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(3) The tongue can be completely withdrawn into a sheath 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 vertebre. 
(5) Nosnakes possess movable eyelids. There is a fixed trans- 
parent scale over the eye. 
(6) Snakes have no external opening to the ear. 
Eves, Ears, AND TONGUES OF SNAKES. 
Snakes have no eyelids. The eye is protected in front by a 
transparent scale, in appearance like a watch-glass, which is 
firmly attached to the surrounding scales of the skin. The eye 
is thus protected 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 tongue of a snake is black, except towards 
the root portion, which is flesh colour. 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When at rest it is contracted, and withdrawn into a sheath in 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 day or two 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 
tongue. I have satisfied myself of this on many occasions, by 
observing captive snakes. At these times when touched, snakes 
