STRUCTURE OF THE VERTEBRATES 61 



one genus (Sphenodon) found in New Zealand. It is an ideally 

 generalized reptile, having been described as a ''living fossil". 

 In its skeletal structure and body shape it is the last remaining 

 specimen of a lost race. 



Order Crocodilia. This order includes the alligators of the 

 United States and China; the crocodiles, which are distributed 

 throughout the warmer regions of the earth; the caimans of 

 Central and South America; and the gavials of southern Asia. 

 These animals are carnivorous in their habits, and in certain 

 regions are dangerous to man. This is particularly true in the 

 Ganges River. 



This is also an ancient order, related to the dinosaurs. The 

 skull and bony skeleton are generalized; the back is well sup- 

 plied with dermal plates which are hidden under the ectodermal 

 scales; and the soft anatomy is typically reptilian, though 

 highly modified. The brain is the best developed among the rep- 

 tiles, and the heart is four-chambered. 



Their breeding habits are much like those of the turtles, the 

 eggs being laid in nests near the water. The American alligators 

 build large nests of sticks or mud, and after the eggs are laid 

 they are covered by the mother and left for the atmospheric 

 heat to hatch them. They grow slowly after hatching, and have 

 a long span of life. This characteristic of gr-owth, coupled with 

 the value of their skin for leather, has rapidly depleted their 

 ranks. 



Order Lacertilia. The lizards, which are included in this 

 order, are so nearly related to the snakes that they are often 

 classified together. Most of the lizards have four legs with five 

 toes on each foot, although some genera have degenerate legs or 

 lack them altogether. A legless lizard can be distinguished from 

 a snake by its eyelids, which are lacking in the snakes, and the 

 small ventral scales. The smaller lizards are popularly confused 

 with the salamanders, but their scales and their rapidity of 

 motion make identification easy. 



Lizards are either oviparous or ovo-viviparous (page 37). 

 AA^ith one exception they are non-poisonous, the genus Heloderma 

 (Gila Monster) of Mexico and the southwestern part of the 

 United States having poison glands. There is wide disagreement 

 as to the violence of their poison, but it is doubtful if their 



