CLASS REPTILIA 



387 



upper wall, but when it is opened widely they are raised and stand nearly 

 at right angles to this surface. In this position when the snake strikes, 

 they are driven straight forward into the body of the animal struck; 

 at the same moment poison is injected into the wound from the poison 

 glands at the bases of the fangs. Snakes use their poison fangs both in 

 securing prey and in defending themselves from enemies. When fangs 

 are lost they are replaced by other fangs which lie concealed behind the 

 functional ones and come up one at a time to take the place of the lost fangs. 



Fig. 264. — Tuatara, Sphenodon punctatum (Gray), of New Zealand, an example of the 

 Rhynchocephalia. X about j^. Compiled from several sources. 



418. Rhynchocephalia. — The only representative of this order is 

 the tuatara of New Zealand, Sphenodon punctatum (Gray). It 

 was formerly found throughout New Zealand but is now restricted to 

 some small neighboring islands and is threatened with extinction. It 

 is lizard-like (Fig. 264), about two feet in length, Hves in burrows, is 

 nocturnal in its habits, and feeds on any other animal it can secure. 

 Among other structural features which it possesses is a more highly 



Fig. 265. — North American alligator, Alligator mississippiensis (Daudin), an example of 

 the Crocodilia. X about He- From several sources. 



developed pineal eye than is possessed by any other animal. This is an 

 eye developed from a median dorsal outgrowth of the diencephalon; 

 it is rudimentary in all living vertebrates, being most highly developed 

 in lizards, and is often called the pineal gland or pineal body. It is 

 believed to have functioned as an eye in types now extinct and in living 

 forms it has been looked upon as a gland of internal secretion. Although 

 this animal has some characteristics which belong to fossil reptiles and 

 has long been looked upon as the most primitive of existing reptiles, 



