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A MANUAL OF ANATOMY 



springs to a large extent from the sides of four fibrous septa, which 

 descend into that part, and the fibres arising in this manner are 

 inserted into the sides of three fibrous septa, which ascend from 

 below. 



The origin of the muscle corresponds with the insertion of the 

 trapezius. The anterior border is related to the pectoralis major, 

 the cephalic vein and humeral artery lying between the two. The 

 posterior border is to a large extent bound down by the splitting of 

 the deep fascia over the infraspinatus. The muscle covers the 

 shoulder- joint, subacromial bursa, coracoid process, coraco-brachi- 

 alis, biceps, tendons of insertion of the supraspinatus, infraspinatus, 

 and teres minor, parts of the long and outer heads of the triceps, 

 teres major, tendon of insertion of the pectoralis major, circumflex 

 nerve, and posterior circumflex artery. 



Subacromial Bursa. — This is a large bursa which intervenes 

 between the acromion process and deltoid, on the one hand, and 

 the upper part of the capsular ligament and the tendons inserted 

 into the great tuberosity of the humerus, on the other. 



Supraspinatus — Origin. — The inner two- thirds of the supra- 

 spinous fossa of the scapula, and the aponeurosis covering the 

 muscle. 



Insertion. — The upper impression on the great tuberosity of the 

 humerus, its tendon being closely connected with the upper part of 

 the capsular ligament, and with that of the infraspinatus. 



Nerve-supply. — ^The suprascapular nerve, which arises from the 

 back of the upper trunk of the brachial plexus, its fibres being 

 derived from the fifth and sixth cervical. 



The direction of the muscle is outwards and downwards. 



Action. — To abduct the arm in association with the deltoid. 



Posterior Belly of the Omo-hyoid — Origin. — The upper border 

 of the scapula internal to the suprascapular notch, and, as a 

 rule, the adjacent portion of the suprascapular or transverse 

 ligament. 



Infraspinatus — Origin. — (i) The infraspinous fossa of the scapula 

 over about its inner two-thirds, the parts excepted being those for 

 the teres muscles, and a portion at the upper and outer part of the 

 fossa ; and (2) the deep fascia covering the muscle. 



Insertion. — The middle impression on the great tuberosity of 

 the humerus, its tendon being closely connected with the back part 

 of the capsular ligament, from which it is sometimes separated by 

 a bursa. The tendon, which is fan-shaped, is at first concealed 

 within the muscle. 



Nerve-supply. — The suprascapular nerve. 



The direction of the muscle is outwards. 



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

 an external rotator. When the arm is raised the muscle carries it 

 backwards in association with the deltoid. 



Suprascapular Artery. — ^The suprascapular artery ( trans versalisj 

 humeri) is a branch of the thyroid axis of the first part of the sub- 



