

H E R P E T O L O G V. 



PABT I. ON THE ANATOMY AND PHYSIOLOGY OF REPTILES. 



Of XIV. 



Skull. 



-. r.r. 



Hi vivo now given a general description of reptiles, 

 ! explained the classification which we intend to fol- 

 low in the subsequent page* ; we shall proceed to ex- 

 hibit a comprehensive view of their anatomy and physio- 

 logy, pursuing the same order which we have observed 

 in the comparative part of our ANATOMY. f 



CHAP. I. 



Of the Motions of Reptiles. 



THE organs of motion in reptiles do not differ so 

 much from those of quadrupeds as some other parts of 

 their organical structure, though there is considerable 

 variety in the several tribes of this class. 



The bones of most species are as firm as those of 

 quadrupeds ; but in the smaller reptiles, as the frogs, 

 they are more cartilaginous. It is asserted by some 

 naturalists, that the bones of tortoises have no medul- 

 lary cavities; but in the larger lizards, these are suffi- 

 ciently apparent The skeleton of a Saurian reptile is 

 figured in Plate CCXCV. Fig. ] . 



The skull of reptiles is generally very small in pro- 

 portion to the body ; but in many species, the jaws are 

 proportionally very large. The cavity of the skull is 

 cither exceedingly small, or not half filled by the brain. 

 A remarkable change takes place in the head of the cro- 

 codile in proportion as the animal advances in growth 

 after its extrusion from the shell. When first hatched, 

 the skull Js thick and rounded, and the forehead pro- 

 minent, and the eyes are nearly at an equal distance be- 

 tween the fore and back parts of the head. In proportion 

 as the animal grows, the frontal prominence gradually 

 disappears, and the jaws lengthen forwards; and in the 

 adult state, the head is quite Hat, and the eyes three times 

 as far distant from the snout as they are from the back of 

 the head. . 



The skull of the crocodile resembles a truncated py- 

 ramid, of which the cavity for the brain forms the base; 

 that of frogs and salamanders is of a form between the 

 cylindrical and the prismatic ; that of tortoises consi- 

 derably resembles that of the crocodile. The cavity of 

 the skull, in reptiles, is of an oblong form, and nearly 

 of an equal breadth. Of the jaws and teeth, we shall 

 speak under the organs of digestion. 



With rc>pect to the vertebral column, we may re- 

 mark, that the number and proportions of its compo- 

 nent vertebra; vary more in this class than in all the 

 other vertebral animals. The tortoises have generally 

 even vertebra in the neck, from eight to eleven in the 

 back, and generally three or four in the sacrum. In 

 this genus all the vertebrae, except those of the neck 

 and tail, are imrnoveahly fixed with what is analogous 

 to nbn, in the horny shield with which they are cover- 

 The crocodile has seven cervical, twelve dorsal, 

 iimbar, two sacral, and thirty-four caudal verte- 

 m the other saurians, the proportional num- 

 vary in almost every species. Frogs and toads 

 ring no n... the ordinary, division of the vertebral 



olumn cnnnot lie distinctly made. The common frog 



n vertebra-, and the pipa, or Surinam toad, 



has in all *" 



The muscles attached to the spine also vary consider- Anatomy 

 ably. In tortoises, where only the head and tail arc and Physio- 

 moveable, the spinal muscles are confined chiefly to 

 these two organs, and those of the neck possess many ^~^ 

 peculiarities. The chief motions of the neck in this 

 genus are those by which the head is thrust out from 

 the shell, and drawn back within it. The spinal mus- 

 cles of frogs and salamanders are few in number, ex- 

 cept that in the latter, the crocodiles, and other saurians, 

 the muscles of the tail are proportionally numerous and 

 powerful. 



The thorax is very differently formed in the different Thorax, 

 orders. In the tortoises, the sternum or breast bone is 

 lost in the breast plate or lower shell, while the ribs are, 

 as we have said, firmly cemented in the shield. Of the 

 saurians, the crocodile has the anterior part of the ster- 

 num bony and prolonged, so as to receive the clavicles ; 

 while the rest is cartilaginous, and extends backward 

 to the pubis, furnishing eight cylindrical cartilages that 

 surround the belly. The ribs of this animal are twelve 

 in number ; but the two most atlantal or forward, and 

 the two most sacral or backward, are not united to the 

 sternum. In the guana and tupinambis, only six of the 

 ribs are united to the sternum. The chameleon has a 

 small sternum, but all the ribs are made to meet round 

 the thorax, by means of intermediate cartilagts. In the 

 salamanders the ribs are extremely short, so as to appear 

 like appendages of the vertebrae. The frogs have a 

 sternum though no ribs. 



In most of the reptiles, there is little peculiar in the 

 muscles of the thorax and abdomen. In the tortoises, 

 however, where the ribs are immoveable, and where 

 the place of abdominal muscles is supplied by the breast- 

 plate, the muscles which would be attached to the ster- 

 num are inserted into the pelvis, upon which they act; 

 and in frogs which have no ribs, the muscles are united 

 to the sternum by strong membranes. 



The superficial or glenoid cavity, in which the hu- Atlanta! ex- 

 merus or large bone of the atlantal or anterior extrerai- tremItT ' 

 ty moves, is in reptiles formed partly by the scapula 

 and partly by the clavicle. The scapula has no spine ; 

 it is elongated, and retracts and becomes thicker to- 

 wards its neck. The clavicle is simple, short and fiat. 

 In tortoises, the disposition of the bones that form the 

 shoulder is most remarkable, and is thus described by 

 Cuvier. Besides the scapula and the clavicle, there is 

 a bone which he calls the fork ; one of the bones stretches 

 from the base of the rudiment of the first rib, to which 

 it is attached by a ligament as high as the glenoid ca- 

 vity, where it is intimately united with the other two. 

 The second bone, which appears like the continuation 

 of the former, is attached by its other extremity to the 

 breast plate, and this extremity is bound by strong liga- 

 ments to that of the bone behind it. These bones thus 

 united are slightly curved outward, so as to leave be- 

 tween them, and those on the opposite side, an oval 

 space for the passage of the gullet, the windpipe, and 

 numerous muscles. Lastly, the third bone is placed 

 below the abdominal and thoracic viscera, nearest tlie 

 breastplate, and is extended from the glenoid cavity as 

 far as the abdomen. It gives attachment to numerous 

 muscles, and resembles the scapula in every thing but si. 

 tuation. See Cuvier, Le f onscfAnat. Comparee, Sec. IV, 



