72 THE SUPERIOR EXTREMITY 



Deep Fascia. The deep fascia of the superior extremity 

 consists chiefly of transverse fibres, which are bound together 

 by oblique and longitudinal fibres. The oblique and longi- 

 tudinal fibres become specially developed in certain situations 

 which will be noted later. The deep fascia is fairly strong in 

 the region of the shoulder over the deltoid muscle. Over 

 the posterior part of the deltoid and the adjoining part of the 

 infraspinatus, which covers the lower part of the back of the 

 scapula, it becomes dense, and it is closely attached by deep 

 processes to the axillary border of the scapula. Over the 

 front of the arm, where it covers the biceps muscle, it is thin, 

 but it is much stronger at the back of the arm, over the triceps. 

 On each side, extending proximally from the lateral and the 

 medial epicondyles deep expansions bind it to the lateral 

 and medial supra -epicondylar ridges of the humerus. The 

 expansions are known as the lateral and medial inter muscular 

 septa, because they separate the muscles on the front from 

 those at the back of the arm. At the elbow it is thickened 

 and strengthened by tendinous fibres, which pass to it from 

 the biceps and triceps muscles, and it is closely attached to 

 the lateral and medial epicondyles of the humerus and to 

 the olecranon of the ulna. A special thickening called the 

 lacertus fibrosus (Fig. 31) is found at the front of the elbow. 

 It extends from the medial border of the proximal part of 

 the biceps tendon and the adjacent part of the muscle to the 

 medial side of the proximal part of the forearm. It separates 

 the median cubital vein, which lies superficial to it, from the 

 brachial artery, which is deep to it. The volar branch of 

 the medial cutaneous nerve of the forearm usually passes 

 between the lacertus fibrosus and the median cubital vein. 



In the forearm the deep fascia is strong over the proximal 

 parts of the muscles which spring from the medial and the 

 lateral epicondyle. Then it becomes thin, especially on the 

 volar aspect. On the dorsal aspect it is bound to the whole 

 length of the posterior border of the ulna by a deep 

 extension which intervenes between the muscles on the 

 dorsal and volar parts of the medial side of the forearm. 



At the wrist the transverse fibres of the deep fascia 

 become very obvious, and they form two marked transverse 

 bands ; one on the volar aspect called the transverse carpal 

 ligament and one on the dorsal aspect called the dorsal carpal 

 ligament. 



