21S THE MUSCLES AND FASCIA OF THE UPPER LIMB. 



ment, or into the humerus near the inner margin of the bicipital groove, the subscapido- 

 capsularis or subscapularis minor. 



Nerves. The supraspinatus and infraspinatus muscles receive their nerves from the 

 suprascapular branch which proceeds from the fifth and sometimes the sixth cervical nerves. 

 The other muscles of this group are all supplied with nerves from the posterior cord of the 

 brachial plexus, as follows : the deltoid (o. G c) and teres minor (5 c) through the circumflex 

 nerve, the subscapularis (5, 6 c) through the upper and lower subscapular nerves, and the teres 

 major (6, 7 c) through the lower subscapular nerve. 



Actions. The acromial portion of the deltoid raises the arm from the side, abducting the 

 humerus as far as the structure of the shoulder- joint permits, viz., through about 90. It is 

 associated in its action with the serratus magnus and trapezius, which rotate the scapula 

 upwards at the same time ; and it may be remarked that the insertion of the latter muscle 

 corresponds almost exactly in extent to the origin of the deltoid, so that the two muscles may 

 be considered continuous in structure as well as in action. The anterior part of the deltoid 

 combines with the pectoralis major to draw the humerus forwards ; the posterior assists in 

 drawing it backwards. The supraspinatus. infraspinatus and subscapularis muscles being 

 placed more closely round the joint, when acting in concert with the deltoid, probably give 

 steadiness and precision, while the deltoid gives the main elevating force to the movement. 

 The supraspinatus simply abducts : the infraspinatus and subscajntlaris carry the arm back- 

 wards or forwards when it is raised, and rotate it outwards or inwards when hanging by 

 the side. The teres major rotates the raised humerus inwards, the teres minor outwards ; 

 acting together, they assist in depressing the arm. The deltoid muscle superficially, and the 

 supra- and infraspinatus muscles, the teres minor and subscapularis, more deeply, afford 

 important protection to the shoulder- joint, and by their tension prevent displacement of the 

 head of the humerus. 



THE MUSCLES AND FASCIA OF THE UPPER ABM. 



FASCIAE. The aponeurosis of the arm is composed chiefly of transverse 

 fibres, held together by others having an oblique or longitudinal direction ; it is 

 thin over the biceps muscle, stronger where it covers the triceps, and particularly 

 dense as it approaches the outer and inner condyles of the humerus. It is pierced 

 on the inner side of the limb by the basilic vein, close below the middle of the arm. 

 It is attached to the condyles and supracondylar ridges of the humerus by the two 

 processes next to be described. 



The external and internal intermuscular septa are two fibrous partitions 

 which bind the aponeurosis of the arm to the humerus, and with which the neigh- 

 bouring muscles of the arm are intimately connected. The external intermuscular 

 septum extends upwards from the outer condyle along the outer supracondylar ridge 

 to the hinder part of the insertion of the deltoid, from which it receives tendinous 

 fibres. It is pierced from behind forwards by the musculo-spiral nerve and superior 

 profunda artery. The internal septum, much stronger, extends along the line from 

 the inner condyle to behind the insertion of the coraco-brachialis muscle. It is 

 pierced near the elbow, from before backwards, by the anastomotic branch of the 

 brachial artery. The internal IracMal ligament of Struthers * is a fibrous band con- 

 nected with the internal intermuscular septum, which extends from the inner side of 

 the humerus, below the insertion of the teres major, to the internal condyle. The 

 ulnar nerve and inferior profunda artery pass backwards between this band and the 

 intermuscular septum. 



At the level of the elbow the aponeurosis is closely united to the periosteum 

 covering the subcutaneous parts of the bones, viz., the condyles of the humerus and 

 the olecranon process of the ulna ; and it is strengthened in front and behind by 

 tendinous fibres sent from the biceps and triceps muscles. There is generally a bursa 

 in the subcutaneous tissue over the olecranon, and occasionally one over the internal 

 condyle. A bursa over the external condyle is of rare occurrence. 



MUSCLES. The coraco-brachialis muscle, elongated in form, arises from the 

 tip of the coracoid process of the scapula, between the pectoralis minor and the short 



1 " Anatomical and Physiological Observations," 1854. p. 208. 



