THE NERVOUS SYSTEM AND SPECIAL ORGANS. 
99 
It will be seen to alternately move the body from side to side in 
order to see what is occurring behind instead of walking straight 
forwards. However, the limited field of vision is fully compensated 
for by the extreme acuteness of smell and perhaps partially by its 
keen hearing. As is the case with maity aiiimals, in addition to an 
upper and lower eyelid there is a membranous fold placed at the 
inner corner of the eye and beneath the lids w^hich is capable of 
being moved outwards over a considerable portion of the eyeball : 
this is called the nictitating membrane, the haw (of horses), and 
by some authors the third eyelid.'' This outward movement is 
effected by a retraction of the eyeball w^hich displaces some fat 
behind the orbit and so mechanically thrusts the lid forwards. 
Lachryjnal apparatus. — The eyelids furnished with eyelashes 
blink every few seconds and a slight watery discharge flow^s over 
the cheek. There is no true lachrymal (tear) gland, but this is 
replaced by a gland situated on the inner side of the orbit called 
the Harderian gland, which pours its secretion on to the third 
eyelid, whence the tears so produced fall on to the face, there 
being no apparatus to convey them into the nose such as exists 
in most animals. 
The diseases of the organs of sight do not vary from those of 
other animals. 
The following departures from the above indicate present or 
past disease, namely — 
(«) Frequent blinking. 
(b) Abnormal discharge, either water}' or turbid, 
(r) Haziness or opalescence of the pupil. 
[d) Opalescence of the cornea. 
(e) Undue redness seen when the lids are separated. 
(/") Blindness, partial or complete. 
Ear. — There is nothing of special interest to note except as 
previously mentioned as an indication of age [see page 2). 
The temporal glands. — These well-known glands, called kapool 
by natives of India, are tw^o in number and are situated one on 
each side about midway betw^een the eye and ear-hole. Their 
ducts open on the skin in this region. The glands are usually 
inactive. They are analogous to the glands in deer which open 
into pits seen under the eyes and to the gland on the back of the 
bead of camels. 
