2 THE SURGICAL ANATOMY OF THE HORSE 



the glenoid cavity of the scapula. These muscles are affected in supra- 

 scapular paralysis, and it will be seen that when this affection has 

 advanced to such a degree that the muscles become atrophied, the long 

 axes of the muscles and their tendons become considerably increased in 

 length on account of the diminution in width of the bellies. This 

 increased length causes a relaxation of the parts, with the result that we 

 have one of the diagnostic symptoms of suprascapular paralysis, viz., free 

 external rotation of the head ot the humerus. Internal rotation is 

 prevented by the tendon of the subscapularis muscle, which is not affected 

 in this paralysis. The two posterior elevations are formed by the 

 underlying deltoid muscle, which arises from the posterior border of the 

 scapula and is inserted into the deltoid tubercle of the humerus. The 

 appearance of two elevations is due to a false septum in the muscle 

 caused by a dipping inwards of the scapular fascia which binds this 

 muscle to the preceding one and to the underlying bone. 



The point of the shoulder is formed by the coracoid process of the 

 scapula. This should be carefully palpated, since it is a common seat of 

 fracture, particularly in young animals, the fracture being usually due to 

 the shoulder being caught in a doorway or narrow gateway. Running 

 over the shoulder joint and spreading out as it descends is the mastoido- 

 humeralis muscle. Inferiorly to the shoulder this muscle again 

 becomes narrower, and runs to its insertion into the outer lip of the 

 musculo-spiral groove. Near the upper border of the mastoido-humeralis 

 and just in front of the point of the shoulder is the common seat of 

 " shoulder tumour " or " abscess." 



The long axis of the scapula runs downwards and forwards, and meets 

 the long axis of the humerus, which runs downwards and backwards 

 forming an acute angle at the shoulder joint. The triangle, of- which 

 these two bones form the anterojsuperior and antero-inferior sides is 

 filled by a large muscular mass which is indicated on the exterior by a 

 well-marked convex bulging of distinct outline. This mass is formed 

 by the triceps extensor cubiti or caput muscles, which are inserted into 



