COMPARATIVE ANATOMY. 



201 



2- 



10- 



Thoy have very short legs and webbed feet The alligator* 



not webbed feet. Tortoises have a complete external 



skeleton, covered with thinner plates, whioh represents a part of 



in. Tho snakes are destitute of thc-.no thick oat ward 



investments, but have scales covering their bodies. 



'/'A.' Teeth. Tho dental apparatus varies according to the 

 ! mode of lifo. Tho crocodiles have long jaws, armed 

 \\.iii a ninglo row of conical tooth, hold in bony sockets. In 

 alligators, the front teeth (canine) of the lower jaw fit into a pit 

 edge of the upper jaw. The Chelonia (tortoises, etc.) 

 have no teeth. Their jaws are covered with a horny bill, which 

 serves the purpose of teeth. Tho teeth of the Ophidia (sorpenta) 

 ire not lodged in sockets. In the cobra, rattlesnake, viper, etc., 

 the teeth aro grooved or per- 

 forated by a canal, which com- 

 municates with a poison gland 

 (see Vol. II., p. 17C), and serves 

 to convey the poison into the 

 wound made by the animal's 

 bite. The opening of the 

 canal is not at the extremity 

 of the tooth, but at a point a 

 little above it, so as not to in- 

 terfere with the cutting ac- 

 tion of the tooth. These teeth 

 are attached to movable bones. 

 When at rest, the poison- 

 fangs are hidden by a fold of 

 the gums. Behind them ore 

 rudiments of other fangs, to 

 replace the former, if lost. 

 The poison of these serpents 

 prove rapidly fatal to hot- 

 blooded animals when intro- 

 duced into the blood current 

 through a wound. When 

 swallowed it is harmless. 



The tongue in some of these 

 animals is very long. In the 

 well-known chameleon it is, 

 when fully extended, nearly 

 as long as the body. By means 

 of an hyoid apparatus it con 

 protrude and retract it with 

 amazing rapidity. It serves 

 as an organ of prehension. 



The Alimentary Canal pre- 

 sents few differences from 

 that already described in the 

 Amphibia. It is compara- 

 tively short, and usually of 

 great width. The gullet is 

 wide and extensible, especi- 

 ally in the snake, which is 

 said to be able to swallow 

 animals of greater bulk than 

 itself. The large and small 



of a fourth, by a septal division of the ventricular cavity into 

 two part* ; so that the blood, arterial and venous, still mixes. 

 In some this intraventricular septum is almost complete, form* 

 ing quadrilooolar heart like that of the higher vertebrates. 



The blood corpuscles are not very numerous. They are oval 

 in shape and of large size, varying from A, to fa of an inch in 

 the long diameter, and ^ to ^ of an inch in the short diameter. 

 Tho nervous system does not indicate any considerable ad- 

 vances in its general structure above that of the higher fishss 

 The brain is of small size in comparison with the skull. 



The young of the Koptilia are developed from eggs. Bone 

 are hatched before being born, as in the viper. The majority, 

 however, deposit their eggs in the sand on river banks, and leave 



them to be hatched by the heat 

 of the sun. The egg of the 

 crocodile is about the size of 

 that of a goose. The turtle 

 makes two or three visitations 

 to the shore in the coarse of 

 a year to deposit her eggs in 

 a cavity she scoops oat to re- 

 ceive them. Her eggs amount 

 to about a hundred at each 

 sitting. She carefully covers 

 them with sand, and leaves 

 them. The mode of develop- 

 ment of the reptilian embryo- 

 resembles that of the higher 

 Vertebrata. The Reptilia 

 possess a completely ossified 

 skeleton. The skull is small 

 the greater part of its balk 

 being made up of jaws. The- 

 head is articulated to the- 

 spinal column by means of 

 a single oondyle. The ribs 

 are numerous in the croco- 

 diles, lizards, and serpents. 

 In the snake they amount to 

 as many as three hundred 

 pairs. In the hitter they are 

 free at one extremity* the- 

 breast-bone and limbs being 

 absent. 



The spinal segments form a 

 series of ball and socket joints, 

 so as to allow considerable lati- 

 tude of motion. The tortoise 

 is invested by a bony habita- 

 tion, consisting of two plate* , 

 united at the sides, to the inner 

 aspect of which it is immova- 

 bly fixed. The anterior and 

 posterior extremities are open, 

 to allow the animal to protrude 

 its head and limbs. The upper 

 or back plate is called the cara- 



___ ._. ___ 



intestines"are~very "distinctly EKPTILIA.-!. ANATOMY or THE COMMON SNAKE (ATOB MILNE-EDWARDS), pace; the under or ventral one, 

 divided, and separated by a Eefs. to Nos. in Fig. 1. 1, tongue and glottis; 2, gullet, cut across at 2" to the plastron. The upper plate 

 curtain or valve. In a tor- show the heart - etc - in situ -' 3 - "tomac!!; *. intestine; 5, cloaca; 6, consists of eight ribs flattsnsd 

 toise of moderate size the anus ; 7, liver ; 8 oyarium; 9, ova, or eggs; 10, windpipe; 11, pnn- Qut> u<mded together, and 

 whole length of the alimentary clpal lung ; 12, little lung. ^^ ^ to ^ Uflk . 



canal was found to be four bone. The lower plate re- 



feet. The small intestines were 20 J inches, and the large 16J presents the breast-bone, arranged in a similar manner. It is 

 inches long. The stomach was 2 inches long. "** *-* ' -* ' ~s TI. .i, nn i^a. * n /l italwiA Hnna* K;^V 



The intestines 



terminate in a cloaca, which is generally also the common point 

 of termination of the urinary and generative organs. 



The Respiratory Apparatus. The Beptilia never breathe by 

 gills at any period of their existence, like the two preceding 

 classes, but by lungs. These ore two in number, and made up 

 of numerous colls, usually of large size, aggregated together. 

 In snakes and lizards the lung called the principal lung is much 

 larger than the other, and, in fact, the working lung. Tho 

 smaller one, called the little lung, is either rudimentary or 

 absent. Tortoises and turtles, like the ribloss frogs, owing 

 to their possessing immovable ribs, are necessitated to breathe 

 by swallowing the air. The reptilian heart consists of throe 

 cavities. There is an evident tendency in many to the formation 



composed of nine pieces. The shoulder and pelvic bones, which 

 afford attachment to the limbs, are situated in the interior of 

 this bony house. The neck and tail portions of the spinal column 

 only are free. The bones of the (in Beptilia possessing) ex- 

 tremities are well developed, and approach in character those of 

 the higher Vertebrata. The toes are usually five in number on 

 each foot, movable, and armed with claws. 



CLASSIFICATION. Professor Huxley groups the Reptflia into 

 the following orders : (1) Ooeodtfto, comprising the modern 

 crocodiles, alligators, and caiman*, and the extinct Teleosauria 

 and bolodonts ; (2) Lacertilia, lizards, blind-worms, and the 

 chameleons ; (3) Ophidia, or snakes ; (4) Chelonia, turtles and 

 tortoises. Besides these, there are five orders of fossil 

 Beptilia. 



