58 THE UPPER EXTREMITY 



border of the coracoid process, whilst by its apex it is attached 

 to the extremity of the acromion (Fig. 39, p. 91). 



The coraco-acromial arch plays a very important part in 

 the mechanism of the shoulder; it might almost be said to 

 form a secondary socket for the humerus. We have already 

 noted the large bursa which intervenes between the acromion 

 and the muscles immediately covering the capsule of the 

 shoulder-joint, to facilitate the movements of the upper end 

 of the humerus on the under surface of the arch. 



Dissection. The supraspinatus, infraspinatus, and teres minor muscles 

 which arise from the dorsal surface of the scapulae, and the subscapularis, 

 which takes origin from the costal surface of the scapula, may now be 

 examined. In order to obtain an uninterrupted view of the supraspinatus 

 muscle, the acromion must be divided, with the saw, close to its junction 

 with the spine of the scapulne (Fig. 21, p. 51). 



Divide also the fascia which covers the teres minor muscle, and 

 reflect it towards the infraspinatus. By this means the septum from the 

 infraspinous fascia, which dips in between the two muscles, will be 

 demonstrated, and their separation rendered easy. Care must be taken 

 not to injure the circumflex artery of the scapula which passes between 

 the teres minor and the bone. 



M. Supraspinatus. The supraspinatus muscle arises from 

 the medial two-thirds of the supraspinous fossa, and also 

 to a slight degree from the supraspinous fascia which covers 

 it. From this origin the fibres converge, as they pass laterally, 

 and, proceeding under the acromion, they end in a short, 

 stout tendon, which is inserted into the uppermost of the three 

 impressions on the greater tubercle of the humerus (Fig. 33, 

 p. 79). This tendon is closely adherent to the capsule of the 

 shoulder-joint. The supraspinatus is covered by the trapezius, 

 and in the loose fat which intervenes between this muscle and 

 the supraspinous fascia some twigs of the superficial cervical 

 artery ramify. It is supplied by the suprascapular nerve, and 

 it is an abductor of the upper extremity. 



M. Teres Minor. This is the small muscle which lies 

 along the lower border of the infraspinatus. It arises from 

 an elongated flat impression on the dorsal aspect of the axillary 

 border of the scapula, and from the septa of the infraspinous 

 fascia which intervene between it and the two muscles 

 between which it lies, viz. the infraspinatus and teres major. 

 It is inserted into the lowest of the three impressions on 

 the greater tubercle of the humerus, and also, by fleshy 

 fibres, into the body of the bone for about half an inch 

 below this (Fig. 36, p. 84). Towards its insertion it is 



