SNAKES. 579 



of the epidermis have much coherence, and are periodically 

 shed in a continuous slough. The scales on the head form 

 large plates, and those on the ventral surface are transverse 

 shields. There are no separate eyelids, but the thin trans- 

 parent epidermis extends over the staring eyes. The nostrils 

 lie near the tip of the head ; there are no external ear open- 

 ings. 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." 



There are many remarkable peculiarities in the skeleton. 



dv-< 



FIG. 199. Snake's head. (After NUHN. 



civ., Poison fangs ; b., sheath of fang ; /. tongue ; rt., muscles ot 

 tongue. 



The vertebrae are very numerous, some pythons having 

 four hundred ; they are proccelous, and are distinguishable 

 only into a pre-caudal and caudal series. 



All the pre-caudal vertebrae except the first the atlas 

 have associated ribs, which are movably articulated and 

 used as limbs in locomotion. In the caudal region, the 

 transverse processes, which are elsewhere very small, take 

 the place of ribs. 



The serpent " literally rows on the earth, with every 

 scale for an oar; it bites the dust with the ridges of its 

 body." On a perfectly smooth surface it can make no 

 headway, but in normal conditions the edges of the 

 anterior ventral scales are fixed against the roughnesses 



