REPTILES. 



65 



from the head than in the Batrachia. In all except the 

 alligators the heart is three- chambered, and in these the 

 ventricle is incompletely divided into two. There are two 

 aortic arches, but the left one, which also supplies the 

 stomach, is smaller where it joins its fellow to form the 

 dorsal aorta. The blood is cold. 



The brain is small, no part being extremely developed, 

 and the optic lobes touch, or may touch, each other in the 



FIG. 22. Brain of Snake, c, cerebrum ; cl, cerebellum ; o, optic lobes ; 

 I, olfactory nerve ; II, optic nerve. 



median line. In snakes, lizards, and turtles the cere- 

 bellum is small ; in the alligators it is larger. 



The vertebrae are usually procoelous, and the vertebral 

 column is divisible into the regions of neck (ribless), 



FIG. 23. Skull of Garter-snake (Eutcenia sirtalis), showing the attach- 

 ment of the lower jaw to the skull by means of the quadrate bone, q. 

 (Slightly enlarged.) 



thorax (with ribs), lumbar (ribless), sacrum (usually two 

 vertebrae which connect with the pelvis), and tail ; but in 

 snakes these distinctions fail, and only trunk and tail ver- 

 tebrae are recognizable. A breast-bone is present in lizards 

 and alligators, but none occurs in turtles or snakes. The 



