MUSCLES OF THE OUTSIDE OF THE SHOULDER. 233 
arises from the cartilage projecting from, or constituting tne 
breast-bone, plate ii. fig. 2. It then traverses the neck in an 
upward direction, and is neither of great dimensions nor 
strength. About three-fourths of its length upwards, it 
changes to a flat tendon, and is exhibited, plate iii. fig. 1, w, 
above which it insinuates itself between the parotid and sub¬ 
maxillary glands, that it may be inserted into the angle of 
the lower jaw. It is exerted in bending the head towards the 
chest. 
b , i 9 Is a muscle which is the raiser of the shoulder, and takes 
its rise from the nipple-shaped process of the temporal bone, 
c, c, plate iii. fig. 2 and 3, and extending down the fore part 
of the neck, is inserted into the middle part of the lower bone 
of the shoulder, and thence continued down to the arm. The 
use of this muscle is to bend the head; or, the head and neck 
being fixed, to elevate and bring forward the arm. When the 
horse is running at full speed, with the head thrown forward, 
this muscle is in powerful action. 
a, d. The serratus major, or great tooth-shaped muscle of the 
shoulder, which constitutes a large proportion of the lower 
part of the neck. It is deeply seated, arising from the five 
last bones of the neck, and the two first ribs. Its lower por¬ 
tion springs from all the true ribs. The whole of its fibres 
have a downward tendency, and are inserted into the inner 
surface of the shoulder; by means of which the shoulder 
is attached to the chest, and the weight of the body thereby 
supported. 
When the horse is in a standing position, this muscle 
occasionally performs another important office. The shoul¬ 
ders and legs, by means of the weight of the body, are fixed 
and immovable; consequently, having no longer any power 
over the motion of the limbs, it now exercises its power in 
enlarging the cavity of the chest, and thus materially con¬ 
tributes to give freedom to the action of the chest in 
breathing. 
In treating of inflammation of the lungs, page 56, we 
mentioned that horses labouring under this disease would 
