ZOOLOGICAL POSITION AND STRUCTURE 29 
while the limbs are short and thick ; but other species 
may have a ridge or hump on the withers. The long 
tail is usually furnished with a tuft of hair at the 
tip. 
The cheek-teeth are characterised by the great 
height of their crowns, which in the upper molars are 
nearly square in section, and have an additional 
slender column on the inner side between the two 
crescentic main columns. 
A large number of ruminants are characterised 
by the possession of what are known as skin-glands 
on the face or limbs, or in both together, the position 
of such glands being frequently indicated by the 
presence of tufts of hair longer than that clothing 
the rest of the face or limb. When these glands — 
which secrete a highly odorous fluid — are present on 
the face, they usually take the form of pits, or sacs, 
opening on the surface by means of narrow orifices ; 
and the same is the case with the so-called inter- 
digital, or hoof, glands, which open either between the 
two main hoofs, or a little above them on the front of 
the foot in the line of their cleft. When such hoof- 
glands are present the cleft between the two main 
hoofs extends a long way upwards. On the other 
hand, the glands which occur higher up on the legs 
of many antelopes and deer — but more especially 
the latter — do not take the form of pits, but are 
constituted by a special thickening and softening of 
the skin. There may also be glands in the groin. 
Apart from those of the face, these glands, by leaving 
their scent on the grass or ground, appear intended to 
aid the members of a species in finding the where- 
abouts of their fellows. 
Now it is not a little remarkable that such glands 
