398 THE MUSCULATURE 



Relations. — The muscle is superficially placed. Near its origin it is covered by the lacertus 

 fibrosus of the biceps, and near its insertion by the radial vessels and nerve and the brachio- 

 radialis and radial extensor muscles. It is the most radial of the group of muscles under con- 

 sideration. The radial border helps to bound an angular space, the cubital fossa, in which lie 

 the brachial vessels, median nerve, and the tendon of the biceps. The median nerve passes 

 between its humeral and ulnar heads. The muscle overlies the supinator, the brachialis, and 

 the radial origin of the flexor digitorum sublimis muscles and the ulnar artery. 



Variations. — Supplementary fasciculi may arise from the humerus, the medial intermuscular 

 septum of the arm, the flexor carpi radialis, the flexor sublimis, or the brachialis muscles. The 

 two portions of the muscle may be distinct from origin to insertion. Either part of the muscle 

 may be doubled. The ulnar head may be absent. The radial insertion may be extensive. 

 Fasciculi may extend to the long flexor of the thumb. There may be a sesamoid bone in the 

 tendon of origin from the humerus. 



The flexor carpi radialis (fig. 370). — Origin. — From (1) the common tendon attached 

 to the medial epicondyle; and (2) the septa between its head and the pronator teres, the flexor 

 sublimis, and the palmaris longus. 



Structure and insertion. — The fibre-bundles descend to converge upon a tendon at first intra- 

 muscular, but which in the middle of the arm appears on the volai* surface of the muscle and soon 

 becomes free from the attachment of fibre-bundles. The fibre-bundles from the epicondyle 

 descend nearly vertically to the front and sides of the tendon, while those from the intermus- 

 cular septa take an oblique com'se to the deep surface of the tendon. The tendon is at first 

 flat, but soon becomes cylindrical, bound to the superficial muscle fascia, and enters the hand 

 through a special osteo-fibrous canal formed mainly by the groove in the os multangulum 

 majus (trapezium) and the transverse carpal (anterior annular) ligament. It is inserted into 

 the base of the second metacarpal. It usually also sends a tendon slip to the third. 



Nen<e-supply. — By a branch from the median nerve which divides into several twigs that 

 enter the muscle near the junction of its proximal and middle thirds on the deep surface. The 

 nerve usually arises near the elbow. The nerve fibres arise from the sixth, seventh (and eighth) 

 cervical nerves. 



Action. — To flex the hand at the wrist. To a slight extent it may also act as a pronator 

 of the forearm and a flexor of the forearm on the arm. 



Relations. — It is superficial except near its insertion. The belly of the muscle lies between 

 the pronator teres and the palmaris longus and upon the flexor digitorum sublimis. The tendon 

 of the muscle passes over the flexor pollicis longus, and near the wrist is a guide to the radial 

 artery, which here lies lateral to it. In the hand the tendon lies beneath the thenar muscles 

 and is crossed by the tendon of the long flexor of the thumb. 



Variations. — It may receive a fasciculus from the brachialis or biceps muscles or from the 

 radius or ulna. It may send tendon slips to the multangulum majus (trapezium), navicular, 

 the transverse carpal (anterior annular) ligament, or the fourth metacarpal. The insertion 

 may take place variously into these structures. 



The palmaris longus (fig. 370). — Origin. — From the common tendon attached to the 

 medial epicondyle and from the surrounding intermuscular septa. 



Structure and insertion. — The fibre-bundles take a nearly parallel course to a tendon which 

 appears high in the middle third of the forearm on the volar surface of the muscle. In the 

 middle of the forearm the attachment of fibre-bundles usually ceases, the tendon becomes 

 bound to the overlying fascia, and descends parallel with that of the radial flexor. Near the 

 proximal border of the transverse carpal (anterior annular) ligament the tendon expands into 

 radiating bundles of fibres of which the medial and lateral are attached to the fascia over the 

 intrinsic muscles of the thumb and little finger, while the middle, much more developed, con- 

 stitute the chief portion of the palmar aponeurosis. 



Nerve-supply. — From a branch which usually arises in company with the nerve to the 

 proximal part of the flexor sublimis. It frequently traverses the superficial fibres of the flexor 

 sublimis. The nerve enters the middle third of the muscle. 



Action. — To flex the hand. It is also a weak flexor and pronator of the forearm. 



Relations. — It is placed between the radial and ulnar flexors over the flexor sublimis. 

 In the distal part of the forearm the tendon lies over the median nerve. 



Variations. — It is absent in 11.2 per cent, of instances (Le Double). It may he highly 

 developed or reduced to a tendinous band. The belly of the muscle may lie in the distal instead 

 of in the proximal part of the forearm. It may be digastric. It may be fused with neighbouring 

 muscles. It may arise from the medial intermuscular septum of the arm or from the lacertus 

 fibrosus, from the radius, from the coronoid process, from the radial or ulnar flexor, or fiom the 

 flexor sublimis nnisc^les. The tendon may terminate in the fascia of the forearm, the thenar 

 eminence, the carpus, or the abductor of the thumb. The muscle may be partly or wholly 

 doublfMJ. 



The flexor carpi ulnaris (fig. 370). — Origin.—By two heads: — (1) the humeral head arises 

 from the common flexor tendon attached to the lower ventral i)art of the medial epicondyle 

 Fibre-bundles of this head arc also attached to the surrountling intermuscular septa and the 

 deep fa.scia of the forearm. (2) The ulnar head arises by sliort tendinous fil)res from the medial 

 side of the olecranon an<l by an aponeurotic band common to it and the flexor digitorum pro- 

 fundus from th<! upper two-thirds of the dorsal l)ord('r of the ulna. Proximally the two heads 

 of tlic nniscle are united l»y a fibrous arch extending from the olecranon to tlie medial epn- 

 condyk!. IJeneatii this band pass the uliuir nerve ancl the dorsal recurrent ulnar artery. (iSee 

 Epituochlko-olechanoni.s, p. 402.) 



Structure and insertion. — 'i'he fil)re-bun(lles of the humeral head descend nearly vertically, 

 tho.se of the ulnar head obli(|U('ly (list ally in a radial direction. They are inserted in a jjonniform 

 manner on a tendon which appears in the proximal ))art of the middle third of the belly of the 

 muscle on the radial margin of the decj) surface, and in the distal third of the forearm forms the 

 radial border of the muscle. On the ulnar side the insertion of fil)re-l)undles continues nearly 



