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Ma rif ean Ai, hte) Ler] ene ’ Mh itd WAM AES Crier vit} Venaneay ’ ed iW aft ; ' a fo Maaiol ty O ‘ nf 44 BUDE bem Han gh op Seed au tebe pe A What ith ihe > " 4 3 ‘ ‘ Hts . i oath etree ity} Hite ses ae phe hr At SNe iSivie a" i if iH ‘ - * tee ’ et ascny SDE Hea big) ” Pies Be i NA yy Net secdiy oe tat spb (eet i SRE bert) ' 4) 2 wt esto me aria) f ‘ ih) ‘ "YL toady ‘ ' VMestt ora bye Pe ibehige ; sete t ¢ 4) nuige pr i VAY Nl i jae ' ' AS i> Digitized by the Internet Archive in 2008 with funding from Microsoft Corporation http://www.archive.org/details/alligatoritsallOOreesuoft i Kuvduro9 2 adeg ‘Arpatqnod Aq *4o06r ysuddog a The Alligator and Its Allies By Albert M’’ Reese, Ph.D. Professor of Zoology in West Virginia University Author of ‘‘ An Introduction to Vertebrate Embryology ’’ With 62 Figures and 28 Plates G. P. Putnam’s Sons New York and London Tbe Knickerbocker Press I9I5 CopyRIGHT, I915 BY ALBERT M. REESE The Knickerbocker Press, Hew Work PREFACE HE purpose of this volume is to bring together, in convenient form for the use of students of zodlogy, some of the more important details of the biology, anatomy, and development of the Crocodilia. For obvious reasons the American Alligator is the species chiefly used. In the first chapter the discussion of the alligator is largely the result of the personal observations of the author; the facts in regard to the less familiar forms are taken from Ditmars and others. The description of the skeleton, with the exception of short quotations from Reynolds, is the author’s. The chapter on the muscular system is a trans- lation from Bronn’s Thierreich, and the author has not verified the descriptions of that writer. The description of the nervous system is partly the author’s and partly taken from Bronn and others. The chapters on the digestive, urogenital, respiratory, and vascular systems are practically all from descriptions by the author. The chapter on “The Development of the Alligator” is a reprint, with slight alterations, of the paper of that title published for the author by the Smithsonian Institution. iii iv Preface The bibliography, while not complete, will be found to contain most of the important works dealing with this group of reptiles. The author is grateful to Mr. Raymond L. Ditmars and to his publishers, Messrs. Doubleday, Page & Co., and Messrs. Sturgis & Walton, for the use of a number of plates; to the Macmillan Company and to the United States Bureau of Fish and Fisheries for the same privilege; to the National Museum for photographs of the skull of the gavial; and to the Smithsonian Institution for the use of the plates from researches published by them and included herein. . Proper acknowledgment is made, under each borrowed figure, to the author from whom it is taken. MorGANtTown, W. Va. May 1, 1915. CONTENTS PAGE CHAPTER I THE BIOLOGY OF THE CROCODILIA . ; ‘ F I CHAPTER II THE SKELETON : : : : ; Bare: CHAPTER III THE MUSCLES . : : é : ; . “90 CHAPTER IV THE NERVOUS SYSTEM J ; : BWR Pol CHAPTER Vi THE DIGESTIVE SYSTEM ; : , : ee 16) CHAPTER VI THE UROGENITAL SYSTEM . : = ; fms 6, CHAPTER VII THE RESPIRATORY SYSTEM . : : : e107 CHAPTER VIII THE VASCULAR SYSTEM : , 4 : ae 2OE CHAPTER IX THE DEVELOPMENT OF THE ALLIGATOR ; ses BIBLIOGRAPHY : ‘ ; : : = 343 INDEX : é : ; : 3 5 #349 ILLUSTRATIONS ALLIGATOR MIssIssIPPIENSIs. (In color.) Frontispiece FIGURE al) Tr ENP ie eee, SKULL OF BELODON : : ; 5 Map SHOWING THE PRESENT DISTRIBUTION OF CROCODILIA 6 HEADS OF AMERICAN ALLIGATOR AND CROCO- DIEER) . s ' : . Facing 7 ALLIGATOR JOE IN THE EVERGLADES . ee AO ALLIGATOR HUNTER IN THE OKEFINOKEE tO NEsT OF C. PoROsuS 21 JACKSON SLOUGH . gt A TYPICAL ALLIGATOR HOLE. mee ALLIGATOR NEsT, MADE CHIEFLY OF GRAss . “ 25 ALLIGATOR Nest, MADE CHIEFLY OF FLAGS . “ 27 Two SPECIES OF CAIMAN : : ‘ 35 Two AFRICAN CROCODILES . : ; eee SALT WATER CROCODILE ; : : Regi at SKULL OF GAVIAL, VENTRAL VIEW : Ameer SKULL OF GAVIAL, LATERAL VIEW : Sige ie) Vii PAGE viii Illustrations FIGURE PAGE 15. ALLIGATOR SKINS . : : : . Facing 46 16. ENTIRE SKELETON OF CROCODILE . : se 50 17. First Four CERVICAL VERTEBRA OF CROcO- DILE- -; : . ; ‘ A . == 52 18. THORACIC AND SACRAL VERTEBR OF CROCO- DILE : é , : : : : 55 19. DorsaL VIEW OF SKULL OF ALLIGATOR Facing 60 20. VENTRAL VIEW OF SKULL OF ALLIGATOR SOs 20, A. LONGITUDINAL SECTION OF TOOTH OF CROCODILE. : E f ; 5 eo 21. LATERAL VIEW OF SKULL OF ALLIGATOR ; 69 22. POSTERIOR VIEW OF SKULL OF ALLIGATOR Facing 70 23. SAGITTAL SECTION OF THE SKULL OF ALLIGATOR 71 24. DorsaL VIEW OF LOWER JAW OF ALLIGATOR Facing 74 25. THE Hyorp APPARATUS ; : : Re 26. THE STERNUM AND THE ASSOCIATED MEM- BRANE BONES i , , : ‘ 79 27. THE PECTORAL GIRDLE AND ANTERIOR LIMB 82 28. THE PELVIS AND SACRUM , : = 85 29. THE POSTERIOR LIMB . é ; 5 sa, PiaTE I. THE SHOULDER MUSCLES = . <2 tZ0 PLateE II. Tue MuscLES OF THE ANTERIOR REGION : : ‘ . Following 130 FIGURE 30. Bi. a2. 33. 34. 35. BO: 37: 38. 39. 40. an Illustrations PLATE III. THe MUSCLES OF THE POSTERIOR REGION : . : . Following PLATE IV. THE MUSCLES OF THE POSTERIOR REGION : : : . Following PLATE V. THE MUSCLES OF THE POSTERIOR REGION : s : . Following THE BRAIN OF THE ALLIGATOR. . Facing ‘Tee BRACHIAL, Prexus or C. AcuTUS THE CRURAL PLEXUS OF A. MISSISSIPPIENSIS INTERIOR OF THE MOUTH OF THE ALLIGATOR. Facing THE DIGESTIVE SYSTEM OF THE ALLIGATOR OUTLINE OF THE DIGESTIVE TRACT OF THE ALLIGATOR COVERING OF THE ANTERIOR REGION OF THE TONGUE COVERING OF THE POSTERIOR REGION OF THE TONGUE GLAND FROM THE POSTERIOR REGION OF THE TONGUE GLAND FROM THE POSTERIOR REGION OF THE TONGUE , é A ‘ é 3 COVERING OF THE ROOF OF THE MOUTH ° TRANSSECTION OF THE ANTERIOR REGION OF THE (2SOPHAGUS PAGE 130 160 161 166 169 x FIGURE 42. 43. 44. 45: 46. 47. 48. 49. 50. 51. Illustrations TRANSSECTION OF THE POSTERIOR REGION OF THE ‘CGESOPHAGUS . x . = : EPITHELIUM OF ANTERIOR REGION OF CESOPHA- GUS : i : . ; 4 : EPITHELIUM OF ANTERIOR REGION OF CESOPHA- GUS TRANSSECTION OF WALL OF PYLORIC STOMACH GLANDS OF FUNDUS OF STOMACH TRANSSECTION OF WALL OF ANTERIOR REGION OF SMALL INTESTINE TRANSSECTION OF WALL OF MIDDLE REGION OF SMALL INTESTINE TRANSSECTION OF WALL OF POSTERIOR REGION OF SMALL INTESTINE Mucosa OF THE ANTERIOR REGION OF SMALL INTESTINE TRANSSECTION OF THE WALL OF THE MIDDLE REGION OF THE SMALL INTESTINE TRANSSECTION OF THE WALL OF THE ANTERIOR REGION OF THE RECTUM EPITHELIUM OF THE ANTERIOR REGION OF THE RECTUM FEMALE UROGENITAL SYSTEM OF ALLIGATOR . MALE UROGENITAL SysTEM OF ALLIGATOR Facing MALE ORGAN OF ALLIGATOR : : " PAGE 170 172 173 176 177 181 182 184 185 186 187 193 195 195 FIGURE 57: 58. 59- 60. 61. 62. Illustrations xi RESPIRATORY ORGANS OF ALLIGATOR . Pros HEART OF ALLIGATOR . : : . Facing 202 VEINS OF THE POSTERIOR REGION OF ALLI- GATOR . i : : F ; « 204 VEINS OF THE ANTERIOR REGION OF THE ALLI- GATOR. 4 ; ; ‘ : i S208 ARTERIES OF THE POSTERIOR REGION OF THE ALLIGATOR . , ; : ei POTS ARTERIES OF THE ANTERIOR REGION OF THE ALLIGATOR . ' : : 3 72 DS PLATES VI TO XXVIII. A SERIES OF FIGURES TO ILLUSTRATE THE DEVELOPMENT OF THE AMERICAN ALLIGATOR . . Following 342 mMHE ALLIGATOR AND ITS ALLIES CHAPTER I THE BIOLOGY OF THE CROCODILIA CLASSIFICATION siderable difference of opinion as to the proper classification of the Crocodilia. One of the older textbooks (Claus and Sedgwick) divides the order Crocodilia into three sub-orders: the Teleosauria, Steneosauria, and Procelia, the last only being represented by living forms. The Proccelia or Crocodilia proper are divided into three families,—the Crocodilide, the Alligatoride (including the caiman as well as the alligator), and the Gavialide. This division into families seems to be based mainly on the shape of the head, or, at any rate, it throws those forms together that have heads of the same outline. A © in most groups of animals, there is con- I 2 The Alligator and Its Allies It is this outline of the head that Ditmars (Rep- tiles of the World) uses in classifying the Crocodilia, which, he says, are all included in the single family —Crocodilide. The following list, taken from his Reptiles of the World (pp. 68-69), will give a clear idea of the number, distribution, and maximum size of the members of the order Crocodilia. More will be said of some of the members of this list later. . Max. Habitat Size A. Snout extremely long and slender, extend- ing from the head like the handle of a fry- ing pan Gavialis gangeticus, Indian Gavial Northern India 30 ft. Tomistoma schlegeli, Malayan Gavial Borneo and Sumatra 15 ft. B. Snout very sharp and slender; of trian- gular outline Crocodilus cataphractus, Sharp-nosed Croco- dile W. Africa 12 ft. Crocodilus johnstoni, Australian Crocodile Australia 6-8 ft. Crocodilus intermedius, Orinoco Crocodile Venezuela 12 it. C. Snout moderately sharp; outline dis- tinctly triangular Crocodilus americanus, American Crocodile | Fla.; Mexico; Central and S. America rashes Crocodilus siamensis, Siamese Crocodile Siam; Java Toit Crocodilus niloticus, Nile Crocodile Africa generally] 16 ft. Crocodilus porosus, Salt-water Crocodile India and Malasia 20 ft. D. Snout more oval; bluntly triangular Crocodilus robustus, Madagascar Crocodile Madagascar 30 ft. Crocodilus rhombiferus, Cuban Crocodile Cuba only 7 giles Crocodilus moreletti, Guatemala Crocodile Guatemala; Honduras 7fsitte The Biology of the Crocodilia 3 Habitat Sieg 1Z€ E. Snout short and broad; conformation barely suggesting a triangular outline _ Crocodilus palustris, Swamp Crocodile India and Malasia 12 ft. _Osteolemus tetrapis, Broad-nosed Crocodile W. Africa (5) bitte D’. Outline of head similar to that of Section Caiman trigonotus, Rough-backed Caiman |Upper Amazon] 6 ft. Caiman sclerops, Spectacled Caiman Central and S. America 7-8 ft. Caiman palpebrosus, Banded Caiman Tropical South America 7-8 it. F. Snout very broad; bluntly rounded at tip Caiman latirostris,s Round-nosed Caiman |Tropical South America 7-8 ft. “Caiman niger,? Black Caiman Tropical South America 20 ft.? Alligator mississippiensis, American Alligator} Southeastern United States LG) its Alligator sinensis, Chinese Alligator China 6 ft. Gadow in the Cambridge Natural History (p. 450) agrees with Boulanger in believing that the recent Crocodilia cannot be separated into different families, yet he describes seven families of Croco- dilia, two of which, the Gavialide and Crocodilide, include the living members of the order; the former includes the gavials, of course, and the latter the crocodiles, alligators, and caimans. Though ‘doctors disagree’’ thus in regard to the scientific classification of this small group of «These species are exceptions in their genus. The snout is blunt like that of the genus Alligator. 2 Alleged to grow to this size by competent observers, 4 The Alligator and Its Allies animals, this fact does not in the least diminish the intense interest in the individual members of the order. ANCESTRY Although the huge dragon-like dinosaurs or “terrible reptiles,’’ some of which were probably more than one hundred feet long, became extinct during the Mesozoic epoch, perhaps millions of years before man made his appearance upon earth, we have one group of reptiles still living in certain parts of the earth of which the Mesozoic lords of creation need not feel ashamed. While most of the living Crocodilia are mere pigmies in size, compared to the Atlantosaurus, there are a few representatives of the living group, to be discussed later, that are said to reach a length of thirty feet, which length makes pigmies, in turn, of most of the other living reptiles. Considering the extinct as well as the living Crocodilia, Gadow says it is very difficult to sepa- rate them from the Dinosauria. In the Mesozoic Crocodilia the fore limbs were much shorter and weaker than the hind limbs, as was often the case with the dinosaurs; they were almost entirely marine, but gave indications of descent from ter- restrial forms. Various facts point, thinks Gadow, ‘to some Theropodous Dinosaurian stock of which the Croc- The Biology of the Crocodilia 5 odilia may well form an aquatic, further developed branch” (Cambridge Natural History, p. 432). Aa Se CrP O COU Oo-& Skull of Belodon. A, from above: B, from below. A, orbit: Bo, basi-occipital; Ch, internal nares; D, pre-orbital fossa; Exo. exocci- pital; Fr. frontal; Ju. jugal; La. lacrymal; Mx. maxilla; Na. nasal; Pa. parietal; Pl. palatine; Pmx. pre-maxilla; Por. post-orbital; Prf. pre-frontal; Pt. pterygoid; Qu. quadrate; S, lateral temporal fossa; S’, superior temporal fossa; Sq. squamosal; Vo. vomer. (From Zittel.) Fic. A. A TRIAssic ANCESTOR OF THE CROCODILIA. From Parker & Haswell, Textbook of Zoélogy. The direct ancestors of the Crocodilia, Gadow Says, are still unknown. 6 The Alligator and Its Allies GEOGRAPHICAL DISTRIBUTION As will be seen by examination of the table (p. 2) from Ditmars, and of Figure 1, the recent / AS =e == crocooices. lilllilaLLicaTORS, Fic. 1. Map SHOWING PRESENT DISTRIBUTION OF CROCODILIA. (After Gadow.) Crocodilia are found in all of the great continen- tal areas except Europe; mainly in the tropical or subtropical regions. The alligator is found in the southwestern United States and in China. The crocodile is the most numerous in species and is the most widely distributed of the group. It is especially characteristic of Africa and Mada- gascar, but is found also in Florida, Mexico, Cen- tral and South America, the West Indies, South Asia, the East Indies, and Australia. The gavial is found in India and some of the is- lands of the Orient, especially Borneo and Sumatra. The caiman occurs in southern Mexico, Central and South America. Fic. 2. HEADS OF AMERICAN ALLIGATOR AND AMERICAN CROCODILE; ALLIGATOR ON LEFT. (After Ditmars.) (Reproduced by Permission of Sturgis & Walton Co.) The Biology of the Crocodilia Fs The distribution of individual forms will be mentioned again when they are discussed in detail. ALLIGATOR MISSISSIPPIENSIS Since this animal, generally known as the American or the Florida alligator (formerly A. lucius), is the one upon which most of the facts of this book are based, it will be discussed first. At this point it may be well to answer the ques- tion that is sure to be asked by someone early in any conversation upon the Crocodilia. The writer, and doubtless every other zodlogist, has been asked countless times, ‘‘What is the difference between an alligator and a crocodile?’’ As a matter of fact there is, perhaps, no absolute distinction be- tween the two groups, but there are certain fea- tures that make it easy to distinguish, say, between the American alligator and the American crocodile. The most striking difference is in the outline of the head; the alligator has a broad, rounded snout, while that of the crocodile is narrower and more pointed (Fig. 2). Again, in the crocodile the - fourth tooth from the front projects slightly out- wards and fits into a notch in the side of the upper jaw, while in the alligator (also in the caiman) the corresponding tooth on each side fits into a socket in the upper jaw and hence is hidden, except in some old animals with very long teeth, in which it may pierce the upper jaw and show from above, 8 The Alligator and Its Allies According to Ditmars, the crocodile has, as a rule, larger and more exposed teeth than the alligator. Finally, as will be brought out later, the crocodile is usually more quick and active, and also more vicious, than the alligator. Very young alligators are nearly black, with distinct, yellow cross bands; as they grow older these markings become less distinct until in ma- turity the animals are of a uniform gray or dirty black color. Habitat. The American alligator is found in the rivers and swamps of the Southern States, from the southern part of North Carolina to the Rio Grande, though Florida is usually thought of as being the region in which they particularly abound. Years ago, before the rifle of the ubiquitous tourist and so-called sportsman had gotten in its deadly work, the alligators were probably very abundant in the Southern States; but they have been so ruthlessly destroyed by native hunters for their skins, and by others for mere wanton sport, that one may travel, perhaps, for days along the rivers of the South without seeing a single ’gator. The account quoted by Clarke from Bartram’s travels of more than one hundred years ago, while probably exaggerated, gives an idea of the abun- dance of the alligators at that time: ‘‘The rivers at this place from shore to shore, and perhaps near a half mile above and below me, appeared to be one solid bank of fish of various kinds, push- The Biology of the Crocodilia 9 ing through the narrow pass of San Juans into the little lake on their return down the river, and the alligators were in such incredible numbers, and so close together from shore to shore, that it would have been easy to have walked across their heads, had the animals been harmless.’’ At the present time it is usually necessary to travel far from the usual routes of the Northern tourists to find alli- gators in any abundance. At Palm Beach, Florida, lived, a few years ago, and probably still lives, a well-known hunter and guide, ‘Alligator Joe.”’ Just what nationality he may be is difficult to determine, but that he knows that trackless waste, the Everglades, at least in the region of Palm Beach, is evident. He has an alligator farm’’ near the great hotels of that famous winter resort, at which he keeps, or did a few years ago, a large number of alligators of all sizes, as well as a number of crocodiles. For a consideration (by no means a modest one) he would take out a party of tourists for a day into the Everglades, guaranteeing that he would find an alligator for them to shoot. It was rumored by the natives that an accomplice was always sent ahead to free the alligator at the psychological moment, after the hunters had been paddled by a devious course to the selected spot, but whether this were true or not the writer was not able to determine. It is true, however, that he and the writer paddled in a rather graceful canoe, dug out 10 The Alligator and Its Allies of a single cypress log, and waded through the Everglades for several days, searching for alligator eggs, and that we found only one nest and saw only one or two alligators (Fig. 3). Doubtless in more remote parts of the Ever- glades the alligators are much more numerous. During another summer the writer, with a guide, penetrated the very center of the State, to the region southeast of Lake Kissimmee, forty miles from the nearest railroad; here the alligators, and in consequence their nests, are fairly abundant, though the native hunters are, even in this remote region, rapidly thinning their ranks. A still greater number of alligators was found, the following summer, in the Okefinokee Swamp in southern Georgia. In the center of this great waste, ten miles or more from dry land, nearly one hundred alligators, ranging from about four to eight feet in length, were killed within a week by a small party of native hunters with whom the writer was traveling (Fig. 4). Whether this wholesale destruction by sports- man and native hunter will eventually exterminate our giant reptile, as has been the case with the buffalo and other game animals, it is impossible tosay. Unless the Everglades and the Okefinokee are largely drained it seems probable that a few alligators will always remain in the most inacces- sible regions. The collection of eggs for sale and for hatching Fic. 3. ALLIGATOR JOE IN THE EVERGLADES. (From a Photograph by the Author.) Fic. 4. ALLIGATOR HUNTER IN THE OKEFINOKEE,. (From a Photograph by the Author.) The Biology of the Crocodilia 11 purposes, as well as their destruction for food by bears and other animals, will also tend towards the annihilation of the species in the course of time. The economic importance of the alligator will be discussed later. While in the old days, as has been said, the alli- gator was common in the larger rivers and lakes, and may even have ventured short distances into salt water, he must now frequently be satisfied to fide his great body in a “’gator hole” that is scarcely more than a puddle. These “holes” (Fig. 7) are common in central Florida and are sometimes scarcely large enough to allow the alli- gator to dive into them to seek the underground cave in which he hides. It is on the edge of such a hole that the nest is built, as will be described later. Often from a small swamp or slough alligator “trails’’ lead off in different directions. These trails are narrow, winding gullies such as might be made by cattle in a damp pasture. If followed from the main slough the trail will usually be found to end in a “‘hole,” in which an alligator will probably be found (Fig. 7). Ina great swamp like the Everglades or the Okefinokee such holes would naturally not be found. On one side of the hole is usually a smooth place where the vegetation is worn away; it is here that the ‘gator ‘“‘pulls out” to sleep in the sun; and wary must the hunter be to approach within sight 12 The Alligator and Its Allies of the animal before being seen or heard by him. At the first alarm he slides quietly or plunges quickly into the muddy water, and the hunter must wait long if he expects to see the ’gator come to the surface. The opening of the cave is always below the surface of the water, but it is possible that there may be a subterranean chamber that is not com- pletely filled with water. How the animal is gotten from his cave will be described later. Ac- cording to some writers the alligator retires to his cave to hibernate during the cooler winter months. This is possibly true in the more northerly limits of his range. It is well known that if kept in cool water the alligator will lie dormant and refuse all food for months at a time. The writer has had young alligators in captivity, under these condi- tions, that refused food from late in the autumn until nearly the first of April. The proprietor of one of the largest alligator farms in the country says: ‘‘Our alligators stop eating the first week in October and do not begin to eat until the latter part of April. We have experimented with our stock to see if we could get them to eat in the winter, and found that by keep- ing the water in the tanks at a certain temperature they would eat, but we found out that the warm water would make their bowels move, and that they would not eat enough to keep themselves up, as in the summer, and as a result they would be- The Biology of the Crocodilia 13 come very poor and thin, so we do not force them to eat any more.” The effect upon the growth of an animal of these two methods of feeding will be noted later when the age and rate of growth are discussed. The same writer says, in answer to a question about hibernation: “‘In their wild state they go into their dens under water and remain dormant all winter.’’ Whether this statement is the result of actual observation the writer is not able to say, but, judging by some other statements from the same source, it is probably from hear- ‘say. The writer, having visited the alligator haunts only in late spring and summer, has had no oppor- tunity of studying the habits of the animal in its natural habitat during the winter season. During the heat of summer the animal does not seek the sun as he is said to do during cooler weather, but spends more time on the bank at night and during the cooler parts of the day. That he sometimes wanders over dry land, per- haps going from hole to hole, is evident from the tracks that are sometimes seen crossing a dusty road or path. These trails are easily recognized by the clawed footprints with a line, made by the dragging tail, between them. Although most awkward on land, he can, if necessary, move very quickly. It is, however, in the water that he shows to best advantage; he is an active, power- ful swimmer, his tail being used as a propeller as in the fishes. When swimming actively the legs 14 The Alligator and Its Allies are held close against the body in order that they may retard the animal’s motion as little as possible. While swimming in a leisurely way the top of the head is at the surface of the water, perhaps just the nostrils and eyes projecting above the surface, so that the size of the animal can be estimated by the distance between these projecting points. One afternoon the writer and a guide, while paddling along an old canal that was dug years ago into the Okefinokee Swamp, were preceded for perhaps half a mile by a large alligator that swam just fast enough to keep out of our reach until he came to the place where he wanted to turn off into the swamp. Although so awkward on land, the alligator is said to be able to defend himself very effectively with his tail, which he sweeps from side to side with sufficient force, in the case of a large specimen, to knock a man off his feet. Although the writer has seen captured and helped to capture alive several alligators up to eight feet in length he has never seen this vigorous use of the tail as a weapon of defense. While the alligator, like most other wild animals, will doubtless defend itself when cornered, it will always flee from man if possible, and the writer has frequently waded and swam in ponds and lakes where alligators lived without the least fear of attack. This might not have been possible years ago when the animals were more numerous and had not been intimidated by man and his weapons. The Biology of the Crocodilia He Food. The food of the adult alligator consists of fishes, birds, mammals, and possibly smaller individuals of its own species. The young eat small fish, frogs, insects, or worms. If the animal be too large to swallow whole it is shaken and torn, the shaking being so vigorous that, according to Ditmars, the entrails of the prey may be thrown to a distance of twenty feet or more. Should two alligators seize the same prey at the same time they whirl about in opposite directions so violently that the prey is torn apart. This action may be illustrated by giving two small captive alligators a piece of tough meat; they hold on with bulldog tenacity, and each, folding its legs close to its body, will use its tail like a propeller until the animal whirls around with remarkable speed. The commotion that two ten-foot alli- gators would cause when thus struggling can easily be imagined. That a large alligator, if it tried, could easily drag under the water and drown a man or possibly a much larger animal is evident. While the alligator has a valve-like fold of skin in its throat that enables it to open its mouth and crush its prey under water, it is said that it must raise its head above water in order to swallow its food. A young alligator on land will usually throw back its head when trying to swallow a large piece of meat, so that it may be simply this motion that brings the head of the alligator above the surface of the water. 16 The Alligator and Its Allies Ditmars thus describes the fate of a dog that approached too near a very large alligator: “As a dog, weighing about fifty pounds, unwarily ap- proached the edge of this creature’s tank, it was suddenly grasped and before completing its first yelp of terror was dragged beneath the surface. A few minutes later the twelve-foot saurian appeared at the top, holding the dead canine in its jaws. The dog was shifted about, amid the sound of breaking bones, and swallowed head first, and entire, after a few gulps.” Sizeand Growth. Although, years ago, alligators of fifteen feet length may have been common in favorable localities in the South, it 1s probable that few if any such monsters now exist. A twelve-foot alligator, owing to its great girth, is a huge animal and but few of this size are to be found in captivity. The largest specimen the writer has ever seen is the one in the Bronx Zoo, which is barely thirteen feet in length. At hatching the alligator is about eight inches in length. Clarke (17) says: “The largest specimen I saw measured twelve feet in length; and none of the many hunters and natives of Florida I have met have seen any longer than thirteen feet. All the hunters agree that it is only the males that acquire the great size; no one had ever seen a female that measured over eight feet, and the majority are not over seven. The male has a heavier, more power- The Biology of the Crocodilia 7 ful head, and during the breeding season especially is more brilliantly colored.” It is a very common belief, even among those who should be most familiar with their habits, that the growth of the alligator is remarkably slow, so that a large specimen may be described by the exhibitor as more than a century old. The same dealer in alligators quoted above says upon this subject: “You can figure about two inches a year to their growth.’”’ He also says: “We judge that an alligator about twenty-five to thirty years old will breed.”” Even scientific writers of reputation have not been free from this error in their writings. That the alligator may live to an extreme age, as seems to be true of some of the tortoises, is quite pos- sible, and it is probable that after reaching a length of twelve or fifteen feet the growth is very slow. In captivity, when kept in warm water and other favorable conditions, the alligator will grow, according to measurements taken at the New York Zoological Park, at the rate of about one foot a year, for about the first ten years. Under unfavor- able conditions the growth may be exceedingly slow. Under favorable conditions in nature the rate of growth may exceed that given above. Instead of requiring twenty-five to thirty years to reach sexual maturity, as quoted above, it is likely that the female may lay eggs at five to ten years, though such a fact is difficult to determine of animals in their native haunts. 2 18 The Alligator and Its Allies Voice. Thealligator, unlike most other members of its class, the Ophidia, Chelonia, and Laceritlia, has a voice, which, in an adult bull, may be heard fora mile or more. This bellowing is difficult to de- scribe; it is something between a moan and a roar, and may be to attract the opposite sex or to serve as a challenge to other large animals. It is usually ascribed to the male, but whether confined to him or not the writer is unable to say. In younger animals the voice is, of course, less deep and in very young individuals it is a squeak or grunt, easily imitated by hunters for the purpose of luring the animals from their hiding places. Breeding Habits. Judging from the statements of native hunters the laying season of the alligator might be thought to be at any time from January to September. As a matter of fact the month of June is the time when most, if not all, of the eggs are laid. S. F. Clarke gives June 9th and June 17th as the limits of the laying season in Florida, but I found at least one nest in which eggs were laid as late as June 26th: no eggs were found before the first date given by Clarke. It seemed quite certain that the laying, during the season in ques- tion, had been delayed by an extreme drought that had dried up the smaller swamps and reduced the alligator holes to mere puddles. Nests were found in considerable numbers as early as June 8th, but no eggs were laid in any of them until the end of the dry period which occurred nearly two weeks later. The Biology of the Crocodilia 19 Almost immediately after the occurrence of the rains that filled up the swamps eggs were deposited in all of the nests at about the same time. From the fact that all of these completed nests had stood for so long a time without eggs, and from the fact that all of the eggs from these nests contained embryos in a well-advanced state of development, it seemed evident that the egg-laying had been delayed by the unusually dry weather. Eggs taken directly from the oviducts of an alligator that was killed at this time also contained embryos that had already passed through the earlier stages of development. Thus it was that the earliest stages of development were not obtained during this summer. It is said that during the mating season, which precedes by some time, of course, the laying season, the males are noisy and quarrelsome, and that they exhibit sexual characteristics of color by which they may be distinguished from the females. Never having been in the alligator country at this season, the writer has made no personal observa- tions along these lines, but from the frequency with which alligators with mutilated or missing members are found it is evident that fierce encoun- ters must sometimes take place, whatever the cause. During June and July, at least, and prob- ably during most of the year, the alligators are very silent, an occasional bellow during the very early morning hours being the only audible evi- dence that one has that the big reptiles are in the 20 The Alligator and Its Allies neighborhood. Whatever may be the sexual differ- ences during the mating season, at ordinary times the two sexes are so much alike that I have, on more than one occasion, seen experienced hunters disagree as to the supposed sex of an alligator that — had just been killed. Although I have never seen a nest actually during the process of construction, it is easy to imagine, after the examination of a large number of freshly made nests, what the process must be like. The alligator, probably the female, as the male, after the mating season, takes no interest whatever in the propagation of his species, selects a slight elevation on or near the bank of the “hole” in which she lives. This elevation is generally, though not always, a sunny spot, and is frequently at the foot of a small tree or clump of bushes. Where the alligator is living in a large swamp she may have to go a considerable distance to find a suitable location for her nest; when her hole is scarcely more than a deep, overgrown puddle, as is often the case in the less swampy regions, she may find a good nesting place within a few feet of her cave. That the female alligator stays in the neighborhood of her nest after she has filled it with eggs seems pretty certain, but that she defends it from the attacks of other animals is extremely doubtful: certainly man is in very little danger when he robs the nest of the alligator, and, accord- ing to the statement of reliable hunters, bears are A NEstT oF C. Porosus; PALAWAN, P. I. (From a Photograph by Rowley.) Fic. 6.—JACKSON SLOUGH; NEAR LAKE KISSIMMEE, FLORIDA. of this pond several alligator nests were found, either within af or on the banks of smaller ‘‘holes’’ which were connected with 1 The Biology of the Crocodilia 21 very persistent searchers for and eaters of alligator eggs. Having selected (with how much care it is impossible to say) the location for the nest, the alligator proceeds to collect, probably biting it off with her teeth, a great mass of whatever vegeta- tion happens to be most abundant in that imme- diate vicinity. This mass of flags or of marsh grass is piled into a conical or rounded heap and is packed down by the builder repeatedly crawling over it. There is a great deal of variation in the size and form of the different nests, some being two meters or more in diameter and nearly a meter in height, while others are much smaller in diameter and so low as to seem scarcely more than an accidental pile of dead vegetation. It is probable that the nests are under construction for some time, per- haps to give time for the fresh vegetation of which they are composed to ferment and soften, and also for the material to settle into a more compact mass. The compactness of the alligator’s nest was well illustrated one day when the writer used an apparently deserted nest as a vantage ground from which to take a photograph: on opening this nest it was found, after all, to contain eggs, and though some of the eggs were cracked, none of them were badly crushed. This nest although it was so low and flat that it was thought to be one that had been used during some previous season, contained forty-eight eggs, a greater number than 22 The Alligator and Its Allies was found in any other nest; while in other nests that were twice as large as this one were found less than half as many eggs, showing that there is no relation between the size of the nest and the number of eggs. The average number of eggs per nest, in the twelve nests that were noted, was thirty-one. One observer reported a nest that contained sixty eggs, but this, if true, was a very unusual case. Reports of still larger numbers of eggs in one nest probably refer to crocodiles, which are said to lay one hundred or more eggs in a nest. Although crocodiles may be found in certain parts of Florida, the writer has had no opportunity of observing their nesting habits. The eggs are laid in the nest without any apparent arrangement. After the nest has been prepared, and has had time to settle properly, the alligator scrapes off the top, and lays the eggs in a hole in the damp, decaying vegetation; the top of the nest is again rounded off, and it is impossible to tell, without examination, whether the nest con- tains eggs or not. As to whether the same nest is used for more than one season there is a difference of opinion among alligator hunters, and the writer has had no opportunity of making personal observations. While it is usually stated that the eggs are in- cubated by the heat of the sun, it is held by some observers that the necessary heat is derived not from the sun but from the decomposition of the Fic. 7. A TypicaL ’GAToR “ HOLE.” Only a few yards across, and surrounded by a dense growth of vegetation. On j far side is seen an opening in the surrounding grass and flags where the ground worn smooth by the alligator in crawling out of the hole. Under the bank, probal near the place where the alligator “pulls out,’’ is the deep cave into which the habitant of this hole quickly goes on the approach of danger. As this cave may fifteen or twenty feet deep it is not an easy matter to get the animal out. Wher female alligator inhabits such a hole, a nest may often be found within three or fe yards of the water, though it is sometimes at a greater distance. Such a hole as t may be connected by narrow, winding ‘‘trails ’’ with larger ponds, as noted unt Fig. 6. (From a Photograph by the Author.) The Biology of the Crocodilia 23 vegetable matter of which the nest is composed. Possibly heat may be derived from both of these sources, but it seems likely that the conditions that are especially favorable to normal incubation are moisture and an even, though not necessarily an elevated, temperature. Moisture is certainly a necessary condition, as the porous shell allows such rapid evaporation that the egg is soon killed if allowed to dry. ‘The inside of the nest is always damp, no matter how dry the outside may become under the scorching sun, so that this condition is fully met. The eggs of the Madagascar crocodile, according to Voeltzkow,* offer a marked contrast to those of the alligator. Instead of being laid in damp nests of decaying vegetation, they are laid in holes that are dug in the dry sand, and are very sensitive to moisture, the early stages, espe- cially, being soon killed by the least dampness. A crocodile’s nest containing eggs is shown in Figure 5. In this species of crocodile, probably C. porosus, the nest resembles that of the Florida alligator. The photograph was taken by Mr. Rowley on the edge of a small lake on the Island of Palawan, P. I. The daily range of temperature in the Southern swamps is sometimes remarkably great, so that if the eggs were not protected in some way they would often pass through a range of temperature of pos- t Voeltzkow, A., ‘‘The Biology and Development of the Outer Form of the Madagascar Crocodile,” Abhandl, Senckberg. Gesell., Bd. 26, it. I, 24 The Alligator and Its Allies sibly fifty degrees or more; while in the center of a great mass of damp vegetation they are probably kept at a fairly constant temperature. Unfortu- nately no thermometer was taken to the swamps, so that no records of the temperatures of alligator nests were obtained, but it was frequently noticed that when, at night or very early in the morning, the hand was thrust deep into the center of an alligator’s nest the vegetation felt decidedly warm, while in the middle of the day, when the surround- ing air was, perhaps, fifty degrees (Fahrenheit) warmer than it was just before sunrise, the inside of the same nest felt quite cool. It is probable, then, that the conditions of temperature and moisture in the center of the nest are quite uniform. One lot of eggs that had been sent from Florida to Maryland continued to incubate in an apparently normal way when packed in a box of damp saw- dust, the temperature of which was about 80 de- grees Fahrenheit. Another lot of eggs continued to incubate, until several young alligators were hatched, in the ordinary incubator, at a tempera- ture of about 95 degrees Fahrenheit.’ The fact that eggs taken directly from the ovi- ducts of the cold-blooded alligator contain embryos of considerable size seems to indicate that no such elevation of temperature as is necessary with avian eggs is necessary with the eggs of the alligator. *Reese, A. M., ‘Artificial Incubation of Alligator Eggs,” Amer. Nat., March, 1901, pp. 193-195. Fic. 8. A TyprcaL ALLIGATOR’s NEsT, MADE CHIEFLY OF GRASS. The guide is feeling for eggs without disturbing the outside of the nest. Bein) made of the same material as the background, the nest does not stand out ver} sharply, though in nature the contrast is somewhat more marked, owing to thi fact that the surrounding grass is green while the grass of which the nest is buil is dead and brown. (From a Photograph by the Author.) The Biology of the Crocodilia 25 The complete process of incubation probably extends through a period of about eight weeks, but no accurate observations along this line could be made. For some hours previous to hatching the young alligators make a curious squeaking sound inside the shell, that may be heard for a distance of several yards: this sound may be for the purpose of attracting the attention of the female alligator, who will open the top of the nest in time to allow the just hatched alligators to escape: unless thus rescued, it would seem impossible for the little animals to dig their way out from the center of the closely packed mass of decaying vegetation. At the time of hatching the alligator is, as already noted, about eight inches in length, and it seems impossible that it should have been contained in so small an egg. The size of alligator eggs, as might be expected, is subject to considerable variation. In measuring the eggs a pair of brass calipers was used, and the long and short diameters of more than four hundred eggs were obtained. A number of eggs of average size, when weighed in mass on the scales of a country store, gave an average of 2.8 oz. per egg. There was more variation in the long diameter of eggs than in the short diameter. The longest egg of all those measured was 85 mm.; the shortest was 65 mm. The widest egg (greatest short diameter) was 50 mm.; the nar- rowest egg (least short diameter) was 38 mm, 26 ‘The Alligator and Its Allies The average long diameter was 73.742 mm.; the average short diameter was 42.588 mm. The greatest variation in long diameter in any one nest of eggs was 15.5 mm.; the greatest varia- tion in short diameter in the eggs of any one nest was II mm. The average variation in the long diameter of the eggs from the same nest was 11.318 mm.; the average variation in the short diameter of the eggs from the same nest was 5.136 mm. It will be seen from the above that the average variation in the long diameter of eggs from the same nest is between one sixth and one seventh of the long diameter of the average egg; while the average variation in the short diameter of the eggs from the same nest is less than one eighth of the short diameter of the average egg. S. F. Clarke’ gives the limits of the long diameter as 50 mm. and 90 mm., and the maximum and minimum short diameters as 45 mm. and 28 mm. No such extremes in size were noticed among the eight hundred or more eggs that were examined. Economic Importance. More than one hundred years ago attempts were made to utilize the skin of the alligator, but it was not until about 1855 that these attempts were successful and alligator leather became somewhat fashionable and some * Journal of Morphology, vol. v. ? The following figures are from an article by C. H. Stevenson in the Report of the Bureau of Fisheries, 1902, pp. 283-352. Af} ; Fic. 9. AN ALLIGATOR’s NEST, SOMEWHAT SMALLER THAN THE ONE REPRESENTED IN FiG. 8, BUILT CHIEFLY OF FLAGS. The nest has been opened to show the irregularly arranged mass of eggs inside. | ‘he size and shape of the egg are shown by the one in the guide’s hand. (From! a Photograph by the Author.) The Biology of the Crocodilia 27 thousands of hides were converted into leather. The demand was short-lived, however, and was not again felt until the demand for shoe-leather during the war between the States revived the business. At the close of the war the business again failed, but about 1869 the demand became greater than ever and has continued unabated to the present time. The supply of skins from our own States proving inadequate, large numbers of skins were soon imported from Mexico and Central America. The skins from South America are so heavy that they are of little value in making leather. Of the States of the Union, Florida has been the chief producer, the most important centers for hides being Cocoa, Melbourne, Fort Pierce, Miami, and Kissimmee. Ten men at the first-named place took, in 1899-1900, 2500 skins; one man took 800 skins in one year; another man collected 42 skins in one night. At Fort Pierce twelve men took 4000 skins in 1889. In 1899, three firms at Kissim- mee handled 33,600 hides. After this time the total number of hides taken and the average per man diminished greatly. Besides being killed for their hides, the alligators have been destroyed by the thousands merely for wanton sport, so that in 1902 it was estimated that their numbers in Florida and Louisiana were less than one fifth of what they were twenty years before that time, and unless steps be taken to prevent it, the alligator hide, as an article of 28 The Alligator and Its Allies commerce, may cease to exist in our Southern States. It has been claimed that the destruction of the alligator has allowed the cane rat and muskrat to increase to a serious extent, the former doing great damage to crops, the latter often injuring the levees to a dangerous extent. Legislation to forbid the killing of alligators of less than five feet in length has been suggested and should be passed, since animals of less size have almost no commercial value for leather. In 1902, the annual output from the tanneries of the United States approximated 280,000 skins, worth about $420,000. Of these about fifty-six per cent. came from Mexico and Central America, twenty-two per cent. from Florida, twenty per cent. from Louisiana, and the remaining two per cent. from the other Gulf States. South American hides are not handled by the United States markets. In 1908, there were marketed from the South Atlantic and Gulf States 372,000 pounds of alligator hides, valued at $61,000. According to the United States Bureau of Fisheries the hunter in 1891 averaged about 60 cents for the skin, while in 1902 the price averaged about 90 cents, varying between 15 cents and $2.00, depending on the size and condition of the skin. ‘Prime hides five feet long, with no cuts, scale slips, or other defects, are worth about 95 cents each, in trade, when the hunter sells them at the The Biology of the Crocodilia 29 country stores, and about $1.10 cash, at the tan- neries. Those measuring seven feet are worth $1.55, six feet, $1.12; four feet, 52 cents, and three feet, 25 cents. Little demand exists for those under three feet in length’’ (Report Commissioner of Fish and Fisheries, 1902, p. 345). Hides of seven feet are in most demand, those over ten feet are not much used. The income of the hunters is largely increased by the sale of otter, bear, deer, and other skins. The different varieties of skins are described by Stevenson (74) as follows: “There are several distinct varieties of alligator skins on the markets, the most important being the Floridian, Louisianian, and Mexican; each differs from the others in certain well-defined characteristics, and owing to these differences each variety has its special uses. “The Florida skins are longer in the body—that is, from the fore legs to the hind legs—than those from Louisiana and Mexico, and consequently they are largely in demand by manufacturers of large handbags. They also have a number of so-called ‘buttons’ or ‘corn marks’ on the inside or under surface of an equal number of the scutes resulting from imbedded horn-like tissues in the center of those scales. These increase the difficulty in tanning the skins and detract somewhat from the appearance of the finished article, and for this reason the Florida skins are ordinarily the cheapest 30 The Alligator and Its Allies on the market. The farther south the skins are secured in Florida the greater the number of ‘corn marks,’ and those from the vicinity of Key West are almost valueless for this reason. “The Louisiana skins differ from those of Florida in the absence of the ‘corn marks’ above noted, and from both the Florida and Mexican skins in being more pliable and in having the scales more artistically curved and shaped. Consequently they are preferred for such small articles as card- cases and pocketbooks, and usually sell at the highest prices. Skins obtained in Mississippi and Texas are similar to those secured in Louisiana, while those from Georgia and South Carolina are similar to those from Florida, except that the ‘corn markings’ are not so numerous. All the Florida and Louisiana skins show greater uni- formity of coloring, being of a bluish black on the upper surface and a peculiar bluish white on the under side. ‘In addition to an absence of the characteristics above noted the Mexican and Central American skins are distinguished by having from one to four small dots or markings like pin holes near the caudal end of each scale. The length of the Mexi- can skins varies greatly in proportion to the width, sometimes equaling that of the Florida skins. Those from the east coast of Mexico are the best, being lighter in color and with neat and attractively shaped scales. The west coast skins are yellowish The Biology of the Crocodilia 31 in color when in the green state, and the scales are larger and not so artistically formed. The Florida and Louisiana skins are almost invariably split down the back, or rather along each side of the back, so as to preserve the under side in a solid piece, but most of the Mexican skins are split down the middle of the abdomen, keeping the back intact, making what is commonly known as ‘horn alligator.’ (See Fig. 15.) ‘““The skin should be removed soon after death as, in warm climates, putrefaction sets in very early and the value of the skin is depreciated. After removal, the flesh side of the skin is thoroughly rubbed with fine salt, and the skin is carefully rolled up with the salted side inside and is ready for shipment, but must be kept in a dry, cool place. Great care must be taken not to cut the hide since small cuts that are not noticeable in the raw skin may be so conspicuous in the dressed skin as to render it of much less value; a large percentage Bt the hides received in the markets are thus damaged. “Formerly only the ‘belly skin’ was removed, by two longitudinal incisions just below the horny portion of the back; but it was later found that the thick horny skin of the back could be tanned nearly as well as the thinner belly skin, so that the entire skin is now usually removed by a longi- tudinal incision along the mid-ventral line, with lateral incisions along each leg to the foot (Fig. 15). 32 The Alligator and Its Allies The entire skin is more commonly taken in Mexico and Central America than in our States. “Although the raw skins are sold according to length, the tanned hides are sold by the width of the leather at the widest part. Standard hides sell for $1.00 to $1.65 per twelve inches of width. — Some skins tanned and dyed in a superior manner sell for $2.00 or more for single skins of 2% feet in length. Asa rule the Louisiana skins fetch the highest prices, and those from Florida the lowest. Imitation alligator leather is now prepared in large quantities, principally from sheepskins or the buffing from cowhides. These are tanned accord- ing to the usual process, and before the skins are finished they are embossed with the characteristic alligator markings by passing them between two rollers.”” (Above-mentioned report, p. 346.) Very little of the leather is now used in mak- ing shoes, the chief demand being for handbags, music-rolls, etc. In hunting alligators for their hides two methods are usually employed, in our Southern States at least. The common method is “fire-hunting”’ at night; the hunters here go, either singly or in pairs, usually in boats, sometimes on foot, with © shotgun and torch. The torch may be fastened | to the hunter’s hat, after the manner of the miner’s lamp. One more progressive hunter that I knew had, as a torch, an acetylene lamp, attached to his | hat, with the tube for the gas extending down his | The Biology of the Crocodilia 33 back to the generator in his pocket. This lamp threw a blinding beam of light far across the swamp into the eyes of the unsuspecting ’gator, which usually remained fascinated until it could be ap- proached to within easy range. A shotgun at close range, of course, blows off nearly the entire top of the animal’s head and kills it instantly; it is then seized before it sinks out of reach and is either taken into the boat or dragged upon the bank to be collected with others in the early morning. In daylight, with no glaring light to hypnotize it, the alligator is difficult to approach within range and it usually disappears into its cave before Pie. unter Can get a shot at it. The daylight hunter, then, should be supplied not, of course, with a light, but with a ten- or fifteen-foot pole with a large iron hook at the end. If the alligator be vigorously prodded with this mammoth fishhook he will usually finally seize it with his mouth and can be pulled out of his hole alive. It is then an easy matter to kill him with a bullet through the base of the brain. I have seen an eight-foot alli- gator thus killed with a little .22 calibre ‘‘cat”’ rifle. An eight-foot alligator will often be all that two men can manage to drag out of his cave in this way; and, in the torrid heat of the Southern swamp, this violent exercise is not to the liking of the usually not very energetic hunter. While the manufacture of leather gives the chief 3 34 The Alligator and Its Allies value to the alligator there are other ways in which it has some economic importance. Chief of these is probably the sale of alligator goods to tourists. In 1891 there were in Jacksonville, Florida, twelve dealers in live and stuffed alligators. In 1890, 8400 alligators were sold to tourists, the price for the live animals varying from $10.00 to $35 per hundred. For individual animals of the smallest size (less than twelve inches long) the price is usually from 50 cents to $1.00. For a three-foot alligator the price is generally $3-$5.00; for sizes over three feet $2.00 per foot may be charged, though for very large specimens the price may be from $50 to $300 each. Besides the live and stuffed animals the teeth are polished and sold as souvenirs; about 450 pounds of teeth were sold 1n 1890, at a price vary- ing from $1.00 to $2.00 per pound. From 75 to 200 teeth will make a pound. In 1891 about forty people, in addition to the regular dealers, were engaged, in the United States, in stuffing alligators, polishing teeth, etc. The teeth are extracted by burying the head until decomposition sets in. The tiny alligators that are most commonly sold to tourists, to be brought North, perhaps, and allowed to freeze or starve to death, may either be caught by a wire noose at the end of a fishing rod, or they may be hatched from eggs that are taken from the nests shortly before they are i 7s, et eu 4 Ny ne “4 i ts , %, ; - * * ia F DANCE Sieg "aye = iis a 4 of q : j 7 J i ¥ ¥ a he A : ae aI cha i » a 70 4 e Ap ’ r e a L ‘ = an t h ’ . ‘ ‘ b ‘ ; : P , : =. rl D} vi ae fs i, 1 he ‘ ' Ais] F ah tal Bi es a) ‘ a e 4 “o ae d x 4 Ya = * . nf ue 4 , ' fad es ‘ J nae, Oe tie ae. ' BrROAD-NOSED CAIMAN. (Caiman latirostris.) Distribution: Tropical South America. Attains a length of about seven feet. (After Ditmars.) (Reproduced by Permission of Sturgis & Walton Co.) FIG. 10. SPECTACLED CAIMAN. (Caiman sclerops.) Tropical America. The length of an adult is about eight feet. (After Ditmars.) (Reproduced by Permission of Sturgis & Walton Co.) \ The Biology of the Crocodilia 35 ready tohatch. Such eggs may readily be hatched by simply keeping them moist and at a fairly constant temperature, as has been previously noted. Besides the above uses Ditmars says: “The eggs are eaten in many portions of the South, and the search for eggs at the proper season fur- nishes profitable employment for many persons, as each nest contains a large number of eggs.” Never having eaten an alligator egg I cannot speak from personal experience of its flavor; but it has always seemed strange to me that more use as; Ot made of the flesh of the alligator. This flesh is often said to have too strong a flavor to be palatable; I have eaten it when it had no such rank taste but was decidedly agreeable, being, as might perhaps be expected of so amphibious an animal, somewhat like both fish and flesh, yet not exactly like either. Perhaps greater care should be taken in skinning an animal that is to be used for food in order that the flesh be not tainted with the musk. It may be a lack of care in preparation that has given rise to the impression that alligator meat is too strong to be pleasant. It is perhaps, also, the “‘idea”’ of eating a reptile that makes the meat unpopular. A half-grown boy, who was once in the swamps with me, had expressed a great aversion to alligator.meat, so the guide, one day, offered him a nicely fried piece of alligator meat, saying it was fish; the meat was eaten with evident relish and the diner was not told until after a 36 The Alligator and Its Allies second piece had disappeared what he had been eating. It always seemed strange to me that the poor people of the South should not more often vary the monotony of fat pork and corn bread with alligator steaks. Whether the meat could be smoked or salted so that it would keep in a hot climate I do not know; I am not aware of any experiments along this line. THE CHINESE ALLIGATOR Beside the American form, Alligator mississip- piensis, the only other species of alligator is found in China, along the Yang-tse-Kiang River; it is Alligator sinensis. It reaches a length of six feet and externally resembles its American relative; it is greenish black above speckled with yellow; grayish below. THE CAIMAN This is the nearest relative of the alligator and is found in Central America and tropical South America. As seen by the table on page 2, it is usually a small animal, though one species, the black caiman, is said to reach a length of twenty feet (Fig. 10). The nasal bones do not form a bony septum as in the alligator and the ventral armor consists of overlapping bony scutes. The canine teeth of the lower jaw fit into a pit in the upper jaw, as in the alligator. The Biology of the Crocodilia 37 They are said by some writers to be extremely abundant in the waters of the upper Amazon, migrating to the flooded forests during the rainy season and returning to the streams on the approach of the dry season. According to Ditmars there are five species of caiman of which the spectacled caiman, C. sclerops, and the black caiman, C. niger, are the most striking. The former is so named because of the spectacled appearance due to the swollen and wrinkled upper eyelids; it reaches a length of eight feet and is said to be of a treacherous disposition. The latter has a blunt snout like the alligator and is the largest of the New World crocodilians. THE AMERICAN CROCODILE Of about a dozen existing species of crocodile, but one, the American crocodile, C. america- mus, is found in the United States, and it is limited to the swamps and coast of southern Flor- ida below Lake Worth; its greater sensitiveness to cold is doubtless the cause of its not being found so far north as the alligator. Its range extends south through Mexico and Central Am- erica into South America. It was first found in Florida by Dr. Hornaday in 1875. It sometimes reaches a length of fourteen feet. As has already been noted there is, besides cer- tain structural differences, a marked difference in 38 The Alligator and Its Allies the dispositions of the Florida alligator and croco- dile. While an alligator may snap its jaws, hiss, and swing its tail from side to side, it is not difficult for a couple of men with ropes and a pole to safely tie up alarge specimen. The struggles of a croco- dile are of a more serious nature. Ditmars thus describes an encounter with a captive Florida crocodile: ‘‘The writer well remembers his first acquaintance with a big fellow from Florida. Driven out of the crate the crocodile looked the picture of good nature. Standing away from what he thought to be the reach of his tail, the writer prodded the apparently sluggish brute with a stick to start it for the tank. Several things hap- pened in quick order. With a crescentic twist of the body utterly beyond the power of an alligator, the brute dashed its tail at the writer, landing him such a powerful blow that he was lifted completely from the ground. As he left terra firma, an almost involuntary inclination caused him to hurl his body away from a pair of widely-gaping, tooth- studded jaws swinging perilously near. Landing with a thud on one shoulder, though otherwise unhurt, the writer threw himself over and over, rolling from the dangerous brute that was actually pursuing him on the run, body raised high from the ground. For an instant it seemed as if the crocodile would win. As the writer sprang to his feet and glanced backward, he beheld the brute throw itself flat on its belly, open the jaws widely, NILE CrocopiLe. (Crocodilus niloticus.) Distribution: Africa generally; Madagascar. Grows to a length of sixteen feet. (After Ditmars.) (Reproduced by Permission of Sturgis & Walton Co.) Fic. 11. West AFRICAN CROCODILE. (Crocodilus cataphractus.) Distribution: West Africa. Does not attain so large a size as the Nile Crocodile. (After Ditmars.) (Reproduced by Permission of Sturgis & Walton Co.) The Biology of the Crocodilia 39 then remain motionless as a statue. Such is the average crocodile—an active, vicious and, above all, treacherous brute.’”’ Ditmars says again, in the same book: ‘‘When the keepers of the reptile house of the New York Zodlogical Park clean out the big pool of the crocodilians, they actually walk over the backs of some of the big ’gators, so tame are these. They never become unduly familiar with the crocodiles, finding it necessary to pen the latter behind heavily barred gates—and in the pro- cess the men are often chased from the enclosure.”’ In contrast to this ferocious aggressiveness in captivity the American crocodile is said to be very timid and retiring when in its native habitat. Young animals are greenish with black marking; as they become older they are of an olive color, and old specimens are dull gray. THE ORINOCO CROCODILE, C. intermedius This is a species with a very narrow snout that is not quite so large as the preceding. It is said to be abundant in the Orinoco River and its tributaries. Besides the two above mentioned there is a small species, C. rhombifera, found only in Cuba and hence known as the Cuban crocodile. THE AFRICAN OR NILE CROCODILE, C. niloticus This well known and much feared species is found throughout the continent of Africa, and is 40 The Alligator and Its Allies very common on the island of Madagascar (Fig. 11). Inthe lower waters of the Nile it is now nearly exterminated. It has always been a conspicuous animal in Egypt and was one of the animals held sacred by the Egyptians and preserved by them as mummies. It is discussed by Herodotus, and the ‘“‘leviathan’’ mentioned in the Book of Job is doubtless this crocodile. In fact the name is said to be derived from the ancient Greek for lizard, just as the word alligator is said to be de- rived from the Spanish for lizard—el lagarto; the resemblance in form between these big saurians and their smaller relatives is evident. The alli- gator, being confined to America and a small part of Asia, was probably not known to the ancients. An excellent account of the development and habits of the present species is given by Voeltzkow (78), who says it is, perhaps, the most common vertebrate in Madagascar. The largest specimen measured by this observer was thirteen feet; Ditmars gives sixteen feet as the maximum size. This man-eating crocodile, according to Ditmars, destroys more human lives than any other wild animal of the dark continent. The story told by Herodotus of the bird, prob- ably a species of plover, which enters the gaping mouth of the crocodile to pick off the leeches found there may be true, since there is such a bird that may be seen perching on the backs of crocodiles, and as the Crocodilia frequently lie with their FIG. 12. SALT-WATER CROCODILE. (Crocodilus porosus.) Distribution: India to North Australia. Occurs at sea. Grows to a length of twenty feet. (After Ditmars.) (Reproduced by Permission of Sturgis & Walton Co.) The Biology of the Crocodilia 41 mouths wide open it is quite possible that these birds may pick off the worms that are often found within. It is also possible that the alertness of these birds to danger may serve as a warning to the crocodiles with which they associate. According to Voeltzkow these crocodiles dig caves of thirty-nine to forty feet length in the banks of the streams they inhabit, into which they retire on the approach of danger. The caves open under water and slope upward towards the surface of the ground where a few small air-holes are found. The natives locate the caves by means of the air-holes and dig out the hidden animal, first stopping up the entrance. In Madagascar the eggs are laid in August and September and hatch in about twelve weeks; they are laid at night, usually shortly before day- break. From twenty to thirty eggs are laid in one nest, which is merely a hole dug in the dry sand. As was said in connection with the Florida alligator, the habits of the two animals are quite different in this respect,—the moisture that is so important in the one case is fatal to the embryo in the other. When the eggs are laid the nest is filled in with sand so that there is nothing to indi- cate its position except that the female crocodile is in the habit of lying on the spot where her eggs lie buried. Like the alligator the young crocodile makes a squeaking noise shortly before hatching and the 42 The Alligator and Its Allies mother doubtless opens the nest, at this time, to allow the young toescape. A fence that Voeltzkow built around a nest was repeatedly broken down by the mother in attempting to get back to her eggs. The character of the crocodile’s egg is discussed, in comparison with that of the Florida alligator, on page 23. THE MaArsH CROCODILE OR MUGGER, C. palustris Found in India, Ceylon, Burmah, the Malay Peninsula, and many of the islands in that region. It has a rather broad snout, and reaches a length of twelve feet. It is a timid form and is harmless to man. It is frequently venerated by the Hin- doos and is kept in a semi-domesticated condition in ponds where it is fed and becomes very tame. In the dry season when the natural ponds are empty they sometimes migrate overland in search of water, but generally they bury themselves in the mud and lie dormant until the rains begin again. THE SALT-WATER CROCODILE, C. porosus This is one of the largest if not the largest of living reptiles (Fig. 12). It is said by Ditmars to reach a length of twenty feet and there is a record of one specimen that was thirty-three feet in ¢e ro was - CL ~ * h £ & z _ tg .; Bt ag te 3S > (il a...” th x P ~~ x SAE \aws ALLIGATOR SKINS; UNDER-SURFACE AND HOoRN-BACK. FIG. 15. The Skeleton 47 The dermal exoskeleton consists of bony scutes that underlie the epidermal scales of the dorsal sur- face of the trunk and anterior part of the tail. The overlying scales, except in very young animals, are always rubbed off, so that the bony scales are exposed. The ventral or inner surface of the scutes is flat, while the outer surface is strongly keeled and in old animals is often rough and pit- ted. The plates are nearly square in outline and are closely joined together in most places. | The scutes are grouped in two fairly distinct areas known as the nuchal and the dorsal shields. The former lies just back of the head, in the region of the fore legs, and consists of four larger and a number of smaller plates (Fig. 15). The latter, or dorsal shield, extends over the back in fairly regular longitudinal rows and quite regular transverse rows. At the widest part of the trunk there are six or eight of these scutes in one transverse row. They become smaller towards the tail. The teeth are exoskeletal structures, partly of ectodermal, partly of dermal origin. They are conical in shape, without roots, and are replaced when lost. They will be described in connection with the skull. Musk glands, said by Gadow to be present in all Crocodilia, are found in both sexes and are deriva- tions of the skin. One pair, each of which may be as large as a walnut, is found on the lower side of the head, one on the inside of each half of the 48 The Alligator and Its Allies mandible. The other pair is inside of the lips of the cloaca. The Histology of the Integument. ‘To understand the structure of the integument of the Crocodilia it is well to begin with the embryo. A cross section of the epidermis of such an embryo wiJl show the rete Malpighii as a single layer of short, cylindrical cells; over these are found more or less flattened, disk-shaped cells formed by transverse division of the underlying cells of the rete. On the outside lies the epitrichial layer which consists of a mosaic of polygonal cells, near the middle of each of which lies an oval nucleus. Between the epitrichial cells are small oval holes, not unlike the stomata in the epidermis of plant tissues. Bronn thinks these are not artifacts, but he does not suggest any explana- tion of their occurrence. In the epidermis of young and half-grown ani- mals the rete Malpighii is seen still as above noted. On these cylindrical cells are found flattened cells that gradually become very flat and lose their nuclei as they pass over into the horny layer. The stratum corneum consists of strongly flat- tened cells in which the nuclei can no longer be clearly seen, though their location can usually be determined by the groups of pigment granules. On the cells of the more superficial layers of the stratum corneum are seen straight, dark lines, perhaps | ridges caused by pressure of the over- or underlying polygonal cells. The individual cells of the horny | a The Skeleton AQ layer are usually easily isolated in the belly and neck regions where they never become very thick; but in the back the cells in this layer are very numerous and fuse with each other to form the bony plates; here the rete is the only clearly differ- entiated layer. Whether prickle cells are present in the epidermis of the crocodile Bronn is not certain, though he thinks they probably are. Rathke pointed out that on the surface of cer- tain folds of the integument, especially in the region of the jaws, are found in all Crocodilia certain small, scattered, wart-like elevations, around each of which is customarily a narrow, shallow, circular groove; they usually have a dark brown but sometimes a gray or even white color. Microscopic examination shows these warts to be of epidermal origin, consisting of bright, round cells that are closely united, without visible inter- cellular substance. Treatment with potassium hydroxid and then with water will show sometimes, though not always, fine granular nuclei in the cells. In probably all members of the genus Crocodilus at least is found, on the thick swelling on the right and on the left side of the neck and trunk, a small, flat pit which has the appearance of the opening of an integumental gland. The pits are present also in the scales of the throat, under the side of the neck, sides of the body, lateral and ventral surfaces of the anterior half of the tail, and the legs. They 4 50 The Alligator and Its Allies © ex cal are near the hinder border of the scales. occasionally are two pits foundinonescale. These pits are found in the gav- ials but are absent in some, probably all, alli- gators. A small knob projects from the cen- ter of some of the pits. These pits are not open- D, dorsal region; L, lumbar region; Sa, sacral region; Ri, ribs; Sc, scapula; H, humerus: R, radius; U, ulpa; Sla, sternum abdominale: Fe, femur; 7, tibia; J, ischium; ings of glands but have ~ 2 about the same structure agp | & as the pits seen in the OR bs a head. xk 3 The integumental SGRN = bones in the Crocodilia CaN & originate in the connec- as F tive tissue of the cutis. “= Vi . Investigations in young Sot SY : E animals show that these me Ny 2 bones usually take their (oes . ; = C \ origin in the under and Sh i 3 middle layers of the cas | & cutis and generally work a % towards the periphery. x : pe Z B. THE ENDOSKELETON L I. The Vertebral Column. ‘ g The vertebral column x > consists of about sixty- The Skeleton 51 five vertebre, which may be separated into the usual regions; there are nine cervical, ten dorsal, five lumbar, twosacral, and about thirty-ninecaudal. It is likely that the number of caudals may be sub- ject to frequent variation; one complete skeleton had sixty-five vertebre in all, another had sixty- eight. A complete skeleton of the crocodile (species not known) had sixty vertebre. A thirteen-foot skeleton at Western Reserve University had only sixty-one vertebrae, but some of the caudals were evidently missing. Two skeletons of C. porosus in the museum at Singapore had sixty and sixty-three vertebrez respectively. A skeleton of Tomistoma schlegalt in the same museum had sixty vertebre. The Cervical Vertebre. Since all of the cervical vertebree bear ribs, we shall assume the distinction between them and the dorsal vertebre to be that the ribs of the latter meet the sternum, while those of the former do not reach to the sternum. As- suming this distinction, there are, as was said above, nine cervical vertebre. With the exception of the first two, to be dis- cussed later, these are all essentially alike and the fourth will be described as a type (Fig. 17). Its centrum is cylindrical or somewhat hourglass shaped, concave anteriorly and convex posteriorly; it is not completely fused with the neural arch but is united with it by sutures. From the anterior end of the ventral surface of the centrum projects downward and forward a small plow-shaped process, 52 The Alligator and Its Allies the hypapophysis. On each side of the centrum, near its anterior end, is a facet with which the lower branch (capitulum) of the rib articulates. The neural arch is strongly developed and is extended dorsally into a prominent neural spine and on each Fic. 17. First Four CERVICAL VERTEBR2 OF A CROCODILE (C. vulgaris). (From Reynolds, partly after Von Zittel.) 1. pro-atlas. 7. tubercular portion of fourth 2. lateral portion of atlas. cervical rib. 3. odontoid process. 8. first cervical rib. 4. ventral portion of atlas. 9. second cervical rib. 5. neural spine of axis. 10. convex posterior surface of cen- 6. postzygapophysis of fourth trum of fourth vertebra. , vertebra. side as a short, blunt, transverse process with which the tubercle or upper branch of the rib articulates. Posteriorly the arch is notched on each side to form the openings for the exit of the spinal nerves. Pro- jecting dorsally and anteriorly from the arch are two short processes which bear the medially and dorsally facing prezygapophyses (Fig. 17). Just caudad to these processes are somewhat shorter The Skeleton 53 processes that bear the laterally and ventrally facing postzygapophyses (Fig. 17, 6). The atlas, as in other vertebrates, is highly specialized. It consists (Fig. 17), even in the adult animal, six feet or more in length, of four distinct portions, a ventral (4), a dorsal (1), and two lateral (2) parts. The ventral portion is relatively more massive than in most animals; its anterior surface is concave and forms the main part of the articular surface for the occipital condyle of the skull. Its postero-dorsal surface articulates with the odontoid process of the axis. On its postero-lateral surfaces are the facets for articulation with the first ribs, which, unlike the other cervical ribs, have but one articular surface. Articulating dorsally with this ventral element of the atlas are the two rather heavy lateral elements which form the neural arch. Anteriorly they form the lateral parts of the articular surface for the condyle and dorsally they unite for a short distance with each other. Pro- jecting ventrally from the posterior part of their dorsal portion are the small postzygapophyses. Ventrally and laterally they articulate with the odontoid process (Fig. 17, 3). Projecting dorsad and cephalad from the dorsal surface of these lateral elements is the dorsal element of the atlas (Fig. 17, 1), the pro-atlas, which may not be properly a part of the vertebral column at all, since it is said to be merely a membrane bone. Gadow says it is the detache neural spine of the atlas. It is 54 The Alligator and Its Allies thin and triangular in shape, resembling in contour a large, mammalian epiglottis. It forms an arch over the space between the skull and the front of the atlas proper. Reynolds calls it the pro- atlas. The Axis. The centrum differs from those fol- lowing it (described above) mainly in its close articulation (not fusion) with the large odontoid process; this process not only projects into the atlas, as is usually the case, but articulates with its postero-lateral border on each side, and is dis- tinctly visible in a lateral view of the neck (Fig. 17, 3). Like the rest of the cervical vertebre the poste- rior surface of the centrum is convex. The neural arch of the atlas differs from those following mainly in having a much wider (in an antero-pos- terior direction) neural spine. ‘The lateral pro- cesses and those bearing the prezygapophyses are also less strongly developed than on the following vertebra. The Thoracic Vertebre. The first thoracic verte- bra differs scarcely at all from the ninth cervical; and the tenth thoracic differs from the first lumbar only in bearing a short rib. Only the first three thoracic centra bear the hypapophyses noted in connection with the cervical vertebre. The ribs of the first two thoracic vertebre articulate with them by two processes, as in the typical cervical vertebrze; the other ribs articulate only with the transverse process. The fourth thoracic may be The Skeleton 55 described as a type of this region (Fig. 18, A). Its centrum is rather longer than in the first two thoracic and in the cervical vertebree and has no process for articulation with the head of the rib, otherwise it is essentially the same. Like all of Fic. 18. ANTERIOR VIEW oF A, A LATE THORACIC AND B, THE First SACRAL VERTEBRA OF A YOUNG CROCODILE (C. palustris). X%. (After Reynolds.) . neural spine. 4. sacral rib. . process bearing prezygapophysis. 5. surface which is united with . facet for articulation with the the ilium. capitulum of the rib. 6. concave anterior face of centrum. the vertebre behind it and unlike those in front it is apparently completely fused with its neural arch. The neural arch is very broad (in an antero- posterior direction) and is extended dorsally as a wide neural spine (1). The neural spines of the following thoracic and the first two or three lumbar vertebre are increasingly broad and truncated. The transverse processes are very broad, long and thin, and in the third to eighth vertebre they have 56 The Alligator and Its Allies two articular surfaces, an anterior and more medial one for articulation with the head of the rib (3) and a posterior and more distal one for articulation with the tubercle of the rib. These two surfaces ap- proach each other as the vertebre are followed caudad until, in the last two thoracic vertebre, they form practically one surface. The processes of the pre- and postzygapophyses spring from the arch at the base of the transverse process; the former surface is directed dorsally and medially, the latter ventrally and laterally. The interverte- bral foramina are smaller and more nearly circular than in the cervical region, and are more closely surrounded by bone. The Lumbar Vertebre. The five lumbar vertebrz are essentially like the thoracic except that the transverse processes, which, of course, bear no ribs, are both shorter and narrower. The postero- lateral border of the centrum of the last of these five vertebree has a small surface for articulation with the antero-medial border of the transverse process of the first sacral vertebra. The Sacral Vertebre (Fig. 18, B). These are two in number. The centrum of the first is con- cave in front and flat behind, instead of being convex behind, and the second is flat (instead of concave) in front, and convex behind. The neural spine and zygapophyses are as in the lumbar region. © Projecting laterally from each sacral vertebra, | forming a close, sutural joint with both centrum The Skeleton 57 and neural arch, is a heavy bone shaped like a truncated pyramid (4); the base of the pyra- mid is ankylosed with the iliua. These bones seem to be much thickened transverse processes, but since they are not completely fused with their respective vertebre and are said to ossify separately they should probably be called sacral ribs. The two sacral vertebree do not seem to be any more closely united than are any other two vertebre. The Caudal Vertebre (Fig. 16, C). These are characterized by the entire absence of ribs, and by the presence on all but the first and the last four or five of V-shaped chevron bones. The first ten or twelve of these chevron bones articulate chiefly with the postero-ventral ends of the centra, but they also articulate with the antero-ventral ends of the vertebra behind themselves; and as they are followed caudad they seem to lie directly below the intervertebral regions and to articulate equally with the vertebre before and_ behind. The chevron bones gradually diminish in size from before back. The neural processes of the first four or five caudals are broad, like those of the more anterior regions, but caudad to this point they become narrower and more pointed, though they retain the same height until about the last ten or twelve vertebre. Towards the tip of the tail the dorsal spines diminish in height and finally dis- appear. The transverse processes of the first five 58 The Alligator and Its Allies or six of the caudals are long and narrow. They gradually diminish in length until the eighteenth caudal, back of which they are no longer to be seen. The zygapophyses are mostly about the same as in the more anterior vertebre, but towardsthe posterior end of the tail the postzygapophyses come to lie between rather than above the prezygapophyses. The neural canal diminishes, of course, in size towards the tip of the tail until it is no longer present, the last five or six vertebre consisting only of the centra. LE The Skull. The skull of the alligator is very massive and has several peculiarities. 1. The bones of the dorsal surface are rough and pitted, especially in old animals. 2. The jaws are enormously large in proportion to the brain cavity, and are armed with many large teeth. 3. The mandibular articula- tion is some distance caudad to the occipital condyle. 4. The interorbital septum is mainly cartilaginous. 5. There is a complicated system of Eustachian passages connecting with the back of the mouth by a single opening. 6. The posterior nares are placed very far back and the palate is correspondingly long. The skull as a whole may be divided into three regions: the cranium, the lower jaw, and the hyoid; these will be described in the order given. The Cranium, As a matter of convenience the The Skeleton 59 bones will be described as seen from the different aspects—dorsal, ventral, lateral, posterior, and in sagittal section—without particular regard to their grouping into segments or regions. The Dorsal Aspect (Fig. 19). At the extreme posterior end of the median line lies the parietal (23), double in the embryo but a single bone in the adult. It forms a part of the roof of the cra- nial cavity and articulates anteriorly with the frontal, laterally with the postfrontals, squamosals, and, according to Reynolds, with alisphenoids, pro-otics and epiotics, and ventrally with the supraoccipital. It forms the median boundary of each of the two supratemporal fosse (sf). On each side of the parietal and forming the posterior corners of the rectangular postero-dorsal region of the skull are the squamosals (7). Each squamosal articulates medially with the parietal, anteriorly with the postfrontal, and ventrally with the quadrate and exoccipital. It forms part of the posterior and lateral boundaries of the supratem- poral fossa and a part of the roof of the external auditory meatus. Articulating with the anterior border of the Squamosals and forming the anterior corners of the rectangular region mentioned above are the postfrontals (6). The postfrontal articulates medi- ally with the parietal and frontal, and ven- trally with the alisphenoid and a small part of the quadrate. It sends, in a ventro-lateral direc- 60 The Alligator and Its Allies tion, a thick process that unites with a similar process from the jugal to form the postorbital bar (pb) which lies between the orbit (0) and the tem- poral fossa (tf). The postfrontal forms the antero- lateral boundary of the supratemporal fossa. Articulating posteriorly and laterally with the parietal and the postfrontals, and forming the highest point of the skull, is the single frontal bone (24), which, like the parietal, is paired in the em- bryo. It is a heavy bone whose dorsal surface is flattened posteriorly, deeply concave in the middle region, and drawn out into a long projection anteri- orly. It forms part of the roof of the cranial cavity and articulates ventro-laterally with the alisphenoid and anteriorly with the prefrontals and nasals. It forms a part of the median boundary of the orbit. The prefrontal (4) is an elongated bone in the latero-median border of the orbit. Medially and anteriorly it articulates with the frontal and nasal, laterally with the maxillary and lachrymal, and ventrally, by a heavy process, with the pterygoid. The nasal (25) is a long narrow bone forming the greater part of the roof of the nasal passage. Along the median line of the skull it articulates with its fellow; posteriorly with the frontal; laterally with the prefrontal and maxillary; and anteriorly with the premaxilla. In the crocodile, caiman, and gavial it also articulates with the lachrymal. In the alligator the anterior ends of the | . to con Nu WwW Fic. 19, ALLIGATOR (A. premaxilla. maxilla. lachrymal. prefrontal. jugal. postfrontal. squamosal. quadrate. WwW tN te tN on DorsaL VIEW OF THE SKULL OF THE Mississippiensis). quadratojugal. parietal. frontal. nasal. an, anterior nares; 0, orbit; pb, postorbital bar; sf, supratemporal fossa; tf, lateral tem- poral fossa. a The Skeleton 61 two nasals form a narrow rod of bone that extends across the anterior nares, and, meeting a projection from the premaxillaries, divides the opening into right and left halves. In the crocodile the nasals project only a very little way into the nares; in the caiman (according to Reynolds) they do not extend into the nares at all, and in the gavial, whose much elongated snout is mainly due to the great length of the maxillaries, the nasals do not extend more than a third of the distance from the pre- frontals to the anterior nares. The maxilla (2) is a large bone that forms a large part of the upper jaw and that holds most of the teeth of that jaw. On the ventral side, as will be described later, it articulates with its fellow in the middle line, with the premaxilla, with the palatine, and with the transpalatine. Dorsally it articulates with the premaxilla in front; with the nasal and prefrontal on the medial side; and with the lachrymal and jugal behind. The premaxilla (1) forms, with its fellow, the extreme tip of the upper jaw. Each bone forms the anterior and lateral borders of its half of the anterior nares. It articulates medially with its fellow and posteriorly with the nasal and maxilla. Ventrally, as will be noted later, it bears five teeth and articulates with its fellow medially and with the maxilla posteriorly. Between the premaxillz on the ventral side is the large anterior palatine foramen. 62 The Alligator and Its Allies The lachrymal (3) is a fairly large bone that forms the anterior border of the orbit. It is bounded laterally by the jugal, anteriorly by the maxilla, and medially by the prefrontals. Its postero- medial border is pierced by a large lachrymal foramen that extends lengthwise through the bone and opens, at its anterior end, into the nasal chamber. The supraorbital, missing in the skull figured, is a small bone lying in the eyelid close to the junction of the frontal and prefrontal. Being unattached it is usually absent from prepared skulls. The jugal or malar (5) is an elongated bone that forms a part of the lateral border of the head, on the one hand, and most of the lateral border of the orbit on the other. Anteriorly it articulates with the maxilla; medially with the lachrymal and prefrontal; posteriorly with the quadratojugal, and ventrally with the transpalatine. With the transpalatine it sends, in a dorso-medial direction, a process that meets the process, described above in connection with the postfrontal, to form the postorbital bar. The guadratojugal (12) is a small bone, wedged in between the jugal in front and the quadrate behind. The quadrate (8) is more irregular and has moré complicated articulations than almost any bone in the skull. Its posterior end, which forms the articular surface for the lower jaw, is elongated laterally and slightly concave. Anteriorly the Fic. 20. VENTRAL VIEW OF THE SKULL OF THE (A. Mississippiensis). ALLIGATOR maxilla. jugal. quadrate. palatine. pteryg id. transpalatine. quadratojugal. 14. basioccipital. a, anterior palatine vacuity; eu, opening of the median Eustachian canal; pn, posterior nares; pv, posterior palatine vacuity. The Skeleton 63 quadrate articulates with the quadratojugal; me- dially with the basisphenoid and exoccipital; dor- sally with the exoccipital, squamosal, postfrontal, and, possibly, with the pro-otic; ventrally with the pterygoid, alisphenoid, and probably with some of the otic bones. Its dorsal side forms most of the floor of the external auditory meatus which will be described later. While the basioccipital may be seen from the dorsal side, it is not really one of the dorsal bones of the skull and will be described later; the same is true of the pterygoids and palatines which may be seen through the empty orbits. The Ventral Aspect (Fig. 20). The larger part of this side of the skull is made up of four pairs of bones: the premaxille, the maxille, the palatines, and the pterygoids, lying, from anterior to posterior, in the order named. The premaxilla (1), as described in the dorsal view of the skull, is a triangular bone which, with its fellow, forms the anterior end of the snout. Each premaxilla bears five teeth, not only in the alligator but in the crocodile, the caiman, and in the gavial. Of these teeth the fourth from the front is the largest; the first two are small, and the third and fifth are of intermediate size. ‘This arrangement as to size is also true, apparently, in the other groups of Crocodilia. The ventral surface of the premaxilla, which is more or less flat and horizontal, is pierced by a number of small fora- mina, in a row parallel to the curved outer margin 64 The Alligator and Its Allies of the bone. Between these foramina and the base of the teeth are four rounded depressions to receive the points of the first four teeth in the lower jaw; of these depressions the first and fourth are the deepest. The first pit often becomes so deep as to perforate the bone; this is true also with the crocodile and, according to Reynolds, with the caiman, but is not true of the gavial, whose inter- locking teeth project outside of the jaws. It will be remembered that one of the chief distinctions, given early in this work, between the crocodile and the alligator is that in the former the fourth tooth in the lower jaw fits into a notch and not into a pit in the upper jaw. The maxilla (2), which with its fellow forms most of the hard palate, has also been mentioned in connection with the dorsal aspect. Each maxilla is notched, posteriorly, to form the anterior border of the posterior palatine vacuity, and together they are notched to receive the rectangular ante- rior ends of the palatines. The postero-lateral extremity of the maxilla articulates with the trans- palatine. |Along the outer border of the bone are the teeth, of which there are fifteen or sixteen in the alligator, about the same number (perhaps one or two less) in the caiman and crocodile, and about twenty-four in the gavial. The first or anterior eight or ten teeth have individual sockets, the rest are placed in a groove. In the crocodile none of the teeth have individual sockets, and in the gavial The Skeleton 65 they all have sockets. The premaxillary and more anterior of the maxillary teeth are slightly recurved and are sharper than the posterior maxillaries which besides being blunt have a constriction above the surface of the socket. The crocodilian tooth consists of three layers (Fig. 20 A). The enamel (e) forms a fairly thick layer over the crown of the tooth; it exhibits a very clear striated structure, the striations being apparently due to stratification. , Some of the tubules of the dentine (d) continue into the enamel, where they may be distinguished by their remarkable fineness and their straight course. The cement (c) covers the root of the tooth that projects into the alveolus of the jawbone; it is much more strongly developed than in the lizards and contains a very large number of bone corpuscles which are distinguished from the bone corpuscles proper by their. greater circumference. The fairly large pulp cavity (p) has, like the tooth itself, a conical form. Parallel to the teeth is a row of small foramina, a continuation of those noted in the premaxilla; some or all of these foramina open into a longitud- | inal sinus along the alveolar border of the maxilla; | this sinus opens posteriorly by one or more large - apertures into the posterior palatine vacuity. The palatines (9) form a broad bar of bone from 66 The Alligator and Its Allies the pterygoids behind to the maxille in front. They are united with each other by a straight median suture and form a considerable part of the floor as well as a part of the side walls and roof of the nasal passage. They form most of the median boundaries of the posterior palatine vacuities (pv). Dorsally they articulate with the pterygoids, pre- frontals, and vomers. The pterygoids (10) are the very irregular bones that project ventrad and caudad from beneath the orbits. Their suture is continuous, caudad, with that between the palatines and at the posterior end of this suture is the posterior opening of the nasal chamber, the posterior nares (pn). This opening is divided by a vertical, longitudinal, bony septum, and the part of the chamber into which it immedi- ately opens, which lies in the pterygoids, is divided by a number of transverse, vertical septa. Poste- rior and dorsal to the posterior nares the pterygoids are fused. Anteriorly the pterygoids articulate with the palatines; dorsally with the quadrates, basisphenoid, alisphenoids, and prefrontals, and dorso-laterally with the transpalatines. The lat- eral vertical border of the pterygoid is roughened and is, according to Reynolds, covered, during life, with a pad of cartilage against which the medial side of the mandible plays. The transpalatine (11) is a T-shaped bone articu- lating ventrally with the pterygoid and dorsally — with the maxilla, the jugal, and the postfrontal. G. 20A. LONGITUDINAL SECTION OF THE JAW AND TOOTH OF A CROCODILE. (After Bronn.) c, cement; d, dentine; e, enamel; p, pulp, of functional tooth; c’, cement; d@’, dentine; e’, enamel, of rudimentary tooth; ¢’’, epidermis; k, bone of jaw. The Skeleton n6i The bastoccipital (14) is seen projecting caudad as the single occipital condyle; it will be described in connection with the posterior aspect of the skull. The jugal (5), quadraiojugal (12), and quadrate (8) may all be seen from this view. ‘The first two have been sufficiently described in connection with the dorsal aspect; the last will be further described in connection with the lateral aspect. Just caudad to the posterior nares is a small opening, the unpaired Eustachian canal (eu). The Lateral Aspect (Fig. 21). As will be seen by the figure, practically all of the bones visible in this view have already been described, except those of the mandible, which will be described separately. At the base of the skull are, however, two bones, the basi- and alisphenoid, that have not been described and that show as well in this as in any other view. The basisphenoid (just below v and hidden by the pterygoid) was mentioned in connec- tion with the quadrate, with whose posterior mar- gin it articulates. It is an unpaired bone of very irregular shape. Anteriorly it is flattened out to form the rostrum, a rectangular process that forms the posterior part of the interorbital septum; in fact it is the only part of the septum present in a prepared skull, since the rest is cartilaginous. Dorso-laterally the basisphenoid articulates with the alisphenoid; posteriorly with the basioccipital; ventrally with the pterygoid; and posteriorly with the exoccipital and basioccipital. On the dorsal 68 The Alligator and Its Allies surface of the basisphenoid is the pituitary fossa, not seen, of course, in this view of the skull. The alisphenoids (crossed by the dotted line from V) are a pair of very irregular bones that form most of the antero-lateral walls of the brain case. They articulate dorsally with the parietal, frontal, and postfrontal; ventrally with the basisphenoid and pterygoid; and posteriorly with the quadrate and some of the otic bones not visible in this view. Between it and the quadrate, plainly visible in this view, is a large opening, the foramen ovale (V), through which, according to Reynolds, the tri- geminal nerve passes. In the middle line, directly under the frontal bone, is an opening between the anterior wings of the two alisphenoids, for the exit of the optic nerves. Ventrad and caudad to this opening, and sometimes continuous with it, is another large foramen, just dorsad to the rostrum, for the exit, according to Reynolds, of the oculo- motor and abducens nerves. Projecting caudad is seen the rounded condylar part of the basi- occipital (14) to be described later, and dorso- cephalad to this is a part of the exoccipital (13) in which four foramina may be seen; of the dorsal three the one nearest the condyle and foramen magnum is for the exit (Reynolds) of the hypo- glossal nerve (XII); slightly dorso-cephalad to this is one for the vagus nerve (X); between these two is a very small one for a vein; the largest and ventrally located foramen is for the entrance of the : *T[MYs s19jU9 A19418 ‘ayeipenb °*g ‘uemBioj jesso[s0ddyq ‘TTX *plouoION “Tz pryorvo gory Aq uame10y ‘eT ‘jesowenbs = *) So ‘UdMIBIOJ OIIJSeZouNndud ‘y “AVBUOP OZ ~ ‘yeztdi000-Iseq "PFT *[Bjuo0Ijysod °g "a[BAO MTOUIBIOJ ‘A “IBINAB "GT ‘[eqidioo0xe = “eT ‘want “ec ‘seatou sueonp ‘IB[nSue-sidns “gy ‘jesnfoyeipenh ZT ‘Teyuorjeid =“ ~qB puBe AOJOMO[NIO jo ‘[eyaoly "PT ‘puUlyR[vdsueIy "TT *‘yeuAIyoRyT “¢e g1x9 410} Sutaedo ‘TA ‘TTT *sny *‘prosfiojd = OT “BI[IXBUL °Z ‘IBe[Nsue "ZZ seat AIOJIPNB [VUIN}XO “OT ‘oulyeied 6 “Byixemoid “T (‘spjouAdy JoqzVy) (SOY “WIg) “EX ‘(stzpjsoyo] upwip)) AOLVOITIY NV 4O T1NHS AHL JO MAIA IWYALV] ‘Iz ‘OT (=, e) _ Bo ” e fe op fa oz fi Y gyi d 92 f= YY ieee WY ¢ ““, 4, Lj CH NY 70 The Alligator and Its Allies internal carotid (15). Another large foramen in the exoccipital bone will be seen and described in connection with the posterior view of the skull. Dorsal to the quadrate and largely bounded by it is the wide external auditory meatus (16), which leads into the tympanic cavity. This cavity is complicated by a number of canals that lead from it in various directions. Overhanging the cavity and meatus is the squamosal bone, described in connection with the dorsal aspect of the skull. The Posterior Aspect (Fig. 22). Most of the bones seen in this view have already been described. The pterygoids (10) form the two prominent, ventro- lateral projections, while dorsal to these is the large process formed by the quadrate (8) and quadrato- jugal (12). The dorsal margin is formed by the edges of the parietal (23) and the squamosals (7). Immediately below the parietal is the supra- occipital (26); it is a small, triangular bone, articu- lating above with the parietal and squamosals, below with the exoccipitals, and anteriorly with the epiotic. It takes no part in the formation of the foramen magnum. The exoccipitals (13) form the entire boundary of the foramen magnum except the narrow ventral portion formed by the basioccipital. Each exoccipi- tal is a wing-shaped bone, articulating dorsally with the squamosal and supraoccipital, ventrally with the quadrate, basioccipital, and basisphenoid, and anteriorly with the opisthotic. It is pierced by ‘iepnsueeidns ‘1c *prousydsiseq jo ‘plouoloo ‘fs ‘Teuotds “61 uorjisod ‘sq “s[ossoA ‘yeqyidtoooiseq =F “IepnoryIe “co ‘AIeyuop “RI -poojq ute41900 pur ‘Teqyidio00xo 9° £1 9AIoU Y}Z IOJ UsUIvIOJ * ‘jesnloyeipenb ‘cI ‘(sisuarddississay VY) YOLVOITTY 40 sgt nd ae ess aT MVE mare IO MAIA Ivsuoq ‘v2 ‘oly “rerouted Ce TALGEMTEAsE Roy *AIO4IV ‘ayvipenb °g prjored I0J uourelogy “ST ‘Tesourenbs *Z “SISNAIddISSISSIJY “VY JO TIONS AHL AO MAIA UOIUALSOG ‘ce ‘Oly FAL The Skeleton ‘ust -sloy yessojsoddy [TX “snjvoul ALoyIpNe [eUsIUL “TITA “MOUIB10J JB[NQIPUBU [VUIOJUL “gz “MaTBIOF JB]NgipusmM jwulayxa 1z “yeant “9g ‘[esomenbs Gz *[Byidio00x9 “Fz ‘prouo109 "ez, “AB[NIIPIB "Zz *IB[nsuB-vidns ‘[z ‘1B[NSUB “OZ ‘yerue[ds = “6T ‘Aleyuep “BT ‘ouryeyed = “ZT (‘spjousayy 107FV) “B[Ixeur “OT "IQUIOA “CT ‘jequoijoid “FT ‘prousydsre “gT “prousydsiseq “ZT *prosfiojd = "TT ‘ayzipenb “OT ‘TeyIdIo00Iseq °G © ‘oyoyysido *g (SHI ‘WIq) “tx *(S144S044D] UDMIDD) AOLVOITTY NV JO TING AHL HONOMHL NOILIAS ‘dAIOM [BUIMIESII} 90} IO} UOUE -B10] JUeTIMOId By SI), aInsy aq} JO UOI ur ATayerpawiMy ‘or001d - *o101d9 *peyidi1o00-eidns *yeqotred *[84U0I} ‘[eseu “erIxeuoid HAOWOOe IVNIGALIONOT ‘€2 ‘Ol 72 The Alligator and Its Allies five foramina, four of which were described in connection with the lateral view. Some distance laterad and somewhat dorsad to the pair already described is the fifth and largest foramen (VII); it really lies between the exoccipital and quadrate, but the former bone forms almost its entire bound- ary; through it, according to Reynolds, pass the seventh nerve and certain blood-vessels. The bastoccipital (14) which, as has been said, forms a small part of the ventral wall of the foramen magnum, consists of a heavy dorsal portion, the ven- trally curved condyle, and of a broader, irregular ventral portion, between which and the basisphe- noid is the single opening of the Eustachian canals (eu). Dorsally and laterally the basioccipital artic- ulates with the exoccipitals; ventrally, laterally, and anteriorly with the basisphenoid which was described in the lateral view. The Sagittal Section (Fig. 23). The only bones shown in this figure (besides those of the mandible, to be described later) that have not already been described are the vomers and those of the auditory capsules. The vomers (15) are delicate bones articulating with the maxille, the palatines, the pterygoids, and with each other. They form a part of the septum and roof of the nasal passage. The mesethmoid is not ossified. Reynolds describes the bones of the auditory capsules as follows: The Skeleton 73 “Three bones, the epiotic, opisthotic, and pro- otic, together form the auditory or periotic capsule of each side. They are wedged in between the lat- eral portions of the occipital and parietal segments and complete the cranial wall in this region. Their relations to the surrounding structures are very complicated, and many points can be made out only in sections of the skull passing right through the periotic capsule. The relative position of the three bones is, however, well seen in a median longitudinal section. The opzsthotic early becomes united with the exoccipital, while the epiotic similarly becomes united with the supraoccipital, the pro-otic (Fig. 23, 7)—seen in longitudinal section to be pierced by the prominent trigeminal foramen—alone remaining distinct throughout life. The three bones together surround the essential organ of hearing which communicates laterally with the deep tympanic cavity by the fenestra ovalts. “The tympanic cavity, leading to the exterior by the external auditory meatus (Fig. 21, 16), is well seen in a side view of the skull; it is bounded on its inner side by the periotic bones, posteriorly in part by the exoccipital, and elsewhere mainly by the quadrate. A large number of canals and passages open into it. On its inner side opening ventro-anteriorly is the fenestra ovalis, opening ventro-posteriorly the «internal auditory meatus (Fig. 23, VIII), while dorsally there is a wide open- 74 The Alligator and Its Allies ing which forms a communication through the roof of the brain case with the tympanic cavity of the other side. On its posterior wall is the prominent foramen through which the facial nerve passes on its way to its final exit from the skull through the exoccipital; this foramen is bounded by the quad- rate, squamosal, and exoccipital. The opening of the fenestra ovalis is in the fresh skull occupied by the expanded end of the auditory ossicle, the columella, whose outer end articulates by a con- cave facet with a trifid extracolumellar cartilage which reaches the tympanic membrane. The lower process of this extracolumella passes into a cartilaginous rod which lies in a canal in the quadrateand is during life continuous with Meckel’s cartilage within the articular bone of the mandible. “The columella and extracolumella are together homologous with the chain of mammalian auditory ossicles. ”’ The Lower Jaw, (Pigs: 21, 23; and )24)—. me mandible consists of two similar rami, rather closely united at the anterior-median symphysis with each other. Each ramus consists of six bones. The dentary (Figs. 23 and 24, 18; Fig. 21, 20) is a long bone that unites at the symphysis with its fellow to form the point of the jaw. It bears, along . its dorsal edge, about twenty teeth; all but the \ posterior four or five of these teeth are in individual sockets; this may vary somewhat with age. The outer surface of the dentary, especially towards the The Skeleton 7G symphysis, is covered with numerous, small, deep pits, while along its inner side, parallel to the row of teeth, is a row of somewhat larger pits like those noted in the maxilla and premaxilla. Articulating with the mesial side of the dentary along the greater part of its length is a flat bone, the splenial (Figs. 23 and 24, 19); between these two bones is a long cavity that makes the ramus hollow almost to the symphysis. A large foramen, not shown in any of the figures, leads through the splenial into this cavity. Articulating with the caudal end of the splenial and forming the anterior border, as seen from the mesial side, of the large external mandibular foramen (Fig. 23, 27) isasmall bone, the coronoid (Figs. 23 Bid 24,° 22, Hie, 21, 21); it articulates with the splenial anteriorly, with the supra-angular dorso- caudally, and with the angular ventrally. The supra-angular (Figs. 23 and 24, 21, Fig. 21, 18)is an elongated bone that forms the dorsal border of the external mandibular foramen; it also forms the lateral edge of the articular surface for the quadrate. It articulates anteriorly with the splen- ial, the dentary, and the coronoid; and posteriorly with the angular and articular. The articular (Figs. 23 and 24, 22, Fig. 21, 19), which is scarcely visible in a lateral view, forms most of the surface for articulation with the quad- rate, and sends back the large process so charac- teristic of the crocodilian skull. On the dorsal side 76 The Alligator and Its Allies of this process is a concavity that looks like another articular surface. lLaterally the articular articu- lates with the supra-angular; ventrally and poste- riorly with the angular. The angular (Fig. 23, 20, Fig. 21, 22) forms the ventro-posterior border of the jaw and of the external mandibular foramen. Its narrow, poste- rior end forms a part of the prominent process men- tioned in connection with the articular. Between it and the posterior edge of the splenial is the internal mandibular foramen, which is much smaller than the external (Fig. 23, 28). Anteriorly the angular articulates with the dentary, coronoid, and splenial; dorsally with the supra-angular and the articular. The Hyoid (Fig.25). The hyoid being mainly of cartilage is usually not seen in prepared skeletons. It is thus described by Reynolds: “The hyoid of the Crocodile consists of a wide flattened plate of cartilage, the basilingual plate or body of the hyoid, and a pair of cornua. “The basilingual plate (Fig. 25, 1) is rounded ante- riorly and marked by a deep notch posteriorly. The cornua (Fig. 25, 3), which are attached at a pair of notches near the middle of the outer border of the basilingual plate, are partly ossified, but their ex- panded ends are formed of cartilage. They pass at first backwards and then upwards and inwards. They are homologous with part of the first bran- chial arches of Selachians.’”’ The Skeleton 77 III. The Ribs and Sternum. The Cervical Ribs. As noted above, all of the cervical vertebrz possess ribs. The first rib, Fic. 25. Hyormps oF AN ALLIGATOR (Caiman latirostris) (TO THE LEFT) AND OF A GREEN TURTLE (Chelone midas) (To THE RIGHT). XX. (Brit. Mus.) (After Reynolds.) ‘The cartilaginous portions are dotted, 1. basilingual plate or body of 3. first branchial arch (anterior the hyoid. cornu), 2. hyoid arch., 4. second branchial arch (pos- terior cornu). attached to the atlas, consists of a single, long blade projecting backward at an acute angle (Fig. 17, 8) as far as the middle of the fourth vertebra. As described above it articulates with the atlas at but one place. All of the other cervical ribs have two articular surfaces, a tuberculum and a capitulum, 78 The Alligator and Its Allies with a well-marked vertebrarterial canal between them. The ventral surface or capitulum articu- lates with a short process on the centrum; the dorsal surface or tuberculum (7) articulates with the transverse process. The third to seventh ribs are somewhat T-shaped, the stem of the T being the tubercle and head, while the cross arm of the T extends parallel to the axis of the neck (Fig. 17, 7). In the eighth rib the posterior arm of the T is elongated and projects out at a wide angle from the body; and in the ninth or last cervical rib this arm extends laterally as far as the vertebral portion of the thoracic ribs and has a cartilaginous tip. The Thoracic Ribs (Figs. 16 and 26). These are ten in number, the first eight pairs being connected with the sternum. The fourth may be taken as typical. It consists of a bony vertebral portion and partially ossified intermediate and sternal portions. The vertebral portion articulates with its corresponding transverse process by two sur- faces, as described in connection with the thoracic vertebre. In the first and second ribs only the tuberculum articulates with the transverse process, the head having a separate articular surface on the side of the centrum, as in the typical cervical rib. In the last thoracic rib the head and tubercle are not distinguishable from each other. Near the distal end of all the vertebral portions except the first and the last two ribs is a caudally projecting, partially ossified, uncinate process. The inter- The Skeleton 79 Fic. 26. STERNUM AND ASSOCIATED MEMBRANE BONES OF A CRO- CODILE (C. palustris). X%. (Brit. Mus.) (After Reynolds.) The last pair of abdominal ribs which are united with the epipubes by a plate of cartilage have been omitted. 1. interclavicle. 4. abdominal splint rib. 2. sternum. 5. xiphisternal horn. 3. sternal rib. 80 The Alligator and Its Allies mediate portion is present in all but the tenth rib, and wherever present, except in the ninth rib, it articulates distally with the sternal portion. The sternal portions extend medio-cephalad in a direction atright angles to the intermediate portion ; the first two articulate with the sternum, the next six with the xiphisternal horns, and the ninth and tenth are missing. The Abdominal Ribs (Fig. 26, 4). While these ribs are membrane bones and are not homologous with the other ribs, they may as well be mentioned at this time. They consist of about seven V-shaped sets of slender bones, the point of each V being directed cephalad. Each V is made up of from two or five slender bones, the number and arrange- ment being subject to considerable variation. The last V of the series (not well shown in the figure) is considerably larger than the rest and is made up of four curved bones that extend around the anterior ends of the pubic bones and are united to them by a broad tough membrane. ‘The first or most anterior V is united by a narrow membrane (not shown in the figure) with the membrane that extends between the xiphisternal horns. All of the V’s are more or less connected with each other by fibrous membranes. Since these ribs lie super- ficial to the recti muscles of the ventral body wall they are sometimes missing in carelessly prepared skeletons. The Sternum (Fig. 26). The sternum consists of The Skeleton 8I the cartilaginous sternum proper (2), the xiphi- sternal horns (5), and the bony episternum or inter- clavicle (1). The latter is an elongated, flattened bone of somewhat spatulate outline, lying in the midventral line; it projects forwards to about the sixth cervical vertebra, while the anterior edge of the sternum is below the eighth cervical. Lying dorsal and lateral to the episternum is the flat, almost membranous sternum, to the posterior border of which the first two thoracic ribs are attached. The xiphisternum consists of two long, slender rods of cartilage; the anterior ends of these rods are in contact with each other and with the posterior border of the sternum; from this point they gradually diverge from each other as they extend caudad. A membrane extends between the horns as far back as the attachment of the last thoracic ribs. IV. The Appendicular Skeleton. The Pectoral Girdle and Anterior Limb. The pectoral girdle (Fig. 27) is of a very simple type, consisting, unless the episternum (interclavicle) be counted, of but two bones, the scapula (s) and coracoid (c). The former consists of an upper, flat, _ paddle-shaped portion and a thicker lower portion which articulates anteriorly with the coracoid, and posteriorly forms about half of the notch-like glenoid cavity. The dorsal edge of the flattened portion is continued as a small, cartilaginous supra- 6 82 The Alligator and Its Allies scapula. The coracoid is a flattened bone, wide at either end and narrow in the middle, so that in a dorsal view it is shaped like an hourglass. It is decidedly curved, with the convex side down. Its outer edge ar- ticulates with the scapula and is thickened to form the anterior border of the glenoid cav- ity. Its median end is attached to the sternum. Near its scapular articu- lation there is a well-marked fora- men that passes entirely through episternum (e) or Fic. 27. PECTORAL GIRDLE AND interclavicle was ANTERIOR LIMB. : : described in con- ¢, coracoid; ce, centrale; cl, claw; e, episternum; . : h, humerus; m, metacarpals; p, pisiform; r, nection with the radius; r’, radiale; s, scapula; u, ulna; ; keane sternum and ribs. There is no clavicle nor other coracoid elements. The anterior limb consists of the usual parts,— the upper arm, forearm, and manus. The hu- merus (Fig. 27, h) is rather thick in proportion to its length; it has an elongated articular surface at its proximal end for articulation with the glenoid the bone. The The Skeleton 83 cavity, and a larger, somewhat bilobed surface for articulation with the radius and ulna. On its ventral side, near the proximal end, is a very prominent protuberance, the deltoid ridge. The ulna (uw) is slightly heavier and longer than the radius and forms the greater part of the elbow joint and about half of the wrist joint. Its proximal end is considerably larger than the distal, but has no olecranon process. Its distal end articulates with the ulnare and pisiform. ‘The ulna as a whole is slightly curved, while the radius is quite straight. The radius (r) consists of a cylindrical shaft with enlargements of about equal size at the ends. The proximal end articulates with the side of the ulna and with the humerus; the distal end with the radiale. The carpus consists of a proximal row of three distinct bones and a distal row of smaller and less fully ossified elements. Of the proximal row the radiale (r’) is much the largest bone. It is hour- glass shaped, with the proximal end somewhat larger than the distal. Proximally it articulates mainly with the radius but also slightly with the ulna and ulnare. Distally it articulates with the centrale. The ulnare (u’), the second bone in size in the wrist, has about the same shape as the radiale but is much smaller. Proximally it articulates with the pisiform, radiale, and, apparently, with the ulna; distally it is in contact with the fused carpalia elements. The pzsiform (p) is a small, 84 The Alligator and Its Allies irregular bone, articulating with the ulna and the ulnare; it is apparently connected by a long liga- ment with the fifth metacarpal but does not actually articulate with it. The centrale (ce) is a flattened, partially ossified element between the radiale and the first and second metacarpals. The distal carpal bones are represented by two irregular, partially ossified elements between the ulnare and the third, fourth, and fifth metacarpals. The manus proper consists of five digits. The metacar pals (m) are of about the same shape, but vary in length and thickness; each consists of a cylindrical shaft with a slight enlargement at each end. The first digit or pollex has two phalanges, the second has three, the third has four, the fourth has four, and the fifth has three. The terminal phalanx of each of the first four digits is pointed, has a pair of lateral grooves, and is encased in a large, horny claw (cl). The Pelvic Girdle and Posterior Limb. ‘The pelvic girdle is described differently by Wiedersheim and Reynolds; the bone called by the former the pubis, the latter calls the epipubis. The bone called by Wiedersheim the pubis takes no part in the forma- tion of the acetabulum; the pubis of Reynolds helps form the acetabulum but is a very small, unossified structure. Gadow also calls the lower bone the epipubis. I shall follow Reynolds’s interpretation. The ilium (Fig. 28, 1) is a heavy bone with The Skeleton 85 a dorso-laterally projecting crest; medially it is firmly united to the sacral ribs (Fig. 18, 5) while its outer side forms the upper and greater part of the Ses ae ees SNR NTRS Thine Athy 5 in 1 Fic. 28. PELVIS AND SACRUM OF AN ALLIGATOR (Caiman latirostris). X3. (Brit. Mus.) (After Reynolds.) ilium. 6. neural spines of sacral verte- ischium, brae. true pubis. 7. symphysis ischii. epipubis (so-called pubis). 8. process bearing prezygapo-) acetabular foramen. physis. acetabulum. Its outer and lower border has two surfaces, the larger and more posterior articulating with the ischium, the other with the cartilaginous pubis. The ischium (2) is a slightly arched bone, its ventral end a flattened blade articulating with its fellow, its dorsal end enlarged and thickened to articulate with the ilium, pubis, and epipubis. 86 The Alligator and Its Allies This dorsal end, which forms the ventral side of the acetabulum, is divided into two distinct articular surfaces by a deep, rounded notch; the posterior and larger surface articulates with the ilium, the anterior surface about equally with the pubis and epipubis. The pubis (3), which is much the smallest ele- ment of the pelvis, is a small mass of cartilage lying between the ilium above and the ischium below. It forms a small part of the anterior wall of the acetabulum. The epipubis (4) is a slightly arched bone, some- what enlarged at its proximal end where it unites with the ischium, and flattened out into a fan- shaped extremity, where it is united with its fellow and with the last pair of abdominal ribs by the broad, thin sheet of cartilage or fibrous tissue noted in connection with the abdominal ribs. As men- tioned above, it is called by Wiedersheim and others the pubis. Near the center of the acetabu- lum there is a small foramen. The posterior limb (Fig. 29) consists of the usual divisions—thigh, shin, and foot. The femur (f) is a bone of the same general outline as the humerus, though slightly longer and heavier. The head, for articulation with the acetabulum, is rather hemi- elliptical than hemispherical in shape, the long axis of the ellipse being vertical. The distal enlargement is of at least as great, if not greater, bulk than the proximal and shows some indication The Skeleton 87 of a division into two articular surfaces. The ventral side of the femur near the proximal end shows a fairly distinct trochantal ridge. The shin or crus is made up of two well-developed bones, the tzbia (t) and jib- ula (fb), the former being somewhat longer and con- siderably thicker than the latter. The tibia consists of a cylindrical shaft with en- largements of about equal size at the ends. The proximal end forms most of the knee joint, the distal end articulates with a tarsal element said by Reynolds to represent the fused astragalus and cen- trale, by Wiedersheim called the astragalus, and Said to represent the united tibiale, interme- dium, and centrale (tb, cd, Fic. 29. POsTERIOR LIMB. calcaneum or fibulare; cl, claw; f, femur; fb, fibula; 12, tibia; 13, 14-5, tarsalia; 1b, 1b1, tibiale- centrale; 1V, V, 4th and 5th metatarsals. tb’). The fibula articulates by a small enlargement at its proximal end with the femur, and by an enlarge- ment of about equal size, at its distal end, with the fibulare or caleaneum (ca), and with a small facet on the above-mentioned tibiale-centrale element. 88 The Alligator and Its Allies The tarsus is much modified and consists of four elements, in two rows; those of the proximal row are much larger than the two distal elements. Articulating with both tibia and fibula, as men- tioned above, and with the first metatarsal and one of the distal tarsalia, is the large and irregular tibiale-centrale element of Reynolds (tb, tb’). In the tarsus here shown it consists of two elements. Post-axial in position is the calcaneum or fibulare (ca), articulating with the preceding tarsal element, with the fibula, with the rudimentary fifth meta- tarsal, and with the distal tarsal element said by Reynolds to represent the fourth and fifth tarsa- lia. The calcaneum is extended caudad into a prominent knob quite like the heel of the higher | mammals. The two distal tarsal bones are small; one is said by Reynolds to represent the first three tarsalia (t°), the other (t**) the fourth and fifth. Wieders- heim says one of these bones represents the first three tarsalia, the other the fourth. In the tarsus here shown these two elements are fused. The foot has five digits, though the fifth is small and consists merely of a small, distally pointed metatarsal bone. According to Wiedersheim this fifth metatarsal is fused with the fifth tarsalia. The metatarsals of the first four digits are long and progressively more slender from the first to the fourth; each is distinctly enlarged at the ends. The first digit or hallux has two phalanges, the The Skeleton 89 second has three, the third has four, and the fourth has four. According to Reynolds, the fourth toe has five phalanges; the figure here shown, which was drawn from nature, has only four on the fourth toe; the latter is the number given by Bronn for the crocodiles. The terminal phalanges of the first three digits are large and pointed, with the same lateral grooves noted in connection with the fore foot; each is sheathed in a horny claw. The four fully developed digits of the pes are nearly twice as long as the corresponding digits of the manus, but they are not proportionately thicker. CHAPTER III THE MUSCLES HE description of the muscles here given is taken from Bronn (11), who, in turn, largely follows Gadow. The animal de- scribed is the crocodile, but while Bronn does not indicate the species, it is probable that the differ- ences between the various members of the Croco- dilia would be slight. The figures of the muscular system are mainly from the Florida alligator. In his description Bronn gives for each muscle the various synonyms (often more than half a dozen) that are employed by different writers; in this work Bronn’s nomenclature is given first and the synonyms follow in parentheses. THE CHEWING MUSCLES Temporalo-maxillaris (Temporalis) (Masseter, Temporal, Aeussere ober Heber or Schlafmuskel). Arises in the temporal fossa, passes under the zygoma, and inserts itself on the inner and outer sides of the lower jaw. 90 EL The Muscles QI Pterygo-maxillaris (Pterygoideus) (Pterygoid- ien, Aeusser Flugelmuskel, Pterygoideus externus, Pterygoideus internus). A large muscle which consists of two portions: the outer, weaker portion springs from the pterygoid process, the inner stronger part from the pterygoid fossa and ptery- goid process; they run together around the angle of the lower jaw, where they form a large, bulging fold. They are the chief muscles of this part of the body since the masseter is lacking and the tempo- ralis is weakly developed. Occipito-maxillaris (Digastricus maxilla) (Nie- derzieher des Unterkiefers, Abaisseur ou l’analogue du digastrique, Senker des Unterkiefers, Aristotelis apertor oris, Digastricus, Aperator oris). Arises from the hinder border of the lateral occipital and is inserted at the hinder end of the lower jaw. Its course is from front to back. If the skull be stationary this muscle drops the lower jaw; if the jaw be fixed it raises the skull. MUSCLES OF THE VENTRAL SURFACE OF THE NECK Intermaxillaris and Sphincter Colli (Intermax- illaire, Mylo-hyoideus, Zwischenkiefermuskel, La- tissimus colli). This muscle consists chiefly of transversely running fibers, and has in its middle third a small, median, longitudinal raphe or apo- Meurosis. In the posterior part of the neck it 92 The Alligator and Its Allies is very thin, but increases in thickness more and more as it passes cephalad. A short anterior and a long posterior portion may be distinguished. The former extends from the inner side of the right to that of the left half of the lower jaw, without a median aponeurosis. The hinder half of this muscle is united by a pair of aponeuroses to the lower jaw, on one hand (the smaller part), and to a fascia, on the other hand (the far larger part), that separates several of the neck muscles. The smaller part begins immediately behind the pterygoid on the inner side of the halves of the lower jaw but ends on the outer side of the two halves of the jaw. Latus Colli (Latissimus colli accessorius). Lies underneath the preceding. Its muscle bundles lie between the collo-capitis muscle and the bodies of the first three cervical vertebree, and form a broad band that extends from the hyoid bone to the backwardly directed cervical ribs of the first and second pairs. Coraco-ceratoideus (Omo-hyoideus, Coraco-hy- oideus). A long, narrow, and moderately thick muscle which takes its origin from the upper border of the coracoid, where the latter touches the scapula. It extends forward near the cesophagus and at- taches itself to about the middle of the backwardly turned border of the horn of the hyoid of that side. Eptsterno-ceratoideus (Niederzieher des Zungen- beins, or Brustbeinzungenbeinmuskel, Sterno-hy- oideus). A flat and fairly broad muscle which The Muscles 93 springs from the ventral surface of the episternum; behind, it is separated by a slight space from the corresponding muscle of the other side, with which it nearly covers the cervical part of the trachea. Towards its anterior end it divides into two heads; one of these inserts itself on the outer border and outer surface of the cornu of the hyoid; the other head, lying laterad to the former, is suddenly re- duced to ashort tendon by which it is attached to the following muscle. Maxillo-coracoideus (Mylo-hyoideus anterior, Sterno-maxillare). This muscle arises from the upper border and inner surface of the caudal third of the lower jaw. In its further course it becomes tendinous and projects by a short tendon outwards from the hyoid cornu to unite with the head of the preceding muscle, as noted above; it then becomes fleshy again and is inserted on the medial part of the upper border of the coracoid. Maxillo-hyoideus (Genio-ceratoidien, Hyomax- illaris, Hyoglossus, Hyomandibularis, Mylo-hyoid- eus posterior). This muscle arises, very thin, from the mandibular symphysis, goes thence immedi- _ ately backward and inward to insert itself, by its broad end, on the whole anterior end of the horn | of the hyoid and on the hyoid itself. | Cerato-hyoideus. Arises from the horn of the | hyoid and inserts itself on the body of the hyoid. Costo-coracoideus. This muscle arises from the distal ends of the first and second ribs and is 94 The Alligator and Its Allies inserted on the ventral surface of the coracoid at the boundary of the scapula. Costo-scapularis (Collo-scapularis superficialis, Levator scapulze superficialis) See shoulder muscles. Costo-vertebralis Medialis (Scaleni). Fairly large, flat, and long-drawn-out three-cornered muscle. Attached by its base to the most anterior sternal rib, by its upper border to the fifth cervical rib, and by its point to the end of the second cervical rib. Costo-vertebralis Lateralis (Longus colli). Origi- nates thin and sharp on the body of the fifth thoracic vertebra, increases in thickness slowly but decidedly cephalad, then again becomes thinner and inserts itself on the inner side of the ribs of the most anterior two cervical vertebre. Collo-capitis (Rectus capitis anterior). Arises, as a rule, from the cervical centra, at times from the second thoracic vertebra (Gavialis). It ex- tends forward and is inserted on the basi-occipital and the hinder border of the pterygoid. For a greater part of their length the two muscles le close together, but forward they separate somewhat from each other. DorsAL NECK MUSCLES Occipito-cervicalis Medialis (Complexus cervicis, Biventer cervicis, Zweibauchiger Strecker or Zwei- The Muscles 95 bauchiger Nackenmuskel, Splenius capitis). It springs, by separate points, from the dorsal pro- cesses of the four anterior body vertebre and the six posterior neck vertebree; it is convex on its dorsal, weakly concave on its ventral surface; it leads cephalad asa short, strong tendon by which it is attached to the angle between the upper hinder border of the skull, z.e. to the superior and lateral occipital region. Squamoso-cervicalis Medialis (Kopfbauchmuskel [Splenius] or durchflochtener Muskel [Complexus], Trachelo-mastoideus, Complexus). This muscle lies laterad and ventrad to the preceding and is at times partly covered by it in its posterior half. It arises from separate heads from the spinal pro- cesses of the two anterior and six posterior cervical vertebre; beginning caudad, thin and sharp, it gradually becomes thicker as it passes cephalad until it becomes partially tendinous and inserts itself on the hinder border of the squamosal, lat- erad to the occipito-cervicalis medialis muscle. Epistropheo-vertebralis (Splenius colli). This muscle springs from the spinous processes of the most anterior three body vertebre and the last cervical vertebra; it receives fibers from the articu- lar processes and intermediate parts of the six posterior cervical vertebrze and is inserted on the | second cervical vertebra. — Collo-squamosus (Splenius capitis, Nackenwar- 'zenmuskel, Trachelo-mastoideus). Springs from 96 The Alligator and Its Allies the upper transverse processes of the last three neck vertebra, and, becoming tendinous, is in- serted on the hinder border of the squamosal. Collo-occipitis. Arises from the transverse pro- cesses of the posterior five cervical vertebre, extends directly forwards on the ribs of the verte- bree, and is inserted under the articular surface of the lateral occipital. Occipito-epistropheus (short, straight, hinder head-muscle, or extensor). This muscle springs from the lateral surface of the body of the second neck vertebra and inserts itself on the basi-exoc- cipital, under the preceding muscle. Cervicalis Adscendens. Arises in great part from the angles under the most anterior ribs; a smaller part appears farther above where it is covered by the rhomboideus muscle. It is in- serted on the upper side of the five posterior cervi- cal ribs and on the distal ends of the long second cervical rib. THE MUSCLES OF THE SCAPULA Capiti-sternalis (Sterno-mastoideus). This is a fairly large muscle, on the side of the neck, that extends from the skull to the breast and from the middle of the neck is divided into two portions: (a) an anterior part or atlanti-mastoideus (Plate I., Figs. 1 and 2, cst") (upper end of the “head nodder,’”’ sterno-mastoideus, anterior part of , ; | | | The Muscles 97 sterno-mastoideus, anterior part of atlanti-mas- toideus); (b) a posterior part or sterno-atlanticus (Plate I., Figs. 1 and 2, cst?) (sterno-mastoideus, inner belly of the “‘head-nodder,”’ posterior part of the sterno-atlanticus). The former part is a rather short but not weak muscle that arises from the squamosum and inserts itself on the rib of the atlas (alligator) or of the atlas and epistropheus (crocodile). The latter part is fairly strong and exceeds the anterior part in length; it springs from the rib of the first cervical vertebra, opposite the insertion of the anterior part, and inserts itself on the ante- rior border of the outer surface near the episternum. At times superficial fibers pass into the pectoral fascia. Dorso-scapularis (Cucullaris) (Plate I., Figs. 1 and 2, Cu) (Trapezius). A broad but thin muscle that begins as an aponeurosis from the dorsal fascia in the middle line of the hinder part of the neck and beginning of the back; with converging fibers it passes within to insert itself partly on the spine of the scapula and partly by superficial fibers in the fascia that cover the deltoides scap- ularis inferior muscle. Collo-scapularis Superficialis (Plate I., Fig. 1, essp) (Levator scapule superficialis, Levator scap- ule, Heber des Schulterblatts, Acromio-trachélien, Teil des Serratus magnus, Levator anguli scap- ule). A considerable muscle on the side of the 7 98 The Alligator and Its Allies neck. It arises from the tips of the ribs of the first and second cervical vertebrae (where it is fused with the sterno-atlanticus muscle), and also from the transverse process of the third and fourth cervical vertebra; it goes with diverging fibers to the entire anterior border of the scapula. Thoraci-scapularis Superficialis (Serratus super- ficialis, Pectoralis minor, Hinterer Theil des inneren grésseren Rtckwartsziehers, Pars posterior m. serrati antici majoris, Theil des Grand dentelé, Serrati posteriores, Latissimus dorsi scapulo- costalis). A strong muscle of three prongs that go directly, by superficial fibers, over into the oblique abdominal muscle and meet the ribs. The first and smallest prong arises from the under end of the rib of the ninth vertebra (last cervical); the second and medium-sized prong comes from the uncinate process of the tenth rib (first thoracic) and from beneath the uncinate process of the second thoracic rib; the third and strongest prong takes its origin from the uncinate processes of the second and third thoracic ribs. All three prongs unite to form a broad, homogen- eous muscle which passes forward and above to the hinder border of the scapula, upon whose entire surface, except at the lower end, it is inserted. Collo-thoraci-suprascapularis Profundus (Plate I., Fig. 3, cthspr) (Levator scapule et serratus pro- fundus, Serrati anteriores, Serratus anticus major, Vorderer Theil des inneren grésseren Rtckwarts- The Muscles 99 ziehers or vorderen grossen gezahnten Muskels, Pars anterior m. serrati antici majoris, Theil des Grand dentelé, Theil des Serratus magnus). This muscle arises in varying extent from the transverse process of the fifth cervical vertebra to the first (crocodile) or second (alligator) ribs. It is inserted on the inner surface of the supra- scapula, except on its forward part, and is made up of two layers—a superficial and a deep one. The former layer (Fig. 3, cthsprt) is weakly developed and is composed of two or three thin, distinct bundles, that extend from the ribs of the eighth, ninth, and eleventh vertebre (alligator) or from the transverse process of the seventh vertebra and the rib of the tenth. The deeper layer is considerably developed; its bundles come, in the alligator, from the fifth to tenth vertebre; in the crocodile from the fifth to ninth. Rhomboideus (Plate I., Fig. 3, rh) (Rautenmuskel, Angulaire de l’omoplate). This is a very small, independent muscle that springs, by two or three distinct bundles, from the fascia covering the longissimus dorsi muscle, in the region of the eighth and ninth vertebre; after a short course it inserts itself on the antero-dorsal angle of the suprascapula. Costo-coracoideus (Plate I., Fig. 3, cc) (Sub- clavius et Triangularis sterni and Levator secundz superioris costz, Petit dentelé, Pectoralis minor, Pectoralis). This is a broad muscle of considerable 100 The Alligator and Its Allies size on the ventral side of the breast; it consists of a lateral and of a medial portion, the- former springing from the last cervical rib, the latter from © the anterior border of the first sternocostal ridge. The two parts unite and are inserted on the whole posterior border of the coracoid. Pectoralis minor (Pectoralis, Costo-coracoideus). A broad, considerable muscle on the under side of the breast, which is made up of two parts, of which the lateral springs from the anterior border of the last (ninth) cervical rib, and the medial from the anterior border of the first sternocostal ridge. Both parts unite into a homogeneous layer which is inserted broadly on the whole hinder border of the coracoid. Pectoralis (Plate J., Figs. 1 and 2, p) (Pec- toralis major, Grosser Brustmuskel). A broad muscle on the under side of the breast, bounded behind by the rectus abdominis and obliquus abdominis externus muscles, with which it is united. It arises from the whole episternum, from the whole sternum, except from the median line of its posterior part, from the sternal ends of the first six thoracic ribs, from all six sternocostal ridges, and, with a small prong, from the eighth rib. It is inserted on the distal part of the convex surface of the processus lateralis humeri. Supracoracoideus (Plate I., Figs. 1 and 2, spc) (Supracoracoscapularis, Deltoideus, Schlussel- beinhalfte, Theil der Schulterblatthalfte des Hebers The Muscles 101 des Armes, Obergratenmuskel, Hebemuskel des Oberarmes, Epicoraco-humeralis). A muscle of considerable size at the anterior region of the coracoid and the under region of the scapula, which is divided into two parts: (a) the coracoid (inferior) division is the stronger and arises from the whole anterior half of the coracoid, from its outer and inner surfaces; it is inserted, together with the second part, on the proximal, little- developed part of the processus lateralis humeri; (b) the scapularis (superior) division is the weaker of the two and is covered by the deltoides scapu- laris inferior muscle; it arises from the surface of the under third of the scapula, behind the spine; it unites with the preceding part to form a single muscle and inserts itself, as said above, on the proximal part of the processus lateralis humeri. Coraco-brachialis (Brevis) (Plate I., Figs. 4, 5, and 6, cbb) (Theil des grossen Brustmuskels oder Hakenarmmuskel, Pectoralis II., Pectoralis minor). A fairly strong muscle. It arises from the outer surface of the coracoid, except the median edge and the anterior section, and runs to the flexor surface of the upper arm where it is inserted on the proximal third between the lateral and median processes. Coraco-antebrachialis (Plate I., Figs. 2 and 5, b*) (Biceps, Coracoideus, Langer Kopf des langen Beugers, Langer Kopf des Biceps, Biceps humeri, Biceps brachii, Coraco-radialis). A slender and 102 The Alligator and Its Allies rather weak muscle on the flexor side of the upper arm. It arises by a fairly broad but thin tendon from the outer surface of the coracoid immediately before the coraco-brachialis. As a weak bundle it passes between the lateral and median processes, lying medially near the brachialis inferior muscle, with which, at the end of the upper arm, it unites; after their union the two muscles continue as a broad tendon that splits into two parts, which are inserted on the proximal end of the radius and of the ulna. A Humero-antebrachialis Inferior (Plate I., Figs. 2 and 6, hai) (Brachialis inferior, Caput breve m. bicipitis, Kurzer Kopf des Biceps, Brachial interne, Brachialis anticus, Erster vom Oberarm ausge- hender Beuger, Portion of Brachizus). Springs from the lateral flexor side of the humerus, from the distal end of the lateral process to the distal end of the bone, except the epiphysis; at the end of the upper arm it unites with the biceps and with it is inserted, by two tendons, to the radius and ulna. Dorso-humeralis (Plate I., Fig. 1, dh) (Latissi- mus dorsi, Breiter Rtickenmuskel, Humero-dor- salis). It springs as an aponeurosis from the back at the level of the first four or five dorsal vertebre, and passes, with converging fibers, cephalo-ven- trad to unite with the teres major muscle; in common with the latter it extends along the exten- sor surface of the humerus to be inserted between the lateral and median processes. The Muscles 103 Dorsalis Scapule (Plate I., Fig. 1, dss) (Deltoides scapularis superior, Unterer Theil des dusseren schulterblattmuskels, Untergratenmuskel, Supra- scapularis, Infraspinatus, Supraspinatus). Springs from the anterior half of the outer surface of the scapula, passes between the deltoides scapularis inferior and the caput scapulare laterale externum m. anconzi, aS a narrow band, to be inserted on the lateral side of the humerus. Deltoides scapularis Inferior (Plate I., Figs. 1 and 2, dsi) (Deltoideus superior, Supra- and Infra- spinatus, Theil der Schulterhalfte des Hebers des Armes, Theil der oberen [Schulterblatt-] Abtheil- ung des Deltoideus, Zweiter Hebemuskel des Ober- armes, Theil des Deltoides). A strong muscle on the side of the shoulder. It springs from the spine of the scapula, passes back with slightly converging fibers, and ends chiefly on the outer surface of the processus lateralis humeri, while a number of superficial fibers end in the humero- radialis muscle. Scapulo-humeralis Profundus (Plate I., Fig. 4, shpr) (Teres minor, Erster Teres major, Scapulo- humeralis). A small muscle that springs from the posterior border of the lower third of the scap- ula, and passes, with converging fibers, to its insertion on the humerus just distal to the medial process. Teres Major (Grosser runder Muskel oder kleiner Rtickwartszieher des Oberarmbein, Zweiter teres 104. The Alligator and Its Allies major). Springs from the posterior half of the upper region of the outer surface of the scapula. It passes down, with converging fibers, to unite with the latissimus dorsi muscle to form a strong tendon that is inserted on the extensor surface of the humerus. Subscapularis (Unterschulterblattmuskel). Springs from the inner surface of the scapula, except from the suprascapula, goes with converging fibers directly over the capsule of the shoulder joint to be attached to the medial process of the humerus. Anconeus. This strong muscle lies on the ex- tensor side of the upper arm. It is made up of two layers: the superficial comes from the pectoral gir- dle in two heads: (a) the caput scapulare laterale externum and (b) caput coraco-scapulare; the deeper layer originates on the humerus by three heads, (c) caput humerale laterale, (d) caput humerale posticum, and (e) caput humerale medi- ale. These five heads of the anconzus muscle with their synonyms will now be described. (a) Caput Scapulare Laterale Externum (Plate I., Figs. 1 and 4, asl) (Brevi proximum caput m. tricipitis, Gewohnlicher [ausserer] langer Kopf des dreikdopfigen Streckers, Portion scapulaire externe du triceps-brachial, Erster langer Kopf des Triceps, [Zweiter] abducirender vom Schulter- gerust entstehender Kopf des Streckmuskels des Vorderarmes, Triceps Nr. 1, Triceps longus). ( The Muscles 105 This muscle springs as a tendon from the hinder border of the scapula directly beneath the articular cavity, and extends back, between the scapulo- humeralis profundus and the dorsalis scapule muscles, into the muscle belly. (b) Caput coraco-scapulare (Plate I., Figs. 2, 4, 5, 6, acs) (Externum caput m. tricipitis, Innerer langer Kopf des dreiképfigen Streckers, Portion scapulaire interne du triceps-brachial, Zweiter langer Kopf des Triceps, [Erster] abducirender vom Schultergerust entstehender Kopf des Streck- muskels des Vorderarmes, Triceps Nr. 2, Triceps longus secundus). Arises by two distinct tendi- nous tips—the upper, weaker one from the hinder border of the scapula, the lower, broader one from the hinder border of the coracoid. (c) Caput Humeri Laterale (Plate I., Figs. 1 and 4, ahl) (Brevius caput m. brachiei interni, [Acus- serer| kurzer Kopf des dreikopfigen Streckers, Por- tion huméral externe du triceps brachial, Aeusserer vom Humerus ausgehender Kopf des Streck- muskels des Vorderarmes, Theil des Triceps Nr. 3, Triceps externum). Springs from the lateral part of the extensor surface of the humerus dorsal to the lateral process and the origins of the humero- radialis and brachialis superior. (d) Caput Humerale Posticum (Plate I., Fig. 4, ahp) (Longissimum caput m. brachiei internum, Theil des inneren [kurzen] Kopfes des dreikopfigen pereckers, Theil des Triceps Nr. 3, Theil des 106 The Alligator and Its Allies Triceps internus, Theil der Portion humérale interne du triceps brachial, [Mittler] vom Humerus ausgehender Kopf des Streckmuskels des Vor- derarmes). Springs from the middle of the ex- tensor surface of the humerus between the lateral and medial heads. (e) Caput Humerale Mediale (Longius caput m. brachiei interni, Theil des [inneren] kurzen Kopfes des dreikopfigen Streckers, Theil der Portion humérale interne du triceps brachial, [Innerer] vom Humerus ausgehender Kopf des Streckmuskels des Vorderarmes, Theil des Triceps Nr. 3, Theil des Triceps internus). This head originates on the medial part of the extensor surface of the upper arm at the end of the medial process where it is united with the scapulo-humeralis profundus muscle. The muscle mass formed by the union of all the above heads goes over, as a broad and somewhat thick tendon, to become inserted on the proximal part of the ulna. Humero-radialis (Plate I., Figs. 1 and 4, hr) (Caput longum m. bicipitis, Eigener kurzer Beuger, [Zweiter] vom Oberarm ausgehender Beuger, Brachialis externus, Portion a of Brachizus). A fairly large muscle on the outer side of the upper arm, lying between the brachialis inferior and caput humerale laterale muscles, with both of which it is, at the beginning, united. It originates with its deeper and chief mass from the outer The Muscles 107 surface of the humerus, just distal to the lateral process; while its superficial layer, especially the upper fibers, come directly from the deltoides scapularis inferior and therefore have their origin on the scapula. In the middle of the upper arm it becomes a slender round tendon that extends, through a tendinous loop, to the radius, on whose outer side, at the end of the proximal third, itis inserted. MUSCLES OF THE FOREARM Humero-radialis Internus (Radialis internus, Lange Vorwartswender, Pronateur, Pronator teres, Pronator quadratus, Oberflachlich gelegener, lan- ger runder Einwartsdreher). This muscle arises from the condylus internus (C. ulnaris s. medialis) and attaches itself to the radius throughout almost its entire length. It is a fairly strong muscle. Ulno-radialis (Carré pronateur, Pronator teres, Pronator quadratus, Muskel welcher dem Prona- tor quadratus entsprect). A strongly developed muscle. It springs from the upper part of the flexor surface of the ulna and is inserted on the lower part of the flexor surface of the radius. Humero-radialis Longus (Plate II., Figs. 1 and 2, 1) (Supinator longus, Long supinateur, Lange Ruckwartswender, Supinator radii longus). Among the Crocodilia this and the following muscle are well developed. This one springs from the con- 108 The Alligator and Its Allies dylus externus humeri and is inserted on the outer side of the entire length of the radius. Humero-radialis Brevis (Plate II., Fig. 4, d) (Supinator brevis, Kurze Ruickwartswender, Ex- tensor carpi-radialis brevis [?]). Arises near the preceding from the external condyle of the humerus and is inserted at the upper end of the radius. Humero-carpi-radialis (Plate II., Fig. 2, a) (Aeusserer oder langer Speichenmuskel, Musculus quem parti superiori extensoris digitorum com- munis respondere videbat, Extensor carpi-radialis longus, Abductor pollicis longus). Towards the ulna, near the supinator longus muscle. It springs from the external condyle of the humerus, covers the supinator brevis muscle, and is inserted on the proximal end of the carpi-radialis. Humero-carpi-ulnaris (Plate II., Fig. 2, ¢) (Extensor carpi-ulnaris, Ulnaris externus). Origi- nates on the external condyle of the humerus, is inserted on the proximal end of the os carpi-ulnare. Humero-metacarpalis III., IV., V. (Plate IL. Fig. 2, b) (Extensor digitorum longus, Aeusserer Speichenmuskel or Speichenstrecker der Hand, Extenseur commun, Extensor radialis longus, Extensor digitorum communis). This muscle lies between the humero-carpi-radialis and the humero- carpi-ulnaris muscles. It springs from the con- dylus externus humeri and divides, on reaching the carpus, into three thin, flat tendons, which in- part fuse with the carpo-phalangei muscle, and in» The Muscles 109 part are inserted on the carpal bones of the third, fourth, and fifth fingers. Carpo-phalanget (Plate II., Fig. 2, d). (Extensor digitorum brevis, Extenseurs courts, Gemein- schaftlicher Strecker der Hand, Extensor digitorum communis brevis). Springs from the carpal and, in part, from the metacarpal bones and is inserted on the terminal phalanges of the five fingers. Ulno-carpi-radialis (Ein dem Strecker und Ab- zieher des Daumens analoger Muskel, Extensor pollicis longus, Extensor carpi-radialis brevior[?]). Springs from the under half of the ulna, and is inserted on the os carpi-radiale. Carpo-phalangeus I (Extensor pollicis brevis). This is a small, thick muscle that originates on the distal part of the os carpi-radiale and is inserted on the phalanx of the thumb. Humero-radialis Lateralis (Plate II., Fig. 1, 6) (Flexor carpi-ulnaris, Innerer Ellenbogenmuskel, Ulnaris internus). A fairly strongly developed muscle. It springs from the internal condyle of the humerus, extends along the ulna, and is inserted on the proximal part of the os carpi-ulnare, and the nearby pisiform bone. Humero-radialis Medialis (Plate II., Fig. 1, 2 (Flexor carpi-radialis, Radialis internus). Ms fant - 1) fib, 11 fib; tib, ant pb is fm post ---transv --qoadr lumb peron-post — - cap.mt gaste - - - flex long dig----- tib ant CHAPTER IV THE NERVOUS SYSTEM SPINAL CORD HE spinal cord extends the whole length of the vertebral canal and ends near the end Orarie cau as’ a thin, round threads. It varies in thickness and shape in cross section, being nearly always elliptical, but at places approach- ing a circle. Large, spindle-formed thickenings of about equal diameter are present in the cervical and lumbar regions. A cauda equina is absent in the alligator, the nerves of the large tail leaving the cord like the intercostals. On its ventral surface the cord has a deep perpendicular fissure, the fissura ventralis, that extends almost to the center; it extends even along the reduced region in the tail. A vascular membrane extends into this fissure. A shallow but distinct furrow extends along the dorsal side of the cord, parallel to which, on either side, is a fine, linear furrow. The first two spinal nerves have no dorsal roots. 131 ta The Alligator and Its Allies BRAIN The cervical cord passes insensibly into the medulla, the dorsal furrow becoming wider and more shallow as it merges into the fourth ventricle. A dorsal view of the brain is shown in Figure 30, A. The most prominent structures here seen are the cerebral hemispheres, VH, whose combined transverse diameter is greater than their longi- tudinal. The tapering, cephalic end of each hemi- sphere forms an olfactory tract, I, which extends cephalad to form the olfactory bulb, B. ol. Lying between the caudal ends of the hemispheres is a small conical body, G.p., called by Bronn and - others the pineal body. The writer has found (62), however, that this body is the paraphysis rather than the epiphysis. Caudad to the cerebra- hemispheres and in contact with them are the optic lobes, MH; they have about the same shape and position as in the frog, but are much smaller in proportion to the size of the hemispheres. Immediately caudad to the optic lobes is the cere- bellum, HH, somewhat elliptical in outline as seen from above. Extending caudad from beneath the cere~ellum is the medulla, NH, with its triangular fourth ventricle. The outlines of the medulla are some- what obscured by the numerous roots of the eighth to eleventh cranial nerves, VIII—-XI, which arise along its dorsal border. ‘The medulla, as was s Bol C jell eater ees IP Fic. 30. BRAIN OF ALLIGATOR. (A, dorsal; B, ventral; and C, lateral view.) (From Wiedersheim, slightly altered.) VH, cerebral hemispheres, each of which gives rise postero-laterally to a hippocampal lobe partially overlying the corresponding optic tract, Tr.opt; ZH, thalamencephalon; MH, optic lobes; HH, cerebellum; NH, medulla oblongata; J-XJI/, cranial nerves; I, 2, first and second spinal nerves; B.o/, olfactory bulb; Tro, olfactory tract; G.p, para- physis; Jnf, infundibulum; Hyp, hypophysis; Med, spinal cord. The Nervous System 133 said above, passes, as is usually the case, without any line of demarcation into the spinal cord, the obex filling in the apex of the fourth ventricle at the anterior end of the median dorsal fissure. A lateral view of the brain is shown in Figure 30, ©. The hemisphere, VH, is conical in outline, with a small projection from the posteroventral region; its continuation forwards as the olfactory bracy, iro., aud bulb, B: ol), is plain. Beneath it and extending forwards are the prominent optic nerve, -II, and tract. Caudad to the latter and projecting ventrad and caudad are the infundibu- lum, Inf., and hypophysis, Hyp. Caudad to the cerebrum are seen the end of the paraphysis, G.p., the optic lobes, MH, and the cerebellum, HH. From the cerebral peduncles (ventrad to the optic lobes) arises the oculomotor nerve, III, and dorsocaudad to this, between the optic lobe and the cerebellum, arises the trochlear nerve, IV. From the middle zone (in a dorsoventral direction) of the medulla, ventrad to the cerebellum, arises the very large trigeminal nerve, V; while from its usual place, on the ventral surface of the medulla, the abducens nerve, VI, takes its origin by several roots. At some dis- tance caudad from the trigeminal, from the dorsal surface of the medulla, as noted above, the very large acoustic nerve, VIII, arises; and immediately ventrad to this, on the side of the medulla, the facial nerve, VII, may be seen. Commencing just 134 The Alligator and Its Allies caudad to the acoustic and extending along the upper border of the medulla and beginning of the spinal cord, are seen a dozen or more small nerve roots, which unite to form the glossopharyngeal, IX, vagus, X, and spinal accessory, XI, nerves. Ven- tral to the roots of the last, on the ventral surface of the medulla, arise the roots of the hypoglossal nerve, XII. A short distance caudad to this nerve are seen the first two spinal nerves, 1 and 2, which have, as noted above, no dorsal roots. A ventral view of the brain is shown in Figure 30, B. ‘The cerebral hemispheres, VH, have the same outline, of course, as in the dorsal view, but the rounded projection from the caudal end of each is here seen on each side of the infundibulum, Inf. The infundibulum is in close contact with the chiasma anteriorly, and lies close between the converging optic tracts, Tr. opt. From the chi- asma the optic nerves, II, extend, in an antero- lateral direction, almost at right angles to each other. The appearance of the olfactory tracts, I, is the same as in the dorsal view. Caudad to the infundibulum, from the cerebral peduncles, ZH, arise the rather small oculomotor nerves, III. Caudad to these, from near the ventral fissure, on the middle region of the medulla, arise the ab- ducens nerves, VI, and from the ventral side of the posterior part of the medulla and of the anterior end of the cord arise the hypoglossal, XII, and the first two spinal nerves, 1 and 2. The ori- The Nervous System 135 gins of the other cranial nerves were described in connection with the lateral view of the brain, where they show more clearly. On each side of the cere- bral peduncles is seen the ventrolateral edge of the corresponding optic lobe. The pyramidal tracts are seen, extending caudad from the region of the peduncles, as a swelling on each side of the median ventral fissure. THE CRANIAL NERVES (CROCODILE) The origin of each of the cranial nerves was de- scribed in connection with the lateral and ventral views of the brain. A full description of the distribution of these nerves would require more space than the limits of this book will allow, but a brief account will now be given. ian lly ihe olfactory and optic. nerves: These two large nerves go immediately to their respective sense organs, so that no further discus- sion of them need be here given. III. The oculomotor nerve. The single stem divides into three branches: a median, going to the externus rectus muscle; a lateral, going to the inferior rectus muscle; and an intermedial, going to the inferior oblique muscle. IV. The trochlear (pathetic) nerve leads to the superior oblique muscle. V. The trigeminal nerve. The distribution of this nerve is very complicated. It has three 136 The Alligator and Its Allies main divisions: (1) the ophthalmic. branch, (2) the superior maxillary branch, and (3) the inferior maxillary branch. (1) The ophthalmic in turn divides into two branches: the smaller, frontal, going to the integument of the upper and lower eyelids; the larger, nasal, going chiefly to the nasal cavity but also sending some small branches to the upper and lower eyelids. (2) The superior maxil- lary branch separates into a number of divisions: (a) a branch that, in the neighborhood of the auditory capsule, fuses with the facial nerve; (b) a twig to the integument of the forehead and to the upper and lower eyelids; (c) a branch to the Harderian gland and the conjunctiva; (d) a branch to the neighborhood of the cheek, to the angle of the mouth, and to the palatine branch of the facial nerve; (e) a branch to the palate; (f) a branch to the integument of the upper jaw; (g) a branch to the teeth of the upper jaw. (3) The inferior maxillary branch divides into four branches: (a) this division supplies the skin of the cheek region; (b) a branch to the chewing muscles; (c) a branch that divides into two mnerves—the first going to the skin of the lower jaw, the second dividing again into two nerves, both of which lead to the integument of the lower jaw; (d) the fourth division of the inferior maxillary, known as the inferior alveolar, itself divides into two twigs—(a’) the first twig divides into two parts, a larger and a smaller, both of which lead, The Nervous System 1 Dy different paths, to the inner. skin of the mouth; (b’) the second twig divides into four parts—two leading to the mylohyoid muscle and to the integument at the corner of. the mouth, one to the integumental glands at the corner of the mouth, and one to the floor of the mouth cavity. VI. The abducens nerve leads to the retractor oculi muscle and to the muscle for the nictitating membrane. Wit. The facial merve gives off three main branches: (1) the first divides again into three twigs—(a) connecting with a branch of the trigemi- nal nerve, (b) and (c) connecting with the trigem- inal and also leading to the palate; (2) the second branch divides into two twigs that connect with the glossopharyngeal nerve; (3) the third branch divides into two parts, a muscular twig, and the chorda tympani. VIII. The auditory or acoustic nerve leads, of course, to the sensory regions of the ear. IX. The glossopharyngeal nerve divides into four main branches, as follows: (1) to the larynx, (2) to the oesophagus, (3) to the hyomaxillary and sterno-maxillary muscles, and (4) to the tongue. There are also certain communicating twigs with the facial and vagus nerves. X. The vagus or pneumogastric nerve gives off four branches: (1) and (2) communicate with each other and supply the pharynx, larynx, cesoph- 138 The Alligator and Its Allies agus, and trachea; (3) goes to the cesophagus; (4) goes to the heart, lungs, and stomach. XI. The spinal accessory nerve. There seems to be some doubt as to the exact identity and distribution of this nerve, but Bronn says that, according to Fischer, it gives twigs to the lower head-muscles and then divides into fine branches in the atlanti-mastoideus muscle. XII. The hypoglossal nerve, going to the region of the tongue, divides into three branches: (1) the median and smallest goes to the sterno-maxillary muscle; (2) the inner and larger goes to the same muscle and also to the coraco-hyoid and sterno- hyoid muscles; (3) the outer and largest divides in- to three twigs of which the first two lead to the hyomaxillary and sterno-maxillary muscles respec- tively, while the third divides into two twigs that lead to the hyoglossal and genioglossal muscles respectively. THE SPINAL NERVES As was noted above, the dorsal roots of the first two spinal nerves are lacking. I, II, and III. The ventral branches of these three nerves supply the smaller, ventral neck muscles. IV. The ventral branch of this nerve innervates | with its chief divisions the ventral muscles, the sphincter colli, and the integument of the neck, The Nervous System 139 and sends a small branch to the levator scapule superficialis muscle. V. The ventral branch of this nerve sends branches to the ventral muscles of the neck, to the levator scapule superficialis; a large branch goes to the sterno-mastoid; and the rest of the nerve distributes itself in the sphincter colli and the integument and ventral muscles of the neck. VI. The sixth nerve distributes itself to the ventral musculature and to the integument of the neck, and sends a fairly strong branch to the levator scapulz superficialis muscle and to the most anterior part of the collo-thoraci-supra- scapularis profundus muscle. VII. The seventh nerve is the first to enter, by a small branch, into the brachial plexus (Figure 31). It also sends a branch to the ventral muscles and the integument of the neck, and three branches to various shoulder muscles. VIII. The ventral branch of the eighth nerve (Figure 31) is the second largest nerve of the brachial plexus. It gives some twigs to the ven- tral muscles and then gives one or two nerves to the collo-thoraci-suprascapularis profundus and the Setrabus superfictalis muscles. The rest of the nerve divides into an inferior and a superior branch which unite with the ninth nerve. IX. The ninth and tenth nerves are the largest of the brachial plexus. The former, after giving off some twigs to the ventral musculature and to 140 The Alligator and Its Allies the serratus superficialis and the hinder regions of the collo-thoraci-suprascapularis profundus muscles, unites with the tenth nerve just after giving off the small thoracicus inferior nerve to the costo-coracoideus muscle. After uniting with the tenth nerve the ninth nerve immediately divides into two branches that form loops with branches of the eighth nerve, the whole making a very complicated plexus. X. The tenth nerve, as noted above, is one of the two largest nerves of the brachial plexus. After giving off a single nerve to the ventral musculature, this nerve unites with the eleventh nerve; it then gives a branch to the costo-coracoid- eus muscle and forms a loop with the ninth nerve. After giving off a couple of nerves it again divides into two equal branches which unite with similar branches of the eighth nerve. XI. The eleventh nerve is next to the smallest of the plexus. Besides branches to the trunk musculature it gives a fine twig to the integument of the axilla and unites with the tenth nerve in the brachial plexus. This is the last nerve that enters into the brachial plexus. The distribution of the nerves of the brachial plexus is as follows (Fig. 31): (a) supracoracoideus to the muscle of that name and to the integument of the breast; (b) thoraci inferiores nerves (10a)— a complex of nerves from the eighth, ninth, and — tenth spinal stems—lead to the costo-coracoideus | o—annn Gibenaiand BiG. 31; TUS. VII-XI. ventral branches of seventh to eleventh Supine | nerves. 3a. thoracicus anterior VII. 4. thoracicus superior V. (GMO maces Superior Wl. 7a. proximally- leading thoracicus superior. 7. distally-lead- ing thoraci- cus superior VIII. g. thoracicus superiorIX. 104, 1041, 1042, 1003. thoracicus inferior. 18. cutaneuspec- toralis. 19. pectoralis. 21. brachialis longus in- ferior. BRACHIAL PLEXUS oF C. Acu- (From Bronn, after Furbringer.) 22. coraco-bra- chialis. 22c. branchforthe distal belly of biceps muscle. ZA Mets Caltielralt branch for thehumero- antebrachi- alisinferior. (25+42). cutaneus brachii and antebrachii medialis. 29. subscapu- laris. 31. dorsalis scap- ule (pos- terior). 32. cutaneusbra- chii superi- or lateralis. 33. deltoides in- ferior. 34. brachialis longus su- perior. 36. anconzus. 36a. scapulo-hu- meralis pro- fundus. The Nervous System 141 muscles and to the anterior part of the transversus abdominis muscle; (c) the pectoralis (19), a large nerve leading to the muscle of that name; (d) cutaneus pectoralis (18), fine branches from the XIth spinal nerve to the integument of the axilla and the neighboring parts of the breast; (e) coraco- brachialis (22) to the like named muscle; (f) cutan- eus brachii et antebrachi1 medialis (25 + 42) to the medial side of the integument of the upper and fore arm; (g) brachialis longus inferior (21), a large nerve that supplies the biceps and humero- antebrachialis inferior muscles, and then divides into the medianus and ulnaris inferior nerves; (h) subscapularis (29) to the like named muscle; (i) scapulo-humeralis profundus (36a) to the like named muscle; (j) axillaris, a large stem that divides into two main twigs that lead to the skin of the lateral side of the upper arm, to the proximal part of the forearm, to the humero-radialis muscle, and to the deltoides coraco-sternalis muscle; (k) dorsalis scapule (posterior) (31) to the deltoideus scapularis muscle; (1) teres major (29b), one (alligator) or two (crocodile) middle-sized nerves to the teres major muscle; (m) latissimi dorsi (29b) to the like named muscle; (n) brachialis longus superior (radialis) (not shown in Figure 31) to the extensor side of forearm and the hand. Of the spinal nerves between the brachial and crural plexuses Bronn gives no description for the Crocodilia. The most posterior nerve of the 142 The Alligator and Its Allies Lf s- XXVI Fic. 32. CRURAL PLEXUS AND IscHIADIC PLEXUS OF THE LEFT SIDE OF A. MISSISSIPPIENSIS. THE NERVE BRANCHES ARE SHOWN AS FAR AS THEIR ENTRANCE INTO THE MuscLEs. THE CRURAL PLEXUS Is MADE UP OF THE PRESACRAL STEMS a, b,c. THE OBTURATOR NERVE 1s Buitt oF Two BRANCHES FROM STEMS A&B. (FROM BRONN, AFTER Gapbow.) a,b,c. presacral nerves. 8. to flexor tibialis externus a & 8. postsacral nerves. muscle. s=XXVI. sacral nerve (26th 9. to flexor tibialis internus spinal nerve). muscle. 2. toextensor ileo-tibialis muscle. 11. to ischio-femoralis muscle. 3. to femoro-tibialis muscle. 13. pubo-ischio-femoralis in- 4. to ileo-fibularis muscle. ternus. 5. to ileo-femoralis muscle. 14. pubo-ischio-femoralis ex- 6. to caudi-ileo-femoralis mus- ternus muscle. cle. 15. to pubo-ischio-femoralis pos- 7. caudi-femoralis muscle. terior muscle. The Nervous System 143 former plexus is the eleventh and the most anterior nerve to take part in the latter is the twenty-third, so that there are eleven nerves that are doubtless distributed to the regions not supplied by the two plexuses. The crural-ischial plexuses (Fig. 32) are made up of branches from five nerves, three presacral (a, b, and c), the sacral (s=xxvi), and one postsacral («); the second postsacral shown in the figure appar- ently does not enter into the plexus. The first and second presacrals terminate chiefly in the abdominal and thigh muscles, though the second sends a large branch to fuse with a branch from the third to form the large obturator nerve (N. obt.) that leads to the muscles of the thigh and knee. The third presacral sends a branch back to fuse with the large sacral (s=xxvi), and these two, together with a branch from the first postsacral, form a complicated network that sends numerous branches to the muscles of the pelvic and femoral regions, to the skin, legs, and tail, as shown in Pieure 32. The large muscles of the tail are innervated by the regular, metameric nerves of that region, and since there are usually thirty-nine caudal vertebra, there are probably about that many pairs of caudal nerves, although the last few vertebre and the muscles of that region are so Small ii may be that some of the nerves are lacking. 144 The Alligator and Its Allies SPECIAL SENSE ORGANS It is not possible in a work of this size to give much space to the discussion of the anatomy of the special sense organs. A few of the main fea- tures will be given here, taken mainly from Bronn’s Thierreich, but for details of structure the reader is referred to that larger work. The Eye. As might be expected, the Crocodilia have the usual upper and lower eyelids and the | nictitating membrane. Except along their thick- © ened rims the lids are usually rather faintly pig- mented, and near the thickened border numerous — goblet cells are found. The structure of the upper and lower lids is | similar except that in the former a bony formation is present, as a support to that lid, even in very | young animals. The arrangement of the muscles, | which are of both smooth and striped fibers, and | the histological structure cannot be described here. | The mnictitating membrane is strongly developed | in the Crocodilia. Its outer surface is marked by | two fairly high folds that are conspicuously pig- | mented. The cartilage described in the nicti- tating membrane of Lacerta is wanting, according ) to Bronn, in the Crocodilia. The glands of the eye are of three types: the | lachrymal glands proper, the Harderian glands, | and the conjunctival glands. The lachrymal gland | is small in proportion to the size of the eye. It | The Nervous System 145 is an elongated, almost band-like structure situ- ated in the roof of the eye-socket, near its border; its long axis lies in an antero-posterior direction. It is so closely inclosed by and united with con- nective tissue that it is difficult to find. The Harderian gland is much larger than the lachrymal gland proper and is easily found. It lies in the forward part of the eye-socket and is of a somewhat three-cornered shape. From its outer and forward base it sends a short, delicate duct to open between the nictitating membrane and the eyeball. The lachrymal canal is well developed in the Crocodilia. Near the forward angle of the eye, on the inner side of the lower lid, are found from three to eight tear dots, lying in a row from behind forward. Each of these dots opens into a small elongated sac. This sac opens downwards and forwards into a common canal, which canal, at first narrow but soon widening, extends for a time parallel to the free border of the eyelid and then enters the opening in the hinder side of the lachrymal bone. Rathke found none of these tear dots on the upper eyelid so concluded that the lachrymal fluid could escape only through the lower lid. This canal, which might correspond to the lachrymal sac of higher forms, is rather narrow until it enters the lachrymal bone, then it becomes considerably wider and forms a sort of re- _ servoir that Rathke calls the “‘saccus naso-lachryma- 146 The Alligator and Its Allies lis.’’ This reservoir is of irregular form and opens forwards into the base of the nasal cavity proper. The third type of gland mentioned above, the conjunctival, is found on the lower eyelid where the conjunctiva passes from the lid to the eyeball. The gland is of a “‘scattered acinose”’ type. The usual muscles of the eyeball are found in the Crocodilia. The four rectus and two oblique muscles have about the usual arrangement and are attached to the eyeball by very short aponeuroses. The retractor oculi muscle is only weakly developed. It consists of two separate bundles which, lying behind the optic nerve, arise from the forward bony wall of the socket and are inserted on the sclera very near the optic nerve. The eyeball consists of the usual layers, includ- ing, as might be expected from the nocturnal habits of the Crocodilia, a typical tapetum lucidum. In the sclera, instead of the bony ring common to the saurians, is found a well-developed cartilage covered with the fibrous layer of the sclera; the fibers of this layer are arranged into two more or less distinct layers. While not worked out in detail the cornea consists of the usual five layers. In the iris the musculature is less Pee than in the birds; Bronn thinks this may be compen- — sated for by the greater development of the | “vascular structures. ’”’ The pupil is a vertical slit. The Nervous System 147 The choroid is very closely united on the outside with the sclera; on the inside it is less closely at- tached to the retina except at the ora serrata. It consists of an outer fibrous coat, an inner, unstrati- fied pigmented epithelium derived embryologically from the pigmented layer of the retina, and the ground substance which is a network of irregular and very vascular cells. As in probably all reptiles there is present in the Crocodilia a vascular pigmented fold of the choroid, the pecten, which projects into the middle of the cavity of the eyeball. In the retina Bronn describes the following ten layers, which are those commonly given in other vertebrate retinas: (1) the inner limiting mem- brane, (2) optic fiber layer, (3) ganglion cell layer, (4) inner granular layer, (5) inner nuclear layer, (6) outer granular layer, (7) outer nuclear layer, (8) outer limiting membrane, (9) cone layer, (10) pigmented layer. The Crocodilia differ from prob- ably all other reptiles in having rods as well as cones in the retina. The rods are more numerous except in the neighborhood of the fovea centralis where the cones predominate; in the fovea itself only cones are found. The lens does not show any characteristics unusual enough to warrant special description. The Ear. The ear is of special interest here because it is in the Crocodilia that are first found the three distinct regions of the ear that are seen 148 The Alligator and Its Allies in the Aves and Mammalia: the external auditory meatus, the tympanic cavity, and the labyrinth. It is the presence of the meatus that lifts the Croco- dilia above the other Reptilia. Two strong folds of integument, one above and one below, completely cover the outer ear and allow it to open as a mere slit on the lateral surface of the head a little back of the corner of the eye. By lifting the upper valve one may perceive the lower half of the meatus and the bottom of the tympanic membrane. ‘The upper valve is the larger and is sickle shaped; the lower is smaller and more three cornered. Both spring from the outer surface of the squamosal bone, from its posterior obtuse angle to its anterior union with the postfrontal. The lower fold is raised highest behind the corner of the eye and is lost in the middle of the rima auditoria; by this Hasse indicates the position of the outer opening of the external audi- tory meatus. The form of the meatus may be compared to a wedge whose base is directed dorso- medio-caudad and whose edge points in a ventro- latero-cephalic direction; its side walls are either soft or bony; its outer end is covered by the folds; at its inner end is the tympanic membrane or drum. The drum is a round, soft, elastic membrane in which a radial arrangement of its constituent fibers may be seen. It is funnel shaped from with- out and above, and the fibers radiate from the apex to which the columella is attached. The membrane The Nervous System 149 is stretched taut and while it does not, as in the higher vertebrates, lie in a bony groove, it possesses around its periphery a strong thickening of circular fibers, the annulus tympanicus, by means of which it is closely united with the lining membrane of the outer ear passage. The drum is attached chiefly to the quadrate but in part to the squamosal bone. The middle ear is divided into an outer part, the tympanic cavity proper, and a part next to the labyrinth, the recessus cavi tympani. Within the tympanic cavity, besides blood-vessels and nerves, is found the columella with its appendage (found in all Reptilia), the recessus scale tympani. The tympanic cavity is formed mainly by the quadrate, though the exoccipital and squamosal bones take some part. In outline it might be compared to a truncated, four-sided pyramid, with its base below, its truncated apex above, and with an anterior, a posterior, a mesial, and a lateral side. From the floor of each tympanic cavity a Eustachian tube leads towards the throat. These tubes unite and connect with the throat by a single small opening just behind the posterior nares, as shown in the figures of the skull. The semicircular canals with their ampulle lie in the usual positions as seen in other vertebrates: the anterior vertical, posterior vertical, and horizontal. The details in structure of the inner ear cannot be -givenhere. The nervous epithelium is said to have the same characteristics as in other vertebrates. CHAPTER V THE DIGESTIVE SYSTEM THE ORAL CAVITY HE mouth in the Crocodilia is large, as is well known, and may be opened very wide. It is bounded anteriorly and laterally by the teeth of the two jaws; these teeth were described in connection with the skull. The mucous mem- brane of the roof of the mouth and of the dorsum of the tongue, especially the former, exhibits numer- ous small papilla (see page 160), and among these, in the posterior region of the mouth, are the ducts of mucous glands. The tongue extends from just back of the mandibular symphysis to the glottis. It is at- tached throughout its entire ventral side except for a short distance at its tip, so that it may be elevated and depressed but not protruded. Among the papillz on its dorsal surface are sense organs, said to be tactile and gustatory corpuscles (see page 165). The posterior margin of the tongue is elevated as a transverse fold that meets a corre- 150 V7 Wy . : ‘ty ea ba Ws ' ee i Ps ha FS oats 2 bak " f A i fl v rs ] i D . : Ss on . a \ We “ay " tat an a Te) \ ites u ise Peles: | ih! j AD ih ' We F Ai) rye v iow ) 4 ie vy Ay | i * om buh if ¢ i via ; oie .. 1 oe §) Soe cute lee Fic. 33. INTERIOR OF THE MoutTH OF A. MISSISSIPPIENSIS f, transverse fold at the base of the tongue; v,v, velum palatinum. SE tetera a_i The Digestive System 151 sponding fold, the velum palatinum, from the lower side of the palate and completely shuts off the mouth from the openings of the trachea and gullet (Fig. 33). Into this hinder chamber open the posterior nares, so that the animal can open its mouth under water without getting water into its trachea; or it may, while holding its prey in its mouth, come to the surface to breathe, without danger of letting water intoits trachea. The nasal passages, leading from the nostrils to the posterior nares, are, of course, completely inclosed by bone, as described in connection with the skull. Ventral to the larynx and posterior part of the mouth is the large, shield-shaped hyoid apparatus, Fig. 25, h, also described in connection with the skull. THE CLSOPHAGUS The cesophagus, Fig. 34, e, is long and of about the same diameter throughout except possibly for a slight enlargement of the anterior region where it leaves the pharynx. The two “olivary enlarge- ments’ mentioned by Chaffanjon (15) are not always present, and when seen were found to contain either food or small stones or both. The outside of the cesophagus is smooth and muscular while the lining is thrown into numerous longitudinal folds that in the empty cesophagus nearly obliterate the lumen; where distended by food or pebbles the longitudinal folds may be almost 152 The Alligator and Its Allies Fic. 34. DIGESTIVE SYSTEM OF A MIssISSIPPIENSIS. bd, bile duct; bs, bile sac; c, cloaca; e, ceso- phagus; f, larger or fundic region of stomach; h, hyoid apparatus; J, liver; p, smaller or pyloric region of the stomach; pa, pancieas; r, rectum; s, small intestine; t, tongue; ir, trachea, obliterated. In) 42 thirty-inch animal the oesophagus is about six inches long, and opens suddenly, but without any ap- parent valve, into the large chamber of the stomach. The his- tology of the cesoph- agus and the other regions of the diges- tive tract will be de- scribed later. THE STOMACH The stomach, as is well known, is made up of two distinct parts; that on (ae animal’s left, into which the oesophagus opens, is many times larger than the part from which the small intestineleads. The larger or fundic re- gion, Fig. 34, f, has, as will be described, very heavy muscular The Digestive System 153 walls. When empty the lining of this part of the stomach is thrown into a few comparatively large folds, but when greatly distended with food, as it sometimes is, the internal folds are com- pletely obliterated and the muscular layers are stretched until they have scarcely an eighth of their original thickness. In Figure 34 the stomach is considerably distended. The large region of the stomach frequently contains a number of stones, and for that reason, probably, is sometimes spoken of as the gizzard. In one thirty-inch alligator fourteen pebbles of irregular shape, varying in largest diameter from four to seventeen mm. and aggregating six grams in weight, were found. Voeltzkow (78) says that gastroliths of two to three cm. diameter are found in the stomach of the adult Madagascar crocodile. Neither the transverse fold nor the smooth, lateral disks (or shields) described by Chaffanjon could be seen in either the empty or in the dis- tended stomach. The smaller part of the stomach, Fig. 34, p, lies to the right and somewhat ventrad to the anterior region of the larger part, near the entrance to the cesophagus. It connects by a fairly large opening with the larger part of the stomach, and by a smaller opening with the duodenum. The former Opening apparently has no valve, unless it be a slight sphincter muscle; the latter is guarded by 154 The Alligator and Its Allies a pair of thickened lips, called by Chaffanjon “‘semilunar valves.” The walls of the smaller part of the stomach are, as might be expected, much thinner than those of the larger region, but they are proportionately fairly thick and are internally thrown into numer- ous folds. THE INTESTINE In the intestine three regions may be distin- guished: a long, considerably coiled small intestine; a wide, nearly straight rectum; and a short, wide cloaca. The small intestine, Fig. 34, s, is of moderate and rather uniform diameter, though somewhat thicker near the stomach, and is not coiled so extensively as figured by Chaffanjon. Near the stomach it re- ceives the ducts of the liver and pancreas. The bile duct, Fig. 34, bd, is a continuation of an elon- gated bile sac, bs, which lies between the large right and smaller left lobes of the liver, 7. The two main lobes of the liver, which appear smaller than in reality because of foreshortening in drawing, are connected, across the base of the cesophagus, by a narrow transverse band. The pancreas, pa, which is of fair size, lies partly dorsal to and partly in a narrow loop of the intestine, so that it is not very evident in a ventral view of the animal, The Digestive System 155 The small intestine has heavy muscular walls whose histological structure will be described else- where. It opens abruptly, without any indication of a ceecum, into the large intestine or rectum. The rectum, r, is of about twice the diameter of the small intestine, though this, of course, varies with the amount of fecal matter it contains; it is nearly straight and possesses much thinner walls than the small intestine, though this, again, varies with the state of collapse or distention. At the posterior end of the rectum is a heavy sphincter valve separating that part of the intestine from the cloaca. The cloaca, c, is widest anteriorly where it is about as wide as the rectum; it gradually diminishes in diameter caudad, and appears flattened later- ally. Its wall has the same general structure as the rectum, as will be described below. The mucous membrane posterior to the openings of the genital ducts is thrown into a more or less com- plete, ring-like transverse fold (Fig. 55 G.). In some species there may be a second, half-ring-like fold in the dorsal wall caudad to the more complete ring. The cloaca is divided by this fold into a larger anterior portion, g, and a shorter posterior portion, h; in the former the mucous membrane is thrown into a large number of small folds that in _ places form a network; in the latter the mucous membrane has a hard, thick epithelium, with a _ smooth surface and only a few longitudinal folds. 156 The Alligator and Its Allies The ureters open, Fig. 55, d, e, at a moderate distance from each other, into the anterior region of the cloaca (about where the dorsal and lateral walls of this region come together). The genital ducts (oviducts or vasa deferentia), c, f, on the other hand, open close together through the ventral wall of the posterior half of the cloaca, just in front of the copulatory organ. Into the cloaca, very near the anus, open two glands of fairly large size that Rathke called musk glands. ‘These glands lie outside of the pelvis between the side walls of the cloaca and a large muscle that surrounds this part of the body. They have an oval form and open usually from their anterior end, sometimes just caudad to this, by a short, fairly wide, slit-like opening which has an anteroposterior direction. The walls of the glands are made up of three closely associated layers of connective tissue, the inner one being thrown into folds. Since these layers contain no muscle fibers the secretion of the gland is probably squeezed out by contraction of the circular muscles of the cloaca. Usually the cloacal glands are stretched full by a thick, yellowish mass that smells strongly of musk. The part of the cloaca caudad to the pelvic opening has a differently arranged musculature from the more anterior region. It consists of two separate pairs of striped muscles that surround the musk glands on the outer side. The first The Digestive System 157 pair form a fairly broad, moderately thick ring muscle next to the anus that is attached anteriorly to the pubis and posteriorly to the second hzmal process. When these muscles draw together they Marrow Or conipletely close the anal slit. The muscles of the other pair are broader but thinner, and extend in a general dorso-ventral direction. Anteriorly, above the cloaca, they are united with each other, but posteriorly they separate and, with the above ring muscle, are inserted on the second hzemal arch. Judging from their attach- ment they widen the anal opening laterally. THe HISTOLOGY OF THE ENTERON OF THE FLORIDA ALLIGATOR _ It has long been known that the sea lamprey, Petromyzon marinus, during the spawning season, when the body is distended with eggs, takes no food, and that the digestive tract during this period shrivels up until it is reduced to a mere thread. This condition doubtless obtains in other forms as well, though it has not been actually observed by the writer elsewhere. A number of small alligators that were kept alive in the laboratory for a year or more caused the writer to wonder whether any very marked change had taken place in their digestive tracts during the months they took no food. In captivity, especially if the water in their tank 158 The Alligator and Its Allies 2.0€s, be kept cold, alligators may re- fuse food for five or sixth months. Whether, during the winter months, in their native haunts, they entirely cease feeding, the writer has had no opportunity to observe, though it is popularly reported that such is the case. The first alligator from which tissues were taken was about a year and a half old, amg measured eighteen inches in length. If was killed in March after a fast of several ‘st months, probably four or five, possibly more, though it was not in the writer’s possession for so long a time. Although carefully | Fig. 35. A diagrammatic outline of the | ps. digestive tract of the alligator from the be- | ginning of the cesophagus to the cloaca, to show the planes of the sections that were — studied. a.oes., anterior cesophagus; ar, — anterior rectum; @.s.7., anterior small intes- | tine; c.st., cardiac stomach; f.st., fundic stom=- — ach; m.s.i., middle small intestine; p.oes., | posterior cesophagus; p.r., posterior rectum | or cloaca; p.s.7., posterior small intestine; | p.st., pyloric stomach. Fic. 35. OUTLINE OF DIGESTIVE TRACT The Digestive System 159 fixed in the usual fluids, the epithelial structures from this animal were not as clearly defined in most cases as could be desired; this rather unsatisfactory fixation may have been due to some physiological condition characteristic of the period of hibernation. That this was the case seems likely from the better fixation obtained by the same methods in the case of animals killed during the feeding season. The other animals from which tissues were taken were considerably smaller than the one mentioned above. They were killed early in the fall, after having been fed regularly for about five months upon bits of meat, both raw and cooked. The Tongue. ‘The covering of the tongue was studied in two regions, near the free end, and towards the base. A section of the former region, drawn under high power, is shown in Figure 36. It consists of a dense mass of fibrous tissue, a, and small scattered cells, overlaid by a stratified epithelium of eight er ten layers. Only a small part of the fibrous base, just beneath the epithelium, is here shown. It is a dense areolar tissue with the elastic fibers apparently predominating. The epithelium, e, consists, as has just been said, of about eight or ten layers of cells, those at the base being generally cuboidal in shape, while towards the surface the cells become more and more flattened until at the surface they form 160 The Alligator and Its Allies a thick horny layer, #, in which no nuclei can be seen. The cells of the horny layer are flattened into mere fibers, which, at places, are seen projecting from the sur face. The bound- ary between the horny cells and those beneath is quite distinct, though perhaps not quite so sharp as shown in the figure under dis- cussion. ; Fic. 36. The covering of the anterior re- “ gion of the tongue of the hibernating animal, In a previous under fairly high magnification; the plane of paper, the writer this section is not shown in Figure 35; a, areolar tissue; e, epithelium; h, horny layer noted that the of epithelium. dorsum of the tongue is covered with small, evenly distributed papille, easily seen by aid of a hand lens. These so-called papille are here seen to be hardly papille at all, but small folds or wrinkles, although the epithelium is some- what thickened at intervals. No glands are to be seen in this region of the tongue. The only difference between the anterior region of the tongue during hibernation and during the feeding season seems to be in the scaly layer of the epithelium. Instead of the compact, sharply dif- | ferentiated layer of scaly cells seen in Figure 36, | | | The Digestive System 161 the anterior region of the tongue during feeding is covered with a layer of rather loose, scaly cells, in most of which the nuclei may be seen. No difference in the amount of slough- ing off can be no- ticed as is the case with the epithe- lium of the roof of the mouth. Figure 37 rep- resents a section, under very low magnification, of the oe of the Fic. 37. Covering of the posterior re- base of the tongue. gion of the tongue of the hibernating ani- The areolar tissue, mal showing glands, under low magnifica- 2 tion; a, areolar tissue; bv, blood-vessels; @,18 about the same g, glands; e, epithelium. as in the preceding section, except that it is more compact just under the epithelium than it is in its deeper regions. It seems also more vascular than in the preceding section. | The epithelium, e, is of the stratified squamous va- riety, but consists of many more layers of cells than in the preceding section and is hence several times as thick. While its cells are flattened towards the surface, after the manner of this kind of epithe- lium, they do not form the definite horny layer de- scribed above. It 162 The Alligator and Its Allies The most marked difference between the two regions of the tongue is the presence, in the poste- rior or basal region, of numerous glands, g, probably mucous- or slime-secreting. They are thickly Fic. 38. One of the glands from the posterior region of the tongue of the hibernating animal, under high magnification; a, areolar tissue; av, alveolus. scattered through the areolar base, close beneath the epithelium. ‘Two large glands and one small one are shown in the figure under discussion. Each | gland opens to the surface by an apparently wide | duct, but since no good section of such a duct | was obtained it is not shown in the figure. Al | though the rest of the tissue was well preserved | The Digestive System 163 and showed cell structure clearly, it was with difficulty that the details of the glands could be determined. A high-power drawing of a portion of one of the glands is shown in Figure 38. The large alveolus, av, to the left, is from the peripheral region of the gland and is surrounded, on its free side, by the areolar tissue described above. The inter-alveolar spaces, which are somewhat exaggerated in the figure, are filled with fibers which are arranged more or less in layers and hence appears different from the surrounding areolar tissue. The alveoli are circular or elongated in section, and have fairly wide lumina. They are lined with a single layer of columnar or cuboidal cells which are very granu- lar, so that their walls are difficult to determine. Each cell contains, near its base, a very large, usually spherical nucleus. These nuclei stain darkly and give the dark appearance to the glands as seen under low magnification, especially in rather thick sections. During feeding the epithelium of this region of the tongue consists of fewer layers of cells than during hibernation but is otherwise unchanged from what is described above. The glands con- sist, at least in all of the material examined, of much fewer alveoli than are shown in Figure 37. One of these glands is shown in Figure 39. _ Although no more care was used in fixation than in the corresponding tissue of the hibernating 164 The Alligator and Its Allies animal the glands here show their cell details far more clearly than in the former tissue; this may have been partly due to the latter sections being thinner. The glands are of a compound, tubulo-alveolar type; although numerous _ sec- tions through ducts were ob- tained (as in Fig. 39), no de- tails of these ducts could be seen. As note above, and as may be seen by Fic. 39. One of the glands from the poste- comparing Figs rior region of the tongue of the feedinganimal, ures 37 and 39, under somewhat higher magnification than the gland during used in Figure 37; av, alveolus; d, duct of af 8 ; gland; e, stratified epithelium. hiber nation, at least in the an- imals studied, consists of many more alveoli than during the feeding season; this, of course, might not prove to be always the case if larger num- bers of animals were studied; the difference in the ages of the animals might have caused this difference in the glands. In the material studied the largest glands from the hibernating animals consist of more than twice as many alveoli as the glands in the feeding animals. As seen The Digestive System 165 under high magnification there is no noticeable difference in the glands at the two seasons. Rathke has given the name of ‘‘Gescmack- warzchen”’ to the conical projections found on the dorsum of the crocodilian tongue; they are distinguished by their softness and thinner epi- thelial covering from the cones that, in many of these animals, bear the openings of the mucous glands. These taste papilla generally have the form of a truncated cone and often are surrounded by a shal- low circular pit, outside of which, in turn, is some- times a small low wall. They are distributed over the entire dorsum of the tongue, usually at con- siderable distance from each other in comparison to the size of the tongue, and are not so numerous as the taste papillae of the Mammalia. Rathke found their absolute number greatest in A. lucius. Rathke mentions other larger and harder pro- jections on the tongue of certain Crocodilia which, though not perforated by a mucous duct, he thinks are of questionable relation to the sense papillz. They usually have more the form of a flattened than of a truncated cone, and are very numerous in some species. The Roof of the Mouth. Inthe paper mentioned above the author notes that the papillz on the roof of the mouth are evenly distributed and are more distinct than those of the dorsum of the tongue. 166 The Alligator and Its Allies One of these papille as seen under fairly high magnification is shown in Figure 4o. The areolar tissue, a, forming the base of the section is of about the same character as seen in Fic. 40. The covering of the roof of the mouth of the hibernat- ing animal, under fairly high magnification; a, areolar tissue; e, epithelium; h, horny layer; f, fibers of horny layer. the section of the tongue. Less than one tenth of the thickness of the entire areolar base is shown in this section. The epithelium, e, where not thrown into papilla, has also about the same character as that of the anterior region of the tongue—the same number of cell layers and the same distinct horny layer. At intervals the thickness of the cellular part of The Digestive System 167 the epithelium is greatly increased, and at the same time the horny layer is also thickened, to form distinct papilla like the one shown in the figure. These, as has been said, are comparatively small and have the shape of a blunt cone. The center of the cone is, of course, made up of the cellular epithelium, while the outside is covered with the thickened horny layer from which fibers, f, are often seen projecting. Near the apex of the cone the nuclei are larger and more widely scattered than those at the base. No glands were seen in the roof of the mouth of the hibernating animal, but since the entire roof was not sectioned it is probable that they may exist in some regions; in fact, as noted below, sec- tions through the posterior region of the roof of the mouth of the feeding animal do show numerous glands. As might be expected there is comparatively little difference between this region of the enteron during hibernation and during the feeding season. The only noticeable difference is in the stratified epithelium; that of the feeding animal not only has less sharp papillae but has also a much thinner scaly layer of cells. As is seen in the figure of the roof of the mouth during hibernation the scaly cells make up, except on the papille, nearly or quite half of the thickness of the epithelium, while in the feeding animal they make up not more than one fourth or one third of the entire epithelium. Very 168 The Alligator and Its Allies few cells are seen sloughing off as in Figure 40; possi- bly the act of feeding keeps the superficial scaly cells rubbed off smooth. In the extreme posterior region of the roof of the mouth the epithelium consists of a greater number of layers (though the number is very variable) than in the region shown in Figure 4o. In this posterior region, as noted above, glands are found. These glands have the same structure as those described in connection with the posterior region of the tongue. The Césophagus. Sections of the cesophagus were made from two regions, an anterior, half-inch caudad to the pharnyx, and a posterior region, half-inch cephalad to the opening of the oesophagus into the stomach (Fig. 35). The general structure of the wall of the cesopha- gus, as seen under a low magnification, will first be described, after which the minute structure of the epithelium, as seen under high magnification, will be discussed. In the anterior region the usual layers of the vertebrate enteron are present, except, possibly, the muscularis mucosa. The epithelium, to be described later, is, together with the submucosa, thrown into complicated folds; its closely arranged and darkly stained nuclei cause it to stand out in strong contrast to the other tissues of the section (Fig. 41, e). The submucosa, sm, is of considerable thickness, The Digestive System 169 It is composed of a fairly dense mass of connective tissue, mainly elastic fibers, through which are scattered small blood-vessels, bv, and small dark areas, mb, that are appar- ently longitudinal bundles of involuntary muscle fib- ers. These few and scat- tered fibers probably represent the muscularis mucosa that is so well developed in the poster- ior region of the cesoph- agus. Outside of the mucosa is a thick circular layer of involuntary muscle fibers, cm, the fibers being col- lected into irregular bun- - Fic. 41. A transsection dles, between which are through the anterior region of the narrow spaces filled with csophagus of the hibernating : ° animal under low magnification connectivetissue thatcon- 4, blood-vessels; mb, muscle tains a few small blood- — bundles; other letters as in Fig- vessels. EAE Surrounding the circu- lar layer is a thinner and less clearly defined layer of longitudinal muscle fibers, Jm. The muscle bundles are more definite than in the circular layer and are separated from each other by a consider- able amount of connective tissue with a few small blood-vessels, 170 The serosa, s, is here quite indistinct. A transsection RIG. 42: through the posterior region of the oesophagus of the hibernating animal, under low magnification; e, epithelium; cm, circular muscles; Jm, longitudinal muscles; mm, muscularis mucosa; sm, sub- mucosa; S, serosa. The Alligator and Its Allies It con- sists of a slightly vascular connective tissue which can- not be distinctly differenti- ated from the connective tissue of the longitudinal layer. In the posterior region of the cesophagus, as may be seen by comparison of figures 41 and 42, the wall as a whole is about one third thicker than in the anterior region just described, though how much of this difference is due to different degrees of dis- tension or contraction it is hard to say. The epithelium, e, is in the tissue studied thrown into less complicated folds than in the anterior region, and is not so thick. The submucosa, sm, if the entirelayer may be so called, has about the same thick- ness and structure as in the more anterior region; but instead of the small and widely scattered bundles of longitudinal muscle fibers there is a distinct layer of muscle The Digestive System 171 which may be called the muscularis mucosa, mm, lying about midway between the epithelium and the circular muscle layer. The muscularis mucosa is somewhat variable in thickness and is thrown into folds that correspond to the larger folds of the epithelium and the sub- mucosa; one of these folds is shown in Figure 42. The fibers of the muscularis mucosa are apparently all longitudinal in position. Outside of the submucosa is a layer of circular muscle fibers, cm; it is here somewhat wider and more dense than in the anterior region. The longitudinal muscle layer (Fig. 42, lm) is much wider and more compact than in the anterior region. The fibers are indistinctly divided into large irregular masses as shown in the figure. The serosa (Fig. 42, s) is a varying but fairly thick layer that is quite distinct from the longi- tudinal muscle layer. It consists of the usual connective tissue groundwork with scattered blood- vessels. The epithelium, as was said above, is thicker and somewhat more folded in the anterior than in OL LLL LLL ee the posterior region, and in the former region is partially ciliated while in the latter cilia are entirely wanting. With these exceptions the epithelium is practically the same in the two regions. Figure 43 represents the epithelium from the an- terior region as seen under high magnification. The outlines of all the cells could not be determined 172 The Alligator and Its Allies but if each nucleus represents a cell there are twenty-five or thirty layers of cells. FIG. 43. anterior region of the cesophagus of the hibernating animal, under high magnification. The epithelium of the The nuclei are arranged in two dense, irregular groups, one along the base of the epithelium, the other about two thirds of the distance from the base to the free border. The basal nuclei are perhaps slightly larger and more rounded than those of the distal group. Be tween these two groups are numerous more scat- tered nuclei; while scattered through the epithelium, except near the free border, are smaller, round nuclei that stain somewhat darker than the rest; these, from their size and appearance, seem possi- bly to belong to an invisible network of connective tissue that has penetrated the epithelium from the surrounding mucosa. The free border of the epithelium consists of long, ciliated, columnar cells in which the cell walls may be easily seen. The cilia are of average length and The Digestive System 173 even in this anterior region are not everywhere present; possibly they are arranged in bands, but the material at hand was not suf- ficient to determine this. As was noted above, cilia are wanting in the posterior region. The only differences noted in the anterior region of the oesophagus between the feeding and the hiber- nating conditions are in the muscu- laris mucosa and the epithelium. As was noted above, the muscularis mucosa is practically absent in the hibernating stage, being represented only byafewsmall, scattered bundles of longitudinal muscle fibers; while in the feeding stage there is a narrow but fairly distinct layer to represent the muscularis mucosa. The difference in the appearance of the epithelium is not striking. The nuclei are somewhat larger in the feeding stage and, instead of being crowded into a basal and a median zone, as noted in the hi- The Fic. 44. epithelium of the anterior region of the cesophagus of the feeding animal, under high magnifica- tion. bernating conditions, they form a dense basal zone, but show no indication of medial zone. From the dense basal zone the nuclei become more scat- tered towards the free surface and are rarely found closer to the surface than is shown in Figure 44. 174 The Alligator and Its Allies The smaller nuclei scattered among the larger ones, noted in connection with the hibernating stage, are not here seem As in the hibernating stage cilia are present on some but not all cells of this region. The only noticeable difference between the feed- ing and hibernating conditions of the posterior region of the cesophagus is in the epithelium, which, as in the feeding condition of the anterior oesophagus, exhibits but one zone of closely set nuclei, that at the base of the epithelium. The Stomach. The stomach was sectioned in three regions, as shown in Figure 35: (1) in the cardiac region very near the opening of the ceso- phagus; (2) in the middle or fundic region; and (3) in the region near the opening of the pylorus. The first two sections are in the first or large region of the stomach; the third section is in the second or small region of the stomach (Fig. 35). The wall as a whole is thickest in the fundus, be- ing there practically twice as thick as in the pyloric and half again as thick as in the cardiac region. This great thickening is due mainly to a thickening of the middle or oblique layer of muscle, which is here remarkably developed. The mucosa is of nearly uniform thickness in the different regions and will be described later. ) Since there is no striking difference beside that of — thickness in the general structure of the wall of the — The Digestive System 175 different regions, the pyloric region, as seen under low magnification, will now be described (Fig. 45). The mucosa, m, consists of fairly long glands underlaid by a well-marked muscularis mucosa, mm, the latter exhibiting a compact circular layer over a wider but more scattered layer of longitudinal fibers. A considerable amount of fibrous con- nective tissue lies among the muscle fibers. The circular layer of the muscularis mucosa sends towards the surface numerous strands or septa between the glands; six or eight of these are seen in the figure. These strands are not nearly so nu- merous in the large region of the stomach. As was said, the outer or longitudinal layer of the muscularis mucosa is wider but less compact than the circular and its bundles of fibers are seen in the figure as a layer of large, scattered dots just beneath the circular layer. The submucosa, sm, is of average thickness and density. In the fundic and cardiac regions it seems to extend between the circular and oblique layers; at any rate, there is a considerable layer of connective tissue between these two muscular layers. The circular muscular layer, cm, is of only moder- ate thickness and is of rather a loose character. In the pyloric region it is not very distinct from the underlying oblique layer, but in the other regions, as has just been said, it is separated from 176 The Alligator and Its Allies the oblique layer by a considerable layer of con- Fic. 45. A transsection through the wall of the pyloric re- gion of the stomach of the feed- ing animal, under low magnifi- cation; m, mucosa; om, oblique muscles; other letters as in Fig- ure 42. nective tissue like that of the submucosa. The oblique layer, om, even in this section of the pyloric region is the thick- est of the three muscle layers; while in the car- diac, and especially in the fundic, regions it is Of great thickness, as was noted above, and is made up of larger bundles with less intervening connec- tive tissue. The outer or longitud- inal muscle layer, lm, is comparatively little de- veloped and consists of small rather scattered bundles of muscles with a correspondingly large amount of connective tis- sue. This connective tissue passes insensibly into that of the surround- ing serosa, s, a loose, vascular layer of varying thickness and density, shown very thick in Figure 45, but often much thinner. So far as could be determined, the mucous mem- The Digestive System 177 brane has the same structure in both anterior and middle regions of the stomach. That of the pyloric or small region, although fixed, stained, et cetera, just as\carefully as the rest, did not show cell details suffi- ciently well to draw; the ducts of the glands in this regionarefairly dis- tinct but thedeeper parts of the glands have the appear- pace of-.series of alveoli or large adi- pose cells. What the significance of this condition may be the writer is not able to say, but since the structure of this region of the gastric mucous membrane is not clear no attempt Fic. 46. The glands of the middle or fundic region of the stomach of the hiber- nating animal, under high magnification; A, through duct; B, through body of gland; C, through fundus of gland. will be made to describe its appearance under higher magnification than was employed in the fig- ure above. However, as will be noted below, there is probably no great difference between the pyloric mucosa and that of the other regions of the stomach. Figure 46 shows portions of typical glands 12 178 The Alligator and Its Allies from the mucosa of the middle region of the stom- ach, the posterior border of the large stomach cavity; A is a longitudinal section through two ducts where they open to the surface; B is a similar section through the body of a gland below the region of the duct; C is a transsection through the bottom or fundus of a gland; all are drawn with a camera under the same magnification. As is seen in Figure 45, under low magnification, the duct is about one third of the entire length of the gland. The lumen of the duct is fairly wide, that of the body of the gland is reduced to a mere slit, while that of the fundus is quite wide. One, two, or possibly more, glands may open to the surface through one duct, as is shown in Figure 46. There is nothing peculiar about the epithe- lium of these glands. Near the opening of the duct the cells are of a typical columnar character with finely granular cytoplasm, each with a nucleus at its basal end. In the deeper parts of the duct the cells become shorter until in the body of the gland (Fig. 46, B) | they are cuboidal in outline. The bodies of the glands are so closely packed | together that it is difficult to pick out an individual tube that will show details clearly enough to draw with a camera lucida. So far as could be observed all of the cells of this region of the gland are alike. The bottom or fundus of the gland, as seen in Figure 46, C, is somewhat enlarged and has a wide | The Digestive System 179 lumen. The cells are of the same general character as in the more distal parts of the gland except that they are somewhat more columnar or py- ramidal than in the body of the gland. The nuclei of the body and fundus are usually somewhat larger and more nearly spherical than in the columnar cells of the duct. The feeding animals from which tissues were taken were considerably smaller than the hiber- nating specimen, so that the stomach walls were proportionately thinner; but, so far as could be discovered, there was no difference in structure. The relative thickness of the entire wall in each of the three regions sectioned was about the same as described above. As has been said, the mucosa or the pyloric or small region of the stomach from the hibernating animal was so poorly fixed that its structure could not be made out. In the feeding stage the mucosa of this region was as well fixed as any of the other tissues and showed that its structure is essen- tially like that shown in Figure 46, except that the glands are proportionately not quite so long as in the fundic and cardiac regions, and are somewhat more open—that is, they have wider lumina; their lining cells are all of one kind and are unchanged from what was seen in the hibernating condition. The Small Intestine. Three regions of the small intestine will be described: (1) an anterior, just 180 The Alligator and Its Allies caudad to the stomach; (2) a middle; and (3) a posterior, one half inch cephalad to the rectum or large intestine (Fig. 35). As might be expected, the general structure of the wall of the intestine is essentially the same in all three regions, the slight differences noticeable being due mainly to variations in the thickness of the various layers. The middle and posterior regions have about the same diameter, while the diameter of the anterior region is considerably greater, due partly to the greater diameter of the lumen but mainly to the greater thickness of the constituent layers, espe- cially the mucosa. The mucosa is also thrown into more numerous and complicated folds in the anterior than in the middle and posterior regions; the complexity of the mucosa seems to diminish as the intestine is followed caudad. In the anterior region the mucosa may form at least one half of the, entire thickness of the wall, while in the posterior region it may form less than one third of the — thickness of the intestinal wall. The minute structure of the intestinal epithelium will be de- | scribed below. | The chief peculiarity of the intestinal wall is | the apparent total absence of a submucosa (Fig. 47). As will be described later, the mucosal epithelium is laid upon the usual bed of fibrous and lymphatic tissue, the tunica propria (Fig. 47, tp). The Digestive System 181 At the outer border of the tunica propria, and with no tissue corresponding to a submucosa between it and the circular muscular layer, is a thin and indistinct layer that has the appearance Fic. 47. A transsection of the wall of the anterior region of the small intestine of the hibernating animal, under low magnification; ln, lymph node; ¢p, tunica propria; other letters as in Figure 42. of a longitudinal layer of muscle fibers; this should correspond to the muscularis mucosa (Figs. 47, 48, 49, and 51, mmz). The circular, cm, and longitudinal, Jm, muscle layers are compact, and are distinct from the other layers of the wall; the former is approxi- mately twice the thickness of the latter. The relative thickness of all the layers in the three 182 The Alligator and Its Allies regions of the intestine may be seen by comparing Figures 47, 48, and 49. The serosa, s, which is of about the same character in the three regions under discussion, is a distinct and fairly dense layer of connective tissue with numerous blood- vessels. The general appear- ance of the mucous membrane as a whole is sufficiently clear in the low-power draw- ing described above, so that all that need Fic. 48. An outline of a trans be shown under a section 19: the wall of the middle higher magnification region of the small intestine of the , r : : hibernating animal, underlow magni- 18 the epithelium (Fig. fication; lettering as in Figure 42. 50). The upper part of this figure repre- sents the lower end of one of the intestinal glands cut longitudinally, below which is the end of another gland in transverse section. Be- tween the two sections is the compact tunica propria of lymphatic tissue. The section from which this particular figure was drawn was in the anterior region, but the corresponding part of a section in either of the other regions would have practically the same appearance. The Digestive System 183 The epithelium is of the stratified columnar type. The superficial cells are very tall and narrow, with the nuclei generally at or near the bases, though an occasional nu- cleus may be seen near the free end of a cell. Below the tall columnar cells are four or five rows of nuclei which represent smaller, irregular cells, though the cell walls could not always be deter- mined between the closely packed nuclei. No goblet cells are to be seen at any place. The relative diameters of the three regions of Fic. 49. Anoutline of a trans- 2 c section through the wall of the the small intestine in posterior region of the small in- the feeding condition are _ testineof the hibernating animal, about the same as noted re Un eneang, oa for the hibernating stage; that is, the anterior re- gion has the greatest diameter and the other regions are smaller and have about the same aver- age diameter. The most marked difference between the intes- tine during hibernation and feeding is in the relative thickness of the mucosa and muscular layers. As described for the hibernating stage, so in the feed- 184 The Alligator and Its Allies ing stage, the mucosa is relatively the thickest in the anterior regions and diminishes in thickness Fic. 50. Part of the mucous mem- brane of the anterior region of the small intestine of the hibernating animal, under high magnification. The upper part of the figure shows a part of a gland cut longitudinally, the lower part of the figure shows another gland cut transversely; e, epithelium; ¢p, tunica propria. caudad; but while, in the hibernating stage, it forms, in the anterior region, as much as half of the entire thickness of the wall, in the feeding condition it forms, in the same region, at least two thirds of the entire wall and in the mid- dle and_ posterior regions more than half of the wall. The feeding ani- mals being the smal- ler, the diameter of the intestine was considerably less than in the hiber- nating stage; but the actual thickness of the mucosa was practically the same, so that the difference in diameter was due to the difference | in the thickness of the muscular and fibrous layers. It is therefore probable that the differences noted above are due rather to the differences in the size The Digestive System 185 of the animals from which the tissues were taken than to the different conditions of hibernation and feeding. The point to be noticed is that the increase in the diameter of the intes- tine is due almost if not entirely to an increase in thickness of the connective tissue and muscle layers. No difference in the com- plexity of the folds of the mucosa of the two stages can be noticed. The thickness of the fibro- muscular part of the wall of the intestine varies consid- erably on different sides of the same region, but it con- sists of the same layers in about the same relative amounts. Picture, 51 represents in outline the wall of the mid- dle region of the small intes- tine during feeding. Fic. 51. An outline of a transsection of the wall of the middle region of the small in- testine of the feeding animal, under low magnification; m, mucosa; other letters as in Figure 42. The epithelium is of the same thickness in the two stages, and the only difference in its character that can be seen under a high magnification is that, in the middle region at least, the nuclei are not crowded so close together at the basal ends of 186 The Alligator and Its Allies the cells as in the hibernating stage but are scat- tered more towards their free ends. Altogether, the differences in microscopic struc- Fic. 52. A transsection of the wall of the anterior region of the rectum or large intestine of the hibernating animal, under low magni- fication; ¢p, tunica propria; other letters as in Figure 42. ture between the small intestine of an alligator at the end of the hibernating period and at the end of a period of regular feeding are very slight. The Large Intestine. The planes of the two sections studied are shown in Figure 35; a low- The Digestive System 187 power drawing of the posterior region is shown in Figure 52. The anterior and posterior regions of the large intestine do not differ from each other sufficiently to make it worth while to represent both by drawings. Had an entire section through either region been drawn it would be seen that the wall is of very different thickness in different places, as was noted in connection with the small intestine; the posterior section was drawn where the wall was thin. It might be supposed that in the feeding season the fecal matter in the posterior re- gion of the rectum would Fic. 53. The epithelium stretch the walls sufficiently of the anterior region of the to obliterate largely the “itmolstenbenetngan: prominent folds seen in Fig- tion; ¢, epithelium; %p, ure 52, but such does not tunica propria. seem to be the case. The usual layers of the vertebrate intestine are present. The epithelium, shown under high magnifica- tion in Figure 53, is of the same character and thick- ness throughout, except that as the anal aperture is approached the columnar epithelium changes into the stratified variety. It consists of very tall and narrow columnar cells apparently in one layer, though it is difficult to be sure of this. With an 188 The Alligator and Its Allies occasional exception, near the top, all of the nuclei are arranged in a fairly wide zone below the middle of the epithelium. The nuclei are oval in shape and lie so close together that it is difficult, as has been said, to be sure that the cell to which each belongs extends throughout the entire thickness of the epithelium. Beneath the epithelium (Fig. 52, e) is a dense tunica propria, ¢p, underlaid, in turn, by the muscularis mucosa, mm, and a submucosa, sm, of the usual character, which is thrown into marked folds. The circular, cm, and longitudinal, /m, layers are of the usual character except that they vary more in thickness, as noted above, and in density than is usually the case. The serosa, s, is comparatively thin and com- pact in both regions, and varies somewhat in thickness at different places. The large intestine of the feeding animal was sectioned in the same regions as in the hibernating. As has been said, the feeding animals used were much smaller than the hibernating, so that, as might be expected, the diameter of the large intestine was much less in the former than in the latter. Except for this difference in diameter there was no noticeable difference between the two stages. In the case of the small intestine, it will be remembered, the greater diameter of the intes- tine of the larger animal was mainly due to the greater thickness of the muscular and connective- The Digestive System 189 tissue layers and not to any increase in thickness of the mucous membrane. In the large intestine the mucosa varies in thickness in the animals of different size as do the other layers of the wall. The glandular character of the lining of the large intestine seems to indicate that his region of the intestine must have some digestive or absorptive function and that it does not act merely as a re- ceptacle for fecal matter; this makes it all the more strange that there should not be some change pro- duced in its structure by five or six months of feeding or of fasting. Summary. The material used in this investiga- tion was taken from young animals at the end of a feeding period of about five months, and towards the end of the hibernating period after fasting for four or five months. The regions of the enteron that were studied were as follows: the tip and base of the tongue; the an- terior and posterior regions of the roof of the mouth; the anterior and posterior regions of the cesophagus; the cardiac, fundic, and pyloric regions of the stomach; the anterior, middle, and posterior regions of the small intestine; the anterior and pos- terior regions of the large intestine. Since the work was started at the end of the hibernating period, the tissues of that period were studied and drawn first. The only difference between the structure of the tip of the tongue during hibernation and during 190 The Alligator and Its Allies the feeding season is that the scaly epithelium with which it is covered is somewhat thicker and more compact in the former than in the latter condition, though even this difference may have been due to differences in the ages of the animals used. The base of the tongue differs from the tip in having a thicker epithelium and in having compound tubulo-alveolar glands. These glands in the hiber- nating animal have many more alveoli than in the feeding animal, though this, again, may have been due to the difference in age. The lining of the roof of the mouth is essentially the same as that of the tongue. The glands are found only in the posterior region. The slight differences in tho papilla here found may easily be due to the difference in age. The cesophagus shows the usual layers for that region. Its epithelium is partly ciliated in the anterior part. The muscularis mucosa is very scant in the anterior region. The only difference between the two stages is that in the feeding the muscularis mucosa in the anterior region is much more strongly developed than in the hibernating stage; and in the former the nuclei of the epi- thelium are not arranged in two zones as in the latter. The stomach has the usual layers, and has es- sentially the same structure in the three regions studied, except that the wall in the fundic region is much the thickest, due mainly to the great The Digestive System 191 thickness of the middle muscle layer. Only one kind of cell is found in the gastric glands. No difference is to be noted between the hibernating and feeding conditions. The chief peculiarity of the small intestine is the apparent entire absence of the submucosa. Gob- let cells are also wanting. The greater diameter of the anterior region is due both to the greater diameter of the lumen and to the greater thickness of the walls. The middle and posterior regions have about the same diameter, though the mucosa becomes thinner and less complicated caudad. There is practically no difference between the hibernating and feeding stages. The anterior and posterior regions of the large intestine have essentially the same structure. No difference can be seen between the hibernating and feeding conditions. CHAPTER’ VE THE UROGENITAL ORGANS IGURE 54 represents the urogenital apparatus of a thirty-inch female specimen of Alligator mississippiensts. Figure 55 shows the cor- responding organs of a male A lucius; reproduced from Bronn. The urogenital organs in the young animal are so similar in the two sexes that one might easily be mistaken for the other; of course in sexually ma- ture animals, especially during the breeding season, this is not the case. The kidneys, Fig. 54, k, Fig. 55, a, are flattened, lobulated organs lying against the dorsal body wall. The large anterior lobe of each kidney is pointed atits anterior end and lies at some little distance from its |- fellow; itis partially divided into secondary lobes and | is traversed onits ventral surface by branching blood- _ vessels. Its antero-medial border is sometimes par- tially concealed, in a ventral view, by the elongated | gonad of that side. Caudad to the main lobe of | the kidney is a smaller, usually distinct, lobe in con- | tact mesially with its fellow of the opposite side. 192 The Urogenital Organs 193 ee taitly wide ureter, Fig. 54, u, Fig. 55, d, extends from the posterior end of each kidney to open (Fig. 54, u', Fig. 55, e) into the anterior region of the cloaca, as described in con- nection with the digestive system. The ovary, Fig. 54, 0, as noted above and as seen in Figs. 54 and 55, in the young animal is of practically the sameshapeasthetestis. The Ova at this stage are of mi- croscopic size and are hence not visible to the naked eye. The ovary, even at this stage, is more or less distinctly marked off into lobules by a series of small grooves. The oviduct, Fig. 54,£, which at this stage is, of course, of small diameter, extendsacross the ventral surface of its cor- responding kidney and opens, f, into the posterior part of nseee—1~ ~seeeerr? .- ‘ \ 4 i ia y N4 \/ Fic. 54. FEMALE UROGEN- ITAL SYSTEM. f, oviduct; f', opening of ovi- duct; k, kidney; m, mesentery; 0, Ovary; uw, ureter; ut, open- of ureter. the cloaca as has already been described. Its peritoneal opening is some distance cephalad to the head of the ovary. Its course from this Opening is straight until about the anterior end of the ovary; it then becomes somewhat con- T3 194 The Alligator and Its Allies voluted for a short distance, but gradually straightens out, to pass to its posterior end as a nearly straight duct. The anterior straight portion of the oviduct is connected with the head of the ovary by a narrow band of mesentery. Each testis, Fig. 55, b, like the ovary, lies along the ventro-mesial border of its corresponding kid- | ney and is connected with the posterior region © of the cloaca by a slender vas deferens, Fig. 55, c, f. | According to Rathke (in C. acutus) a small, slender epididymis lies along the outer side of the — posterior half of each testis. | The Copulatory Organs. The penis, Fig. 56, usu- | ally lies completely hidden in the cloaca; with its glans projecting backwards it is strongly arched; © along the convex side of the arch, which is directed towards the upper wall of the cloaca, runs a groove, | which serves as a penial urethra to conduct the | semen. According to Rathke there may be recognized | in connection with the penis two fibrous strands |~ (resembling the corpora cavernosa of mammals), | a corpus cavernosus urethrea, and a covering derived from the mucous membrane of the cloaca. | The two fibrous strands arise from the pubis as two | thick plates that soon completely fuse together by | their adjacent sides to form the shaft, c, of the} penis. These fused strands taper gradually to- wards the glans, in which they end in a point. | From their mode of fusion there is left between | Fic. 55. Mate UROGENITAL APPARATUS OF ALLIGATOR Lucius. (After Bronn.) a, kidney; b, testis; c, vas deferens; d, ureter; e, opening of the ureter into the cloaca; f, opening of the vas deferens into the cloaca; g, upper region of the cloaca; h, hinder region of the cloaca; i, rectum. Fic. 56. MALE ORGAN OF ALLIGATOR Lucius, XI: (From Bronn, after Rathke.) a, the right crus penis; b, the mucous membrane of | the cloaca that covers the organ; c, shaft of the penis; d, base of glans; e, point of glans; f, part of the ring muscle of the cloaca. The Urogenital Organs 195 them, on the side towards the upper wall of the cloaca, a fairly deep furrow that extends to the tip. According to Rathke these shafts are not of cavern- ous tissue, but the tube is lined by a layer of this tissue. The glans, e, consists of two parts between which, where they leave the shaft of the penis, is a funnel-shaped hole, wider towards the free end of the penis and divided into similar lateral halves by a fold of skin. The glans is much shorter than the shaft of the penis. The covering of the penis is much thinner than the mucous membrane of the cloaca and is thinnest along the groove; it extends from the shaft over the glans without forming a foreskin. : The base of the penis is attached to the pubis near its symphysis. With this base the most anterior part of the strong ring-muscle of the cloaca is closely attached by a fairly large mass of fibrous tissue. Rathke fails to find any muscles that are concerned alone with the copulatory organs. In the copulation of the crocodile, according to Rathke, the penis is erected, though how this is caused is difficult to say since the corpora cavernosa consist only of fibrous tissue and the cavernous tissue lining the groove is very thin. The penis can, therefore, project only a short distance from the cloaca. The cavernous tissue is capable of Causing only a slight elongation of the shaft, but 196 The Alligator and Its Allies the glans is considerably elongated by the strong influx of blood into that structure. According to Voeltzkow (78) the penis in the Madagascar crocodile is 20 cm. in length. The clitoris of the sexually mature female crocodile is very much smaller than the penis of a male of the same size, but, according to Rathke, | it varies greatly in size in different species. It is built on exactly the same plan as the penis. According to Bronn the clitoris as well as the penis projects from the cloaca, out through the anus, in the embryo of the crocodile; this was not observed by the present writer in the embryo of the Florida alligator, A. mississippiensis. CHAPTER Vil THE RESPIRATORY ORGANS The Larynx and Trachea. In the Crocodilia the framework of the larynx consists of three cartilages, of which two represent the arytenoids of the Mammalia; the third represents the thyroid and cricoid of mammals. The last is considerably larger than the first and is a broad closed ring, dif- fering in form in the different species. In spite of the fact that some of them have a voice, the vocal cords, according to Bronn, are wanting in the Crocodilia. According to Henle the vocal appara- tus is produced by the projection into the laryngeal cavity of the inner border of the small arytenoid cartilages and by the infolding, under these carti- lages, of the mucous membrane of the larynx; this forms the thick but fairly free folds that, when the glottis is narrowed, are well adapted to produce the harsh tone of the animal. The epiglottis is absent in the Crocodilia. In many Crocodilia (C. vulgaris, for example) the trachea, Fig. 57, tr, forms a loop which begins in some species before hatching, in other species not 197 198 The Alligator and Its Allies until long after hatching. In the genus Alligator the trachea is straight. More universal than this looped structure there is found another peculiar structure in the crocodilian trachea. It is a short vertical partition in the stem just before its divi- sion into the two branches. This partition is partly mem- branous and possesses one or more stiffening cartilaginous strands which are outgrowths of somany cartilaginous rings of the trachea. The number of the stiffening fibers varies in the different species. The number of the tracheal rings varies not only in the different species but also in different individuals of the same species. There are be- tween fifty and sixty in A. mississippiensis. According Fic. 57. RESPIRATORY to Rathke thenumber of rings RGANS. b, bronchus: ¢, esophagus: g, 10 the individual, aninaciae lottis; /, lung; 1, tongue; fr, : ; trachea. SS Ss most. certainly does not in- crease with age. The number of rings is smallest in the gavials and greatest in the crocodiles (genus Crocodilus). The number of rings in the two The Respiratory Organs 199 divisions of the trachea does not increase with age except, perhaps, in C. acutus and biporcatus. The lateral bend that the tracheal stem of so many Crocodilia exhibits is not due to the greater number of rings because in some species (gavials) where the bend is present the number of rings is smaller than in the Crocodilia where the bend is absent. According to Rathke and others most of the tracheal rings are closed, but a varying, though at most small, number are open on the dorsal side. These openings become wider as the larynx is approached. The transverse muscle fibers which are found in the most anterior and largest of these breaks in the tracheal rings were found, says Rathke, in embryos after the middle period of incubation. The cartilaginous rings of the bronchi, b, are also apparently open for a time after their for- mation, but soon close. Not infrequently in em- bryos and in young animals are found rings that are split like a fork, with one or both branches fused with neighboring branches. The Lungs. The lungs, Fig. 57,1, are more highly developed among the Crocodilia than among any other Saurian or Hydrosaurian group. ‘The histo- logical groundwork of the whole lung tissue is a con- nective tissue of fine elastic fibers. In the lungs, on the canal that appears as the elongation of the bronchus, cartilage appears, according to Rathke, as bands lying one behind the other; some of these 200 The Alligator and Its Allies bands form complete, others partial rings; some — of the latter are forked. The hindermost appear — to be the broadest and most irregular. Their number is different in different species and varies in different individuals of the same species. They range in number, according to Rathke, from nine, in A. lucius, to twenty-five, in C. acutus.’ The arterial branch, carrying venous blood to the lungs, develops a capillary network close to the alveolar walls, which leads away over the low alveolar septa, while over the tops of the higher septa and on the inner surface of the tube-like bronchial processes it forms a wide-meshed net- work of capillaries that are apparently chiefly nutrient. All the respiratory capillaries are attached by only one side to the alveolar wall; the free side that projects into the air space of the alveolus is covered by a continuous pavement epithelium. While the respiratory surfaces are covered with an alveolar epithelium of large polygonal cells, the free borders of all high septa and ridges, as well as the inner surfaces of the bronchial processes, are covered with ciliated cylindrical cells. I Miller (45c) says: ‘‘In the crocodile and alligator the bronchus enters the lung near its center, and passes somewhat obliquely into the lung until it reaches the junction of the lower middle third; here it breaks up into eight to fifteen tubular passages. These tubular passages are studded with a great many air-sacs. In these animals the lung for the first time gives the structure as it is found in mammals. There are many air-sacs which communicate with a common cavity, or atrium, all of which in turn communicate with a single terminal bronchus. A single lobule of the mammalian lung is simply enlarged to form the lung of the crocodile; the lung of the former is only a conglomerate of that of the latter.”’ CHAPTER VIII THE VASCULAR SYSTEM HE account given by Bronn in his Thierreich is apparently the only published description of the circulatory organs in the Crocodilia. This account, even when translated, is not very » satisfactory, especially because it contains no dia- grams of the circulation. It was, therefore, deemed worth while to work out the circulation in the Florida alligator in order that we might have not only a written description, but also a series of more or less accurate diagrams of the veins and arteries. A number of departures from the description of Bronn were found, some of which are noted below. Most of the work was done upon animals of about thirty inches length, which were obtained alive from the Arkansas Alligator Farm at Hot Springs, Ark. The arteries were injected with a colored starch mass by inserting a two-way cannula into the dorsal aorta. With the blood thus forced into them from the arteries, the veins could, in most cases, be traced without difficulty. 201 202 The Alligator and Its Allies In the diagrams the outlines of the more impor- tant organs are accurately shown by dotted lines, and the relative diameters of the blood-vessels are shown as accurately as possible by the solid black lines. THE HEART In the Crocodilia, as is well known, the heart is four-chambered and has about the same general shape as in the higher vertebrates, Fig. 58. The venous blood is emptied into a thin-walled sinus venosus on the dorsal side of the heart by three large vessels and one small one. The largest of these, the postcava, empties into the posterior side of the sinus venosus and brings blood from the posterior regions of the body; it is quite wide, but is exposed for a very short distance between the liver and the heart. Two large hepatic veins empty into the postcava so near the sinus venosus that they practically have openings into the sinus, as is shown in a somewhat exaggerated way in Fig. 59. Near the postcaval and hepatic openings is the distinct coronary vein, lying in a slight depression between the right and left ventricles. From the anterior regions of the body the blood is brought back through two fairly wide but very thin-walled precaval veins which pass across the dor- sal surface of the heart to enter the sinus venosus. The arterial blood is brought from the lungs by = y Vend Fic. 58. Heart oF A. Lucius. (Dorsal View.) (From Bronn, after Fritsch.) Ao, d, Ao, s, right and left aorte; At, d, At, s, right and left atria; Au, d, Au, s, right and left auricles; Ca, pr, primary carotid; P, d, P, s, right and left pulmonary arteries; Sc, d, Sc, s, right and left subclavians; Sv, sinus venosus; V, cc, coronary vein; V, c, d, V, c, i, right precava, and inferior cava; Ven, d, Ven, s, right and left ventricles; V, h, hepatic vein; V, p, d, V, p, s, right and left pulmonary veins. The Vascular System 203 two wide, thin-walled pulmonary veins, Fig. 58, Reps., V-p.d» They leave the lungs somewhat caudad to their middle region, near the point of entrance of the bronchii and the pulmonary ar- teries, pass mediad in a direction almost at right angles to the long axis of the body, and enter the left auricle at the same point. Blood leaves the heart through five large vessels: (1) the pulmonary artery, (2) the two aortic arches, (3) the right subclavian, (4) the primary carotid. The pulmonary leaves the small right ventricle as a single stem, which soon branches into two arteries that pass cephalad and laterad to the lungs, along with and close to the main bronchi. The other arteries that carry blood into the systemic circulation are fused at their base to form a sort of conus arteriosus which may be distended in injected specimens until it is larger than the two ventricles together. When opened this conus is found to contain two chambers that lead into the left ventricle; the larger chamber gives origin to the right systemic arch, the right subclavian, and the primary carotid; the smaller chamber is the basal part of the left systemic arch. The two systemic vessels, Fig. 58, Ao.s, Ao.d, pass, in the usual manner, as two arches to the dorsal region, just posterior to the ventricles, where they form the dorsal aorta in the manner to be described in connection with the arterial system. The further course of the primary carotid and 204 The Alligator and Its Allies of the right subclavian will also be described in connection with the arterial system. The auricles are very large in proportion to the Fic. 59. The veins of the posterior region of the Florida alligator. The postcaval system and its associated veins are shown in the main figure; the hepatic portal system is shown in the smaller figure to the left.—For lettering, see pages 224-25. ventricles, though their relative sizes will, of course, vary with the amount of contained blood. THE VENOUS SYSTEM The Posterior Vena Cava and its Branches. ‘The postcava, Fig. 59, pce, as noted above, is a wide, The Vascular System 205 thin-walled vessel seen extending across the short space between the anterior face of the right lobe of the liver and the sinus venosus. As was also noted above, the hepatic veins, vh,—at any rate that from the left lobe of the liver,—enter the postcava so close to the heart that they may be considered to have one or more distinct openings into the sinus venosus. Followed caudad, the postcava may be traced through the large right lobe of the liver, from which it receives several branches. Emerging from the posterior border of the liver, it is seen to extend caudad, in the median line, as a rather inconspicuous vessel that receives blood from the reproductive organs and the kidneys that lie close on either side of it. The hepatic portal vein, h, has the usual distri- bution for that vessel. Entering the liver in the neighborhood of the bile duct, it receives first (2.e., nearest the liver) a small branch from the pan- creas, pv; near the pancreatic are one or two branches from the stomach, g, and a branch from the spleen, sp. A short distance caudad to these vessels are two or three mesenteric veins, m, leading from the mesentery and small intestine. Caudad to the mesenterics, the portal system may be seen as a vein of diminished caliber, i, leading from the posterior part of the small intestine and from the large intestine. The connection mentioned by Bronn between the rectal branch of the portal vein and the caudal 206 The Alligator and Its Allies vein could not be demonstrated. After entering the liver, the portal, of course, breaks up into capil- laries, and the blood thus distributed is re-col- lected by the capillaries of the hepatic veins above eT | mentioned. The internal epigastric veins, ep, are, perhaps, the most conspicuous vessels of the postcaval system. When the ventral abdominal wall of the animal is removed, they may be seen extending forward from the pelvic region, on each side of the © | body, to enter the posterior edge of the liver. The epigastric of the right side enters the large or right lobe of the liver, where it breaks up into capillaries; the left epigastric sends its main branch into the left lobe of the liver, but also sends a branch over to enter the right lobe. Following the epigastrics caudad, they are seen to receive vessels from nearly all parts of the posterior region of the body. ‘The left epigastric, which extends across the ventral side of the stom- ach, receives from that organ four or five branches, g'*; while the farther removed right epigastric receives only one or two branches from the stom- ach. Posterior to these gastric veins the epigas- trics receive one or more veins, b, from the body wall and skin. Posterior, again, to the last- named veins, each epigastric receives, in the pelvic region, a large vein, the zlzac, il, which receives, in turn, a vein from the pelvis, pl, and continues down the thigh and lower leg to the foot as the femoral, The Vascular System 207 f, the chief vein of the posterior appendage. After receiving small branches from the muscles of the thigh, the femoral receives near the knee a small branch from the posterior surface of the lower leg, fb, and a larger one, t, that leads from the anterior surface of the lower leg and foot. The veins of the pes were so small, in the com- paratively small animals it was necessary to use, that their distribution could not be determined with certainty, though they seemed to parallel very closely their corresponding arteries to be described below. A short distance caudad to the iliac veins, each epigastric receives one or two fairly large branches from the pelvic region, called by Bronn the zschiadic veins, is. Caudad to the ischiadics and dorsal to the cloaca, each epigastric is united with a short but wide renal portal or renal advehente vein, rp, leading to the posterior border of its respective kidney and receiving, on the way, a short branch from the pelvic region, shown just cephalad to the reference lines rt and rp. Very close to its junction with the renal portals each epigastric gives off a small branch which unites with its fellow of the opposite side to form a median vein, rt, the rectal leading from the posterior part of the large intestine. A very short distance caudal to these last veins, in the region just dorsal to the anal opening, the epigastrics are formed by the division of the caudal vein, cv, which, of course, brings blood from the tail and is, 208 The Alligator and Its Allies on account of the large size of that organ, of con- siderable caliber. The Anterior Vene Cave and their Branches. The entrance of the precaval veins into the heart was mentioned above; their branches, in order from the heart cephalad, will now be de- scribed. Since the two precave are alike, it will be necessary to describe the branches of only one side of the body. After leaving the heart, the precava may be traced forward, for a short dis- tance, at the side of the trachea and cesophagus, as a wide, thin-walled trunk, Fig. 60, vca. The first tributaries that it receives are the internal mam- mary and vertebral veins, which join it at the base of the neck at almost the same place. The internal mammary, Fig. 60, im, is a rather small vein, bringing blood from the ventral wall of the thorax. It may be followed along the inner surface of the ribs, near the sternum, in company with its corresponding artery. The vertebral vein, Fig. 60, v, is also of small dia- meter and extends to the dorsal body wall.near the spinal column, from which region it returns blood to the anterior vena cava; it is drawn too large in the figure. Just cephalad to the vertebral and internal mammary, the znternal jugular, j, enters the pre- cava. The internal jugular may be followed directly forward, close to the side of the trachea and oesophagus, from which it receives numerous The Vascular System 209 eee Wrew amen n ne \ Loe. <-22- . . x iN . tee : aS, The veins of the anterior region of the The veins of the left foreleg are Fic. 60. Florida alligator. shown at A.—For lettering, see pages 224-25. Near its point of entrance to, or rather branches. exit from, the skull, it anastomoses, by two or 14 210 The Alligator and Its Allies three short branches, with the external jugular, ej, to be described later. Its distribution in the cranial cavity could not be determined in the available material. At the point of entry of the internal jugular the precava passes laterad for a short distance and then divides into two more or less equal branches, the above-mentioned external jugular, ej, and the subclavian, s, of which the latter will first be described. The subclavian, s, of course, returns blood from the regions of the shoulder and arm. On reaching the body wall, where it might be called the axzllary, ax, it receives, on its posterior side, a large thoracic | vein, t, which returns blood from the thorax, shoulder, and skin. The thoracic receives a branch from the posterior surface of the arm, which might be called the postbrachial, pb; this postbrachial may be traced, as a rather small vessel, to the hand; at the elbow it is connected, by one or more small branches, with the brachial. Just distal to the thoracic the axillary vein receives two fairly large vessels, the subscapulars, sc, that return blood from the shoulder and upper arm. After receiving the subscapulars, the axillary may be followed into the upper | arm as the brachial, br. As has been said, the brachial and postbrachial anastomose near the elbow, and in this region the former receives a small vessel that extends parallel to it from the manus. The Vascular System 211 In the forearm the brachial may be called the radial, Fig. 60, A, ra; on the back of the manus the radial receives branches from the various digits and from a rather complex plexus of vessels in the carpal region. The external jugular, Fig. 60, ej, after separating from the subclavian, may be traced cephalad, close beneath the skin, to the base of the skull, where it is connected with the internal jugular by short branches, as has already been noted. It receives several small branches from the skin and muscles of the neck and shoulder regions. At the region of its anastomosis with the internal jugular it receives a large branch, the muscular, ms, from the massive muscle at the angle of the jaw and from the skin of that region. A short distance cephalad to the muscular the external jugular receives, on its mesial side, two or three branches from the trachea, larynx, and cesophagus, tr. Anterior to these vessels the external jugular is formed by the union of two chief veins, the lingual, 1, from the ventro-lateral surface of the tongue, and the inferior dental, id, from the mesial surface of the lower jaw. The connection of the superior dental (extending along the bases of the maxillary teeth) with the jug- ular could not be determined with certainty, hence that vessel is not shown in the figure. The same is true of the small veins in the region of the cranium. 212 The Alligator and Its Allies THE ARTERIAL SYSTEM The Abdominal Aorta and its Branches. The right and left aortic arches, Fig. 61, Aod, Aos, arising from the heart in the manner already described, form a rather long loop and approach each other in the middorsal line. Here they are united by a short, wide connective in such a way that the left arch seems continued into the coeliac artery and the right into the dorsal aorta proper. Each arch, anterior to the connective, gives off two fairly large branches, oe, to the posterior region of the cesophagus. The celiac artery, Fig. 61, c, is the largest branch of the abdominal aortic system. After giving off a couple of small branches, oe, to the posterior region of the cesophagus, it gives off a large spleno-intesti- nal artery, si, to the spleen and small intestine. The coeliac then breaks up into three arteries of about the same size: the gastro-hepatico-intesti- nal, ghi, carrying blood to the stomach, liver, and small intestine; the pancreo-intestinal, pi, leading to the pancreas and small intestine; and the gustric, ga, to the greater part of the stomach. From the dorsal aorta proper, da, which, as has been said, seems to be the direct continuation of the right aortic arch, several arteries are given off; these will be described as they occur in an antero-posterior direction. At about the point of union of the two aortic The Vascular System ais arches arises the most anterior of seven or eight pairs of lumbar arteries, lu 1-7; this first lumbar artery is contin- ued cephalad for some distance as a longitudinal trunk that gives off severallateral branches to the walls of the thor- acicregion. The other six or seven lumbars are dis- tributed to the dorsal body wall, and arise, at more or less reg- ular intervals, as far caudad as the sacrum, or even mack of that point. The first large branch of the aorta is the un- paired mesen- teric artery, ‘ Aad i Heart. Aas : ( ; j £ : s om e = oe : —, ¢ “fie ‘ . “ : H i A. His H f OSE ‘ oe i ‘ \ : : : fee L—€ 2 : {_ = ' / A 7] G2 EL SONS G4) Wann) is al WX ey f - Ne ey i 27 SE ss a, ors, af k / oe aye Mey Z , i sf Th og RK 8 Ee > y So er : \ mee 29 / y > Zi \ ‘ dd D SOR Sy es wa FASS uo H <2" _ 3 fs a ray = H / 7, ‘ , : \ Zz é Mer! Sages ied egies: ee, ee. -: aa -- —_ Fic. 61. The arteries of the posterior region of the Florida alligator.—For lettering, see pages 224-25. m*, which is given’ off im about the region of the fourth pair of lumbars; it 214 The Alligator and Its Allies carries blood through the mesentery to the greater part of the small intestine and also sends a small branch to the large intestine. Posterior to the mesenteric, the aorta gives off four or five pairs of short arteries, the urogenztals, u 1-4, that lead to the nearby reproductive organs and kidneys. About the middle region of the kidneys, a short distance anterior to the sacrum, is given off a pair of rather large arteries, called by Bronn the zschi- adice@, is’; each ischiadica, after giving off a couple of small branches to the back, passes laterad and divides into three main branches: (1') to the ventral body wall, (3') to the anterior border and deeper region of the thigh, and (2') to the pelvis. In the region of the sacrum is given off a pair of tliac arteries, il'. Each iliac is of about the same diameter as the ischiadica and gives off, soon after leaving the aorta, an artery, ab, that apparently leads chiefly to the abdominal muscles. Distal to the origin of the abdominal, the iliac gives off a small pelvic artery, pa, which leads, as the name would indicate, to the pelvis. The iliac then passes into the thigh, where it gives off several large branches and may be called the sciatic, sc. At the knee the sciatic gives off two rather small branches: one, the fibular artery, ft, extends down along the posterior side of the lower leg; the other is parallel to the first and may be called the ¢tzbzal artery, tb, since it extends along the anterior or The Vascular System 215 aS) Pees | FEED > Wi i) wm, ie ip ia x 4 , gy wa, : 5 5 ! ssetessane, fone on oo ~ % =< a pa) WS i y y } y= Tce i i T7750, ‘ me, sm RS — ‘ ; Se » i t4 Wo res SCS: a! Ps \ Aod. y ; i WO. capr 7 0e s Vpd Ss Heart oe Fic. 62. The arteries of the anterior region of the Florida alligator. The arteries of the left foreleg shown at A.—For lettering, see pages 224-25. ) tibial side of the shank. These two arteries give - off numerous branches to the muscles of the lower 216 The Alligator and Its Allies leg. After giving off the fibular and tibial arteries, the sciatic passes, as a large vessel, through the lower leg, to which it gives but few branches, and may here be called the crural artery,cr. At the tar- sus it divides rather suddenly and, perhaps, vari- ably, into four chief branches, leading to the toes. A short distance caudad to the origin of the iliacs the dorsal aorta gives off a pair of small pelvic arter- ies, pat, going to the muscles of that region. Cau- dal to these pelvic arteries is given off the unpaired first hemorrhoidal artery, het, which divides into a rectal, tt*, and a cloacal, cl >branch. Caudal to the first heemorrhoidal arises the second hemorrhoidal, he’; also unpaired, leading to the cloaca. Posterior to the second hemorrhoidal, the aorta continues into the tail as the large caudal artery, ca. The Anterior Arteries. The origin of the great ar- terial trunks—the pulmonary, aortic arches, primary carotid, and right subclavian has already been given and the distribution of the pulmonary arteries and aortic arches has been described, so that it now re- mains to describe the distribution of the right sub- clavian, Fig. 62, sc.d., and the primary carotid, capr. The right subclavian, sc.d., since it has an independent origin from the heart, instead of aris- ing as a branch of the primary carotid, will be described first. After leaving the heart it passes cephalad and laterad and gives off the following branches in order, beginning at the heart: an The Vascular System 217 esophageal artery, oe, a small, caudally directed vessel carrying blood to the posterior region of the cesophagus. Close to the cesophageal arises an- other small, caudally directed vessel, the pleural artery, plu, extending to the pleura and possibly to the pericardium. From the same region as the preceding two arteries, but extending cephalad along the trachea and cesophagus, arises the much larger branch of the right subclavian, the right collateralis colli, cc, whose course and distribution will be described later. Close to the distal side of the collateralis colli arises the very small thyroid artery, th, leading to the oval thyroid gland that lies against the ventral surface of the trachea a short distance anterior to the heart. A short distance distal to the thyroid artery the subclavian gives off a fairly large artery, the internal mammary, im* (shown too large in the figure), that passes to the inner surface of the ribs near the sternum and lies parallel to the vein of the same name, described above. A short distance distal to the internal mammary arises an artery of about the same diameter, the vertebral, v*; it passes dorsad and caudad to the region of the thoracic vertebre. After giving off the five vessels just described, the subclavian artery passes into the shoulder where it divides into three main branches: (a) the subscapular, sc', going to the skin and muscles 218 The Alligator and Its Allies of the shoulder; (b) the thoracic, tt, carrying blood to the posterior muscles of the shoulder and to the posterior region of the upper arm; (c) the brachial, br', which is really the continuation of the subclav- ian and is the chief artery of the anterior appendage. After sending several branches to the upper arm the brachial divides, in the region of the elbow, into two main vessels, the radial, rat, and ulnar, ul', arteries, Fig. 62, A. The radial artery, in the carpal region, divides in a complicated way into five main vessels that extend into the digits. The ulnar artery gives off several branches to the forearm, but apparently does not connect directly with the branches to the digits. The primary carotid, capr. After leaving the heart, this very large vessel passes cephalad and laterad for some distance on the left side of the body and then gives off, from its anterior side, the large left subclavian artery, sc.s., to be described later. After giving off the subclavian artery, it makes a short loop, still farther to the left, and then turns sharply mediad to pass to the head in the median plane directly dorsal to the oesophagus. Its distribution in the cervical and cephalic region will be described later. The mate to the cesoph- ageal branch, oe (near heart), of the right sub- clavian which was mentioned above is apparently sometimes given off from the primary carotid near | its base (as shown in Fig. 62) and sometimes as a | branch of the left pleural artery. The Vascular System 219 The left subclavian artery, sc.s., although it has a different origin, has the same branches as described in connection with the right subclavian. The exact order in which the first of these (the thyroid, th; the internal mammary, im’; the collateralis colli, cc; the pleural, plu; and the vertebral, v‘) are given off is, as might be expected, subject to some variation. The collateralis colli, cc (foilowing Bronn’s nomenclature), whose origin was noted above, will now be discussed; since the two are alike only one need be described. After leaving the sub- clavian, it passes cephalad, at the side of the trachea and oesophagus, in company with the internal jugular vein, so that in this part of its course it would seem to be the internal carotid artery. It gives numerous small twigs to the trachea and cesophagus, oe. In the region of the posterior part of the huge jaw muscle it is connected directly, x, with the adjacent branch, cm (called by Bronn the common carotid) of the primary carotid, and indirectly, x',with a complicated group of branches from the common carotid. Cephalad to the connective x’, which extends dorsad and is hence foreshortened in the figure, the collateralis colli gives off a small vessel, y (too largein Fig. 62), to the shoulder and skin; it then sends a fairly large branch, jm, into the large jaw muscle, close to which it now lies. Next a small branch, lg, is sent to the larynx. Continuing cephalad and laterad 220 The Alligator and Its Allies (in Fig. 62 it is drawn farther to the side than it actually lies) for a short distance farther, it divides into three branches: (1) a short twig, mg, that goes to the musk gland on the side of the mandible and to the skin of that region; (2) a large branch, the mandibular, md, that enters the large foramen on the mesial side of the mandible and extends in the cavity of that bone throughout its entire length; (3) the lingual artery, 1', which in turn divides, some distance cephalad, into two branches, one extending along the lateral region, the other nearer the mid-ventral surface of the tongue. It is seen, then, that the collateralis colli arteries supply directly the lower side of the head—tongue, mandi- ble, etc.—though they may also send blood through the above-mentioned connectives to the brain and dorsal regions of the skull. The primary carotid, capr, as was noted above, makes a curve to the left after leaving the heart and then passes back to the median plane, where it may be seen lying against the ventral side of the neck muscles and dorsal to the cesophagus; in this place it gives off a series of unpaired cervical arteries, Fig. 62, ce, each of which almost imme- diately divides into an anterior and a posterior | branch, that carry blood to the cervical vertebrae. | At the base of the skull, in the region where it is — united by the first connective, x, with the collater- | alis colli, as described above, the primary carotid divides into two similar branches, called by Bronn © The Vascular System 221 the common carotids, cm. The distribution of these two vessels is symmetrical, so that only one need be described. While the collateralis colli, as has been said, carry blood chiefly to the tongue and lower jaw, the common carotids supply the cranium and upper jaw. Soon after its formation by the division of the _ primary carotid, the common carotid is joined, as — noted above, with the collateralis colli of that side by the connective, x; since the common carotid and its branches all lie dorsal to the collateralis colli and its branches, the connectives x and x’ extend in a more or less dorso-ventral direction. The two common carotids, almost completely surrounded by bone, in passing cephalad sweep first laterad, then mediad, so that they together form almost a com- plete ellipse, as seen in Fig. 62; there is, however, no apparent connection between them at the an- terior region where they lie so close together. A short distance cephalad to the connective x the common carotid is connected laterally, z, with a rather complicated plexus of vessels lying at the base of the skull; it is through this plexus that the common carotid is connected with the collateralis colli by the second connective, x". The short branch z quickly divides into three parts: (1) a small anteriorly directed vessel which may be called the internal carotid, ic, since it enters the skull through the most ventral of the three foramina in the exoccipital, and probably supplies 222 The Alligator and Its Allies the brain, though its further course could not be followed; (2) a somewhat larger posteriorly directed artery, oc, going to the muscles at the occipital region of the skull; (3) a short laterally directed stem, z’. The last-named branch, 2’, in turn, leads in three directions: (a) to the collater- alis colli artery through the connective x’; (b) a short anteriorly directed vessel, e, that passes into the skull, possibly to the ear, through the large foramen that lies between the exoccipital and quadrate bones; it gives off a small twig, q, to the muscles in the region of the jaw articulation (quadrate); (c) the main stem of the branch Z continues laterad and cephalad as one of the chief arteries, z’, to the anterior region of the skim giving off a fairly wide branch, jm’, to the large jaw muscle, and then two branches, o* and 0’, to the lateral surface of the eyeball and socket; it then anastomoses, just cephalad and laterad to the eye, with the forward continuation, cm’, of the corresponding main stem, cm, of the common carotid, already mentioned. The vessel cm’, after almost meeting its fellow in the middle line, passes cephalad and laterad across the ventral surface of the eye to the union, above mentioned, with the lateral branch, 27; at the posterior-mesial border of the eye it gives off a branch that divides into two twigs, one, o%, for the posterior eye muscles, and one, e’, to the region of the ear and the top of the skull. The Vascular System 223 At the point of union of the branches cm* and a sort of simple plexus may be formed from which o vessels, n, pass to the posterior nasal region, nd two vessels pass forward along the side of the yper jaw. Of the latter two vessels one, which ay be called the zuferzor dental of the maxilla, dm, is very small and extends along the maxilla to its ve y tip, at the base of the teeth and ventral to the palatine bone; the other, which is larger and may be called the superior dental of the maxilla, dm’, extends cephalad along the mesial side of the maxilla, dorsal to the palatine bone; it sends nu- merous twigs into the maxillary bone among the roots of the teeth. After passing nearly to the of the snout, the superior dental, dm', suddenly ms a loop towards the median line and passes as a straight branch, n’, directly caudad, near and parallel to the median plane. The branch n! sxtends along the floor of the nasal cavity and, ufter giving off twigs to this chamber, ends in a 1etwork of vessels, 07, on the anterior surface of he eyeball and socket. _ A pair of very small arteries, n?, may be seen in the nasal chamber between and parallel to the ranches, n‘; they lie close to each side of the nasal eptum and supply the anterior nasal region. [They apparently arise, as shown by the broken ines, from the loop of the superior dental irtery, dm’, though this could not be definitely ermined. 224 LETTERING FOR FIGURES 59-62 Aos., Aod., arches. ab, abdominal artery. ax, axillary vein. left and right aortic b, veins from body wall. br, brachial vein. br', brachial artery. c, coeliac artery. ca, caudal artery. capr, primary carotid. cc, collateralis colli artery. ce, cervical artery. cl, cloacal artery. cm, cm!, common carotid artery. er, crural artery. cv, caudal vein. da, dorsal aorta. dm, inferior dental artery of max- illa. dm', superior dental artery of maxilla. e, e', artery into skull, perhaps to ear. ej, external jugular vein. ep, internal epigastric vein. f, femoral vein. ft, fibular artery. fb, fibular vein. g, gastric vein of portal. gt, gastric vein of epigastric. ga, gastric artery. ghi, gastro-hepatico-intestinal artery. h, hepatic portal vein. he’, he?, hemorrhoidal arteries. i, intestinal vein. ic, internal carotid artery. id, inferior dental vein. il, “iliac vein. il', iliac artery. im, internal mammary vein. im?*, internal mammary artery. The Alligator and Its Allies is, ischiadic vein. is?, ischiadic artery. j, internal jugular vein. jm, jm’, artery to jaw muscle. — 1, lingual vein. 17, lingual artery. lg, laryngeal artery. lu, 1-7, lumber arteries (num on left side of figure). m, mesenteric vein. m?, mesenteric artery. md, mandibular artery. mg, artery to musk gland. ms, muscular vein. n, artery to posterior nasal regior n', artery to anterior and nasal region. n?, artery to anterior nasal regii ot-o4, arteries to eye. oc, artery to muscles at base skull. oe, cesophageal arteries. pa, pelvic artery. pat, second pelvic artery. pb, post brachial vein. pc, post cava. pd, right pulmonary artery. pi, pancreo-intestinal artery. pl, pl, pelvic vein. plu, pleural artery. ps, left pulmonary artery. q, artery to muscle at angle of j ra, radial vein. rat, radial artery. re, reproductive vein or artery. rp, renal portal vein. rt, rectal vein. rt', rectal artery. rv, renal vein. s, subclavian vein. sc, sciatic artery (Fig. 61). The Vascular System 225 , subscapular vein (Fig. 60). v, vertebral vein. «, subscapular artery. v‘, vertebral artery. .d., sc.s., right and left subclavian | vca, anterior vena cava. arteries. vh, hepatic vein. , spleno-intestinal artery. vpd, vps, right and left pulmonary , Splenic vein. veins. ., sinus venosus. x, x7, connectives between collater- thoracic vein. Ble caliercinerond , thoracic artery. , tibial artery. é , thryoid artery. y, artery to shoulder and skin. tracheal vein. z, z* z?, branches of common I-4, urogenital arteries (num-| carotid. bers on right side of figure). I?, 2%, 3', branches of ischiadic ulnar artery. artery. 15 CHAPTER 1X THE DEVELOPMENT OF THE ALLIGATOR (A. mississippiensis) INTRODUCTION ITH the exception of S. F. Clarke’s well- | known paper, to which frequent refer-- |) ence will be made, practically no work has been done upon the development of the American alligator. This is probably due to the great difficulties experienced in obtaining the nec- essary embryological material. Clarke, some twenty years ago, made three trips to they swamps of Florida in quest of the desired ma- | terial. The writer has also spent parts of three summers in the Southern swamps—once in the Everglades, once among the smaller swamps and lakes of central Florida, and once in the Oke- finokee Swamp. For the first of these expeditions | he is indebted to the Elizabeth Thompson Science | Fund; but for the more successful trip, when } most of the material for this work was collected, he : is indebted to the Smithsonian Institution, from 226 The Development of the Alligator 227 which a liberal grant of money to defray the ex- penses of the expedition was received. The writer also desires to express his appreciation of the numerous courtesies that he has received from Dr. Samuel F. Clarke, especially for the loan of several excellent series of sections, from which a number of the earlier stages were drawn. In preparing the material several kinds of fix- ation were employed, but the ordinary corrosive sublimate-acetic mixture gave about the most Sauls acronye nesults. hen. per eent., formalin, Parker’s mixture of formalin and alcohol, etc., were also used. In all cases the embryos were stained zm toto with borax carmine, and in most cases the sections were also stained on the slide with Lyon’s blue. This double stain gave excellent results. Transverse, sagittal, and horizontal series of sections were made, the youngest embryos being cut into sections five microns thick, the older stages ten microns or more in thickness. THE EGG _ FIGURES I, Ia (PLATE VI.) The egg (Fig. 1) is a perfect ellipse, the relative lengths of whose axes vary considerably in the eggs of different nests and slightly in the eggs of the same nest. Of more than four hundred eggs measured, the longest was 85 mm.; the shortest 65 mm.. Of the same eggs, the greatest short 228 The Alligator and Its Allies diameter was 50 mm.; the least short diameter was 38 mm. ‘The average long diameter of these four hundred eggs was 73.74 mm.; the average short diameter was 42.59 mm. ‘The average variation in the long axis of the eggs of any one nest was 11.32 mm., more than twice the average variation in the short axis, which was 5.14mm. Norelation was noticed between the size and the number of eggs in any one nest. Ten eggs of average size weighed 812 grams—about 81 grams each. Voeltzkow (78) states that the form of the egg of the Madagascar crocodile is very variable. No two eggs in the same nest are exactly alike, some being elliptical, some ‘‘egg-shaped,’” and some “cylindrical with rounded ends.”” The average size is 68 mm. by 47 mm., shorter and thicker than the average alligator egg. When first laid, the eggs are pure white, and are quite slimy for a few hours, but they generally become stained after a time by the damp and decaying vegetation composing the nest in which they are closely packed. The shell is thicker and of a coarser texture than that of the hen’s egg. Being of a calcareous nature, it is easily dissolved in dilute acids. The shell membrane is in two not very distinct layers, the fibers of which, according to S. F. Clarke, are spirally wound around the egg at right angles to eachother. Noair-chamber, such as is found in the hen’s egg, is found in any stage in the development. The Development of the Alligator 229 In most—probably all normal—eggs a white band appears around the lesser circumference a short time after being laid. This chalky band, which is shown at about its maximum development in Fig. 1a, is found, on removal of the shell, to be caused, not by a change in the shell, but by the appearance of an area of chalky substance in the shell membranes. Clarke thinks this change in the membrane is to aid in the passage of gases to and from the developing embryo. Generally this chalky area forms a distinct band entirely around the shorter circumference of the egg, but sometimes extends only partly around it. It varies in width from about 15 mm. to 35 mm., being narrowest at its first appearance. Sometimes its borders are quite sharp and even (Fig. Ia); in other cases they are very irregular. If the embryo dies the chalky band is likely to become spotted with dark areas. The shell and shell membrane of the egg of the Madagascar crocodile are essentially the same as those just described, except that the shell is some- times pierced by small pores that pass entirely through it. The same chalky band surrounds the median zone of the egg (78). The white of the egg is chiefly remarkable for its unusual density, being so stiff that the entire egg may be emptied from the shell into the hand and passed from one hand to the other without danger of rupturing either the mass of albumen or the enclosed yolk. The albumen, especially in the 230 The Alligator and Its Allies immediate neighborhood of the yolk, seems to consist of a number of very thin concentric layers. It varies in color, in different eggs, from a pale yellowish white, its usual color, to a very decided green. As might be expected, no chalazz are present. The yolk is a spherical mass, of a pale yellow color, lying in the center of the white. Its die ameter is so great that it lies very close to the shell around the lesser circumference of the egg, so that it is there covered by only a thin layer of white, and care must be taken in removing the shell from this region in order not to rupture the yolk. The yolk substance is quite fluid and is contained in a rather delicate vitelline membrane. The albumen and yolk of the crocodile’s egg, as described by Voeltzkow, differ from those of the alligator only in the color of the albumen, which in the crocodile is normally light green (78). As pointed out by Clarke, the position of the embryo upon the yolk is subject to some variation. During the earliest stages it may occur at the pole of the yolk nearest the side of the egg; later it may generally be found toward the end of the egg; and still later it shifts its position to the side of the egg. It is probable, as Clarke says, that the position at the end of the egg secures better pro- tection by the greater amount of white, at that point, between the yolk and the shell; while the later removal to the side of the egg, when the vascu- The Development of the Alligator 231 lar area and the allantois begin to function, secures a better aération of the blood of the embryo. Around the embryo, during the stages that precede the formation of the vascular area, is seen an irregular area of a lighter color and a mottled appearance. This area is bounded by a distinct, narrow, white line, and varies in size from perhaps a square centimeter to one third the surface of the yolk. During the earliest stages of development the embryo is very transparent; so that, as there is no fixed place upon the yolk at which it may be expected to occur, it is often very difficult to find. Owing to this transparency, to the extreme delicacy of the embryo, and to the character of the white, the removal of an early embryo from the egg of the alligator is a difficult operation and is accom- plished only after some practice. THE DEVELOPMENT OF THE EMBRYO As the writer has pointed out elsewhere (59), the embryo of the alligator is often of considerable size when the eggislaid. This makes the obtaining of the earliest stages of development a difficult matter; so that the writer, as has already been said, like S. F. Clarke (17), made three trips to the South in quest of the desired material. Voeltzkow (78) experienced the same difficulty in his work on the crocodile, and made several trips to Africa 232 The Alligator and Its Allies before he succeeded in obtaining all the desired stages of development. To obtain the earliest stages, I watched the newly made nests until the eggs were laid, and in this way a number of eggs were obtained within a very few hours after they had been deposited, and all of these eggs contained embryos of a more or less advanced stage of development. Gravid females were then killed, and the eggs removed from the oviducts. These eggs, although removed from a ‘‘cold-blooded”’ animal, generally contained embryos of some size, and only one lot of eggs thus obtained contained undeveloped embryos, which embryos refused to develop further in spite of the most careful treatment. Voeltzkow (78) found, in the same way, that the earlier stages of the crocodile were extremely difficult to handle; so that, in order to obtain the earlier stages, he was reduced to the rather cruel expedient of tying a gravid female and periodically removing the eggs from the oviducts through a slit cut in the body wall. The older embryos are hardy and bear trans- portation well, so that it is comparatively easy to obtain the later stages of development. For the stages up to the formation of the first four or five somites, I am indebted, as I have already said, to Professor Clarke, and, since I have had opportunity to examine only the sections and not the surface views of these stages, I shall The Development of the Alligator 233 quote directly Clarke’s paper in the Journal of Morphology (17) in description of these surface views. STAGE I FIGURES 2-2f (PLATEs VI., VII.) The youngest embryo that we have for descrip- tion is shown in Figures 2 and 2a. Of Figure 2 Clarke says: “The limiting line between the opaque and pellucid areas is clearly marked, and within the latter is a shield-shaped area connected by the nar- rower region of the primitive streak with the area opaca. The blastopore is already formed near the posterior end of the shield. ‘“‘A ventral view of another embryo of the same age (Fig. 2a), seen from the ventral side, shows that the blastopore extends quite through the blastoderm, in an oblique direction downwards and forwards, from the dorsal to the ventral side. The thickened area of the primitive streak is here very prominent. There is, too, the beginning of a curved depression at the anterior end of the shield, the first formation of the head-fold.”’ Transverse sections of this stage are shown in Figures 2b-2f. Figure 2b, through the anterior region of the blastoderm, shows a sharply defined ectoderm (ec) which is composed of three or four layers of cells 234 The Alligator and Its Allies in the median region, while it gradually thins out laterally. Closely underlying this ectoderm is a thin sheet of irregular cells, the entoderm (en). Figure 2c is about one fifth of the length of the blastoderm posterior to the preceding and rep- resents approximately the same conditions, except that there is an irregular thickening of the entoderm in the median region (ev). This thickening appar- ently marks the anterior limit of the mesoderm, to be discussed shortly. Figure 2d represents the condition of the blasto- derm throughout about one third of its length, posterior to the preceding section. The somewhat regular folds in the ectoderm (ec) are probably not medullary folds, but are such artificial folds as might easily be produced in handling the delicate blastoderm. The thickening of the entoderm, noticed in the preceding figure, is here more sharply defined, and as we pass toward the blasto- pore becomes separated somewhat from the ento- derm proper as a middle layer or mesoderm (Fig. 2e, mes). It would thus seem, from a study of these sections, that most of the mesoderm is derived from the entoderm. In fact, all of the mesoderm in front of the blastopore seems to have this origin, for it is not until the anterior edge of the blastopore is reached that there is any connection between the ectoderm and entoderm (Fig. 2e). Figure 2e is a section through the region just The Development of the Alligator 235 mentioned, where, medially, the ectoderm, meso- derm, and entoderm form a continuous mass of cells. Laterally the mesoderm (mes) is a distinct layer of cells of a fairly characteristic mesodermal type. Lhe notochord is not yet discernible, though a slight condensation of cells in the middle line may indicate its position. Figure 2f is one of the four sections that were cut through the blastopore (b/p), which is a hole of considerable size that opens, as the figure shows, entirely through the blastoderm. Along the walls of the blastopore the ectoderm and entoderm are, of course, continuous with each other and form a sharply defined boundary to the opening. As we pass laterally from the blastopore the cells become less compact, and are continued on each side as the mesodermal layer (mes). In this series the sections posterior to the blastopore were somewhat torn, and so were not drawn; but they probably did not differ materially from those of the corresponding region of the immediately following stages, which are shown in Figures 3m and 62 and will be described in their proper order. STAGE II FIGURES 3-30 (PLATE VII., VIII., IX.) The next stage to be described is shown in sur- face views in Figures 3 and 3a. Of this stage Clarke says: 236 The Alligator and Its Allies “The head-fold rapidly increases in depth and prominence, as shown in Figure 3, which is a ventral view a few hours later [than the preceding stage]. The time cannot be given exactly, as it is found that eggs of the same nest are not equally advanced when laid, and differ in their rate of development. The lighter curve in front of the head-fold is the beginning of the anterior fold of the amnion. (The notochord has been rapidly forming, and now shows very distinctly on the ventral side, when viewed by transmitted light. A dorsal view of the same embryo (Fig. 3a) shows that the medul- lary or neural groove is appearing, and that it ends abruptly anteriorly near the large transverse head- fold. Posteriorly it terminates at the thickened area in front of the blastopore, which still remains Open.’ Figures 3b-m are drawn from transsections of an embryo of about this stage of development. Fora short distance in front of the beginning of the head- fold, there is a mass of cells of considerable thick- ness between the ectoderm and entoderm. In Figure 3) these cells appear as an irregular thicken- ing of the entoderm, while in Figure 3c they form a continuous mass, uniting the upper and lower germ layers. This condition is seen, though in a much less striking degree, in the following stage of development. As to its significance the writer is not prepared to decide. Figure 3d passes through the head-fold, which Ne Lee ee Ee The Development of the Alligator 237 in this embryo was probably not so far developed as it was in the embryo shown in Figures 3 and 3a. Not having seen the embryo, however, before it was sectioned, the writer cannot be certain of this point. The ectoderm and entoderm are here of nearly the same thickness. Figure 3e is a short distance posterior to the preceding. It shows a marked thickening of the ectoderm in the medial region (ec), which is con- tinuous posteriorly with the anterior ends of the medullary folds that are just beginning to differ- entiate (Figs. 3f—h). Figure 3g passes through the anterior end of the medullary plate or folds (mf), whichever they may be called. The ectoderm of the folds is thickened and is considerably elevated above the rest of the blastoderm. There is scarcely any sign, in this region, of a medullary groove. The entoderm (en) is considerably thickened in the medial region, this thickening being continuous posteriorly, as in the preceding stage, with the mesoderm. In Figure 3h, cut in a plane at some distance posterior to the preceding, the medullary groove (mg) is well marked; its bordering folds grad- ually thin out laterally to the thickness of the ordinary ectoderm. The medial thickening of the entoderm is very marked, but it has not in this region separated into a distinct mesoblastic layer. Immediately under the medullary groove is a 238 The Alligator and Its Allies dense mass of cells (zt), apparently the anterior end of the notochord in process of formation. Figure 37, still farther toward the blastopore, shows the medullary groove wider and shallower than in the more anterior sections. The mesoderm (mes) is here a layer laterally distinct from the entoderm. In the middle line it is still continuous with the entoderm, and at this place it is the more dense mass of cells that may be recognized as the notochord (vt). It is evidently difficult to decide whether this group of cells (ut), which will later become a distinct body, the notochord, is derived directly from the entoderm or from the mesoderm, which is itself a derivative of the ento- derm. There is here absolutely no line of demar- cation between the cells of the notochord and those of the mesoderm and entoderm. In Figure 37 the ectoderm (ec) is nearly flat, scarcely a sign of the medullary groove appearing. The mesoderm (mes) is here a distinct layer, entirely separate from both notochord (nt) and entoderm (ev). The notochord is a clearly defined mass of cells, distinct, as has been said, from the mesoderm, but still closely united with the under- lying entoderm, which is much thinner than the ectoderm. This condition of the notochord, which is found throughout about one third of the length of the embryo, would give the impression that the notochord is of a distinctly entodermal origin. The Development of the Alligator 239 In Figure 3k there is no sign of the medullary groove, though the ectoderm (ec) is still much thick- ened in the middle line. The section passes, pos- terior to the notochord, through the anterior edge of the ventral opening of the blastopore (0/p). The mesoderm (mes) is here again continuous with the entoderm, around the edge of the blastopore, but is distinct from the ectoderm. Figure 3/ represents the third section posterior to the preceding. The blastopore, which passes upward and backward through the blastoderm, is seen as an enclosed slit (b/p). Itissurrounded bya distinct layer of compactly arranged cells contin- uous with the thickened ectoderm (ec) above, with the thin entoderm (en) below, and laterally with the gradually thinning and scattering mesoderm (mes). Figure 377 is the next section posterior to the one just described. It passes through the dorsal opening of the blastopore (b/p), which appears as a deep, narrow cleft with thick ectodermal borders. The three germ layers are still continuous with each other, though the connection of the entoderm with the other two is slight. |The sections poste- rior to this one will be described in the next stage, where they have essentially the same structure and are better preserved. Figures 37 and 30 are sagittal sections of an embryo of about the stage under discussion. In both figures the head-fold is seen as a deep loop 240 The Alligator and Its Allies of ectoderm and entoderm, while the head-fold of the amnion is seen at a. The beginning of the foregut is seen in Figure 3” (fg), which is the more nearly median of the two sections, Figure 30 being a short distance to the side of the middle line. In Figure 30 the thin entoderm (em) is separated from the much thicker ectoderm (ec) by a consider- able layer of rather loose mesoderm (mes). In Figure 37, which is almost exactly median in posi- tion, there is, of course, no mesoderm to be seen in front of the blastopore, and the entoderm shows a considerable increase in thickness, due to the formation of the notochord (nt). The blasto- pore (dlp) is the most striking feature of the figure, and is remarkable for its great width in an antero- posterior direction. Its anterior and posterior borders are outlined by sharply defined layers of ectoderm and entoderm. Posterior to the blasto- pore the lower side of the ectoderm is continuous with a considerable mass of cells, the primitive streak (ps). STAGE III FIGURES 4, 40, 5, 5@, AND 6-67 (PLATES X., XI.) ‘“‘Figures 4 and 4a are of an embryo removed, on June 18th, from an egg which had been taken out of an alligator two days before. Figure 4, a dorsal view, is of special interest in that it shows a second- The Development of the Alligator 241 ary fold taking place in the head-fold. This grows posteriorly along the median dorsal line, forming a V-shaped process with the apex pointing back- ward toward the blastopore. There is quite a deep groove between the arms of the V. The head- fold on the ventral side, as seen in Figure 4a, made from the same embryo as Figure 4, grows most rapidly on the mid-line, and also becomes thicker at that place. The medullary folds now begin to form on either side of the medullary groove, end- ing posteriorly on either side of the blastopore and anteriorly on either side of the point of the V- shaped process in the middle of the head-fold. This is seen in Figure 5, which is a dorsal view of an embryo from an egg three days after it was taken out of an alligator. A ventral view of the same embryo (Fig. 5a) represents the thickened process on the mid-line at its greatest development. For some reason the notochord did not show in this embryo, possibly owing to particles of the yolk material adhering about the mid-line. _ “Tn an embryo a day or two older, the V-shaped fold of the head-fold is seen to have broken through at the apex, and each of the arms thus separated from one another unites with the medullary fold of its respective side. This can be seen in Figure 6, which is a dorsal view of part of an embryo a day or two older than the one represented by Figures 5 and sa. “This is so unexpected a method of formation 16 242 The Alligator and Its Allies for the anterior part of the medullary folds that I have made use of both Figures 4 and 5. They were made from very perfect specimens, and the sections of both of them, and of the specimen from which Figure 6 was drawn, proves that the structure is what it is indicated to be in surface appearance. That is, the transverse sections pos- terior to the V, in the embryos shown in Figures 4 and 5, show the medullary groove and the medul- lary folds; the several sections passing through the apex of the V show neither groove nor folds, but only a median thickening; and in front of the point or apex of the V the successive sections discover a gradually widening groove between the arms, which is also much deeper than the shallow groove found posterior to the V. While I have not seen, and from the nature of the conditions one cannot see, the change actually proceeding from the form of Figure 5 to that of Figure 6, still the explanation given appears to be the only one possible”’ (17). A somewhat extended series of transverse sec- tions of an embryo of about this age is represented in figures 6a-2. Figure 6a is a section through the head-fold; it passes through the extreme anterior end of the secondary folds (sf) that were described, in surface view, above (Figs. 5 and 6). The section was not quite at right angles to the long axis of the embryo, so that the fold on the right was cut farther toward its anterior end than was the fold on the left. The Development of the Alligator 243 The pushing under of the head causes a forward projection of the secondary folds, so that the fold to the right appears as a rounded mass of cells with pmemallecaviny mear its, center. On the left the plane of the section passes through the posterior limit of the head-fold, and shows the cells of the secondary fold continuous with the dorsal side of the ectoderm (ec). As pointed out above by Clarke, the secondary folds are here some distance apart, and gradually approach each other as we proceed toward the posterior. The entoderm (em) is here flat and takes no part in the secondary folds. In Figure 6), a short distance back of the one just described, the secondary folds (sf) are much larger and are closer together. On the right the section passes through the extreme limit of the head-fold, so that the secondary fold of that side is still a closed circle, with a few scattered cells enclosed. On the left the section is posterior to the head-fold; on this side the secondary fold is seen as a high arch of ectoderm, with a thick mass of entoderm beneath it. Figure 6c represents a section which passes back of the head-fold on both sides. The second- ary folds (sf) are seen as a pair of ectodermal arches continuous with each other in the middle line of the embryo. The ectoderm of the folds is much thickened and gradually becomes thinner distally. On the right the entoderm shows the same thicken- ing (en) that was shown on the left side of the 244 The Alligator and Its Allies preceding figure. This thickened appearance of the entoderm is due to the fact that the section passes through the anterior limit of a tall fold of that layer, which underlies the similar fold of the ectoderm that has already been described. This secondary fold of the entoderm is seen on the left side of the section. It may be traced through several sections, but soon flattens out posteriorly. Figure 6d is a short distance posterior to the preceding. The secondary folds are here much less pronouncedly arched and the deep groove between them is reduced to a line (J). The ento- derm (e7) is no longer markedly arched and is closely adherent, along the median plane, to the ectoderm, where there is seen the thickening (th) that has been mentioned by Clarke (see above). Springing from the entoderm on each side of this thickening is a small mass of mesoderm (mes). The section immediately posterior to the one just described is represented in Figure 6e. The line (J) which separated the two secondary folds in the preceding section is no longer present, so that the ectoderm (ec) is continuous from side to side, with only a shallow depression (mg), which may be considered as the extreme anterior end of the medullary groove. The median thickening (th) is cut near its posterior limit and still shows a close fusion of the germ layers. ‘There is no line of demarcation between the gradually flattening The Development of the Alligator 245 secondary folds of the anterior end of the embryo and the just forming medullary folds of the pos- terior end, so that it is impossible to say whether the thickening of ectoblast in this figure should be called secondary folds or medullary folds. As a matter of fact, the secondary folds become, of course, the anterior ends of the medullary folds. The mesoblast (mes) is here of considerable extent, and its entodermal origin is beyond doubt, though not well shown in the figure. Figure 6f is about one sixth of the length of the embryo posterior to the preceding. The medul- lary thickening of the ectoderm (ec)is still marked and the shallow medullary groove (mg) is fairly dis- tinct. The entoderm (e7) is medially continuous with both mesoderm (mes) and notochord (nt), though these two tissues are otherwise distinct from each other. Figure 6g is nearly one third the length of the embryo posterior to the preceding and passes through the posterior third of the embryo. The medullary thickening of the ectoderm (ec) is marked, but shows no sign of a medullary groove; in fact, the median line is the most elevated region of the ectoderm. The notochord (nt) is larger in cross-section than in the more anterior regions. It is still continuous with the entoderm (en) and is fairly closely attached to, though apparently not continuous with, the mesoderm (mes) on each side. 246 The Alligator and Its Allies Figure 6 passes through the blastopore (lp). The appearance of the section is almost identical with that of Figure 2f, already described. Figure 67 is five sections posterior to the preced- ing and has about the same structure as the corre- sponding sections in the preceding two stages, where this region of the embryo was injured, and hence not drawn. Continuous with the posterior bor- ©} der of the blastopore (seen in the preceding fig- ure) is the deep furrow, the primitive groove (pg). The ectoblast (ec) bordering this groove is much thickened and may be called the primitive streak. The lower side of this primitive streak is continuous with the mesoblast (mes), while the entoderm (em) is here entirely distinct from the mesoderm. It is evident that the mesoderm posterior to the blastopore is proliferated from the lower side of the ectoblast and not from the upper side of the ento- blast, as is the case anterior to the blastopore. The primitive groove gradually becomes more and more shallow, as it is followed toward the poste- rior, until it is no longer discernible; back of this point the primitive streak may be traced for a con- siderable distance, becoming thinner and thinner until it too disappears, and there remains only the slightly thickened ectoblast underlaid by the thin and irregular layers of mesoblast and entoblast. The primitive streak may be traced for a distance equal to about one third the distance between the head-fold and the blastopore. The Development of the Alligator 247 STAGE IV FIGURES 7a-7h (PLATES XI., XII.) No surface view of this stage was seen by the writer, and hence is not figured. The figures were drawn from one of the series of sections obtained ~parough the courtesy of Prof. S. F. Clarke. This series was marked ‘3 Urwirbeln,’’ so that the embryo was apparently slightly younger than the youngest stage obtained by myself and represented in Figures 8 and 8a. nieure, 7@) represents a section that ‘passed through the head-fold of the amnion (a) just in front of the head-fold of the embryo; the amniotic cavity here appears as a large empty space. Figure 7b is several sections posterior to the preceding; it passes through the head-fold of the embryo, but is just back of the head-fold of the amnion. ‘The deep depression of the ectoderm (ec) and entoderm (en) caused by the head-fold is plainly seen. In this depression lie the ends of the medullary folds, distinct from each other both dorsally and ventrally. Each medullary fold is made up of two parts—a medial, more dense nerv- ous layer (nl), and a distal, less dense epidermal layer (ep). The section corresponding to this one will be more fully described in connection with the following stage. Figure 7c is some distance posterior to the pre- ceding, though the exact distance could not be 248 The Alligator and Its Allies determined because of a break in the series at this point. The section passes through the posterior limit of the head-fold. The medullary groove (mg) is very deep and comparatively wide; around its sides the germ layers are so closely associated that they may scarcely be distinguished. Ventral to the medullary groove the foregut (fg) is seen as a crescentic slit. Figure 7d is about a dozen sections posterior to the one just described and is about one seventh the length of the embryo from the anterior end. The embryo is much more compressed, in a dorso- ventral direction, and the medullary groove (mg) is correspondingly more shallow. Where the ecto- derm (ec) curves over to form the medullary folds it becomes much more compact and somewhat thicker. The notochord (nf) is large and distinct, but is still fused with the entoderm (en). The mesoderm (mes) forms a well-defined layer, en- tirely distinct from both the notochord and the entoderm. From this region, as we pass caudad, the size of the embryo in cross-section gradually decreases and the medullary groove becomes more shallow. Figure 7e is about one third of the length of the embryo from the posterior end, and is only a few sections from the caudal end of the medullary groove. The ectoderm (ec) is much thinner than in the preceding figure and the medullary groove (mg) is much more shallow. The notochord (uz?) The Development of the Alligator 249 is of about the same diameter as before, but is here quite distinct from the entoderm (em) as well as from the mesoderm (mes). Figure 7f is seven sections posterior to Figure 7e. The medullary groove has disappeared and the medullary folds have flattened to form what might be called a medullary plate (at the end of the reference line ec), which continues to the anterior border of the blastopore. The notochord (it) is larger in cross-section than in the more anterior regions; it is still distinct from the entoderm. Figure 7g passes through the blastopore and shows essentially the same structure as was de- scribed in connection with the corresponding section of Stage I (Fig. 2f). * Figure 7 represents the region of the primitive groove (pg) and primitive streak (ps). The sec- tion shows the typical structure for this region— a thick mass of cells is proliferating from the ventral side of the ectoderm (ec) and is spreading laterally to form a distinct mesoderm (mes). The entoderm (en) is entirely distinct from the other layers. STAGE V FicureEs 8-87 (PLATEs XII., XIII., XIV.) On opening the egg this embryo (Figs. 8 and 8a) was found to lie on the end of the yolk, near the center of the irregular, lighter area which was mentioned in connection with the description of 250 The Alligator and Its Allies theegg. The length of the embryo proper is 3 mm. This was the youngest stage found in 1905, and approximates quite closely the condition of the chick embryo after 24 hours’ incubation. The dorsal aspect of this embryo, viewed by trans- mitted light, is shown in Figure 8. The medullary folds (mf) have bent over until they are in contact, though apparently not fused for a short distance near their anterior ends. As will be described in connection with the sections of this stage, the medullary folds are actually fused for a short distance at this time, though in surface views they appear to be separated from each other. In the Madagascar crocodile (78) the first point of fusion of the medullary folds is in the middle region of the embryo, or perhaps even nearer the posterior than the anterior end of the medullary groove. Throughout the greater part of their length the medullary folds are still widely sepa- rated; posteriorly they are merged with the sides of the very distinct primitive streak (ps), which seems, Owing to its opacity, to extend as a sharp point toward the head. Extending for the greater part of the length of the primitive streak is the primitive groove (pg), which, when the embryo is viewed by transmitted light, is a very striking feature at this stage of development and resembles, in a marked way, the same structure in the embryo chick. Clarke (17) figures the blastopore at this stage as a small opening in front of the primitive The Development of the Alligator 251 streak, but does not mention any such condition as above described at any stage of development. Five pairs of somites (s) have been formed and may be seen, though but faintly outlined, in both dorsal and ventral views of the embryo; they lie about half-way between the extreme ends of the embryo. The head-fold (h, Fig. 8a) shows plainly in a ventral view as a darker, more opaque anterior region, extending for about one fourth the length of the embryo. The still unfused region of the medullary folds may be seen also in the ventral view at mg. The head-fold of the amnion (a) forms a very thin, transparent hood over the extreme anterior end of the embryo. The tail fold of the amnion has not made its appearance, and in fact is not apparent at any stage in the development. This is true also of the Madagascar crocodile. The notochord (nf) may be seen in a ventral view as a faint, linear opacity extending along the middle line from the head-fold to the primitive streak. Two sagittal sections of this stage are shown in Figures 8b and 8c. The embryo from which the sections were made was apparently somewhat crooked, so that it was not possible to get perfect longitudinal sections. For example, in Figure 8) the plane of the section is almost exactly median in the extreme posterior and middle regions, but is on one side of the middle line elsewhere. This explains the enormous thickening of the ectoblast 252 The Alligator and Its Allies in the region of the head, where the section passes through one of the medullary folds (mf) at its thickest part; and also explains the fact that the ectoblast is thinner in the middle region (ec), where the section passes through the medullary groove, than it is farther toward the blastopore where the section cuts the edge of the medullary folds. The outlines of the middle and extreme posterior regions of the ectoblast are much more irregular and ragged than is shown in the figure. The plane of the section passes through the noto- chord (zt) in the posterior region, but not in the anterior end of the embryo, where a layer of mesoblast (mes) is seen. The great size of the blastopore (b/p) is well shown, as is the beginning of the foregut ( fg). Comparison of this figure with the more anterior transverse sections and with the dorsal surface view of this stage will make the rather unusual conditions comprehensible. Figure 8c is cut to one side of the median plane, distal to the medullary folds. Being outside of the medullary folds, the ectoderm (ec) is thinner and less dense than in Figure 8); anteriorly it is pushed down and back as the head-fold, and pos- teriorly it becomes thin where it forms the dorsal boundary of the primitive streak (ps). The foregut (fg), as would be expected, is not so deep as in the median section (8b). The most striking feature of the section is the presence of five mesoblastic somites (s). Each somite, espe- The Development of the Alligator 253 cially the second, third, and fourth, is made up of a mass of mesoblast whose cells are compactly arranged peripherally, but are scattered in the center, where a small myoccel may be seen. A series of transverse sections of the embryo shown in Figures 8 and 8a is represented in Figures 8d-j. Figure 8d is through the anterior end of the embryo; the posterior edge of the amnion is cut only on one side (a). The medullary folds (mf) are shown as two distinct masses of tissue, sepa- rated by a considerable space from each other, both dorsally and ventrally; they are underlaid by the ectoderm of the head-fold, through which the section passes. A mass of yolk (y) is shown at one side of the section. Figure 8e represents a section a short distance posterior to the one just described, and passes through the short region where the dorsal edges of the medullary folds have fused with each other. The ventral side of the medullary groove (mg) is, as in the preceding section, still unclosed. An epidermal layer of ectoblast (ep) is now distinct from the nervous layer (z/). Figure 8f is through a region still farther toward the posterior end. 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