STRUCTURE OF SNAKES 705 



General notes on snakes. — Snakes, especially when 

 poisonous, are often brightly coloured. The scales on the 

 head form large plates, and those on the ventral surface are 

 transverse shields. In many cases there are odoriferous 

 glands near the cloacal aperture. 



The muscular system is very highly developed, and the 

 limbless serpent, Owen says, " can outclimb the monkey, 

 outswim the fish, outleap the zebra, outwrestle the athlete, 

 and crush the tiger." 



The vertebrae are very numerous, some pythons having 

 four hundred ; they are procoelous, and are distinguishable 

 only into a pre-caudal and caudal series. 



n 



Fig. 415. — Snake's head.— After Nuhn. 



dv., Poison fangs ; b., sheath of fang ; /., tongue ; rl., muscles of 



tongue. 



All the pre-caudal vertebrae except the first— the atlas — 

 have associated ribs, which are movably articulated, and 

 used as Umbs in locomotion, being attached to the large 

 ventral scales which grip the ground. In the caudal region 

 the transverse processes, which are elsewhere very small, 

 take the place of ribs. 



One of the most distinctive characteristics of the skull 

 is the mobility of some of the bones. Many of the 

 Ophidians swallow animals which are larger than the normal 

 size of the mouth and throat. The mobility of the skull 

 bones is an adaptation to this habit. Thus the rami of the 

 mandible are united by an elastic ligament ; the quadrates 

 and the squamosals are also movable, forming " a kind of 

 jointed lever, the straightening of which permits of the 



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