns; §, 8’, anterior and posterior median fissures, a, b, ¢, cells of anterior cornu; d, posterior cornu and substantia gelatinosa of Rolando ; : ‘ e, central canal; 7, veins; g, anterior root-bundles; h, posterior root-bundles ; i, white q commissure ; j, grey commissure ; 7, reticular formation. ‘ The medullated fibres are supported by a peculiar reticular tissue (neuroglia) which contains a number of nuclei embedded in it and appears to be composed of branched fibrillated cells (neuroglia-cells). The neuroglia is accumulated in greater amount at the surface of the — cord underneath the pia mater (fig. 222), and it extends into the grey matter, of which it may be said to form the basis, and in which it is especially accumulated at the apex of the posterior cornu and around the central canal (substantia. gelatinosa of Rolando). ; ud aii Maat * nenhdghn fii + OF “eran st of Mee vice hi Rae ho Lea ett Aged Fp it. le ae OEY ha —= - 4 ee © eee i oe - - - f = i “. i |, ‘ ’ yy « ar 4 > bee e . = - ’ 7 x ‘ ( . x « 4 ' 4 3 , ’ ‘ “i t Pu ; j whit P ’ ; : e Jiige i cee thsy niet . < es ths aS > Spay siege Bet ly tA ‘ ; eT, HORMES 5 the Lyre pe tae eae. fos TN f : hana Hh eI” pir sai) re pots { Ahm et; 6B Ht tiksrent. Telomere ty wip, ae cry - linge revi ee fi Pe ial ion. } Yared ph ya) ‘ weet} it. al " oe r ib APESE TEGAN go) n ne deiryw. ty +4 ihe lusebe Techad j Be Rental VORP owed” Hhyctes ot ro nonvk, atha leave? 4 aie | — Ag. x aaa Waa) act, sil the pustetion odbc 54 3 ft ee nis, shat yak bose Raa ‘mm reas LS, > & a . BF ee aecue optieulie % aad if motial oti tu . , gon, \ot ved lod, 9 ioGr nie ig Psy | : Hy Up! geeky (Ayal ia is 7 - ae ae ee a whaly Lit pie a | th. ~ Shy at, he pean ete Pie Ne Sy = ‘ ’ ’ a * ead, bial ut. Ses < 4a; é STRUCTURE OF THE SPINAL CORD 187 The grey matter, besides neuroglia, consists of an interlacement of nerve-fibres and of the branching processes of the nerve-cells which are embedded in it. : Fic, 222._A SMALL PORTION OF A TRANSVERSE SECTION OF THE HUMAN SPINAL CORD _ IN THE REGION OF THE LATERAL COLUMN, TO SHOW THE SUPERFICIAL NEUROGLIA, a, a, superficial neuroglia; 6, 6, transverse section of part of the lateral column of the cord, in which the dark points are the axis-cylinders, and the clear areas the medullary substance of the nerve-fibres. The superficial neuroglia is seen to exhibit the appearance of a fine net- work in which numerous nuclei and one or two corpora amylacea are embedded, and to extend inwards among the nerve-fibres, : Disposition of the nerve-fibres of the white columns in tracts.— . The nerve-fibres vary in size in different parts of the white columns. They are smallest in the posterior columns, especially in that part of the posterior column which is next the posterior median fissure (posterior median column), and largest in the posterior part of the lateral column, but also of considerable size in the anterior column. This difference corresponds in some measure with the functions of the nerve-fibres in those parts respectively. Thus the posterior part of the lateral column which is characterised by the large size of its nerve- fibres constitutes the tract along which voluntary motor impressions pass down the spinal cord from the opposite side of the brain, after having crossed at the pyramids of the medulla oblongata (crossed pyramidal tract, fig. 223, c.p.t.). The large fibres which lie in the anterior columns next to the anterior median fissure, and the upper part of the cord, belong to a portion of the same tract which has not undergone decussation (direct pyramidal tract, d.p.t.). The small fibres of the posterior median column belong to a tract which is only distinct above the middle of the dorsal region of the cord, and is known as the tract of Goll (fig. 223, g). The rest of the posterior column is termed the cuneate fasciculus, and is chiefly composed of the fibres of the posterior nerve-roots which run for a short distance in it before entering the grey matter. In the lateral column there’is another tract which is distinct in the cervical and dorsal regions. This lies external 188 to the crossed pyramidal tract, and consists of large fibres which pass THE ESSENTIALS OF HISTOLOGY up into the cerebellum (direct cerebellar tract, c.t.). The course of the nerve-tracts in the spinal cord, and in other parts of the central nervous system, can best be made out by the study of sections of the foetal cord, for it is found that the development of the medullary substance occurs sooner in some tracts than in others, so that it is easy to make out the distinction between them. Another method consists in investigating the course which is pursued by degenerations of the nerve-fibres in consequence of lesions produced accidentally or purposely, definite groups. Disposition of the nerve-cel Fic. 228.— DIAGRAMMATIC SEC- 7 TIONS OF THE SPINAL CORD AT DIFFERENT PARTS, TO SHOW THE CHIEF LOCALISED TRACTS OF FIBRES IN THE WHITE SUB- STANCE. (One and a half times the natural size.) at the level of the sixth cervical nerve; J/. of the third dorsal; J///. of the sixth dorsal; JV. of the twelfth dorsal; V. at the level of the fourth lumbar, d.p/. direct or an- terior pyramidal tracts; ¢.p./. crossed or lateral pyramidal tracts ; c.f. direct cerebellar tract ; g, tract of Goll.. ls in the grey matter.—The nerve-cells which are scattered through the grey matter are in part disposed into Thus there is a group of large multipolar nerve-cells in the anterior cornu; their axis-cylinder processes pass out into the anterior nerve-roots (column of the anterior cornu, fig. 221, a, b,c). In- the middle dorsal region there is a well-marked group of large rounded Make ae tee Boelerar Tn) wh 4 i Ji-* al my Shel Otho ou sare ot UL baw yi Beast PGE le molortgn ss. « Wil “ 2t- r Bie At f i : 4 7 aah tae Se q ‘ : - ? . . 4 ‘ > > 7 saws, + ~ r | > * \ ; ¢ . ~’ 5 a = | as rth oe, pret % ri ae se <= a ‘ “4 % re uy yy cs ‘ ) , > tg aust pba sha , ia. te “Dyce e iene hal e) a AN gat Aro i eS 2 » ES SE, Oe in ; 2 prehile WFAN R A) pent (aa (ee) BD ¥ pay uke pa ‘ ‘ier 5a, fvaa iho t 5 De epee ie teas CoH woke PCa iiiant . he i Gleote ta. Sapa 9 a : \% 2 ww i eucl by Woe baa t " — 4748 H, i Pas ~ ss STRUCTURE OF THE SPINAL CORD 189 nerve-cells at the base of the posterior cornu (Clarke’s colwmn). Another group is seen on the outer side of the grey matter lying in a projection which is sometimes known as the lateral cornu (intermedio- lateral tract). This also is only distinct in the dorsal region. The cells of the posterior cornu are not collected into a special group. Course of the nerve-roots in the spinal cord.—The anterior roots enter the anterior cornu in a number of bundles (fig. 224, a, a). Some of their fibres (1, 1) are directly connected with the nerve-cells there, others pass through the grey matter into the posterior cornu, others into Fic. 224.—D1aAGRAM TO_IL- LUSTRATE THE PROBABLE COURSE TAKEN BY THE FI- BRES OF THE NERVE-ROOTS ON ENTERING THE SPINAL CORD. a, a, two bundles of the anterior root of a nerve; 1, 1, some of their fibres passing into the lateral cells of the anterior cornu; 1‘, 1’, others passing into the mesial cells of the same cornu; 2, 2, fibres passing to the lateral column of the same side without joining nerve-cells ; 3, 3, fibres passing towards the posterior cornu; 4, 4, fibres passing across the anterior commissure, to enter nerye-cells in the anterior cornu of the other side; p, bundle of the posterior root ; p, Z, fibres of its lateral or external division coming through and around the gelatinous substance of Rolando; some of these, 5, are 3 represented as becoming longi- : a eo pees - tudinal in the latter; others, 54 Ip gl anf (4 6, 6,.as passing towards the 7 4 anterior cornu, either directly or after joining cells in the posterior cornu, and others, 7, as curving inwards towards the grey commissure ; p, m, fibres of the mesial or inner division, entering the posterior column and then becoming longitudinal ; p’, m’, fibres from a posterior root which had joined the cord lower down and entered the posterior column, now passing into the grey matter at the root of the posterior cornu. Of these, 8 is represented as entering Clarke’s column, 9, as curving around this and cours- ing to the anterior commissure, and 10 as passing towards the anterior cornu. The axis-cylinder processes of the cells of Clarke’s column are shown arching round, and taking the direction of the lateral column, «.m.?., anterior median fissure ; p.m.f., posterior median fissure ; ¢.c., central canal; S.R., substantia gelatinosa of Rolando. the lateral white column of the same side of the cord (2, 8), and others again pass across in the isthmus to the anterior cornu of the opposite side (4). The fibres of the posterior roots (fig. 224, p) chiefly pass into the posterior white columns, from which after a short course they enter the grey matter and are partly connected with its cells, and partly pass to the other side of the cord. Some of the fibres of the posterior roots enter the posterior cornu directly, and are believed to be con- nected with the scattered cells of that cornu. : _ The central canal of the spinal cord is lined by columnar ciliated epithelium-cells, which are surrounded by a quantity of neuroglia. 190 THE ESSENTIALS OF HISTOLOGY a in the human adult they have frequently become proliferated, and their cilia are no longer visible. Characters of the spinal cord in the several regions (fig. 225). In the cervical region the white matter, especially that of the lateral The cells are best seen in the spinal cord of animals and in the child ; a i. se Fic. 225.—TRANSVERSE SECTIONS OF THE SPINAL CORD AT DIFFERENT LEVELS. (Twice the natural size.) The letters and numbers indicate the position of each section ; Ca. at level of coccygeal nerve ; ee Sac. 4 of 4th sacral ; L3 of 3rd lumbar, and soon, The grey substance is shaded dark, and the nerve-cells within it are indicated by dots. columns, occurs in largest proportion. “he grey matter, especially in the cervical enlargement, is in consid AN se amount (C 5), and it en- croaches in the form of a network upon the adjacent part of the lateral white column. The anterior cornua are thick and the posterior slender, The posterior median column is pesca marked off. 2 , 1 sl | +c metal FEF INT ein ey, CATA eG bunt ih i Ci) el , } i, Zi ¥ : iv ' « ° — } . i ~ > « ve ‘ * \ si w . = 5 : / . ~~ Z iT ’ es i y - 5 . a. ° t es \ a i , “ ¥ / - - } * = . ; > : 4 yy ual 4 , , >, \%, 1 “ah moe pinall ts Lh ies sake ee tAken itor}, ua! ebay LOnINs 4 a ai ia oe mit’ oferta Sera edale Gas fa 4 iat “ eS eke we Ree ae i> — ae Ais the dorsal region the grey eaee. is small § in écnount, and both ® ~cornua, are slender (D 5). The whole cord is smaller in diameter than either in the cervical or lumbar region. The column of nerve-cells JES known as Clarke's column, and the intermedio- lateral tract, are well marked. ‘In the lumbar region the crescents of grey matter are very thick, and the white substance, especially the lateral columns, relatively small - >in. amount (L. 5). The isthmus lies nearly in the centre of the cord, whereas in the cervical and dorsal regions it is nearer the anterior surface. The posterior median columns are not seen. In the part of the spinal cord from which the sacral and coccygeal nerve-roots take origin the grey matter largely preponderates, the | erescents forming thick irregular masses, and the grey isthmus being also of considerable thickness. ~ 192 THE ESSENTIALS OF HISTOLOGY LESSON XXXVII. THE MEDULLA OBLONGATA, PONS, AND MESENCEPHALON. | 1. Sections of the medulla oblongata made, (a) at the level of the decussation of the pyramids, (b) opposite the middle of the olivary body, and (c) just above the olivary body. 2. Section through the middle of the pons Varolii. 3. Sections across the region of the corpora quadrigemina, one at the level of the inferior, the other at the level of the superior, pair. In all the above sections sketch under a low power the general arrange- ment of the grey and white matter, inserting the positions of the chief groups of nerve-cells. [The tissue is hardened and the sections are prepared, stained, and mounted in the same way as the spinal cord. | The structure of the medulla oblongata can best be made out by the study of a series of sections taken from below upwards, and by tracing in these the changes which occur in the constituent parts of the spinal cord, taking note at the same time of any parts which may ~ be superadded. A section through the region of the decussation of the pyramids (fig. 226) has much the same form as a seetion through the upper part Fic. 226.—SEcTION OF THE ME- DULLA OBLONGATA AT THE MIDDLE OF THE DECUSSATION OF THE PYRAMIDS. J, anterior, /.p. posterior fissure; a.p. pyramid ; a, remains of part of anterior cornu, separated by the crossing bundles from the rest-of the grey matter; 7, continuation of lateral column of cord; &, continua- tion of substantia gelatinosa of Ro- lando; p.c. continuation of posterior cornu of grey matter; /.g. funiculus gracilis. of the spinal cord, and most of the structures of the cord can be easily — recognised. A considerable alteration of the grey matter i is, however, — produced by the passage of the large bundles of the crossed Prrenidet ~ ~ at Tt ii tee. PENG AP FOG aha Shiv icar ait Thelpity Gar Bar mh ons: seria : Reade abayeelis 4a Fas rereseri id y ae ees Pie inee. AME ESE epmarri def. coe, - . $3 4 - : a ‘ ‘ res 7 a = . > 4 Y 3 . ‘ . ts . 7 a bf 3s J : £35. , a . t ’ - < ) \ - rs - . ~ 2% a ‘ i) ee } | “ , a : zat iM j a . i 4 HOG Bie oo ake PAG RyZOD Uh s tel , us A + aa Se al ae a he 7 \ fricevdiatae | wt oa ae Pate citcePicortel ft: tht apie | a Ts. ry Coo celica bs e) (Dedih eraapn: ety. ; te, wate: Sanh #5 hl aS te hrs els 4 ip oP . Det, We WA a a ay Tet ise oN, Ct PF gat a my rem ? oA eee te FS oe RR A at — © vin > a ¥- = ~ STRUCTURE OF THE MEDULLA’ OBLONGATA 193 tract (p) from the lateral column of the spinal cord on each side ‘through the root of the anterior cornu and across the anterior median fissure to the opposite anterior column of the medulla, where, together with the fibres of the direct pyramidal tract, they constitute the promi- nent mass of white fibres which is seen on the front of the medulla on each side of the middle line, and is known as the pyramid. By this passage of fibres through the grey matter the tip of the anterior cornu (@) is cut off from the rest and becomes pushed as it were to the side; in sections a little higher up it appears as an isolated mass of grey matter which is known as the lateral nucleus (fig. 22, 7.1.) A change also occurs in the posterior cornu in consequence of the increased development of the posterior median and cuneate fasciculi. This causes the posterior cornu (fig. 226, p c) to be pushed towards the side, the V which they form with one another being thus opened out; at the same time the tip of the cornu swells out and causes a prominence upon the surface of the medulla, which is knownas the tubercle of Rolando (f). Grey matter also soon becomes formed within the upward pro- longations of the posterior median column and of the cuneate fasciculus Fie, 227.—SEcrion OF THE MEDULLA OBLONGATA IN THE REGION OF THE SUPERIOR PYRAMIDAL DECUS- SATION. a.m.f. anterior median fissure; /.a. superficial arciform fibres emerging from the fissure; py, pyramid; m.ar. nucleus of the arciform fibres; j.a’. deep arciform fibres becoming super- ficial ; 0, lower end of olivary nucleus ; \ Re o', accessory olivary nucleus; J. nu- \ weap cleus lateralis; jr. formatio reticu- laris 5 f.a?. arciform fibres proceeding irom formatio reticularis ; g, substantia gelatinosa of Rolando; a.V. ascending root of fifth nerve; n.c. nucleus cunea- tus; n.c’, external cuneate nucleus; J. funiculus cuneatus; ag. nucleus gracilis ; /.g. funiculus gracilis; p.m./. posterior median fissure; c.c. central canal surrounded by grey matter, in which are, n.X/, nucleus of the spinal accessory, and n.X//J. nucleus of the hypoglossal; s.d. superior pyramidal decussation. (fig. 227, n.g., n.c.), but most of the grey matter of the cornu becomes broken up, by the passage of bundles of nerve-fibres through it, into a reticular formation (/.7), the production of which is already foreshadowed in the upper part of the spinal cord. The central canal of the spinal cord _ is still seen in the lower part of the medulla oblongata (c. c), but it comes nearer to the posterior median fissure. The grey matter which sur- rounds it contains two well-marked groups of nerve-cells ; the anterior of these is the nucleus of the hypoglossal or twelfth nerve (n. xz.), the posterior that of the spinal accessory or eleventh (n. xz.). Instead of the ) 194 THE ESSENTIALS OF HISTOLOGY comparatively narrow isthmus which joins the two halves of the spinal cord, a broad raphe now makes its appearance; this is formed of obliquely and antero-posteriorly coursing fibres, together with some grey matter containing nerve-cells. In a section at about the middle of an olivary body (fig. 228), it will be seen that a marked change has been produced in the form of the medulla and the arrangement of its grey matter, by the opening out of the central canal into the fourth ventricle. This causes the grey matter which below surrounded the central canal to be now spread nXI nX't Fic, 228.—Secrion OF THE ME- WX DULLA OBLONGATA AT ABOUT THE MIDDLE OF THE OLIVARY BODY. 4 ‘ia. anterior median fissure; n.ar, nucleus arciformis; p, pyramid; XII. bundle of hypoglossal nerve emerging from the surface; at b it is seen coursing between the pyra- mid and the olivary nucleus, 0; Jae, external arciform fibres; 7./, nucleus lateralis ; a, arciform fibres passing towards restiform body partly through the substantia gela- tinosa, g, partly superficial to the ascending root of the fifth nerve, a.V.; X, bundle of vagus root, emerging ; .7. formatio reticularis ; cr. corpus restiforme, beginning to be formed, chiefly by arciform fibres, superficial and deep: m.c. nucleus cuneatus; 2g. nucleus gracilis; ‘, attachment of the ligula; fs, funiculus solitarius; X. n.X’. two parts of the vagus nucleus; n,XII. hypoglossal nucleus; 2.¢. nucleus of the funiculus teres; num, nucleus ambiguus ; 7, raphe ; A, continuation of anterior column _ of cord; o', 0’, accessory olivary nuclei; olivary nucleus; p.0./. pe- dunculus olive, TNr.aiN. rn out at the floor of that ventricle, and the collections of nerve-cells from which the hypoglossal and spinal accessory nerves respectively arose now, therefore, lie in a corresponding situation. At this level, how- ever, the outer group which corresponds with the nucleus of the spinal accessory in the lower part of the medulla has become the nucleus of the vagus or tenth nerve. The nerve-bundles of the roots of these nerves can be seen in the sections coursing through the thickness of the medulla and emerging, those of the hypoglossal (xzz.) just outside the pyramids, those of the spinal accessory and vagus (x.) at the side of the medulla. The two sets of emerging fibres thus appear to sub- divide each lateral half of the medulla into three areas—a posterior, a middle, and an anterior. Of these the posterior is chiefly occupied by the grey matter of the floor of the fourth ventricle, and, with fibres which are passing obliquely upwards and outwards towards the cere- bellum, forming its inferior crus (restiform body, c.7.) ; and in addition there is the continuation upwards of the portions of grey matter forming the nuclei of the funiculus gracilis (n.g.), of the funiculus cuneatus apk Sid, be ‘ira ot (Oe ae Tc ae - il, by ake were rod 6 fed, Hee Der + Pie fp & Solid aL sabes am pike sa, SVR ate Yi Mabe wi ares bl a3 6 mphiares sarjace, | Gath Ghvie (ik ar ayia . 7 Ayres aia Ua Sug bilinear 28 Mois : tag Pras, ‘ie ? : . ext. 13 kee OR tril ies yt rive 6 +» £ : "+ aly - i ; ‘ A uA P Wo Agel trees twots, tors) te 16 ate deer path | , . ~-< . x a * , . ts ‘ rd - ‘ : uy 7 r - 4 z #7 = 4G : ’ ~~; - ae aay: ~ ~ > 7 "7 Ps 1 = ' r c . f ‘ E - j . . ¥) a a * < ca ' es fy finde bahase wl / Se - : of a - - = . es j Pa \ ? -- -2he aie. t — *. > 4 * = PF t - “a —< : - + que bY * A ies Li *' ‘ 9S i . re ata se ‘ 3 oy > | " ¢ ; 2 : . - ve . ‘ rl t PP 1 . * . - on a , ; aa +A a ’ E 4 . - - Fe — ‘ * os as ’ 4 ee yk } ’ c 7 : y 4 . i ah € 3 i 4 : x _ + . «7 . * <)? £.. - : ; ' . < 7 . ‘ Thin on eo ee a AKG AY Res Oh 240 er Sie Wied hire eins oe, oh aia Oa: - pee) > es ? ie UD hilbved! 2 P eat Ta thy 14 ny ‘ae? thar met yrairut bli ha bere wig te oe —o Fe THE MEDULLA OBLONGATA | 195 (n.c:), and of the tubercle of Rolando (g). The anterior or mesial area is occupied in front by the pyramid (p), and behind this by a reticular formation (reticularis alba, A) composed of longitudinally coursing bundles of fibres interlaced with fibres that are passing obliquely from the opposite side, through the raphe, towards the restiform body (fig. 229, r.a.). The middle area, which lies between the issuing bundles of the two sets of nerve-roots, consists in its deeper part of a similar \ x \S NASR eat aT CAy ti. BS rit an w ee 20 MERE) 119 RNAS EE) ENE VJs > RET: ra. Fic. 229.—PArtT OF THE RETICULAR FORMATION OF THE MEDULLA OBLONGATA. ra. reticularis alba 3 TJs reticularis grisea; between them a root-bundle of the hypoglossus (XIL.). The longitudinal fibres of the reticular formation are cut across ; the transversely aed fibres are internal arcuate fibres, passing on the right of the figure towards the raphe, reticular formation (fig. 228, fv), but with more grey matter and nerve-cells (reticularis grisea, fig. 229, r.g.) Superficially there is developed within it a peculiar wavy lamina of grey matter containing a large number of small nerve-cells; this is the nucleus of the olivary body (fig. 228, 0). : The floor of the fowrth ventricle is covered by a layer of ciliated epithelium-cells, continuous below with those lining the central canal, and above, through the Sylvian aqueduct, with the epithelium of the a . 02 196 ‘THE ESSENTIALS OF HISTOLOGY third and lateral ventricles. The fourth ventricle is roofed over by a thin layer of pia mater, with projecting choroid plexuses, the under surface of which is covered by a thin epithelial layer continuous at the side with the ciliated epithelium of the floor. A section taken ust above the level of the olwary prominence will still show very much the same form and structural arrangements as that just described. The nucleus of the hypoglossal (fig. 280, n. XII.) is still visible in the grey matter of the floor of the ventricle, but the nerve which is now seen arising from the outer part of that grey matter is the eighth or auditory (VIII.), the bundles of which, as they leave the medulla, enbrace the inferior crus of the cerebellum (c.7.), which is now passing into that organ. The reticular formation still Fic. 230.—TRANSVERSE SECTION OF THE UPPER PART OF THE MEDULLA OBLONGATA., » 4 py, pyramid ; 0, olivary nucleus; V.a. ascending root of the fifth nerve; V/J/J/. inferior (pos- terior) root of the auditory nerve, formed of two parts, a, (strie acustice), and b, which enclose the restiform body, c.7.; n.V/J/.p. principal nucleus of the auditory nerve; n.VIll.ac. accessory nucleus; g, ganglion-cells in the root; ./.t, nucleus of the funiculus teres ; ».XJJ, nucleus of the hypoglossal ; 7, raphe. occupies the greater part of each lateral half of the medulla between the grey matter at the floor of the fourth ventricle and the pyramids (py), and a small portion of the olivary nucleus (0) may still be seen, as may also the upward continuation of the grey matter of the tubercle of Rolando; this is intimately connected with some well-marked bundles of nerve-fibres, which are passing up to the pons to join even- tually the root of the fifth nerve (Va). _ A section through the middle of the pons Varolii (fig. 231) shows yery much the same arrangement of grey and white matter as that ‘ = {ofth stare oe ee F ae REA Vacs Gee ant am tbe inher parr the aban! Went tiie. dense ot. he DE Ber Meetion jA aries tomiind bo *)e 2 re met ee tree: mylvsirie bundles @ serey-B) pass se Prot sis yi bert) br i +h aristyea tunis Setsreaie. cha Sith tikes . Sa a dae : « 4s 15¢ Tush iaiiled G Pe A + y a J 7 ; \ “i 2) ' ~ i 4 a { } : fe \ ‘ ' i) 1 ‘ a. = 4 2 nee . ik ; is 4 ~ [ 7 +o" orer mat ~ Sue f a. trai ta. HE Tne (3) i4 ey 2 : ye dp Mie antdicveer. las oud iv F bargacr SG P, bad aT ah be sunerice fener wh: bj: coy we Wile, dake : hn +» Lumet Top heart at i Fe bmg Gere 2 ped, iy ; aia. } ak ies Ag tae OAD pagal The ; Lah O88 vais ns ik TAS cca 4 Nia Serre be a tenilet Era? phd ey | ‘ vot vite . - ra . “4 co a” mH ME = - : ‘ . ( \ * ‘ = a r ~ ar z ,* ey. - jyot a ¢ . ' x. a? vy 3 7 9 rR : a ie fry . 7 (i ila int ahe nla vant enh yt Uke STRUCTURE OF THE PONS VAROLII 197 which is met with at the upper part of the medulla, but the general appearance of the section is much modified by the presence of a large number of transversely coursing bundles of nerve-fibres which are passing from one hemisphere of the cerebellum to the other. Intermingled with these bundles is a considerable amount of grey matter. The continuation upwards of the pyramids of the medulla (py) is embedded between these transverse bundles and separated by them from the reticular formation. The olivary nucleus is no Fie. 231.—SEcTION ACROSS THE PONS AT ABOUT THE MIDDLE OF THE FOURTH VENTRICLE. ? py, pyramid-bundles continued up from the medulla; po, transverse fibres of the pons passing from the middle crus of the cerebellum, before ( po ) and behind ( po’) the chief pyramid bundles ; ¢, deeper fibres of the same set, constituting the trapezium; the grey matter between the transverse fibres is not represented either in this or in the two following figures ; 7, raphe; 0.s. superior olivary nucleus; a.V. bundles of the ascending root of the fifth nerve, enclosed by a prolongation of the grey substance of Rolando ; V/. the sixth nerve ; n.V/. its nucleus ; V/Z. the facial nerve ; V//a. intermediate portion of the same nerve; ”.VJJ. its nucleus ; V/IJ, anterior (superior) root of the auditory nerve; 2.V///. part of its outer or anterior (superior) nucleus ; v, section of a vein. longer seen, but there are one or two small collections of grey matter which lie in the antero-lateral part of the reticular formation and are known as the superior olivary nucleus (0.s.) The nerves which take origin from the grey matter of this region are part of the. eighth, the seventh, the sixth, and somewhat higher up the fifth cranial nerves (see figs. 231, 2382). Of these the eighth and fifth take origin from groups of nerve-cells which occupy the grey matter opposite the external border _ of the floor of the ventricle ; the sixth from a group which is placed also 198 “THE ESSENTIALS OF HISTOLOGY’ » Fic. 232.—OBLIQuE SECTION - OF THE PONS ALONG THE LINE OF EXIT TRAVERSED - BY THE FIFTH NERVE. } The section passes through the , lower part of the motor nu- cleus (n'v) from which a bundle a of fibres of the motor root is — a seen passing, V’; a part of the q upper sensory nucleus (nv) is also shown in the section in the - form of a number of small iso- lated portions of grey matter, : ‘ Amongst these are a few bundles of the ascending root cut across, but most of these have already become diverted outwards to join and assist in — forming the issuing part of the main or sensory root, V; J, small longitudinal bundle of fibres near the median sul- cus (m.s.), passing outwards to join the root of the fifth nerve; f.7. formatio reticu- laris; 7, raphe; sf. substan- tia ferruginea, Fic. 238.—TRANSVERSE SECTION THROUGH THE UPPER PART OF THE PONS. (Rather more than twice the natural size.)! - Ss : d « M ~~ p, transverse fibres of the pons; py, py, bundles of the pyramids; a, boundary line between : the tegmental part of the pons and its ventral part; 7’, oblique fibres of the fillet, passing towards J, 7*, longitudinal fibres of the fillet; f.7. formatio reticularis; p.J. posterior _ longitudinal bundle ; s.c.p. superior cerebellar peduncle; v.m, superior medullary velum ; b, grey matter of the lingula; v. 4, fourth ventricle ; in the grey matter which bounds it laterally are seen, d.V. the descending root of the fifth nerve, with its nucleus, s.7. sub- _stantia ferruginea, g.c. group of cells continuous with the nucleus of the aqueduct. 1 The details of this and of several of the preceding figures are filled in under a somewhat higher magnifying power than that used for tracing the outlines, — * <=15 FL i + all RO het 225° Tha sty ia) 0H, 7B. , me Poe hits iol toes. iy ta rt dP tote t relat IER Hine of th Bers a eiceaeele tb Uke Con ox the P ~ ethan Aastra ish. S07 pet ras Iv J he : Hi Ae hg DEER at a ‘Hew wri A. Pree OF" ds the alas tif Lah *y has —< 2 4) 5 , ; tits bUpuer part sf-the pews (| aie Sa Foe Pay tye ifs ? - F ioe vs >t ¢ = j : re ‘ ar. a , e - = " 7 Sire . | , a " ; : Ag ’ i uy a : ' } - , a . a ‘a s 7 — = = ¥ ~ ay 7 - . 1 = oy 4 i 3 ‘at ‘ . oo x a " } } ~< © = i ‘ * = _ ; n of } ty 7 i : i's ea rn “ ot A > ‘ Siry ny ns . . Ml inss ‘ ' & ase) ohare tetbets ) (vats al » bea yreate *,! Vera 43 . PUSe; e £ we gin’ 4 ae dus beh eae ggi ? Oe ss ue mn * Ps aK Fs ry - : Hosts Be fe | ,: is ty - —e “ "3 . E (AQ BAS vat wasn ) S > ‘ STRUCTURE OF THE MESENCEPHALON 199 in the grey matter of the floor of the ventricle but nearer the middle line, and the seventh from a nucleus which lies in the formatio reticularis, and from which the fibres of the nerve pass backwards to the floor of the ventricle, then longitudinally upwards for a short distance, finally bending forwards and downwards and emerging between the transverse fibres at the sides of the pons. At the upper part of the pons (fig. 233) the fourth ventricle narrows considerably towards the Sylvian aqueduct, and behind and on either Fie, 234.—SECTIONS THROUGH THE ORIGIN OF THE FOURTH NERVE. # A, transverse section at the place of emergence of the nerve-fibres. B, oblique section carried along the course of the bundles from the nucleus of origin to the place of emer- gence. Ag, Sylvian aqueduct, with its surrounding grey matter; /V. the nerve-bundles emerging ; /V’, decussation of the nerves of the two sides; /V”. a round bundle passing downwards by the side of the aqueduct to emerge a little lower down; »./V. nucleus of the fourth nerve. J, fillet; s.c.p., superior cerebellar peduncle; d.V. descending root of the fifth nerve; pl, posterior longitudinal bundle ; 7, raphe. side of it two considerable masses of longitudinal white fibres make their appearance. These are the swperior crura of the cerebellum (s.c.p.), and they tend as they pass upwards gradually to approach the middle line (fig. 284 A), across which in the region of the posterior pair of the corpora quadrigemina they pass, decussating with one another, to the formatio reticularis of the opposite side (fig. 285, A). * Fic. 235.—Our.iInE OF TWO SECTIONS ACROSS THE MESENCEPHALON. (Natural size.) A, through the middle of the inferior corpora quadrigemina. B, through the middle of the superior corpora quadrigemina, c7, crusta; s.n. substantia nigra; ¢, tegmentum; s, Sylvian aqueduct, with its surrounding grey matter; c.g. grey matter of the corpora qua- drigemina ; /.g. lateral groove ; p.l. posterior longitudinal bundle; d.V. descending root of the fifth nerve; s.c.p. superior cerebellar peduncle ; J, fillet; n.///. its nucleus; //J/. third nerve. The dotted circle in B indicates the situation of the tegmental nucleus. In sections across the mesencephalon (fig. 235), the upward con- tinuity of the parts which have thus been described in the lower parts of the nerve-centres, can still in great measure be traced. 200 “THE ESSENTIALS OF HISTOLOGY The Sylvian aqueduct (s), with its lining of ciliated epithelium, re- presents the central canal of the cord and the fourth ventricle of the medulla. In the grey matter which surrounds it (central grey matter) there is seen in all sections of the region a group of large nerve-cells lying anteriorly on each side of the middle line, close to the reticular formation. From this group the root-bundles of the fourth nerve arise at the lower part of the mesencephalon and pass obliquely backwards and downwards around the central grey matter, decussating with those of the opposite side to emerge just above the pons Varolii (fig. 234). Higher up the bundles of the third nerve spring from the continuation of ihe same nucleus (fig. 235, 2. 77.), and these pass forwards and down- wards with a curved course through the reticular formation, to kage is at the mesial side of the crusta. The reticular formation of the pons is continued up into the mes- encephalon, and is here known as the tegmentum. It is composed as before of longitudinal and transverse bundles of fibres with much grey matter intermingled. The transverse fibres include the decussating fibres of the superior crura of the cerebellum ‘s.c.p.), and the fibres of the fillet (f), which are passing in an oblique manner from the raphe to the side of the mesencephalon, to reach eventually the grey matter of the prominences of the corpora quadrigemina. The pyramid bundles of the pons are continued upwards on each side into the crusta (cr.). This forms a mass of longitudinally coursing bundles of fibres lying on the ventral aspect of each half of the mesencephalon, and diverging above into the internal capsule of the cerebral hemisphere. The crusta is separated from the tegmentum by a layer of grey matter containing a number of very deeply pigmented nerve-cells which give it the name of substantia nigra (s.n.) The crusta and tegmentum, together with the intervening substantia nigra, constitute the crus cerebri. The prominences of the corpora quadrigemina are formed mainly of grey matter containing numerous small nerve-cells. From each a bundle of white fibres (brachium) passes upwards and forwards towards the geniculate bodies, eventually joining the optic tract of the same side. On the other hand, each of the prominences receives from below fibres of the fillet, which are themselves traceable into the posterior part of the lateral column of the medulla oblongata. Bs : i? 2 i 5 a : v - : ; i ; Pgs ries - pe 2 x ee 7 | J ; ' / - ett ait te i a “ - . : & ! : — : etre Te a mi Neel | ae : mT , : - ° : ; , ‘ Le Ar ie aie os : ri ne cigs 4 weed "4 UP RET te wel % ; /' yea ee ye : > F at ; * S ; r _Theayiite omkgen ao Weta aioe | " 4 b Zs ; 7 ’ r ” . on } . ‘ { ; J ~ ‘ os ~ c _* ts + ee Gorse > S801 LESSON XXXVIII. _ STRUCTURE OF THE CEREBELLUM AND CEREBRUM. 1. Sections of the cerebellum across the direction of the lamine and vertical to the surface. ’ 2. Section across the whole of one hemisphere of the cerebrum of a monkey or man, passing through the middle of the third ventricle. 3. Vertical sections of the cerebral cortex, one from the ascending frontal gyrus, another from the occipital lobe, and a third across the hippocampal gyrus. and hippocampus. 4, Transverse sections of the olfactory tract and bulb. In all these preparations make sketches under a low power of the general arrangement of the grey and white matter, and also of the nerve-cells in the grey matter. Sketch some of the details under a high power. The cerebellum is composed of a white centre, and of a grey cortex, both extending into all the folds or lamine, so that when the lamine are cut across, an appearance is presented of a white arborescence - | Fic. 236.—SrecTioN THROUGH ONE OF THE HEMISPHERES OF THE CEREBELLUM, TO SHOW THE MEDULLARY CENTRE AND ITS PROLONGATIONS INTO THE LAMELL.A. covered superficially by grey matter. The white matter is in largest amount in the middle of each cerebellar hemisphere (fig. 286). There is here present also a peculiar wavy lamina of grey matter, similar to that in the olivary body, and known as the nucleus dentatus (n.d.).. 202 THE ESSENTIALS OF HISTOLOGY Other isolated grey nuclei lie in the white matter of the middle lobe. ; The grey matter of the cerebellum consists of two layers (fig. 287). The inner one (that next the white centre) is composed of a large number of very small nerve-cells (granule layer, d). The outer layer Fic. 238.—PRocEssES OF THE CORPUS- CLES OF PURKINJE, CONNECTED BY THEIR FINER BRANCHES WITH COR- PUSCLES OF THE OUTER LAYER OF THE CEREBELLAR CORTEX. (Highly magnified. ) «at, a, processes of the corpuscles of Purkinje; b, a branch from one of them, which is con-- nected with two of the corpuscles of the outer layer; c, ¢c, scattered branched cor- puscles of this layer. Fig. 237.—SEcrTION OF CORTEX OF CERE- BELLUM. a, pia mater ; 6, external layer ; ¢, layer of cor- puscles of Purkinje; d, inner or granule layer ; e, medullary centre, (b) is thicker, and is formed of neuroglia, with rounded and angular small nerve-cells and neux ‘lia-cells scattered through it. Into its outer part processes of the pia mater conveying blood-vessels pass vertically, and there are also in this part a number of long taper- ing cells, somewhat like the Miillerian fibres of the retina. Lying ae —s Pt weet. - ee a Oo ae aes Fo ee a... ; yt he x: settee Ex wrt Src mhe ¥ ; | a) boat Farge Aik Shi att , t 4 . {eiraie uy eae be) a ' La * a i, yer’ Ciipies sere Cit iron ee; Tite ee e! wy tht is : p oe oF SER rhe | ia oti! ph = a St Bw Sak die} Paes / 4 ‘ey 2 * = ae ‘z z é : f \ i 7" — h' ae ae. thames tarer «kts es ‘ E : sy Sacro mit Pek via - # ie hans. Moe leit chaaly: 44. - : | WOE ist sigs au tie |. Gh? ae 3 ‘ ; Bic, eae ap f tiie Inver Cans Sm ote Goes ia ed her hy ‘yt < ¥ pe: “Te Ave bein Lite rvetbely eat : \ t : ¢ Te IE OTS § Fz / / < ta " a aq a - * ; ha of vu ‘ C \ Ki . i = “STRUCTURE OF THE CEREBRAL CORTEX 203 between the two layers of the | Pa OE Te grey matter is an incomplete stratum of large flask-shaped cells (cells of Purkinje, c). Each of these gives off from its base a fine process, which be- comes the axis-cylinder of one of the medullated fibres of the white centre, while from the opposite pole of the cell large ramified processes spread out : into the superficial layer of | the grey matter, and some of these processes become con- nected with its small nerve- cells (fig. 238). Structure of the cerebrum. The grey matter of the ce- rebral cortex is described as 7 being composed of a number of layers, but they are not | sharply marked off from one _. another. The following are usually distinguished (fig. 239). 1. Most externally a thin stratum containing a few scat- tered cells, probably neuro- glia-cells. In the most super- ficial part of this layer imme- diately under the pia mater, is a very thin stratum of medullated nerve-fibres. 2. A layer of closely set small pyramidal nerve-cells _ several deep. ‘This layer is also thin. 3. A thick layer contain- ing larger and longer pyra- midal cells less closely set. These cells are largest in the deepest part of the layer ; and in the region of the motor centres of the brain some of them are of very large size, _ and are collected into small groups. ———————— , : 4 Fic, 239. 204 THE ESSENTIALS OF HISTOLOGY - — a 4, A thin layer of numerous small irregular angular cells. 5. A rather thicker layer of small scattered cells, many of a fusi- form shape. This layer lies next to the white centre. In the island of Reil this stratum is considerably developed, and is somewhat sepa- \" \ iH \we\ i AY ci ven Mt Sh a Fic, 240,—SEcTION ACROSS THE HIPPOCAMPUS MAJOR, DENTATE FISSURE, DENTATE " FASCIA AND FIMBRIA. Gh, part of the gyrus hippocampi or uncinate convolution ; Fd, fascia dentata, or dentate convolution; between them is the dentate fissure; Fi, fimbria, composed of longitudinal fibres here cut across; 1, 2, medullary centre of the hippocampal gyrus prolonged around the hippocampus, H, as the so-called alveus, into the fimbria; 3, layer of large pyramidal cells ; 4, their processes (stratum radiatum) ; 5, reticular neuroglia (stratum laciniosum) ; 6, superficia! medullary lamina, involuted around the dentate fissure ; * *, termination of this lamina, the fibres here running longitudinally ; 7, superficial neuroglia of the fascia. dentata ; *, ring of small cells within this (stratum granulosum). rated from the rest of the grey matter by a layer of white substance It is known as the claustvwm. - \ ; From the white centre bundles of medullated nerve-fibres pass in vertical streaks through the deeper layers of the grey matter, to lose ¢ a ; Oe ied Boe “alts a Rive one Sith fe wre Fy i aes aha ANS frothy pei co remion pn terwtabbe ditt tered of eirnots a Med rtiye. Desh). Ei eipetreigt Bayet at Pewhy - *}s i obpal din. hich eyeviies it ae nw ilau & +5 Br bo; 3 Gams Doth yabioety 7 . pel hav TOP 45ers stent ¢ rote Ga ASL a ea aeble ATT ¥ "Aiea the writtars t Sa TRI iy rs wart ¥ ‘ _ Py, Ghat wy fe aia A J = tt? ra a ve ~ + \ >: i. PATHS AF edit. 5 iit , + } WIE TF ret) + J aD) yt ae eT Es : Bs alu de 1 (Raa <7) rR aE i753 belay A i. - rt 4 as . i ” * r i . \ ‘: eh w ; Sede bse tick an : eae Deal ere i e is ‘ ra ; Pa - r i —_ 4 ’ : "S me “*, ; mo = 7 i - Pa] ij rn Ps Whe’ Or nai allay os b ithe BLL sw teh Seka veh ts ere shake ‘peed 2) BUY. 4 eee liy ere ie cfg SP aid, boves nduitplin sated. nye ary vipat aia: uduial aibibeitmonttae Cs a a React ‘Yeats, tobe we sig emis ih 7 1, Al ig dS ‘ U Si mY ee i AS Pay ES os “ =i 7 P 7 act olle, Mae iB ‘ . ' 4 ole, Ter a ' S oa i —~— > - Pr .c Tite a one bat Sune lasnGy he "he 7? her, Wie wh Lae STRUCTURE OF THE OLFACTORY TRACT AND BULB 205 themselves amongst the pyramidal cells of the more superficial layers, with processes from which they are probably continuous. In the hippocampal region a remarkable difference of structure manifests itself (fig. 240). The superficial layer of neuroglia and the white stratum, which overlies it as a thin band in other parts of the cortex, are in this region both very strongly marked (5, 6), the neuroglia layer having a very distinctly reticular aspect, and being in part beset with small cells. All the rest of the thickness of the grey matter appears to be mainly composed of, or at least to contain, long conical cells (3, 4), the distal processes or apices of which are prolonged into fibres which lose themselves in the superficial layer of neuroglia. The pyramidal cells rest upon the white centre, here known as the alveus (1), which is the part. of the hippocampus seen within the ventricle, and which is prolonged externally into the fimbria (Fi), where its fibres be- come longitudinal in direction. In the dentate gyrus (fascia dentata, fig. 240, Fd) the pyramidal cells are arranged in an irregularly radiating manner, occupying the centre of the convolution, and surrounded by a ring of closely packed small cells (*), external to these being the relatively thick layer of superficial neuroglia (7). The olfactory tract is an outgrowth of the brain which was ori- ginally hollow, and remains so in many animals; but in man the cavity has become obliterated, and the centre is occupied by neuroglia, containing, however, no nerve-cells (fig. 241). Outside the central 1 1 Fic. 241.—SrcrioN ACROSS THE OLFACTORY TRACT. neuroglia lies the white or medullary substance, consisting of bundles of longitudinal white fibres. Most externally is a thin superficial layer of neuroglia. The olfactory bulb (fig. 242) has a more complicated. structure. Dorsally there is a flattened ring of longitudinal white bundles enclosing neuroglia (1, 2,3), as in the olfactory tract, but below this ring a number of layers are superadded as follows : : 1. A granule layer (fig. 242, 4), characterised by the presence of a 206 THE ESSENTIALS OF HISTOLOGY large number of small nerve-cells with reticulating bundles of medul- lated nerve fibres running between them. . 2. An intermediate nerve-cell layer (6) consisting of neuroglia, in which small pyramidal nerve-cells are embedded. This layer is also traversed by medullated nerve-fibres, and is partly separated from the granule layer by irregular clefts (5). 8. The layer of olfactory glomeruli (7) consists of rounded nests of small ganglion-cells, which appear to give origin to the olfactory nerve- fibres. These pass between the glomeruli to enter the close plexus of non-medullated nerve-fibres which lies directly over the cribriform plate. 4, This is the layer of olfactory nerve-fibres (8), and from it branches (*) pass directly downwards to the nasal fosse. Fic, 242.—SkxcTION ACROSS A PART OF THE OLFACTORY, BULB. 1, 3, bundles of very fine transversely cut nerve-fibres, forming the flattened medullary ring, enclosing the central neuroglia, 2; 4, granule-layer; 5, loose tissue with irregular spaces (? lymphatic) ; 6, intermediate layer; 7, layer of olfactory glomeruli, f; ff; 8, layer of olfactory nerve-fibres. Basal ganglia.—Besides the grey matter of the cerebral cortex the cerebral hemispheres conceal in their deeper parts certain other masses of grey substance (fig. 243).. The principal of these are the corpus striatum (nucleus caudatus, c, and nucleus lenticularis, str) and optic thalamus (th). Between them run the bundles of white fibres which are > a® 2 2 “Sit ’ + an ora ars at whites sms mii ’ Abner hate ma Hakata vin cera! ipl Eames thi SebeorPice heey clarke: 5 olan iets piles, \s , heel St aul g25 ath Sizes VLeuew srt sitet j a j i r : 2 a. ee cag “ r ae. —2- " u ; 5 é 3 mt ‘ign i * e nt 4 \ ic ~ - } q | ' r f { i 4 23 : " i Yves: © > «aati t ‘7? tt rs ° po Byer ae) fF iG or) Ti Bo esp rl: ee ee uy pee crs! Re jE pasierrd Sa Bais 30) ibe aateliina of ti. cy ) ; a rar MUcCeys ton bewaris. mss! Sa Lt haa a thre ile? 1th vee) at) ne © PTV Wary yee es 4 ie ‘ane 7 Die abpmesies OR Bide Psy : al aetem) } copia? bitad@s #' x vhg dee ie CA hi. at, WAY eoomabeE. (a ullew- Stamnes ers vant! brtynedt hae tite Wein Ow Aesth if peleyis. cet hk, Dane: aide: Ase ex wp te eee read bes tly paid oils . aha ua ropes ney th wc ke Ah Oo is ‘ : . - 7 ‘ * a ‘ ‘ . tet a tori ee t ‘ c $ ; 2° Tee RA tad Py y ’ | 4 , * ; s . { \ { “ z 3 te a y a , F o © ‘ a 5 i rote ws ‘ ‘ - ; ¢ te [bby ay “eV gy ‘ . s ‘ cathe Gli" Mi -z Pete ot te ae ; hag’ ,* * Se Haen! | par airs a é Ch) oe AP Oiihe aery gare en a8 a STRUCTURE OF THE CORPUS STRIATUM 207 passing upwards from the crus cerebri, forming a white lamina termed the internal capsule. Above the level of these nuclei the internal capsule expands into the medullary centre of the hemisphere (see also figs. 244 and 245, with their description). Fic. 243.—FRONTAL SECTION THROUGH THE BRAIN AND SKULL MADE WHILST FROZEN. 4% ¢.c, corpus callosum ; below its middle part the septum lucidum, and below that again the fornix; LZ V, lateral ventricle ; ‘h, thalamus ; between the two thalami the third ventricle is seen ; below the thalamus is the subthalamic prolongation of the tegmental region, and below this the prolongation of the crusta; sf7, lenticular nucleus of the corpus striatum ; c, caudate nucleus of the same ; between c¢, ¢h, and st7, the internal capsule is seen ; outside sir is the thin grey band of the claustrum, and outside this again the island of Reil at the bottom of the Sylvian fissure ; n.a. nucleus amygdale ; immediately within this is the optic tract seen in section ; p, pituitary body ; B, body of the sphenoid bone ; sa, subarachnoid space ; v, villi of the arachnoid. The nucleus caudatus of the corpus striatum is composed of a reddish-grey neuroglia containing both moderately large and small multi- polar nerve-cells. It receives fibres from the part of the internal capsule which separates it from the nucleus lenticularis, and next the lateral ventricle it is covered by a thin layer of neuroglia, and over this by the epithelium of the cavity. The nucleus lenticularis, which corresponds in position internally with the island of Reil externally, is divided by two white lamine into three zones. It is separated from the nucleus caudatus and optic thala- mus by the internal capsule (figs. 244, 245, 2c), which consists of the bundles of medullary fibres which are passing between the white centre of the hemisphere and the crus cerebri; it receives on its inner side many white fibres from the capsule, and these impart to it a radially striated aspect: Many of the nerve-cells of the nucleus lenticularis contain yellow pigment. > . 208 THE ESSENTIALS OF HISTOLOGY Fic. 244.—SECTION ACROSS THE OPTIC THALAMUS AND CORPUS STRIATUM IN THE th, REGION OF THE MIDDLE COMMISSURE. (Natural size.) thalamus ; a, e, i, its anterior, external, and internal nuclei respectively ; w, its external white layer ; m. c. middle commissure ; v. 3, third ventricle ; a small part is also seen below the middle commissure ; ¢. ¢. corpus callosum ; f, fornix, separated from the third ventri- cle and thalamus by the velum interpositum. In the middle of this are seen the two veins of Galen and the choroid plexuses of the third ventricle; and at its edges the choroid plexuses of the lateral ventricles, v./.; ¢.s. tenia semicircularis ; c7, forward prolongation of the crusta passing laterally into the internal capsule, i. c.; s. ¢. 7. subthalamic prolonga- tion of the tegmentum, consisting of (1) the dorsal layer, (2) the zona incerta, and (3) the corpus subthalamicum ; s. 7”. substantia nigra ; ”. c. nucleus caudatus of the corpus stria- tum; 7.7. nucleus lenticularis ; e. c, external capsule ; cl. claustrum ; J, island of Reil ; h, hippocampus; d, fascia dentata, Fic. 245.—HorizontTau SECTION THROUGH THE MIDDLE OF THE RIGHT CEREBRAL HEMISPHERE. (Natural size.) v.1. lateral ventricle, anterior cornu; ¢.c. corpus callo- sum ; s./7, septum lucidum ; a. f. anterior pillars of the fornix; v. 3, third ven- tricle; ‘h, thalamus opti- cus; s.¢. stria terminalis; n. c. nucleus caudatus, and n. 1. nucleus lenticularis of the corpus striatum; 4. c. internal capsule; g, its angle or genu; n. c. tail of the nucleus caudatus ap- pearing in the descending cornu of the lateral yen- tricle; cl, claustrum; J, island of Reil. =F) 4 : ue a ~ > ; iM iatag, Wi Tihs St thie Yi: oF Wye cet > Eid Boor tie ata Beratine Bo Wm eters al ceeehi Sinker rated fet dee ree tp ~ « tis « , = + — * “< vggae 5 G -- Peet is fat if ma iat ; ? J 6.F 2 : 4 i ' Hi j i¢ at | . ? gmet 32% s rr. nh ; : ’ ‘ j 7 y . = es r - ra \ pepe : . r pes / ’ ~ » “ < - fa i : i AN 3 “4 i oir: | j : rn , t ee ‘ ‘7 y ‘ i : — - —~ " : ‘ 4 + a Sy ae 4 ¥ Mat ~ my A Jo. ' : ig? : ’ > ty . Uy ° - ad t ey ' ’ err i . ie Tage vipit + ’ Pat oe oe . : ; oh H i> P ~ ey, ! - : ar she) - ’ . t » ay ‘wat c ieee ri ’ : eo te 5 x, 2 ig aie 1 Renee c.. naeaer ‘. ? > Ws . 4 aie . ; ts, ars i ite te i+ oe dans, faa ft (tet Sighs ° r * 3 ote > ; .THE PINEAL AND PITUITARY BODIES 209 The optic thalamus, which lies at the side of the third ventricle and forms part of the floor of the lateral ventricle, is covered externally by a layer of white fibres, most marked next to the internal capsule, fibres from which pass into the thalamus and serve to connect it with the hemisphere. The grey matter of the thalamus (fig. 244) is eicalty subdivided by an oblique white lamina into a smaller, inner (7), and a larger, outer, nucleus (¢); these contain a number of small scattered nerve- cells. Anteriorly another portion of grey matter (a) is divided off in a similar way; this contains comparatively large nerve-cells. Attached to the optic thalamus below and externally are the two geniculate bodies which are connected with the optic tract. The outer geniculate body has a lamellated structure consisting of alternating layers of grey and white matter. The tegmentum of the crus cerebri is prolonged below the thala- mus opticus into a mass of grey substance, with longitudinally and obliquely crossing white bundles, which is known under the name of subthalamic region. In it at least three parts differing from one another in structure may be distinguished (see fig. 244, 1, 2, 3). The pineal gland, which is developed in the roof of the third ventricle, is composed of a number of tubes and saccules lined and sometimes almost filled with epithelium, and containing deposits of earthy salts (brain sand). These may, however, occur in other parts Fic. 246.—SrEcTION OF THE UPPER PART OF THE BRAIN AND MENINGES TO SHOW THE RELATIONS OF THE ARACHNOIDAL VILLI. (Magnified.) c.c. corpus callosum; f, falx cerebri; s.a. subarachnoid space, pervaded by a network of fine trabecule ; from it the fungiform villi are seen projecting into the Cure mater, Some are projecting into the superior longitudinal sinus, s. : of the brain as well. The follicles are separated from one another by vascular connective tissue derived from the pia mater. The pituitary body is a small reddish mass which lies in the sella . P Va. —<_ 210 ‘THE ESSENTIALS OF HISTOLOGY turcica, and is connected with the third ventricle by the infundibulum. It consists of two lobes, a larger anterior, and a smaller posterior. The anterior lobe is originally developed as a hollow protrusion of the buccal epithelium. It consists of a number of tubules, which are lined by epithelium, and united by connective tissue. In some of the tubes the epithelium is ciliated, and sometimes a colloid substance like that occurring in the vesicles of the thyroid has been found in them. The posterior lobe of the pituitary body, although developed from the floor of the third ventricle, contains scarcely any perceptible nervous elements in the adult. It consists chiefly of vascular con-- nective tissue. The membranes of the brain are similar in general structure to those _- of the spinal cord, p. 185. The dura mater is, however, more closely adherent to the under surface of the bony cavity than is the case in the vertebral canal. The arachnoid is in many places close to the dura mater, and separated by a wide subarachnoid space, which is bridged across by finely reticulating bands of areolar tissue (subarach- noid trabecule, fig. 246, s.a.) from the pia mater. In the vicinity of the longitudinal sinus, small rounded elevations (arachnoidal villi, Pacchionian glands) project into the dura mater, and even become em- bedded in the skull itself. d i = =, ‘ A f ‘ 4 ‘ r ; i a 5 © = M | - x , I { ' s.= _ te : 7 \ = A ~ ‘ ; AV jibe 3 ‘ ise, mn =F Lat 205x) may : ie F eM ty " ’ yy mor iy (OS ‘ 5 } "Sm thoserdes| a) 1 , i hee OFF ih ey oer TUR arse NE SON ET: Ee a ped ‘ f 7 bin we, FE aye a}? : ; bela tics Be. Hare scl ; a: ay ad Beep pkiy ye (ARs hati of 4 ple ice fed wir) be Lh akith titer fee ae i bier ces a sawn att ae inns ; ‘ ToS ae eth : ; r- & ee a soul we ‘3 ; ny . " , 5 a 4 : - a : LS a TERRE ; . yyy * i * | y A 5 3 i” R ‘ if . Os ig \ ’ 5? 2 ; q F ~ 211 ~ LESSON XXXIX. ano XL. STRUCTURE OF THE EYELIDS AND OF THE PARTS OF THE EYEBALL. LESSON XXXIX. 1. Sections of the eyelid vertical to its surfaces and transverse to its long axis. The lid should be hardened in alcohol, and the sections may be stained with hematoxylin and mounted in the usual manner. Notice the long sacculated Meibomian glands lying in dense connective tissue close to the conjunctival surface, and their ducts opening at the margin of the lid. External to these the small fibres of the orbicularis pal- pebrarum cut across; a few of the fibres of the muscle lie on the conjunctival side of the duct. A short distance from the Meibomian gland may be observed another tolerably large sebaceous gland ; outside this again are the eyelashes. In the skin covering the outer surface of the eyelid a few small hairs may be seen. At the attached part of the eyelid are some bundles of involuntary muscular fibres cut longitudinally in the section, and in the upper eyelid the fibrous attachment of the elevator muscle may be observed attached to the dense connective tissue. Make a genera] sketch under a low power. 2. Sections through the posterior part of an eyeball thathas been hardened in Miiller’s fluid. The sections are stained and mounted-in the usual way. These sections will show the relative thickness of the several coats and the layers of which each coat is formed. Sections which pass through the point of entrance of the optic nerve will also exhibit the manner in which the nerve-fibres pierce the several coats to reach the inner surface of the retina. The modifications which are found in the neighbourhood of the yellow spot may also be made out if the sections have been taken from the human eye. _ 8. Sections of the anterior half of an eyeball which has been hardened in Miiller’s fluid. These sections should pass through the middle of the cornea. The lens may be left in situ, but this renders the preparation of the sections and the mounting of them much more difficult. In these sections make a general sketch under a low power, showing the relations of the several parts one with another ; and study carefully, and sketch in detail, the layers of the cornea, the place of junction of the cornea and sclerotic, the ciliary muscle, the muscular tissue of the iris, the mode of sus- pension of the lens, and the pars ciliaris retin. 4. Mount in glycerine thin tangential sections of a cornea, stained with ' chloride of gold by Cohnheim’s method. Sketch three or four of the con- nective-tissue cells (corneal corpuscles). The arrangement and distribution of the nerve-fibres and their termination amongst the epithelium-cells as re in chloride of gold preparations have been already studied (Lesson -A .) A » : P2 212 THE ESSENTIALS OF HISTOLOGY 5. Mount in Canada balsam sections of a cornea which has been stained with nitrate of silver. Notice the branched cell-spaces corresponding with the connective-tissue cells of the last preparation. : [This preparation is best made by rubbing the surface of the cornea with lunar caustic after scraping off the epithelium. After ten or fifteen minutes (by which time the nitrate of silver will have penetrated the thickness of the cornea) the eye is washed with distilled water, placed in spirit, and exposed to the light. When brown and sufficiently hardened, tangential sections may be made with a razor. | LESSON XL. 1. Remove the sclerotic from the anterior part of an eye which has been preserved in Miiller’s fiuid, and tear off thin shreds from the surface of the choroid, including amongst them portions of the ciliary muscle. Stain the shreds with logwood and mount them in Farrant’s solution. Sketch the branched pigment-cells, the elastic network, the mode of attachment of the fibres of the ciliary muscle, &e. 2. Injected preparation of choroid and iris. Mount in Canada balsam por- tions of the choroid coat and iris from an eye, the blood-vessels of which have been filled with coloured injection. Make sketches showing the arrangement of the capillaries and veins. , 3. Teased preparation of retina. Break up with needles in a drop of glycerine a minute fragment of retina which has been placed in 1 per cent. osmic acid solution for a few hours, and has subsequently been kept in dilute glycerine. Complete the separation of the retinal elements by tapping the cover-glass. Draw carefully under a high power some of the isolated elements—e.g. the rods and cones with their attached fibres and nuclei, the inner granules, the ganglion-cells, the fibres of Miiller, hexagonal pigment- cells, &c. In some of the fragments the arrangement of the elements in the retinal layers may be made out even better than in actual sections. Measure the length and diameter of some of the cones, the length of the cone-fibres, and the diameter of some of the outer and inner nuclei. 4. Teased preparation of lens. Separate in water the fibres of a crystalline lens which has been macerated for some days in weak bichromate of potash solution. Sketch some of the fibres, together and separate. The eyelids (fig. 247) are covered externally by the skin, and in- ternally or posteriorly by a mucous membrane, the conjunctiva, which is reflected from them over the globe of the eye. They are composed in the main of connective tissue, which is dense and fibrous under the conjunctiva, where it forms what is known as the tarsus. Embedded in the tarsus is a row of long sebaceous glands (the Mei- bomian glands, f), the duets of which open at the edge of the eyelid. The rest of the tlickness of the eyelid is composed of a somewhat loose connective tissue, and éontains the bundles of the orbicularis muscle (b). In the upper eyelid the levator palpebre is inserted into the tarsus by a fibrous expansion, and some bundles of involuntary muscle are also present near the attachment of the eyelid. The skin yc, & ards, rwiall ewir? Ee yrs rhe fe = pine bei, Aid, 1) who, i he nerf si & gece yar’ ts vehi} y thsi eo adhe sn wes jer cde frnetiog. Peeling (8 -colmmnal, ps YG ‘- ante “he dire ri temieiurh Of ihe : ryt Sy 3 = _ - 1 4 } ~ - ~~ +, Ae 7? . J ~ od Pe é te . t s . - . 2 : E ‘ firth : _ ‘ a = ' “ = \ = q A * ‘ ¢ ? ‘ ’ , 4 i ‘ \ - be - # ; 2 Beas atl Nae Si? aca ' etbats 7, vaelthta aves i, oie : c= | eer J sete fen; a epweryely |) * : mi. ' meted win. : ri ae per ae U “ : bye Fi BB." 4 4 Het tony ‘ Se bid Feb busi phi « fa] lyaliend Wwishe)) jus bia: ch wr ers of, pebpis ted Taney bane ap : ing Berikies ie te ‘ - bed > f I r ' »* be ; | .Oas *Tee t piat dal F itn & Tap y! » CU el eral pean vA x fi 7” eo)". T\At Serhan a) paw ok Bu» edge fa! ben we ‘ore of 4 fe Peis te to -~¢ ace w Hens wr MH STRUCTURE OF THE EYELIDS 218 has the usual structure ; it contains small sweat-glands and the fol- licles of small hairs, and, in addition, at the edge of the eyelid, the - large hair-follicles from which the eyelashes grow. The epithelium of the conjunctiva palpebre is columnar, passing at the edge of the lid into the stratified epithelium of the skin; it also becomes stratified in Fie, 247,.—VERTICAL SECTION THROUGH THE UPPER EYELID. (Magnified.) a, skin ; 6, orbicularis ; 6’, ciliary bundle; ¢c, involuntary muscle of eyelid; d, conjunctiva; e, tarsus; f, Meibomian gland; g, sebaceous gland near eyelashes, with modified sweat- gland opening with it; h, eyelashes; i, small hairs in outer skin; j, sweat-glands ; k, posterior tarsal glands. the part which is reflected over the globe of the eye. The nerves of the conjunctiva terminate for the most part in end-bulbs, which in man are spheroidal, and formed chiefly of a small mass of polyhedral cells, but in the calf and most animals they are elliptical, and consist of a core and lamellated sheath (see Lesson XIX.) SA 214 THE ESSENTIALS OF HISTOLOGY The lachrymal gland may be briefly mentioned in connection with the eyelid. It is a compound racemose gland, yielding a watery secre- tion, and resembling in structure the serous salivary glands, such as the parotid. : SS (Magnified.) 1, epithelium; 2, anterior homogeneous lamina; 3, substantia propria eornes; 4, posterior homogeneous (elastic) lamina ; 5, epithelium of the anterior chamber; a, oblique fibres in the anterior layer of the substantia propria; 6, lamelle, the fibres of which are cut across, producing a dotted appearance ; ¢, cornea! corpuscles appearing fusiform in section ; d, bundles of fibres cut longitudinally ; e, transition to the sclerotic, with more distinct fibrillation, and surmounted bya thicker epithelium; , small blood-yessels ent across near the margin of the cornea, - ee ee The sclerotic coat is composed of dense fibrous tissue, the bundles _ of which are intimately interlaced. It is thickest at the back of the . oa Factcisiy vos iy donee at <: Ir€ 4 Ny q Layct i CBG WED Var? peses) iu ley ’ ena Stars “Appear rey Sstiiten Fuerte is 50 Tues Harv Hie by: Puy (awe? wink. eee ts PONE are, scar Pardes OF Winch, “ ‘ : meeps Bo ha. Perk Mawar or ; The ents Le 6 hes citi Mea Sfore Pieth Ff a Ff eet ey ac y . a ( | » } : a. } 3] f H + é x —o— ’ ‘ ‘ ‘ 7 | aa vy 7 LY he aes. cP > _ ad -. . Trce Pats bie ct ear mec tet ‘ i % c: hi ‘ Beil tp peer satan Mbt Apis wal ' = h Tatate a tise Se Ye i ‘4 4 ' hy i ; Pale: V Se vi he i ; : uid: ¥ FC raayriaigag © i §- Wart tle DAB. 4% oe wt Ur i ee Yeti ek fee “ppg Sains Speer shee Pica 8 whaiets lM * a4 oa” fe wo. ' ~ 7 , ~ AS is we pee ~, A say “ 1 2 . a - “2 nh STRUCTURE OF THE COATS OF THE EYEBALL 215 eyeball. It is covered externally with a lymphatic epithelium, while internally it is lined by a layer of connective tissue containing pig- - ment-cells, which give it a brown appearance (lamina fusca). At the entrance of the optic nerve the sclerotic is prolonged into the sheath of that nerve, the bundles of which, piercing the coat, give a sieve-like aspect to the part (lamina cribrosa, fig. 257, L). - The cornea (fig. 248) consists of the following layers enumerated from before back : 1. A stratified epithelium continuous with the epithelium of the conjunctiva (1). 2, A thin lamina of homogeneous connective tissue (membrane of Bowman), upon which the deepest cells of the epithelium rest (2). 8. A thick layer of fibrous connective tissue which forms the proper substance of the cornea (3). This is continuous laterally with the tissue of the sclerotic. It is eomposed of bundles of white fibres arranged in regular lamine, the direction of the fibres crossing one another at right angles in the alternate lamine. Between the lamine lie flattened connective-tissue corpuscles, which are branched and united by their processes into a continuous network ; there is of course a corresponding network of cell-spaces (fig. 249, A, B). In vertical Fic. 249.—A. CoRPUSCLES OF THE RAT’S CORNEA. (From a preparation treated with chloride of gold.) 8B. CELL-SsPACES OF THE RAT’S CORNEA, (From a preparation stained with nitrate of silver.) sections the cells appear narrow and spindle-shaped (fig. 248, c). In the superficial lamine there are a few bundles of fibres which run obliquely towards the surface (a). 4. A homogeneous elastic layer (membrane of Descemet) (fig. 248, 4). This completely covers the back of the cornea, but at the angle which the cornea forms with the iris it breaks up into separate fibres, which are continued into the iris as the ligamentum pectinatum, or pillars of the iris. 216 THE ESSENTIALS OF HISTOLOGY 5. A layer of pavement-epithelium covering the posterior surface of. the elastic lamina, and lining the front of the anterior chamber of the eye (fig. 8348, 5). At the sides it is continued over the ligamentum pectinatum into a similar epithelium, covering the anterior surface of the iris (fig. 253, JV). The nerves of the cornea pass in from the periphery, losing their medullary sheath as they enter the corneal substance. They form a primary plexus in the substantia propria, a secondary or sub-epit- helial plexus immediately under the epithelium which covers the anterior surface, and a terminal plexus of fine fibrils which pass from the sub-epithelial plexus in pencil-like tufts and become lost between the epithelium-cells (see figs. 105, 106, Lesson XIX.) There are no blood-vessels or lymphatics in the cornea, although they come close up to its margin. The choroid or vascular coat of the eye is of a black colour in many animals, but in the human eye is dark brown. It is composed of connec- tive tissue, the cells of which are large and filled with pigment (fig. 251), and it contains in its inner part a close network of blood-vessels, and CAG AT. UEu. GBADSOUKEAY, sc. Fic, 250.—Srcrion oF cHoroIpD. (Cadiat.) a, membrane of Bruch: the chorio-capillaris is just above it; 6, vascular layer; c, vessels with blood-corpuscles ; d, lamina suprazhoroidea, in its anterior part the involuntary muscular fibres of the ciliary muscle, which pass backwards from their origm at the junction of the cornea and sclerotic, to be inserted into the choroid. The choroid is separable into the following layers, enumerated from without in (fig. 250) : 1. The lamina suprachoroidea (fig. 250, d). This is a thin mem- brane composed of homogeneous connective tissue pervaded by a net- work of fine elastic fibres, and containing many large branched pigment-cells and lymph-corpuscles (fig. 251). It is covered super- ficially by a delicate lymphatic epithelium, and is separated from the lamina fusca by a cleft-like lymphatic space which is bridged across here and there by the passage of vessels and nerves, and by bands of connective tissue. 2. The vascular layer of the choroid (fig. 250, b), which resembles i e-. , . - be he >" f “, LES cm e i \. i : ' 1 my } ‘ aaa ~*~ 4 Top - . a ee | i Fair i wht Mie Sire . pe! ty RGA ie 3 thea | & cnc ot Sow ee Aiea eta ie ' wee bh tig; ghiibhiy. mer ae 7 ¥ i, m\ rae ots Re ast - Inde eave on Moats Gene Teeth ae | any 4 , Aa tly 15 why : ‘ee bs rey i. ee: ¥ ‘y Ne Medi * Us ve VI) Wee ANS; Fic, 251.—A sMALL PORTION OF THE LAMINA SUPRACHOROIDEA. (Highly magnified.) p, pigment-cells ; /, elastic fibres; m, nuclei of epithelioid cells (the outlines of the cells are not indicated) ; 7, lymph-cells. Fic. 252.—INJECTED BLOOD-VESSELS OF THE CHOROID COAT. 1, one of the larger veins; 2, small anastomosing vessels; 3, branches r dividing into the smallest vessels. 218 THE ESSENTIALS OF HISTOLOGY ° - the suprachoroidea in structure, but contains the blood-vessels of the coat. In its outer part are the larger vessels (arteries and veins), the veins having a peculiar vorticose arrangement; in its inner part (chorio-capillaris) are the capillaries, which form an extremely close network with elongated meshes, the capillaries radiating from the ) «fitetiee ie = = SSS ———— St 3 9= ——— ees QR SSS ITS Fic. 253.—Srcrion (FROM THE EYE OF A MAN, AGED 380), SHOWING THE RELATIONS OF THE CORNEA, SCLEROTIC, AND IRIS, TOGETHER WITH THE CILIARY MUSCLE, AND THE CAVERNOUS SPACES NEAR THE ANGLE OF THE ANTERIOR CHAMBER. (Magnified.) A, epithelium ; B, conjunctival mucous membrane ; ©, sclerotic ; D, membrana suprachoroidea ; E, opposite the ciliary muscle ; F, choroid, with ciliary processes ; G@, tapetum nigrum and: pars ciliaris retinee; H, cornea (substantia propria); J, iris; K, radiating and meridional, and L, circular or annular bundles of the ciliary muscle; M, bundles passing to the sclerotic ; N, ligamentum pectinatum iridis at the angle, 0, of the anterior chamber; Pp, line of attachment of the iris. 1, anterior homogeneous lamina of the cornea ; 2, posterior * , homogeneous lamina, covered with epithelial cells which are continued over the front of 7 the iris ; 3, cavernous spaces at the angle of the anterior chamber (spaces of Fontana); _ ] 4, canal of Schlemm, with epithelial lining, and with a vessel, 5, leading from it; 6, other vessels’; 7, bundles of fibres of the sclerotic having a circular direction, cut across; 8, larger ones in the substance of the sclerotic; 9, fine bundles cut across, at limit of cornea ; 10, point of origin of meridional bundles of ciliary muscle; 11, blood-vessels in sclerotic and conjunctiva, cut across ; 12, section of one of the ciliary arteries. : extremities of the small arteries and veins in a highly characteristic manner (fig. 252). In the ciliary processes the vessels have for the most part a longitudinal direction, but there are numerous convoluted transversely disposed capillaries uniting the longitudinal vessels (fig. 255). | es ~. < - r= - \ ; he - 4 YY - r ‘ f : Ey C wah ‘ 4 be : < . : ~ — +) =~ rn a) ; * ws \ xi 3 § / . A es + 2 ; f aid = ~ i ra = rk F At - F { r & eS lee C2 re A ~m th by inf!) i He moat ek) Ween te 4 GQitigta ae mas ae ri Tiaeting RPC ’ aa i Ried utara tiny ’ wa OE pas a ane Hitt ee Beale. pi ir ie Y ahongshins oe tee ‘sl i Ht ce en) ere a TAP rs, i > —T ' ‘ f r 1 my — . . ' ‘ “pp ‘ F: 4 rPvué’ Ov eaeas ee whale le Lt STRUCTURE OF THE RETINA 221 optic nerve after it has passed through the coats of the eye (fig. 257). At its entrance it forms a slight eminence (colliculus nervi optici). The nerve-fibres lose their medullary sheath on reaching the retina. The layer becomes gradually thinner in the anterior part of the retina. nh Hi | | NYA ae a M0! “Veo VmVe ‘Fic. 257.—SEcTION THROUGH THE COATS OF THE EYEBALL AT THE POINT OF ENTRANCE OF THE OPTIC NERVE. (Toldt.) Ve, dural sheath ; Vm, arachnoidal sheath, and Vi, pia-matral sheath of the optic nerve, with lymphatic spaces between them ; 0, 0, funiculi of the nerve ; Z, lamina cribrosa ; A, central artery; S, sclerotic ; Ch, choroid; R, retina, The small letters refer to the various parts of the retina, 6 being the layer of rods and cones, and 7 that of nerve-fibres. The layer of nerve-cells, or ganglionic layer, is composed of large nerve-cells somewhat like the cells of Purkinje of the cerebellum, and having on the one side a fine axis-cylinder process prolonged into a nerve-fibre, and on the other a thick branching process, the ramifica- tions of which become lost in the next layer. The inner molecular layer is comparatively thick, and has an appearance very like the neuroglia of the grey matter of the nerve- centres. A few nuclei are scattered through it, and it is traversed by the processes of the nerve-cells and of the inner granules, as well as by the fibres of Miller. The inner nuclear layer is mainly composed of bipolar cells con- taining large nuclei (inner granules). The processes of these cells extend on the one hand inwards through the inner molecular layer, probably to join with nerve-fibres or with the processes of the gan- glion-cells, whilst the other process is directed outwards, and is con- nected with the extremity of a rod or cone fibre. Besides these bipolar cells, there are other inner granules which are different in character, being devoid of processes and resting on, or even embedded in, the © 222 THE ESSENTIALS OF HISTOLOGY inner molecular layer, with the formation of which they are probably connected. Others, which are larger and more rounded, are applied to the outer molecular layer. The fibres of Miiller have nucleated enlargements in the inner nuclear layer. The outer molecular layer is thin, and is composed of flattened and branched cells, the ramified cell-processes being united into a close — network (fig. 258). Fic. 258.—BrANCHED CELLS WITH THE UNITING FELTWORK OF FIBRES FROM THE OUTER MOLECULAR LAYER OF THE HORSE’S RETINA. As far as the outer molecular layer the retina may be said to con- sist of nervous elements, but beyond this layer it is formed of modified epithelium-cells. The outer nuclear layer and the layer of rods and cones are com- ~ posed of elements which are continuous through the two layers, and they should properly, therefore, be described as one. It may be termed the neural or sensory epithelium of the retina (fig. 260, 6 and 7). The elements of which the neural epithelium consists are elongated, nucle- ated cells of two kinds. The most numerous, which we may term the rod-elements, consist of peculiar rod-like structures (rods proper) set closely side by side, and each of which is prolonged internally into a fine varicose fibre (rod-fibre) which swells out at one part of its course into - a nucleated enlargement. The rod proper consists of two segments, an outer cylindrical and transversely striated segment, which during life has a purplish-red colour, and an inner slightly bulged segment, which in part of its length is longitudinally striated. The nucleus of the rod-element often has, in the fresh condition, a transversely shaded aspect (fig. 259). The cone-elements are formed of a conical taper- ing external part, the cone proper, which is direetly prolonged into a nucleated enlargement, from the farther side of which the cone- fibre, considerably thicker than the rod-fibres, passes inwards, to ter- minate by an expanded base.at the outer molecular layer. The cone proper, like the rod, is formed of two segments, the outer of which, much the smaller, is transversely striated, the inner, bulged segment fo ~2 ai > 7 7 ~y ! *, 7 . \ } 7h . < a P. ‘ j > x 2 ) c 7 r > * u ‘ a t d ; ¥ ~~) - - . - — i e t . . es > Ve i = 7 ' a | F isthe Lb WE Veber’ Ane Sim gntza % at ( wl : > . no ' 4 te ? 4 ps - "opr ot YuleH ca (cis ¢ / / share Tn 20a: hag “: PRD Mri She sect gies : : whi Megan ed . n me) Ore tar & rouse, Wee lode at orntly , be ho ier rieee eer PEP ty Lt rebel See ate oa ee Giri ad eepovide 3 : Pees ies fee Ids, a = Qu; : ML ay a a, eae ae . mae 259. “pate = ora REPRESENTATION OF THE NERVOUS AND EPITHELIAL - ELEMENTS OF THE RETINA. bag 5 herons elements. 6, 7, epithelial elements, The designation of the numbers is the same et in fig, BAB, The extent of the molecular layers is indicated merely by linear saan : 224 THE ESSENTIALS OF HISTOLOGY being longitudinally striated. The inner ends of the rod- and cone-. fibres are believed to be connected with processes from the inner granules, and through these with the nerve-cells and nerve-fibres. In © birds, reptiles, and amphibia, a small oil-globule, often brightly coloured red, yellow, or green, is found in the inner segment of each cone, and other variations of structure are met with in animals. The - cones are most numerous at the back of the retina ; they are fewer in number, and the rods are proportionally more numerous, towards the anterior part. Fic, 260.—PIGMENYTED EPITHELIUM OF THE HUMAN RETINA. (Highly magnified.) a, cells seen from the outer surface with clear lines of intercellular substance between ; }, two cells seen in profile with fine offsets extending inwards; c,a cell still in connection with the outer ends of the rods. Fic. 261.—A Fisré or MULLER FROM THE HUMAN RETINA, ISOLATED. +92 b, base of the fibre; n, its nucleus; m.e/. mem- brana limitans extertia; e.m.J, external mo- lecular layer. The pigmentary layer is the most external part of the retina. It is formed of hexagonal epithelium-cells (fig. 260), which are smooth exter- nally where they rest against the choroid, but are prolonged internally into fine filaments which extend between the rods. The pigment-granules, re cn ie iis Peaks Se eh ee en La, — mae after pen pare Beery ain ee SSN Mai * vr Tren aes aha PEP) : “2s ‘i > = es 7 : Ley fedlberily md mil et th ait he: cod arbes 5 + fee ricaphiad wh ast Bike Sms Niel My we Mite , a) Rg tsch Bi A ‘ . a t Fs Iw th Ay ey t Sr ; < ‘ ' . i. . , : - <7 7 , t . } } ' tJ ~ « - 7) ‘i ay = Hi =! hi A ° 3 ‘ a Pe s Fa - \ _* —_ } ‘ oa = _ J = © ce e's ; 4 é . . 5 \ I A o . aad . ad - a ia , . - . , a 3 as = ‘ 3 w eS 2 iit oad 2 : ¢ x whens sie 30 Pe ~% y . ry t Rabie et ‘ Pes sees ate’ Py aes Ue ata svar sy ug Pus So or # 7 = STRUCTURE OF THE RETINA 225 many of which are in the form of minute crystals, lie in the inner part of the cell, and after prolonged exposure to the light they are found extending along the cell-processes between the rods (8, c), their function being probably connected with the restoration of the purple colouring matter which has been bleached by the light. _ Fibres of Miiller.—The fibres of Miller (fig. 261) are long stiff fibres which pass through several of the retinal layers. Commencing at the inner surface of the retina by expanded bases which unite with one - another to form the so-called internal limiting membrane (fig. 856), the fibres pass through all the layers in succession, until they reach the outer nuclear layer. Here they branch and expand into a sort of reti- cular tissue which serves to support the fibres and nuclei of the rod- and cone-elements. At the bases of the rods and cones, this sustentacular tissue ceases, being here bounded by a distinct margin which has been called the external limiting membrane (m. e. l.), but delicate sheaths have been described passing from it round the bases of the rods and cones. Each-Miillerian fibre, as it passes through the inner nuclear layer, has a nucleated enlargement (mn), indicating the original cell ~ nature of the fibre. There are two parts of the retina which call for special description. The macula lutea (yellow spot, fig. 263), with its central fovea, lies in the visual axissand is the part of the retina which is most immedi- C0 Owns D Fic. 262.—_VERTICAL SECTION THROUGH THE MACULA LUTEA AND FOVEA CENTRALIS 3 ; DIAGRAMMATIC., 1, nerve-layer ; 2, ganglionic layer ; 3, inner molecular ; 4, inner nuclear ; and 5, outer molecu- lar layers ; 6, outer nuclear layer, the inner part with only cone-fibres forming the so-called external fibrous layer ; 7, cones and rods. ately concerned in direct vision. It is characterised first by its greater thickness (except at the fovea), secondly by the large number of ganglion-cells, which are all distinctly bipolar (2), and thirdly by the large number of cones it contains as compared with the rods. In the Q =~“ 5 Le ot i- . -_ 4 226 THE ESSENTIALS OF HISTOLOGY central fovea itself there are no rods, and the cones are very long and slender; moreover, all the other layers become gradually thinned down almost to complete disappearance, so that the middle of the central fovea is the thinnest part of the retina. Since there are few-rods, the — outer nuclear layer (6) loses in great measure its appearance of being composed of closely packed nuclei, and the cone-fibres are very distinct. The direction of all the fibres is very oblique in this part of the retina. The pars ciliaris retine which commences at the ora serrata, where the retina proper abruptly ends, is composed of two epithelial layers (fig. 263), and has no nervous structures. Of the two layers, the Fic. 263—A SMALL PORTION OF THE CILIARY PART OF THE RE- r in TINA. (350 diameters.) vi 1, pigment-cells ; 2, columnar cells, eh HN hy ' il external is a thick stratum of pigmented epithelium formed of rounded cells and continuous with the pigmentary layer of the retina on the one hand, and with the uvea of the iris on the other ; the inner is a layer of columnar cells each containing an oval nucleus. The retina contains but few blood-vessels. The artery enters and the vein leaves it in the middle of the optic nerve. The larger vessels ramify in the nerve-fibre layer, and there are capillary networks in this layer and in the inner nuclear layer. There are peri-vascular lymphatic spaces around the veins and capillaries. The neural epithe- lium receives no blood-vessels, but is nourished from the vessels of the choroid. Structure of the lens. The lens is a laminated fibrous body en- closed by a transparent elastic capsule into which, around the circum- ZA LZ Liisa Fic. 264.—SECTION THROUGH THE MARGIN OF THE RABBIT’S LENS, SHOWING THE TRANSITION OF THE EPITHELIUM INTO THE LENS-FIBRES. ference, the fibres of the suspensory ligament are inserted: Immedi- ately within the capsule, in front and at the sides, there is a layer of cubical epithelium termed the epithelium of the capsule, but at the margin of the lens the cells become longer and pass by a gradual transition into the lens-fibres (fig. 264). The fibres which compose the lens are long and riband-shaped, with finely serrated edges (fig. 265, A) ; et ee hernte ce faena tin 7) he joa Rhee genie orien ® * t * *. ¥ —_~ \ es . a 5 é . = * ’ y ‘ x . . u - , p . 4 Y : 4 s .. . " . = / ‘ >. eel - j 2 ; * 4 woe ts, Zier 4 és * ry by - . “ ~ : ’ : Le Ly ay Ue : ‘ wla> " 4 ~ fs : : : = { ¥ } " heen Sipe dse? ee 3 gu - | Ob iia, TELS. Vie pe ecm cto Ee + Sie es Ba Bek Le Dain sie! per BB) Burgess . Phar ay ul Piet STRUCTURE OF THE LENS AND VITREOUS HUMOUR 227 ‘in transverse section they appear prismatic (B). Many of the superficial fibres are nucleated (c), the lens-fibres having originally been developed by the elongation of epithelium-cells. Y Li, YY Mt, Fic. 265.—F1BRES OF THE CRYSTALLINE LENS. (350 diameters.) A, longitudinal view of the fibres of the lens from the ox, showing the serrated edges. B, transverse section of the fibres of the lens from the human eye. O, longitudinal view of a few of the fibres from the equatorial region of the human lens. Most of the fibres in C are seen edgeways, and, towards 1, present the swellings and nuclei of the ‘nuclear zone ;’ at 2, the flattened sides of two fibres are seen, The vitreous humour is composed of soft gelatinous tissue, appa- rently structureless when examined in the fresh condition, but contain- ing a few scattered amceboid cells, the processes of which are often long and varicose, and the cell-bodies distended by large vacuoles. The hyaloid membrane, which invests the vitreous humour, is homogeneous and structureless except in the region of the ciliary processes, where it is fibrous in structure, forming the zonule of Zinn and spreading out into _ the suspensory ligament of the lens. Q 2 228 THE ESSENTIALS OF HISTOLOGY LESSON XLI. STRUCTURE OF THE OLFACTORY MUCOUS MEMBRANE AND OF THE EXTERNAL AND MIDDLE EAR. 1, VeRTICAL sections of the olfactory mucous membrane. The sections may be carried either across the middle turbinate bone, after decalcification in 0-2 per cent. chromic acid, or across the upper part of the nasal septum. Make a sketch under the low power. Notice the difference in the character of the epithelium in the olfactory and respiratory parts of the membrane. 2. Teased preparation of the epithelium of the olfactory mucous mem- brane. A piece of the membrane is placed quite fresh in osmic acid (1 per cent.) for a few hours, and is then macerated for two days or more in water. The epithelium is broken up in dilute glycerine ; the cells easily separate from one another on tapping the cover-glass. Notice the two kinds of cells. Sketch some of the cells under a high power. 3. Sections of the external ear (these have been already studied for the cartilage, Lesson XII.) 4. Sections across the cartilaginous part of the Eustachian tube. Sketch under the low power. 5. Preparation of the membrana tympani. A piece of the membrane, stained with hematoxylin. and mounted flat in Canada balsam. Determine the composition of the membrane—.e. the several layers com- posing it—by focussing carefully with the high power. STRUCTURE OF THE OLFACTORY MUCOUS MEMBRANE. The olfactory region of the nasal fosse includes the upper and middle turbinate processes and the upper third of the septum. It is covered by a soft vascular mucous membrane of a yellow colour in man. The epitheliwm of the olfactory mucous membrane (figs. 266, 267) is very thick and is composed of long tapering cells, set closely side by side and bounded superficially by a cuticular lamina, through which the free ends of the cells project. The cells are of two kinds: 1. Long narrow. spindle-shaped or bipolar cells consisting of a larger part or body (6), containing the nucleus, and of two processes or poles, one (c) straight and cylindrical and extending to the free surface, the other (d) very delicate and varicose, looking not unlike a nerve-fibril and extending » 4 +7 a —_ , Pin eee MAS 7V . ete eee Borges 07 Shs THE pryeene “Oh pare itigita Bee ees chez 17 > i fh ne te ven eae SEA: UR, G Tot ’ ‘ - - 4 . \ - ; “ ‘ ' 3 i - " ~ x : zt 1 — i a \ ‘ : i td c * 7 J : a - 7 , : a t 2 ~ c gh “i + re i . ‘ te i . ' « \4 S 5 ; ai it ; a ra é " er aS ~ i an Jats peer apa baie } , ade Sts gt wre! ei ive" ays en : : ginal > anos ore in; SAY ete ot ' . she ~ Live ' ry a | ‘ = ibe ig i sabia y jaat Sol | ved — i, Vin sold Ves 4. ON : ‘ , 7 : : = ae | eee eer =< cighe ielal Girth » Tings fii polis tors jhoedaitah | nite the. dip.qiv: art ow ais Ae ate =o ey 1%" a | ie’ & pnd pres darter: pLe=2t] Vite sind: (ts 4 ‘ a , \ To" \e . 4, Vd ¥ ad . ; pes = re Lisoplowt ih ’ : lye (WS) (hae, Ke, i a\ (ict will. we pray 7 ii i \ dv a kae lito ilies os if-¥ lp abun , ne as amici eae . ‘reress 1 Salis trices ont THE OLFACTORY. MEMBRANE 229 down to the corium. The position of the nuclear enlargement varies, and with it the relative length of the two processes. The distal or free process terminates in a small clear projection, which passes beyond the cuticular membrane ; inamphibia, reptiles, and birds, and perhapsin some Fie. 266.—CELLS AND TERMINAL NERVE-FIBRES OF THE OLFACTORY REGION. (Highly magnified.) 1, from the frog; 2, from man; a, epithelial cell, extending deeply into a ramified process ; ‘b, olfactory cells ; c, their peripheral rods; e, their extremities, seen in 1 to be prolonged into fine hairs; d, their central filaments, mammals, it bears fine stiff hairlike filaments (e). The proximal or vari- cose process becomes lost amongst the plexus of olfactory nerve-fibrils at the base of the epithelium, and is believed to be connected with a fibril. These cells have accordingly been termed olfactory cells. 2. Long colum- nar epithelium cells (a), with comparatively broad cylindrical nucleated cell-bodies placed next the free surface, and long, forked, and branching tail-like processes extending down to the corium. These are usually regarded not assensory epithelium-cells, but merely as serving to support the proper olfactory cells; but, according to Exner, they are also con- nected with the olfactory fibres, and there is no sharp distinction between them and the bipolar cells. 8. Tapering cells are present, at least in some animals, in the deeper part of the epithelium. They rest by their bases upon the corium, and project between the other cells, which they assist to support. ° __ The coriwm of the olfactory mucous membrane is also very thick. (fig. 267). It contains numerous blood-vessels, bundles of the olfactory nerve-fibres (which are non-medullated), and a large number of serous 230 THE ESSENTIALS OF HISTOLOGY glands known as Bowman’s glands (b), which open: upon the surface by fine ducts passing between the epithelium-cells. cat Tr F 1G, 267.—SEcTION OF OLFACTORY MUCOUS MEMBRANE. (Cadiat.) a, epithelium ; b, glands of Bowman; c, nerye-bundles. STRUCTURE OF THE AUDITORY ORGAN. The external ear proper (pinna) is composed of elastic fibro-carti- lage, invested by a thin, closely adherent skin. The skin is covered by small hairs, and connected with these are the usual sebaceous follicles. In some parts—e.g. the lobule—there is a considerable amount of adipose tissue ; and voluntary muscular fibres are in places attached to the cartilage and may be seen in sections of the ear. The external auditory meatus is a canal formed partly of cartilage continuous with that of the pinna, partly.of bone. It is lined by a prolongation of the skin and is closed by the membrana tympani, over which the skin is prolonged as a very thin layer. Near the orifice the skin has hairs and sebaceous glands, and the meatus is also provided throughout the cartilaginous part with small convoluted tubular glands of a brownish-yellow colour, which yield a waxy secretion (cerwminous glands). They appear to represent modified sweat-glands. The tympanum is lined by a mucous membrane which is continuous through the Eustachizn tube with the mucous membrane of the pharynx; it is also prolonged into the mastoid cells. The epithelium is columnar and ciliated in some parts, but in others—e.g. roof, promon- tory, ossicles, and membrana tympani—it is a pavement-epithelium. The membrana tympani is a thin membrane formed of fibrous bundles which radiate from the umbo. Within the radial fibres are a few annular bundles. Covering the fibrous membrane externally-is a thin — - were j 7 = Ta > 19 _ The ad hs ia Lee f° Aen ta Vs a a) oe 7 ' =< . { ' 7 a } ’ . . - « ‘ ¥ cath Lk oo * ‘ic Saliba eee - hee need wails, Yh say | 1 , Deg a ytbal atte. ) be »* r p. : ee Pe ae “Fol op ry z é a eo out ‘ STRUCTURE OF THE EUSTACHIAN TUBE 231 layer continuous with the skin of the meatus; covering it internally is another thin layer, derived from the mucous membrane of the tympanic cavity. Blood-vessels and lymphatics are distributed to the membrane chiefly in the cutaneous and mucous layers. The Eustachian tube is the canal leading from the tympanum to the pharynx. It is formed of bone near the tympanum, but below, Fic. 268.—SEcCTION ACROSS THE CARTILAGINOUS PART OF THE EUSTACHIAN TUBE. 1, 2, bent cartilaginous plate; 3, muse. dilatator tube ; to the left of 4, part of the attachment of the levator palati muscle ; 5, tissue uniting the tube to the base of the skull; 6 and 7, mucous glands; 8, 10, fat; 9 to 11, lumenof the tube ; 12, connective tissue on the lateral ~ aspect of the tube. near the pharynx, it is bounded partly by a bent piece of cartilage (fig. 268, 1, 2), partly by fibrous tissue. The latter contains numerous mucous glands (6, 7), which open into the tube; and on the outer side a band of muscular tissue (3) which joins the tensor palati. The epithe- lium is ciliated. 232 ‘THE ESSENTIALS OF HISTOLOGY — LESSON XLII. STRUCTURE OF THE LABYRINTH. 1. SEcTIONS across one of the membranous semicircular canals of a fish (skate). 2. Longitudinal sections through the ampulla of a semicircular canal (skate). 3. Vertical sections through the middle of the cochlea of a mammal. The cochlea is put quite fresh into 0°2 per cent. chromic avid containing a few drops of 1 per cent. osmic acid. When decalcified, it is well washed, and then placed in spirit for a day or more. In preparing sections of the above three preparations it is advisable, in order that the epithelium should be kept in position, to mount them by the creosote-shellac process. They may previously be stained in bulk either by alcoholic magenta or borax-carmine. 4. Teased preparations of the auditory epithelium of an ampulla or of the macula of the utricle, from the fish. 5. Teased preparations of the epithelium of the organ of Corti from the guinea-pig. Both 4 and 5 are made from osmic preparations. Make sketches from all these preparations under the high power. The labyrinth, which is the essential part of the auditory organ, consists of a complex membranous tube lined by epithelium and filled with endolymph, contained within a bony tube—the osseous labyrinth —of corresponding complexity of shape (figs. 269, 270). The mem- branous labyrinth does not wholly fill the bony cavity ; the rest of the space is occupied by perilymph. The membranous labyrinth (fig. 269) is composed of the wtricle (w), and the three semicircular canals, each with an enlargement or ampulla which opens into it, the saccule (s) and the canal of the cochlea (c. ¢.) The branches of the auditory nerve pass to certain parts only of the membranous labyrinth, viz.: the macule of the utricle and ~ saccule; the criste of the NE and along the whole length of the canal of the cochlea (the shaded parts in fig. 269). : x We ae ral Leo Wee, oe # i i) j b>. Witwed sing Lot caer cared bg 5 es in» daggmauit e opalia woe he . 4 EAT . >>, s Wp et ie ty tay aARS : feb, Jomredras: ts Hs ceptas lest ie ere © +e STRUCTURE OF THE LABYRINTH _ 233 At these places the lining epithelium is specially modified to form a sensory or nerve-epithelium; elsewhere it is a simple pavement- epithelium, Fic. 270.—ViIEW OF THE INTERIOR OF : 7 7RID ~ Se Fic. 269.—PLAN OF THE RIGHT MEM- CEE Ler) Cleese Levee BRANOUS LABYRINTH VIEWED FROM THE MESIAL ASPECT. 23 The bony wall of the labyrinth is removed a: superiorly and externally. 1, fovea hemi- elliptica ; 2, fovea hemispheerica ; 3, common u, utricie, with its macula and the three opening of the superior and posterior semi- semicircular canals with their ampulle; circular canals; 4, opening of the aqueduct 8, saccule ; ag. v. aqueeductus vestibuli; s.e. of the vestibule; 5, the superior, 6, the saeccus endolymphaticus; c.7. canalis re- posterior, and 7, the external beaten ays uniens ; c.c. canal of the cochlea. canals; 8, spiral tube of the cochlea ;.9, scala tympani; ; 10, scala vestibuli. The membranous semicircular canals and the utricle and saccule are composed of fibrous tissue, which is adherent along one side to the endosteum of the bony canal; from the opposite side bands of fibrous tissue pass across the perilymph. Within the fibrous membrane is a thick clear tunica propria, which, in the semicircular canals, forms papillary elevations in the interior of the tube (figs. 271, 272). The places of entrance of the nerve-fibres into the ampulle are marked by a transverse, inwardly projecting ridge (crista), in the saccule and utricle by a thickening of the tunica propria (macula). The epithelium at these places is formed of columnar cells (fig. 273), which are surmounted by long, stiff, tapering hairs (auditory hairs, fig. 273, i), and to these hair-cells the axis-cylinders of the nerve-fibres pass directly (fig. 274); they are therefore—like the rod- and cone- elements of the retina, the bipolar cells of the olfactory membrane, and the gustatory cells of the taste-buds—sensory or neural epithelium-cells. Between them are a number of thin and somewhat -rigid nucleated cells (fibre-cells of Retzius, fig. 274, f), which rest upon the basement- membrane, and are connected at their free extremity with a cuticular membrane, through which the auditory hairs project. The auditory hairs do not project free into the endolymph, but into a soft mucus-like substance, of a dome-like form, in the ampulle (fig. 273), and which in the saccule and utricle has a mass of calcareous - particles (otoliths) embedded in it. ‘ 234 THE ESSENTIALS OF HISTOLOGY Fie, 271.—SECTION OF ONE OF THE HUMAN SEMICIRCULAR CANALS. (Magnified.) 1, osseous wall ; 2, fibrous bands with included blood-vessels, united at 3 with the periosteum ; -& 4, membranous canal with its three layers; 5, short fibrous bands (with intervening spaces) uniting the membranous canal firmly to the periosteum ; 6, union of its outermost layer with the periosteum. Fic. 272.—SEcTION OF MEMBRANOUS SEMICIRCULAR CANAL. (Much magnified.) 1, outer fibrous layer ; 2, tunica propria ; 3, 6, liform projections with epithelial covering; j 5, fixed side of the canal, with very thin tunica propria without papille; 7, fibrous bands passing to periosteum, 7 - Je - POTeay Ae Jak oe m4 , ‘jeoe errs dk YO cL ewm el pet & ee hag ot ed J ae . STRUCTURE OF THE COCHLEA 235. — 8 ISCISISSt Seo easissgs = < Se aS SAC SEC Fig. 273.—LONGITUDINAL SECTION OF AN AMPULLA THROUGH THE CRISTA ACUSTICA. amp, cavity of the ampulla; sc.c, semicircular canal opening out of it; c, connective tissue attached to the wall of the membranous ampulla and traversing the perilymph; e¢, e, flattened epithelium of ampulla; h, auditory hairs projecting from the columnar cells of the auditory epithelium into the cupula, cup. term. ; v, blood-vessels ; ”, nerve-fibres entering the base of the crista and passing into the columnar cells, % ; b 4 Fic. 274. —Avpirory EPITHELIUM FROM THK MACULA ACUSTICA OF THE SACCULE OF AN ALLIGATOR. (Highly magnified.) ; C164 08 columnar hair-cells ; /, 7, fibre-cells ; n, nerve-fibre, losing its medullary sheath and ane te in the columnar auditory cells ; h, auditory hair; 2’, base of auditory hairs, ollie up into fibrils, 236 THE ESSENTIALS OF HISTOLOGY The cochlea consists of a bony tube coiled spirally around an axis, which is known as the columella (fig. 275). The tube is divided - longitudinally by a partition which is formed partly by a projecting Fic, 276.—VERTICAL SECTION OF THE FIRST TURN OF THE HUMAN COCHLEA. (Retzius.) 8.v. scala vestibuli; s.t. scala tympani; D.C. canal of the cochlea; sp.i. spiral lamina; m, nerve-fibres ; /.sp. spiral ligament ; s/7.v, stria vascularis ; s. sp. spiral groove ; R, section of Reissner’s membrane ; 7, limbus laminz spiralis; M.t. membrana tectoria; ¢.C. tunnel of “| Corti ; b.m. basilar membrane ; /.i., f.e., internal and external hair-cells. lamina of bone (spiral lamina), partly by a flat membrane (basilar Py membrane), into two parts or scale; the upper (supposing the cochlea resting base downwards) being termed the scala vestibuli (fig. 276, sv.) the tina nen mr iar | rippin wre va ; , by: a i tie wm < é a ae twit j 7 Pree’ acHs er # =) Fit aatnonh hd Sa Big = 2 As aus “ie Elec min a! e + + . a - 4 : " ‘ ant my i! Fy . ; : 4 et : 2 Pe A - > _ “tt | 2 ' ‘ ‘ i - : ve a j , 3 “! 4 x ; . \ 4 < ' , . ri ; 3 L y Z a . es 7 * , we _ - & te 4 tere c to i , J = or 4 | 1 7 ’ ' va 49 5 : iolf? erty ry 7.8 ; | a3 eters Eb we ere eet: | ‘ te Whe AVP {2 a. $ ae ig - << as i * ear . ace + ihe Oe oe | 4 “a wie 6 teva’ 2h, =tr¢ z is ‘ : ee ee yr ' @ ks . ‘ ‘ae . ti i all 4 a y AO Stay f beige (ett ar é hy ivi So enc ot al : — a j _ «STRUCTURE OF THE COCHLEA 237 | the lower the scala tympani (s.t.); the latter is closed at its larger end by the membrane of the fenestra rotunda. The scale are lined by endosteum, and are filled with perilymph, continuous with that of the L-- rest of the osseous labyrinth at the commencement of the scala vestibuli; they communicate at the apex by a small opening, the helicotrema. _ The scala vestibuli does not occupy the whole of that part of the bony tube of the cochlea which is above the partition. Its outer third is cut off by ‘a delicate connective-tissue membrane (membrane of Reissner, ; fig. 276, R), which. springs from near the end of the spiral lamina, and passes upwards and outwards to the outer wall, thus separating a canal (D C) triangular in section, which is lined by epithe- lium, and represents the membranous labyrinth of the cochlea (canal of the cochlea). | or Canal of the cochlea. The floor of the canal of the cochlea is formed (1) of the extremity of the spiral lamina, which is thickened above by a peculiar kind of connective tissue, forming an overhanging projection known as the limbus (fig. 276, 1) ; (2) of the basilar mem- brane (b.m.), which stretches across from the end of the bony lamina to the.outer wall, and is attached to this by a projection of reticular connective tissue termed the spiral ligament (I.sp.) The basilar membrane is composed of stiff, straight fibres, which extend from within out, and themselves rest on a homogeneous stratum. It is covered below by a layer of connective tissue continuous with the endosteum of the scala tympani ; above the modified epithelium which forms the organ of Corti rests upon it. It becomes gradually broader i in the upper turns of the cochlea (rather more than twice as broad in the uppermost as in the lowermost turn), and its constituent fibres become therefore gradually longer. _ The organ of Corti consists of the following structures : 1. The rods of Corti, two series (inner and outer) of stiff, striated fibres of a peculiar shape, the inner rods somewhat like a human ulna, the outer like a swan’s head and neck (fig. 277). They rest by one ex- tremity (the foot) on the basilar membrane a short distance apart, and Fic. 277.—A PAIR OF RODS OF CoRTI, FROM THE RABBIT’S COCHLEA, IN SIDE view. (Highly magnitied.) : b, b, basilar membrane; i.7. inner rod; e.7. outer rod. The nucleated protoplasmic masses at the feet are also shown. are inclined towards one another, their larger ends (heads) being jointed together ; the series of rods thus enclose a sort of tunnel, the floor of which is formed by a part of the basilar membrane. Close to their 238 THE ESSENTIALS OF HISTOLOGY feet may usually be seen the remainder of the cells from which they have been formed. The inner rods are narrower and rather more © numerous than the outer. Each outer rod has a process which extends outwards and is known as the phalangeal process. This forms part of— ; 2. A reticular lamina (fig. 279, l.7.), which is a cuticular structure extending like a wire-net over the outer epithelium-cells of the organ of Corti, and is composed of two or three series of stiff fiddle-shaped rings (phalanges) cemented together in such a manner as to leave. square or oblong apertures through which the hair-cells (see below) project. 8. The outer hair-cells placed external to the rods of Corti. These are epithelium-cells of columnar shape, arranged in three or four series Fic. 278.—SECTION OF THE ORGAN OF CoRTI OF THE DOG. £92 a, a’, end of spiral lamina; b, c, middle (homogeneous) layer of the basilar membrane; wu, ves- tibular (striated) layer; v, tympanal (connective-tissue) layer ; d, blood-vessel ; 7, nerves in spiral lamina; g, epithelium of spiral groove ; hf, nerve-fibres passing towards inner hair- cells, i, k; 1, auditory hairlets on inner hair-cells ; J, 7’, lamina reticularis ; m, heads of the rods of Corti, jointed together ; n, base of inner rods; 0, base of outer rod; p, gq, 7, outer hair-cells ; ¢, lower ends of hair-cells ; w, nerve-fibrils passing across the tunnel of Corti ; z, cells of Deiters. (fig. 278, p, g, v). The free extremity of the cell is surmounted by a bundle of short auditory hairs, and projects through one of the apertures in the reticular lamina; the fixed extremity is prolonged into a stiff cuticular process (fig. 280, pf), which is attached to the basilar membrane. Between them are other supporting cells which are tapered in the same manner, resting by theirlarger end upon the basilar membrane, and prolonged above into a cuticular process which is attached to the reticular lamina (cells of Deiters, fig. 278, z).- They are said by Waldeyer to be sometimes united with the outer hair-cells, so as to form double cells. . 4, The inner hair-cells (fig. 278, 7), placed internal to the rods of Wear ibe ch cosy ti o ™ er Osa. aie SNRs Ue ae u ie rf ; v ee hoes a 0) eee os ae. 4 eae urea tec abe, by, ce atin oy - ai ; pS - ; the me Hee fh, ¥ " + oe) owes wig tre’ ae ae Pitas 4 i eA le 7) a = 5 rw ‘ Wits 5 mL ' ne > 4 eon, abt weir te off ay Dav es i : | . by | eetahy a / oy ae L Ln t H 3 Pe au WY vtue aes! ‘ g: ot aa. at & SPR, - hele Dy Eye, aba: dé elt ' Od” peri iss 1% - ‘ite ert: er a aber latizk iq ‘bee in i 7 att. = STRUCTURE OF THE COCHLEA 239 Fig. 279. — SEMI-DIAGRAM- MATIC VIEW OF PART OF THE BASILAR MEMBRANE AND TUNNEL OF CORTI OF THE RABBIT, FROM ABOVE AND THE SIDE. (Much magnified.) ~ . limbus ; C7. extremity or crest of limbus with tooth-like pro- jections ; 6.0. basilar membrane; sp.l. spiral lamina with, p, perforations for transmission of nerve-fibres. In part of the spiral lamina here represented the nerve-fibres are left, and are supposed to be seen through the upper layer of that lamina, con- verging to three of the perfora- tions ; to the right, in the section of the lamina, they are shown occupying acanal, or cleft, in the osseous substance; i.7. fifteen of the inner rods of Corti; h.i. their flattened heads seen from above ; e.7. nine outer rods of Corti; h.e. their heads, with the phalangeal processes ex- tending outward from them and forming, with the two rows of phalanges, the lamina reticu- laris, 1.7. On the left of the figure the connective-tissue fibres and nuclei of the under- most layer of the basilar mem- brane are seen through the upper layers. Portions of the basilar processes of the outer hair-cells remain attached here and there to the membrane at this part. Fic. 280.—AN OUTER HAIR-CELL IN CONNECTION WITH ITS BASILAR PRocEss. From the guinea-pig. (Highly magnified.) 3 h, one or two hairlets which have remained attached to the cell ; 6, bulged lower end of cell; p, basilar process, protoplasmic above, but becoming cuticular below and slightly expanded at the extremity, 7, which is broken away from the basilar membrane. 240 ‘THE ESSENTIALS OF HISTOLOGY Corti. They form a single series of columnar cells surmounted by auditory hairs, lying in close apposition to the inner rods. , The rest of the epithelium-cells have no important characteristics. , —Ts.. They are long and columnar next the outer hair-cells, but soon diminish — 4 in size, becoming cubical, and in this form they are continued over — the outer wall of the cochlear canal. Here they cover a very vascular membrane (stria vascularis, fig. 276, str), which is frequently pigmented ; its capillary blood-vessels may even penetrate between the epithelium- cells. Internal to the inner hair-cells the epithelium also soon becomes cubical; it is prolonged in this form over the limbus of the spiral lamina. The epithelium of Reissner’s membrane is of the pavement variety. The membrana tectoria (fig. 276, M.t.) is a soft, fibrillated structure, which is attached along the upper surface of the limbus, and lies like a pad over the organ of Corti. It thins out towards the distal margin, here becoming somewhat reticular, and, according to Retzius, attached to the lamina reticularis. In sections it usually appears raised a short distance above the auditory hairs, but it is possible that it may rest upon them during life. Fic, 281.—GENERAL VIEW OF THE MODE OF DISTRIBUTION OF THE COCHLEAR NERVE, ALL THE OTHER PARTS HAVING BEEN REMOVED. The fibres of the cochlear branch of the auditory nerve enter the base of the columella, and run in canals through its substance, being gradually deflected outwards as they pass upwards into the spiral lamina, at the base of which they swell out into a ganglionic cord (spiral ganglion). After deeuvetinds the spiral lamina they emerge in bundles, and the fibres then, having lost their medullary sheath, pass into the epithe- lium of the inner hair-cell region. Here some of them are connected directly with the inner hair-cells, whilst others pass in the form of delicate fibrils across the tunnel of Corti, to become connected with the outer hair-cells (fig. 278). > =" es, wom -! bet eae at (We. « ARAL is aba ye + PWR 1) ae & l,l 6» belies ee ity asia o» 0 ie if ‘ i’ © «ode eee w Mi - etx “ Ard ta = ) Ay Biter t . n Nak é 2 ie — 4 y a5 Wie f Usha « <3), \ ee ? 40° prone “Sie Yaa prima Asp Se ae Po be ee ae ak Oy .* APPENDIX General Methods of Preserving and Hardening Tissues and Organs.'—The fluids which are most commonly used are alcohol, chromic acid solution (1 in 500), picric acid solution (saturated), bichromate of potash solution (2 per cent.), Miiller’s fluid (bichromate of potash 2} parts ; sulphate of soda 1 part; water 100 parts), and bichromate of ammonia (2 per cent.) The following are the methods of hardening the several tissues and organs which are found to give the best general results :— Tissue or Organ Bladder Blood-vessels Brain Elastic ligament Embryos | . . ‘ Eye . : ‘ Eyelids. : Ganglia . : Heart : Injected organs Intestine . . : . Kidney . : . Lachrymal gland ‘ ‘ Larynx . : ‘ . Liver Lung . Mammary gland Marrow of bone . Muscular tissue, striated . F. - non-striated Nerve ‘ : A (Esophagus > : Ovary ; Pancreas . Retina : Salivary glands. Sclerotic and cornea . Skin . a Methods of preparation required for special purposes are given in the Lessons. Hardening Fluid Chromic acid. Alcohol, or bichromate of potash. Bichromate of ammonia. Bichromate of potash. Chromic acid or picrie acid. Miiller’s fluid. Alcohol. Picric acid. Alcohol, or bichromate of potash. Alcohol. Distend with chromic acid. Bichromate of potash. Alcohol. Chromie acid. Bichromate of potash. Distend with chromic acid. Alcohol. Alcohol. Bichromate of potash. Chromic acid. Picric acid. Distend with chromic acid. Chromic acid. Alcohol. Miiller’s fluid. Aleohol. Alcohol, or Miiller’s fluid. Alcohol. R. 242 THE ESSENTIALS OF HISTOLOGY Tissue or Organ Hardening Fluid Spinal cord , an 1% . Bichromate of ammonia. Spleen. ; ; .". Bichromate of potash. Stomach . : ’ : . Distend with chromic acid or with alcohol. Suprarenal capsule . : . Alcohol. Tendon and ligament : - Alcohol. Testis ; : @ : . Alcohol. Thymus gland . ; ° . Alcohol. Thyroid gland . : ; - Alcohol. Tongue . ; A : . Bichromate of potash. Tonsils . : 3 é . Alcohol. Trachea . , . 2 . Chromic acid. Ureter : : i , . Chromic acid. Uterus > F < < . Chromic acid. Tissues to be hardened in alcohol may either be placed at once in strong spirit (90 per cent. alcohol), or the hardening may be effected gradually, the tissue being placed first in weak spirit (50 per cent.) for twenty-four hours, then in somewhat stronger, and finally in strong spirit or absolute alcohol. They are ready for cutting after having been twenty-four hours in strong spirit. For tissues that are to be hardened in } per cent. chromic acid, an immer- sion of from 7 to 14 days is generally necessary; they may then be washed with water, and placed in alcohol for preservation and to complete the pro- cess of hardening. Organs placed in bichromate of potash or Miiller’s fluid are ready for sections in a fortnight or three weeks; they may, however, be left for a much longer time in those fluids without deterioration. With picric acid the hardening process is generally complete in two or three days; the organs should then be washed for some hours under a tap and transferred to spirit. The hardening of the brain and spinal cord in bichromate of ammonia takes three or four weeks. These organs should not be left too long in the solution, since they are apt to become brittle, but sections should be prepared from them as soon as ready. In no case should the pieces of tissue to be hardened be too thick for the fluid readily to penetrate to every part. Embedding of Hardened Tissues, and Preparation of Sections.—Sections are most advantageously made with some form of microtome. It is generally needful to support the hardened tissue whilst it is being cut, and with this object it is embedded in some fatty or other substance which is applied to it in the fluid condition and becomes solid on standing. The embedding sub- stance can either simply enclose the tissue, or the tissue may be soaked in it: the latter method is the one most commonly employed. The embedding substance chiefly used is paraffin. Embedding in paraffin——Before being soaked in melted paraffin, the piece of tissue is stained with borax-carmine or hematoxylin, dehydrated by absolute alcohol, and is then soaked in turpentine. From turpentine it is transferred to melted paraffin, which should not be too hot, and soaked in this for an hour or more, according to thickness. It is then placed in any desired _ position in a paper tray or on the microtome and surrounded by melted - , is ’ , = ry i . j = e > 2 = ‘e >. al od * F = ‘ * h ss : “ ' . j 4 : ‘ 7 * ~ - . - - : i* : 7 +4 . vy °%t i net P 7 \ ee it 2 ' (tatty ; weeds a ‘ - ods > be a Sims ae nl ee ie LAM scdlg a is = ae |e: vein ale Oe ». ( Saee rf ashavie Bi re Varo. % per 1 bie Zz ' ; > tlhe ane aig : : i aie) Je at ah | r 7 : Che ay \< : . c Ute Wowk Gan de i, i192, > i! rar ily eth , Me Se alae, ay y + r ie pehee dig 1 Uf ee Nye d, i lolnks caceyis mambo ee ee ee “pond slave! pa” i pupaiies, Re ey Ps he, ; 4 . 'S -*% ea 9 godt or > i ogee | ? a oh. o/) iY ° ere 4 * +\- Z APPENDIX 243 paratiin. When cold, thin sections can be cut, the paraffin dissolved out. by turpentine, and the sections mounted. Preparation of frozen sections.—The bichromate solutions are the best } fluids to use for preserving tissues which are to be frozen in place of being: ; embedded. The tissue in such cases,should not be put into alcohol, but merely requires to be dipped in strong gum before being placed upon the freezing microtomé. Portions of the central nervous system need to be soaked in gum to which a little syrup has been added. Staining and mounting of sections.—The fluids most commonly employed for the staining of sections are :—1. A dilute watery solution of hematoxylin - and alum; 2. A solution of carmine; 3. A solution of picro-carminate of am- monia. The time of immersion in the staining fluid varies according to the strength of the fluid and the mode by which the tissue has been hardened. The necessity of staining sections may be avoided if the piece of tissue -is stained in bulk before embedding. For this purpose a carmine solution is mostly used, on account of its penetrative power, that known as borax-carmine being the best. The tissue must be left in it for twenty-four hours or more, and then placed in acidulated alcohol. An alcoholic solution of magenta can be used for staining in bulk; from this the tissue goes into a small quantity of oil of cloves or into turpentine, and, after being soaked with this, into the melted paraffin. Q ; If the tissues have not been stained in bulk, the following is the order of transference of the sections (they are supposed, if cut from paraffin, to have been freed from this by immersion in turpentine) :— . From turpentine to absolute alcohol (5 minutes). . From alcohol to distilled water (4 minute). . From distilled water to hematoxylin or carmine (5 minutes or more). . From hematoxylin to distilled water ($ minute). . From distilled water to alcohol (2 or 3 minutes). - From alcohol to oil of cloves (1 minute). . From oil of cloves to Canada balsam. AA or wD If the tissues have already been stained in bulk, the sections are simply mounted in Canada balsam after the paraffin used for embedding has been dissolved away from them in turpentine. Creosote-shellac method of mounting.—Friable sections, such as sections of small embryos, and ribands of sections such as are cut with many micro- tomes, are mounted in the following way :—The slide is smeared with a solu- tion of shellac in creosote, the sections are placed in this and warmed so as to melt their paraffin. They are thus fixed by the shellac, and the slide can be immersed in turpentine to remove the paraffin, and the sections then covered in Canada balsam. For this method the tissue should always have been pre- viously stained in bulk. Solutions employed for Staining :—1. Solution of hematoxylin in water.— ‘Rub together in a mortar 10 grammes of powdered alum and 5 grammes of extract of hematoxylin with 25 cubic centimeters of 70 per cent. alcohol, gradually adding 100 cubic centimeters of distilled water. Decant into a bottle and add a drop or two of ammonia. Let the mixture stand a few days, occasionally shaking it. For staining, add two or three drops to a watch-glass full of distilled water, and filter if necessary. _ 2. Grenacher’s hematoxylin.—To 150 cubic centimeters of a saturated 244 THE ESSENTIALS OF HISTOLOGY solution of alum in water, add 4 cubic centimeters of saturated solution of hematoxylin in alcohol. Let the mixture stand 8 days, then decant, and add 25 cubic centimeters of glycerine, and 25 cubic centimeters of methylic alcohol. 8. Kleinenberg’s hematoxylin.—This, serves better for staining in bulk. Saturate 70 per cent. alcohol first with calcium chloride and then with alum, and after filtration add six to eight volumes of 70 per cent. alcohol. Take a freshly prepared saturated solution of hematoxylin in absolute alcohol, and add it drop by drop to the above mixture until it is of a distinct purplish colour. . This solution improves on keeping. It may if necessary be diluted with more of the mixture. When hematoxylin solutions become red instead of blue, a trace of ammonia will restore the requisite colour. 4. Carminate of ammonia.—Prepared by dissolving carmine in ammonia and allowing the excess of ammonia to escape by slow evaporation. The salt should be allowed to dry and be dissolved in water as required. 5. Picro-carminate of ammonia (picro-carmine).—To a saturated solution of picricacid add a strong ammoniacal solution of carmine, until a precipitate begins to form. Evaporate on the water-bath to ith; filter from the sedi- ment and evaporate the filtrate to dryness. Make a 5 per cent. solution of | the residue, diluting further as required. 6. Borax-carmine.—a. Dissolve 4 grammes borax and 3 grammes carmine in 100 cubic centimeters of warm water. Add 100 cubic centimeters of 70 per cent. alcohol, filter and let stand. This solution improves on keep- ing. It is useful for staining in bulk. 8. Boil 0°5 gramme carmine and 1 gramme borax in 100 cubic centi- meters water. Filter and add acetic acid drop by drop until the original violet colour becomes crimson; then filter once more. This solution is used for staining sections. After staining with borax-carmine, the tissue should in all cases be placed in 70 per cent. alcohol containing 5 drops of hydrochloric acid to 100 cubic centimeters. 7. Magenta.—This may be kept in solution in alcohol (0°5 to 1 per cent.) For fresh tissues and for sections to be mounted in glycerine, an excellent staining fluid is obtained by adding one or two drops toa watch-glass of water. For sections to be mounted in Canada balsam a solution in oil of cloves is used. This is best made by adding a drop of the alcoholic solution to a little oil of cloves in a watch-glass: the sections after being stained are washed in spirit of turpentine. 8. Gentian violet.—Mix 20 cubic centimeters water with 10 cubic centi- meters alcohol and 10 cubic centimeters glycerine, and add to the mixture 10 drops of a 1 per cent. solution of gentian violet in alcohol and 10 drops of a 25 per cent. solution of formic acid in water. This solution gives excellent results with fresh tissues, especially with epithelium. 9. Safranin.—A saturated alcoholic solution is used for staining cell- nuclei. The tissue elements having been fixed by dilute chromic acid or by alcohol, small shreds or thin sections are placed for 12 to 24 hours in a little of the solution, mixed with half its bulk of water. The shreds are rinsed in absolute alcohol (which must contain no trace of free acid) until the colour is ——. £ oy a mea : ‘ rk ek . j = * Tis sags » ee? 2 net Pe ~ aoe ae ' ‘ , 5 “ ory, My ie: 2 ra, Sb, tied TT | : : oe fe Desh J \ 2aall arede or ; iy’ —- -—_=.-- APPENDIX : 245 washed out from-everything except the nuclei; they are then at once trans- ferred to turpentine, and from this are mounted in Canada balsam. 10. Aniline blue-black.—Dissolve 1 gramme of aniline blue-black in a mixture of 30 parts of water with 20 of alcohol. This serves for staining the central nervous system either in bulk er in sections. 11. Staining with chloride of gold.—a. Cohnheim’s method.—Place the fresh tissue for from 30 to 60 minutes in } per cent. solution of chloride of gold; then wash and transfer to a large quantity of water just acidulated with acetic acid. Keep for 2 or 3 days in the light in a warm place. B. Léwit’s method.—Place small pieces of the fresh tissue in a mixture of 1 part of formic acid to 2 to 4 parts of water for 4 to 1 minute; then in 1 per cent. chloride of gold solution for 10 to 15 minutes; then back again into the formic acid mixture for 24 hours and then into pure formic acid for 24 hours more. After removal from the gold, and whilst in the acid, the tissue must be kept in the dark. y. Ranwier’s method.—Immertse in lemon-juice for 5 to 10 minutes, then wash with water and place in 1 per cent. gold chloride solution for 20 minutes. Then treat either as in Cohnheim’s or in Léwit’s method. 12. Staining with nitrate of silver.—Wash the fresh tissue with distilled water; immerse in } to 1 per cent. nitrate of silver solution for 5 to 10 minutes ; rinse with distilled water and expose to bright sunlight either in water, alcohol, or glycerine. Mounting Solutions :—1. Saline solution.—A 0°6 per cent. solution of common salt is used in place of serum for mounting fresh tissues for imme- diate examination. 2. A mixture of glycerine and water in equal parts. 3. Farrant’s solution.—Take a mixture of equal parts of glycerine and saturated watery solution of arsenious acid, and stir gum arabic with it until a thick syrupy fluid is formed. Filter. 4. Canada balsam, from which the volatile oils have been driven off by heat, dissolved in benzole. LONDON: PRINTED BY SPOTTISWOODE AND CO., NEW-STREET. SQUARE AND PARLIAMENT STREET STANDARD MEDICAL AND SURGICAL BOOKS. = ra Kighth Edition. ERICHSEN’S SCIENCE AND ART OF SURGERY. Being a Treatise on Surgical Injuries, Diseases, and Operations. By Joun Enric - Enricusen, F.R.C.S.; Surgeon Extraordinary to H.M. 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