HIGHER CHORDATES 



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New Mexico. Although it Hves close to the Colorado 

 River, its presence has never been authenticated in 

 California. This large, heavy-bodied, seemingly 

 sluggish lizard can, as some humans have discovered 

 to their sorrow, move very rapidly. It would be diffi- 

 cult to touch an aroused Gila monster without being 

 bitten. In nature they are usually active at night and 

 at dusk, moving about with a slow, awkward gait. 

 They are powerful diggers who can construct their 

 own daytime retreats and can dig 3- to 5-inch deep 

 holes in damp sand to lay and cover their eggs. 



The Gila monster is the only protected venomous 

 animal. An Arizona law protects both it and horned 

 lizards from being sold, given, ofTered for sale, or 

 exchanged, except by written permission of the Ari- 

 zona Game and Fish Commission. 



Suborder SERPENTES (= OPHIDIA) (Sr^akes) 



Diagnosis: body elongate, legless; lower jaw bones 

 unfused anteriorly, joined by ligaments; eyelids 

 absent; tongue usually forked; United States species 

 with only claw-like vestiges of hind limbs (Figure 

 16.22). 



Most snakes, like most lizards, lay eggs. However 

 boas, pit vipers (including rattlesnakes), garter 

 snakes, water snakes, and certain others bear their 

 young alive. Some snakes brood their eggs. 



Nonvenomous snakes use their long, slender in- 

 curved teeth to grab their prey. Small prey is fre- 

 quently grabbed and swallowed alive and is killed by 

 the powerful digestive juices. Larger prey is killed 

 by suffocation or constriction before being swallowed. 

 The whipsnakes and racers seize and sufTocate their 

 prey by pushing it against the ground or some con- 



Figure 16.22 The head and port of the body of a snake, Masticophis. 

 (After Ruthven.) 



venient object, sometimes the snake's own body. The 

 kingsnakes are examples of snakes that constrict their 

 prey, a process also causing the prey to die of suffoca- 

 tion. 



Venomous snakes secrete a poison that paralyzes 

 or kills and starts digestion of the prey. There are two 

 main types of poisonous snakes, those with fangs in 

 the front and those with fangs in the rear of the 

 mouth. The front-fanged snakes in turn have two 

 groups, those with fixed and those with movable 

 fangs. In the movable-fang snakes, pit and Old 

 World vipers, the fangs are on a movable bone at the 

 front of the upper jaw. This apparatus allows the 

 fangs to be larger than those of fixed-fang snakes, 

 because they can be folded against the roof of the 

 mouth when not in use. The fixed-fang snakes, in- 

 cluding the cobras and their relatives, have immov- 

 able, shorter fangs. In the front-fanged snakes each 

 venom gland is connected by a duct to a hollow fang 

 and there is a series of replacement fangs behind each 

 functional fang; the fangs are replaced periodically. 

 The rear-fartg snakes have two or three pairs of rear 

 teeth enlarged and grooved along the front or side. 

 These "fangs" are frequently separated by a gap 

 from the other teeth. The poison flows down the 

 grooves into the victim, a relatively inefficient process. 

 Frequently, rear-fang snakes must chew their victim 

 to get the venom into it. 



Snake venom is a mixture of digestive juices and 

 poisonous proteins that can be classified as either 

 nerve- or blood-affecting. Venomous snakes usually 

 have both types, but a preponderance of one or the 

 other. The nerve-affecting venom is most efficient 

 on "cold-blooded" animals; the blood-affecting, on 

 "warm-blooded" animals. 



The lower jaw in most snakes is specialized to 

 swallow prey without the necessity for chewing. 

 The jaw is loosely attached to the skull. Also, the 

 jaw consists of two bones connected at the "chin" by 

 muscle, elastic tissue, and skin. These specializations 

 allow a snake to make an extreme gape with the 

 mouth, and the teeth are specialized so that the snake 

 can pull its way over its prey. Swallowing is facili- 

 tated by the inward curving of the teeth, which pre- 

 vents prey from escaping outward, and independent 

 movement of each side of the jaw, allowing one side 

 to obtain a forward "grab" while the other side holds 

 fast. 



There are four types of poisonous snakes in the 

 United States. The cobra family is represented by 



