THE UPPER LIMB 323 



wards sep^ated by a bursa, and there is usually a bursa behind 

 the teres major at its insertion. 



Subscapularis — Origin. — (i) The venter of the scapula, except 

 near the neck, and along the front of the base where the serratus 

 magnus is inserted ; and (2) the sides of tendinous septa which 

 intersect the muscle and are connected with the ridges on the 

 venter. 



Insertion. — ^The small tuberosity of the humerus, and the surgical 

 neck of the bone for a short distance below. 



Nerve-supply. — The upper or short, and part of the lower, sub- 

 scapular ner\'es, which are branches of the posterior cord of the 

 brachial plexus, their fibres being derived from the fifth and sixth 

 cervical. 



The direction of the muscle is outwards. 



Action. — When the arm is by the side of the tnmk the muscle is 

 an internal rotator, and, when it is raised, it carries it forwards and 

 do\^Tiwards. 



The muscle is closely connected with the front of the capsular 

 hgament. Between its upper border and the coracoid process and 

 neck of the scapula there is a bursa, which usually communicates 

 with the synovial membrane of the shoulder- joint through an opening 

 in the capsule. 



Triangular and Quadrangular Spaces. — When the long head of the 

 triceps is cut and displaced a large triangular space is seen, which, 

 as viewed from behind, is bounded above by the teres minor, below 

 by the teres major, and exUrnally by the surgical neck of the 

 humerus. As viewed from before, the subscapularis replaces the 

 teres minor. Wlien the long head of the triceps is in position it 

 descends in front of the teres minor, and behind the teres major. 

 It therefore passes through the triangular space and divides it into 

 two, one triangular and the other quadrangular. 



Triangular Space. — This, as viewed from behind, is bounded 

 above by the teres minor, below by the teres major, and externally 

 by the long head of the triceps. As viewed from before, the sub- 

 scapularis replaces the teres minor. The dorsalis scapulae artery 

 passes back\vards through this space, so long as the subscapularis 

 forms one of its boundaries, but thereafter, and as seen from behind, 

 it only hes in it preparatory to piercing the teres minor and winding 

 round the axillary' border. 



Quadrangular Space. — ^This space, as viewed from behind, is 

 bounded above by the teres minor, below by the teres major, i«- 

 ternally by the long head of the triceps, and externally by the surgical 

 neck of the humerus, the subscapularis replacing the teres minor 

 in front. The structures which pass through it are the circumflex 

 nerv'e and posterior circumflex vessels. It is covered by the 

 deltoid. 



Scapular Anastomoses of Arteries. — ^The anastomoses of arteries 

 apon the scapula are divided into tNVO sets — scapular proper, and 

 acromial. 



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