THE JAWS. 35 
On the outer side of each horizontal ramus, 
The 
The 
The 
beneath the first premolar, is a smaller 
opening, the mental foramen, through 
which a branch of the dental nerve 
makes its exit. 
point of junction of the two horizontal 
rami is termed the symphysis; on the 
lower border of which the digastric 
muscle is inserted in a small depression. 
actions of the muscles moving the 
lower jaw may be briefly indicated as 
follows: 
lower jaw is raised by the masseter, 
internal pterygoid, and temporal mus- 
cles; the depression of the jaw is 
accomplished by the digastric muscle, 
and a series of hyoid muscles. The 
larger portion of the external ptery- 
goid muscle, having their fibres nearly 
horizontal, draw the jaw forward ; while, 
when these muscles act alternately, the 
jaw is moved from side to side: this 
movement, however, in the dog is 
very restricted. The retraction of 
the jaw is effected by the hinder part 
of the temporal muscle. 
