THE SNAKE. 209 



3. Protective resemblance; i.e., likeness in form and 

 coloration to the natural objects by which it is surrounded 

 when in its native haunts. Considering that the snake is 

 a predacious animal, what are the advantages, both pro- 

 tective and offensive, of being inconspicuous ? 



External Features. Place the snake and a small pieco 

 of sponge or bunch of cotton saturated with chloroform 

 in a tight box or under a bell jar, and as soon as the snake 

 is dead extend it lengthwise on the table and note its 

 external features. Observe : 



1. The general form of the body. 



2. The more or less distinct head. 



3. The long tapering tail. 



4. The complete covering of scales. 



5. The relation of the scales to each other and to the 

 underlying skin. . 



6. The form of the scales 



(a) On the head. 



(b) On the back and sides. 



(c) On the ventral surface of both body and tail. The 

 wide ventral plate-like scales on which the body rests are 

 the gastrosteges. The hindmost of the gastrosteges is the 

 anal plate. Observe whether it is entire or bifid. The 

 paired plates beneath the tail are the urosteges. 



Search the eye for eyelids ; the sides of the head for 

 ears ; the front of the head for nostrils. 



Dissection. Stretch the snake back downward upon a 

 board, and fasten it so with a tack through the tail and 

 two others through the edges of the upper jaw. Leave 

 the lower jaw free. With forceps pull this upward and 

 sidewise, and note how loosely its halves (rami) are 

 united at their tips. Note : 



1. The looseness of the hinge by which the lower jaw 

 is attached to the cranium. 



NEED. ZOOL. 14 



