356 



ZOOLOGY 



SECT. 



to be hatched by the heat of the sun. Some, however, as already 

 stated, are viviparous ; in all cases the young are left to shift for 

 themselves as soon as they are born. 



Most of the Snakes also are extremely active and alert in their 

 movements ; and most are very intolerant of cold, undergoing a 

 hibernation of greater or less duration during the winter season. 

 Many live habitually on the surface of the ground some kinds by 

 preference in sandy places or among rocks, others among long 

 herbage. Some (Tree-Snakes) live habitually among the branches 

 of trees. Others (Fresh-water Snakes) inhabit fresh water ; others 

 (Sea-Snakes) live in the sea. The mode of locomotion of Snakes 

 on the ground is extremely characteristic, the reptile moving along 

 by a series of horizontal undulations brought about by contractions 

 of the muscles inserted into the ribs, any inequalities on the surface 

 of the ground serving as fulcra against which the free posterior 

 edges of the ventral shields (which are firmly connected with the 

 ends of the ribs) are enabled to act. The burrowing Blind-Snakes 

 and other families of small Snakes feed on Insects and Worms. 

 All the rest prey on Vertebrates of various kinds, Fishes, Frogs, 

 Lizards, Snakes, Birds and their eggs, and Mammals. The Pythons 

 and Boas kill their prey by constriction, winding their body closely 

 round it and drawing the coils tight till the victim is crushed or 

 asphyxiated. Some other non-venomous Snakes kill with bites 

 of. their numerous sharp teeth. The venomous Snake sometimes, 

 when the prey is a small and weak animal such as a Frog, swallow 

 it alive ; usually they first kill it with the venom of their poison- 

 fangs. 



When a venomous Snake strikes, the poison is pressed out from 



the poison-gland 

 by the contraction 

 of the masseter 

 (Fig. 1020, Me), 

 one of the muscles 

 which raise the 

 lower jaw ; it is 

 thus forced along 

 the duct (Gc) to 

 the aperture (za), 

 and injected into 



FIG. 1020. Poison apparatus of Rattlesnake. A, eye- Gc the WOUnd made 



poison-duct entering the poison-fang at f; Km, muscles of Kir flio for.fr TV, Q 



mastication partly cut through at * ; Me. constrictor (masseter) U J tlle Idn g- 1 ne 



muscle; Me', continuation of the constrictor muscle to the lower pffpp.t i<5 to r>rn 

 jaw ; N. nasal opening ; S, fibrous poison sac ; z, tongue ; za, 



opening of the poison-duct ; zf, pouch of mucous membrane duce acute pain 

 enclosing the poison-fangs. (From Wiedersheim's Comparative , -i 



Anatomy.) witn increasing 



lethargy and 



weakness, and in the case of the venom of some kinds of Snakes, 

 paralysis. According to the amount of the poison injected (in 



