ELEMENTARY ZOOLOGY 



among the turtles and crocodiles there may be, in addition 

 to the epidermal plates, a real deposit of bone in the skin 

 whereby the effectiveness of the armor is increased. The 

 epidermal covering of snakes and lizards is periodically 

 molted, or, as we say, the skin is shed. The bright colors 

 and patterns of snakes and of many lizards are due to the 

 presence and arrangement of pigment-cells in the skin. 

 Among some reptiles, notably the chameleons, the colors 

 and markings can be quickly and radically changed by 

 an automatic change in the tension of the skin. 



Structure. In reptiles, as in batrachians, the chief 

 variations in the body skeleton are correlated with differ- 

 ences in external body form. In the short compact body 

 of the turtles and tortoises the number of vertebrae is much 

 smaller than in the snakes. Some turtles have only 34 

 vertebrae; certain snakes as many as 400. The reptilian 

 skull, in the number and disposition of its parts and in the 

 manner of its attachment to the spinal column, resembles 

 that of the birds, although the cranial bones remain sep- 

 arate, not fusing as in the birds. In the snake the two 

 halves of the lower jaw are not fused in front but are 

 united by elastic ligaments, which condition, together 

 with the extremely mobile articulation of the base of the 

 jaws, allows the snakes to open their mouths so as to take 

 in bodies of great size. All of the reptiles, except the 

 turtles, are provided with small teeth which serve, gen- 

 erally, for seizing or holding prey and not for mastication. 

 The poisonous snakes have one or more long, sharp, and 

 grooved or hollow fangs (fig. 131). In the legless reptiles 

 both shoulder and pelvic girdles may be wholly lacking; 

 in the limbed forms both girdles are more or less well 

 developed. 



The tongue of many reptiles, notably the snakes, is 

 bifid or forked, and is an extremely mobile and sensitive 

 organ. The oesophagus is long and in the snakes can be 



