MUSCLES OF THE OUTSIDE OF THE SHOULDER. 233 



arises from the cartilage projecting from, or constituting the 

 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, Wy 

 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, if Is a muscle which is the raiser of the shoulder, and takes 



its rise from the nipple-shaped process of the temporal bone, 

 c, Cj 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. 



c, d. The sen-atus 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 5Q, we 

 mentioned that horses labouring under this disease would 



2h 



