Digestive Organs of the Ox and Sheep. 
31 
is carried by it between the incisor teeth and an elastic pad placed 
opposite to them in the upper jaw — between these the herbage is 
pressed and partly cut asunder, its complete severance being 
effected by tearing. Most ruminants possess a great freedom of 
action in the tongue, of which we have a good illustration in the 
ffiraffe when browsing. 
The aliment, being received into the mouth, is next conducted 
Ibetween the molar teeth, where it is subjected to a grinding pro- 
cess (mastication), during which it is also mixed with the fluid 
called saliva — in other words, it is insalivated. The action of the 
jaws in mastication diflPers even among vegetable feeders, arising 
from the peculiar attachment of the lower maxillary bone to the 
skull. This difference is most striking between ruminating and 
non-ruminating animals. In the ox, the mouth being slightly 
opened, the lower jaw is carried to one side, next elevated so as to 
approximate the surfaces of the molars, and then moved in the op- 
posite direction, bruising the food between the teeth. This action, 
having commenced, is generally continued either from right to 
left or vice versa, depending on the will of the animal. A sepa- 
ration of the jaws does not take place to the same extent in the 
horse, but the provender is comminuted by an alternate motion 
of the jaw from side to side. In the dog and the carnivora the 
lips are simply retractile, and the molar teeth are used for crush- 
ing only, there being no lateral action of the lower maxillary 
bone. The incisor teeth in this class may likewise be viewed as 
organs of prehension. 
In the mammalia the teeth are situated in grooves formed in 
the bones which compose the mouth; in fishes they often occupy 
the upper part of the gullet, and are attached to the lining mem- 
brane of the oral cavity ; and in the Crustacea they are placed in 
the stomach. The gizzard of the fowl performs an analogous 
office to mastication in animals, its function being assisted by 
earthy matter which is swallowed by the bird. 
We will add a few remarks on some of the leading peculiarities 
of the teeth. The incisors in the horse are twelve in number, 
arranged in two sets — six in the upper and six in the lower jaw — 
their faces, which are flattened, have an indentation (the mark), 
which affords evidence of the age of the animal. This hollow is 
surrounded by the central enamel, between which and the outer 
border of the tooth the dentine, or ivory, is exposed to attrition. 
The development of enamel in this situation tends to keep up an 
irregularity on the surface of the organ, by which its cutting 
property is preserved ; for this substance possesses a far greater 
density than the other structures composing the tooth. The ox 
and sheep have eight incisors; they are situated in the lower jaw, 
