ANATOMY OF THE SNAKE. 497 



movements of the large ventral scales, which are successively 

 advanced, the hinder edges of the scales resting on the 

 ground and forming fulcra ; resting on these the body is 

 then drawn or pushed rapidly forwards. 



The brain of serpents is small, much as in the lizards, the 

 cerebellum being especially small and flat, while the cerebral 

 hemispheres together form a mass broader than long. 



The more characteristic features of the internal anatomy 

 of snakes is a want of symmetry in the paired organs, as seen 

 in the absence of a second functional lung, and second pul- 

 monary artery, one of the lungs being minute, rudimentary, 

 while the other is very long and large ; the trachea is also 

 yery long, while the right ovary is larger than the left *;nd 

 placed in front of it. The other viscera are so arranged as to 

 pack well in the long narrow body-cavity. 



The student should dissect a snake with the aid of the ac- 

 companying figure of the common striped snake (EutcBnia 

 sirtalis Baird). 



A few snakes are viviparous, as the vipers ; others are ovo- 

 viviparous. In the oviparous Natrix torquata of Europe, 

 the embryo partly develops before the egg is laid, while the 

 young hatches in two months after the egg is deposited. At this 

 time the amnion is fully formed, the head is distinct, as well 

 as the eyeball, and ear sac. The long body grows in a series 

 of decreasing spirals, and when five or six are formed, the 

 rudiments of the liver and of the primordial kidneys may be 

 detected, while at the latter third of embryonic life, the 

 left lung appears as a mere appendage to the beginning of 

 the right. The embryo, at the time of hatching, is provided 

 with a temporary horny twth on the snout to cut through 

 the egg shell. 



Most snakes conform in coloration to the nature of the 

 soil or places they frequent ; some being, as in the rattlesnake 

 of the western plains, of the color of the soil in which they 

 burrow ; the little green snake is of the color of the grass 

 through Avhich it glides ; others are dull gray or dusky, har- 

 monizing with the color of the trunks of trees on which 

 they rest. The poisonous Elaps of the Central American 

 fprest is gaily and conspicuously colored ; indeed it can af- 

 ford to be brightly colored, as no birds dare to attack it. 



