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 
very long, while the right ovary is larger than the left snd 
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 (Hutenia 
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 tooth 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 which it glides ; others are dull gray or dusky, har- 
monizing with the color of the trunks of trees on which 
they rest. The poisonous Flaps of the Central American 
forest is gaily and conspicuously colored ; indeed it can af- 
ford to be brightly colored, as no birds dare to attack it. 
