MUSCLES ON THE INSIDE OF THE SHOULDER. 



331 



and for the same reason it is that we regard his lying down as one of the most. 

 favourable symptoms, because it shows us that the breathing is so much relieved 

 as not to need the assistance of this muscle. 



At e is a small portion of the splenius muscle, which was spoken of when the 

 neck was described, p. 212. 



/represents a muscle sometimes described as a portion of the levator humeri, 

 or elevator of the shoulder, arising from the nipple-shaped process or tubercle 

 of the temporal bone, running down the somewhat lateral but fore part of the 

 neck, inserted into the upper and middle part of the lower bone of the shoulder, 

 and thence continued down to the arm. Its office is to bend the head ; or, the 

 head and neck being fixed, to elevate and bring forward the arm. It is in 

 powerful action when the horse is running at his speed with the head projected. 



At g is a portion of the sterno maacillaris, or muscle common to the fore part 

 of the chest and the lower jaw, and described at p. 212. 



h designates the principal portion of this muscle extending from the shoulder 

 to the humerus, and employed in drawing this bone towards the shoulder-blade, 

 and bending the whole of the limb. Exceedingly powerful action is required 

 from this muscle, therefore it is very tendinous, and inserted in such a direction 

 as to aet with great mechanical advantage, and that advantage increased in pro- 

 portion to the slanting position of the shoulder. 



The muscle i, antea spinatus, is situated on the outer and anterior part or 

 the shoulder, below and behind the muscle next mentioned ; and its office is to 

 extend the humerus on the scapula. It is also attached to the greater tubercle 

 of the humerus, and to a bony ridge extending from it to the capsular-ligament 

 of the shoulder-joint. Its action is to assist in the flexion of the humerus, and 

 to give it a motion outwards. 



The muscle j, postea spinatus, behind the spine or ridge, occupies that space 

 of the shoulder, and is inserted into the outer and upper head of the bone. It 

 draws this bone outward and upward. 



At k, is a muscle common to the breast 

 and the shoulder-blade, and called the pee- 

 toralis parvus. It arises from the breast- 

 bone, and reaches to the covering of the shoulder- 

 joint, and the muscles of the shoulder. Its action, 

 in common with that of a larger muscle, seen at 

 m, the great pectoral, is to draw the head of the 

 shoulder backward, and also the lower part of 

 the shoulder-blade, and to give the latter a more 

 upright position. 



At q is the tendon of a very important muscle, 

 the extensor long us of the arm, reaching from the 

 upper angle and the posterior border of the 

 shoulder-blade to the point of the elbow and the 

 inside of the arm, and which will be presently 

 described. At r and s are the three divisions 

 of another muscle concerned in the same office, 

 arising from the shoulder-blade and the lower 

 bone of the shoulder, and likewise attached to 

 the point of the elbow by a very strong tendon. 



This cut represents the muscles on the inside 

 of the shoulder and fore-arm. a is a very pro- 

 minent one. It is called the pectoralis trans- 

 versus (the muscle crossing the breast). It 

 arises from the first four bones of the sternum, and runs across to the inner 



