THE PINE LIZARD AND ITS ALLIES 



357 



Snakes. The snakes, which belong to the class Ophid'ia 

 (Gr. ophis, " serpent "), are usually very easily distinguished 

 externally by the absence of eyelids and limbs, although 

 rudimentary hind legs are found in a few forms, such as the 

 pythons. Teeth are present in all snakes, and are of two 

 types, — the ordinary teeth, used for seizing food, and the 

 poison fangs, which are perforated, forming a passage for 



Fig. 183. Photograph of a Mexican iguana with broken tail 



the poison secreted in a gland at their base. Both kinds of 

 teeth are shown in the illustration of the skull of the rattle- 

 snake (Fig. 184), which shows also the gland where the 

 poison is secreted (Fig. 184, 9), and the reserve fangs 

 (Fig. 184, 11) which replace the first pair when the former 

 are broken or shed. In the nonpoisonous species the num- 

 ber of teeth is much greater than in the rattlesnake. 



The tongue of a snake is a long, slender, forked structure, 

 used principally as an organ of touch, not as a fang as many 

 people believe. The lower jaw is joined to the upper jaw 

 in such a way (Fig. 184) as to admit of so much freedom 

 of movement that the snake's mouth can be opened wide 



