74 THE SURGICAL ANATOMY OF THE HORSE 



inner aspect respectively, and playing over the front of the joint, whilst on 

 the inner aspect we have the tendon of the subscapularis muscle which is 

 inserted into the posterior division of the internal tuberosity of the 

 humerus. 



The outer aspect of the shoulder joint is supplied by the circumflex 

 vessels and nerve. These make their appearance through the triangular 

 space which is bounded by the teres minor and the large and 

 middle heads of the triceps extensor cubiti muscle. They are covered 

 by the deltoid muscle. Great care should therefore be taken, in 

 operating near the inferior half of the deltoid, not to injure the vessels 

 and nerve mentioned. The circumflex nerve supplies the teres minor, 

 the deltoid, and partially the mastoido-humtralis, and a point of con- 

 siderable importance to remember is that it supplies the skin covering 

 the joint. 



In the region of this joint there are three synovial bursae to which 

 attention may be drawn. One is placed beneath the tendon of origin of 

 the biceps muscle to facilitate its play in the bicipital groove. Another 

 is placed beneath the tendon of the subscapularis near its insertion into 

 the inner tuberosity, whilst a third is situate on the outer aspect of the 

 humeral convexity beneath the outer tendon of insertion of the infra- 

 spinatus muscle. The last-named bursa is most frequently injured, since it 

 is placed on one of the prominent points which come into contact with 

 the ground when the animal falls on its broadside. 



Running obliquely downwards and forwards on the inner aspect of 

 the joint, and in intimate relationship to it, is the nerve to the biceps and 

 coraco-humeralis, which passes outwards between the two insertions of 

 the last-mentioned muscle. Just above the articular surface the long 

 muscular branch of the suprascapular artery passes, whilst slightly pos- 

 terior to the joint the axillary artery and vein and the median nerve cross 

 the angle formed by the scapula and humerus. It is also important to 

 remember that to the inner side of the joint, but at a somewhat higher 

 level, the brachial plexus is placed. 



