32 Anatomy, Physiology, and Pathology of the 
and differ altogether in their shape from those of the horse : 
viewed in front they present a sharp edge, from which they slope 
inwards and backwards, giving them a scoop-like form. The 
edge is formed by enamel, which covers the dentine : its greater 
hardness causes the tooth to retain its original shape for some 
time, but long-continued wear renders it more or less flat, a con- 
dition which is indicative of advanced age. The early-formed 
teeth are temporary and small ; they give place to a permanent and 
larger set at the period of adultism, when all parts of the frame 
are matured. Many of the rodents are said to change their teeth 
several times: the hare and the rabbit belong to this class. Most 
ruminants are devoid of tushes ; the camel and some of the deer 
tribe are, however, exceptions. The molars of the horse, ox, and 
sheep are twenty-four in number, arranged in sets of six on either 
side of each maxillary bone. Their composition and development 
are essentially the same, although they vary in size and form in each 
animal ; it is, however, unnecessary to enter upon these details. 
Mastication and insalivation are important processes in the 
digestive function, and any derangement of them is certain to be 
associated with impaired health. The saliva is furnished by a 
number of secreting organs (glands) ; the chief of these are the 
parotid, the submaxillary, and the sublingual, all of which are 
of large size in ruminants ; besides which, in these animals we 
meet with a number of other glands, which receive the name of 
buccal, from being placed directly beneath the lining membrane 
of the mouth. Physiologists are divided in opinion with reference 
to them, some viewing them as salivary, and others as mucous 
glands. 
The quantity of saliva which is secreted is very considerable, 
and several pints may be obtained in the course of a few hours 
from even one of the parotids. The action of this fluid on the 
aliment is twofold — chemical and mechanical ; by the first the 
food is rendered alkaline, and by the second soft and pulpy. The 
saliva is also viscid — a condition that depends on its being com- 
mingled with mucus, which is secreted by glandular structures 
that thickly stud the parietes of the oral cavity. We can only 
allude to the viscosity of the saliva, which serves, according to 
Liebig, an important use in the animal economy, by conveying 
oxygen, in the form of atmospheric air, into the stomach. The 
figure on the following page will explain the salivary apparatus. 
In the ox and sheep the food undergoes but little preparation 
when first taken in, being quickly conveyed through the oeso- 
phagus (gullet) to the rumen, from whence it is subsequently 
returned for a second mastication. Deglutition or swallowing is 
a compound act, and may be divided into three distinct stages : 
