460 



VERTEBRATE LIFE AND ORGANIZATION 



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Figure 23.12. A gopher snake eating a rat. (Courtesy of the New York Zoological 

 Society.) 



osoma), burrow to some extent for protection, and some have taken to 

 a burrowing mode of life. Appendages are lost in many burrowing 

 lizards, though vestiges of girdles are present. The eyes may be reduced, 

 and the body form becomes wormlike. The glass snake (Ophisaurus), 

 although it burrows only part of the time, is a lizard of this type. The 

 glass snake derives its name from its ability to break off its tail when 

 seized. The tail, which constitutes about two thirds of the animal's 

 length, fragments into many pieces that writhe about, attracting atten- 

 tion while the lizard moves quietly away. Other lizards also have this 

 ability, though developed to a less spectacular degree. Lost tails are 

 regenerated, but the new tails are supported by a cartilaginous rod 

 rather than by vertebrae. 



The only poisonous lizards are the beaded lizards, such as the Gila 

 monster (Heloderma) of the Southwestern United States. Modified 

 glands in the floor of the mouth discharge a neurotoxic poison, which 

 is injected into the victim by means of grooved teeth. This is a rela- 

 tively inefficient method, so the bite is not as dangerous as the bite of 

 most poisonous snakes. Charles Bogert of the American Museum 

 of Natural History reports that 8 of 34 bites that have come to his 

 attention were fatal and he believes that the majority of minor bites 

 are never reported. It is probable that the poison is used for defense 

 rather than for killing prey, for the Gila monster crushes its food with 

 its powerful jaws. 



Snakes (suborder Ophidia) differ from lizards most notably in 

 being able to swallow animals several times their own diameter (Fig. 

 23.12). This is made possible by an unusually flexible jaw mechanism. 

 The posterior ends of the lower jaw of a lizard are movably articulated 

 with the quadrate bones of the upper jaw, and the two halves of the 

 lower jaw are firmly united with each other at the chin. In snakes there 

 is a movable joint between each half of the lower jaw at the chin, and 

 another on each side midway between the chin and the quadrate. Then 



