MUSCLES ON ANTEEIOK AND MEDIAL ASPECTS OF FOBEAKM. 385 



applied to the bones during flexion of the fingers. Within each digital sheath are 

 the flexor tendons, enveloped in a mucous sheath which envelops the tendon 

 and lines the interior of the sheath. The mucous linings of the digital 

 sheaths extend a short distance proximally in the palm, and in some cases com- 

 municate with the large mucous sheaths enclosing the flexor tendons beneath 

 the transverse carpal ligament. There may be a separate distinct mucous 

 sheath for each digit; but most commonly only the sheaths for the three 

 middle digits are separate ; those of the flexor pollicis longus and the flexor 

 tendons of the little finger usually communicate with the mucous sheaths placed 

 beneath the transverse carpal ligament. 



THE MUSCLES ON THE ANTERIOR AND MEDIAL ASPECTS 

 OF THE FOREARM. 



The muscles on the anterior and medial aspects of the forearm comprise the 

 pronators and the flexors of the wrist and fingers. In the forearm they are 

 arranged in three strata : (1) a superficial layer consisting of four muscles which 

 radiate from the medial epicondyle of the humerus, from which they take origin 

 by a common tendon. They are named, from radial to ulnar side, pronator teres, 

 flexor carpi radialis, palmaris longus, and flexor carpi ulnaris. These muscles 

 conceal the muscle which by itself constitutes (2) the intermediate stratum the 

 flexor digitorum sublimis, and this again conceals, for the most part, (3) the deep 

 layer of muscles, including the flexor digitorum profundus covering the ulna, the 

 flexor pollicis longus on the radius, and the pronator quadratus, which is more 

 deeply placed than the previous muscles, and stretches across the forearm between 

 the distal portions of the radius and ulna. 



I. Superficial Muscles. 



M. Pronator Teres. The pronator teres is the shortest muscle of this group. 

 It has a double origin: (1) a superficial head (caput humerale), the main origin, partly 

 fleshy, partly tendinous, from the most distal part of the medial epicondylic ridge 

 of the humerus and from the medial intermuscular septum, from the medial epi- 

 condyle of the humerus, from the fascia over it, and from an intermuscular septum 

 between it and the flexor carpi radialis (Fig. 346, p. 387) ; (2) a deep head (caput 

 ulnare), a slender tendinous slip from the medial side of the coronoid process of the 

 ulna, which joins the superficial origin of the muscle on its deep surface (Fig. 348, 

 p. 389). The median nerve separates the two heads from one another. 



The muscle passes distally and laterally to be inserted by tendon into an 

 oval impression on the middle of the lateral surface of the body of the radius 

 (Figs. 346, p. 387, and 348, p. 389). The fibres of the muscle are twisted on them- 

 selves, so that the most proximal humeral fibres form the most distal fibres of the 

 tendon of insertion, and the most distal humeral fibres and those arising from the 

 coronoid process are most proximal at the insertion. 



The pronator teres forms the medial boundary of the hollow of the elbow. It is 

 superficially placed, except near its insertion, where it is covered by the brachio- 

 radialis muscle and by the radial vessels and superficial branch of the radial 

 nerve. 



Nerve-Supply. Median nerve (C. 6.). 



Action. The muscle is a flexor of the elbow-joint and a pronator of the forearm. 



M. Flexor Carpi Radialis. The flexor carpi radialis muscle takes its origin 

 from the common tendon from the medial epicondyle of the humerus, from the 

 fascia over it, and from the intermuscular septa on either side. 



Its fleshy belly gives place, in the distal half of the forearm, to a strong round 

 tendon which, at the wrist, enters the hand in a special compartment under cover 

 of the transverse carpal ligament, and after occupying the groove on the large mult- 

 angular bone, is inserted into the proximal ends of the second and third metacarpal 



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