222 THE MUSCLES AND FASCIAE OF THE UPPER LIMB. 



impression on the lower and posterior part of the external condyle of the humerus 

 (fig. 93). From this the fibres diverge, the upper being transverse, the rest passing 

 downwards with increasing degrees of obliquity, and are inserted into the olecranon 

 on its radial aspect, and into the adjacent impression on the upper third of the shaft 

 of the ulna (fig. 95). Its superior fibres are parallel to the lowest fibres of the 

 internal head of the triceps, and are generally continuous with them. 



Relations. This muscle is subcutaneous in its whole extent. Its deep surface is in 

 contact with the supinator brevis and the external lateral ligament of the elbow-joint. 



Varieties. The anconeus varies chiefly in being more or less united to the triceps or the 

 extensor carpi ulnaris. 



Nerves. The coraco-brachialis (7 c) receives a branch from the outer cord of the brachial 

 plexus, the biceps (5, 6 c) is supplied by the musculo-cutaneous nerve, and the brachialis 

 anticus (5, 6 c) mainly by the musculo-cutaneous. but also by a small twig from the musculo- 

 spiral nerve. The triceps (7. 8 c) and the anconeus (7. 8 c) receive their nerves from the 

 musculo-spiral. 



Actions. The Itlccps muscle raises the arm at the shoulder and flexes the elbow-joint ; 

 the short head of the biceps draws the arm inwards as well as upwards, as does also the 

 coraco-brachialis. If the biceps be called into action when the hand is in pronation, its first 

 effect, from its insertion into the back part of the tuberosity of the radius, is to produce 

 supination of the forearm. The biceps also makes tense the fascia of the forearm. The 

 brtu-Jtialig anticus is a simple flexor of the elbow. The external and internal heads of the 

 triceps are simple extensors of the elbow-joint ; the long- head, while it assists in extending 

 the elbow, also tends to depress the arm on the scapula. The anroncus acts with the triceps 

 in extending the elbow, and draws the ulna outwards in pronation of the hand (p. 170). 



THE MUSCLES AND FASCIA OF THE FOREARM. 



FASCIA. The superficial fascia of the forearm is most distinct opposite 

 the bend of the elbow, where the superficial veins contained between its laminae are 

 numerous and large. In the palm of the hand the subcutaneous tissue forms a firm 

 connecting medium between the skin and a strong aponeurosis named the palmar 

 fascia ; it consists of a network of fibres passing between those two structures, 

 dividing the subcutaneous fat into small granular masses, and preventing the skin 

 from shifting to any considerable extent. 



The aponeurosis of the forearm, like that of the arm, is composed principally 

 of transverse fibres, strengthened, however, by longitudinal and oblique fibres 

 descending from the condyles of the humerus, .from the olecranon, from the semi- 

 lunar fascia of the biceps, and from the tendon of the triceps. It is attached along 

 the subcutaneous margin of the ulna, and may be conveniently divided into an 

 anterior and a posterior part. 



The anterior part of the aponeurosis of the forearm is much weaker than the 

 membrane on the posterior aspect of the limb. It is continued below into the 

 anterior annular ligament of the wrist. Over the hollow immediately below the 

 bend of the elbow, it presents a small oval aperture for the transmission of a short 

 communicating branch between the superficial and the deep veins of the forearm. 

 It increases in density towards the hand, and a little above the wrist affords a 

 sheath to the tendon of the long palmar muscle, which passes over the annular 

 ligament to be inserted into the narrow end of the palmar fascia. Several white 

 lines seen on the surface of the fascia near the elbow mark the position of the septa 

 between the origins of the muscles descending from the inner condyle, which are 

 continuous with it, and which, together with the adjacent portions of the fascia, 

 give origin to the muscular fibres. Between the superficial and the deep flexor 

 muscles, another layer of fascia is stretched from side to side ; it is stronger below 

 than above, where it generally consists of little more than thin connective tissue. 



The anterior annular ligament of the carpus, previously described at p. 174, is 



