14 THE SNAKES OF SOUTH AFRICA. 



(2) The upper jaw and palate in the vast majority of snakes 

 are more or less movable, which, with the distensible lower jaw, 

 allows the snake to swallow comparatively large prey. 



(3) The tongue can be completely withdrawn into a sheath 

 in the mouth. 



(4) The presence of additional articulations to the vertebrae. 



(5) No snakes possess movable eyeUds. There is a fixed trans- 

 parent scale over the eyeball. 



(6) Snakes have no external opening to the ear. 



(7) Large transverse shields are on the underpart of the body 

 on the great majority of snakes. These are never present on 

 legless lizards. 



Eyes, Ears, and Tongues of Snakes. 



Snakes have no eyeUds. The eye is protected in front by a 

 transparent scale — in appearance like a watch-glass — which is 

 firmly attached to the surrounding sldn. The eye is thus 

 shielded from all external injury, unless, of course, this window 

 pane gets broken. The eyes themselves are movable to a 

 limited extent. Little glands secrete tears, which are for the 

 purpose of lubricating the eyes, the fluid being drained off into 

 the cavities of the nose by two little channels or ducts. Odd- 

 coloured eyes are sometimes seen in snakes. This is particularly 

 noticeable in the house snakes {Boodon). 



The ears of snakes have no external opening, but beneath the 

 skin is an intricate mechanism which registers the sound- vibra- 

 tions and conveys them to the brain ; and in spite of having no 

 external ear openings, snakes have very fair hearing. They hear 

 mainly by vibrations carried through some solid substance such 

 as the ground. Sharp, high-keyed sounds have an exciting effect 

 upon snakes. The tongues of most snakes are black, except 

 towards the root portion, which is flesh colour. In a few it is 

 fleshy or red. It is bifid, which means forked. The tongue is 

 exceedingly sensitive, and is used mainly as a feeler. It is quite 

 innocent of any " stinging " powers. When at rest it is 

 contracted, and withdrawn into a sheath in the centre of the 

 lower jaw. 



A few days previous to the skin-shedding process, the eye 

 scales become opaque, and the snake is temporarily blind, but 

 can find its way about fairly well by means of its very sensitive 



