FLEXOR DIGITORUM SUBLIMIS 399 



to the pisiform bone. The insertion of the tendon takes place chiefly into the pisiform bone, 

 but from it tendinous bundles extend to the palmar aponeurosis, volar Ugament of the carpus, 

 to the pisohamate ligament (pisi-unciform), and to the bases of the fifth, fourth, and third 

 metacarpals. 



Nerve-supply. — From two or three branches of the ulnar nerve, the most proximal of which 

 arises near the elbow-joint. These branches, which maj' arise by a single trunk, enter the deep 

 surface of the proximal third of the muscle and send long twigs distally across the middle third 

 of the constituent fibre-bundles. The nerve fibres arise from the seventh and eighth cervical 

 and first thoracic nerves. 



Actio7i. — To flex the hand and to abduct the hand ulnarward. 



Relations. — It is superficially placed. Its aponeurotic origin is adherent to the fascia 

 of the forearm. It hes medial to the palmaris longus and flexor subhmis and upon the flexor 

 profundus. Beneath the muscle hes the ulnar nerve. The ulnar artery extends along the 

 radial border of the tendon near the wrist. 



Variations. — These are rare. Slips from the tendon may pass to the metacarpo-phalangeal 

 articulation of the little finger. (See, however. Abnormal Muscles, p. 402.) 



b. Second Layer 



This is composed of one muscle, the flexor digitorum sublimis, which, 

 although in part covered by the muscles of the preceding laj-er, is in part super- 

 ficial. It arises from the medial epicondyie of the humerus, and from the radius 

 and the ulna, and sends tendons to the second row of phalanges of the fingers. 

 It corresponds probably with the soleus and the tendons of the flexor digitorum 

 brevis in the leg and foot. 



The flexor digitorum sublimis (figs. 371, 373, 375). — Origin.— By two heads: the ulnar 

 or chief head arises (1) by the tendon common to it and the superficial group of muscles from 

 the medial epicondyie, and by short tendinous bands from the ventral surface of the epicondyie; 

 (2) from the ulnar collateral hgament of the elbow, the ulnar tuberosity, the rnedial border of 

 the coronoid process, and the inferior extremity of the tendon of the brachiahs; and (3) .from 

 the intermuscular septum between the flexor sublimis and the overlying muscles. The radial 

 head arises from an oblique line on the volar surface of the radius, and from the middle third 

 of the anterior border. 



Insertion. — Into the sides of the volar surface of the shafts of the second row of phalanges of 

 the fingers. 



Structure. — The fibre-bundles of the ulnar head and the upper part of the radial head con- 

 verge, the ulnar fibre-bundles nearly vertically, the radial obliquely, to form a common belly 

 the deep surface of which on the ulnar side is backed by a dense tendinous band. On the radial 

 side of this a less dense membrane covers over an oval canal which passes distally along the 

 line of junction of the two heads and lodges the ulnar artery and the median nerve. 



The fibre-bundles of the ulnar head form a superficial and a deep group. The superficial 

 portion near the middle of the forearm divides into a lateral and a medial division, the fornier 

 being inserted on a tendon that goes to the middle and the latter on one that goes to the ring 

 finger. The fibre-bundles of the radial head join with the lateral division of the superficial 

 layer of the ulnar head and are inserted on the tendon of the middle finger nearly as far as the 

 wrist. A small muscle fasciculus of the superficial portion of the ulnar head is usually united 

 by a tendon to the long flexor of the thumb. 



The deep portion of the ulnar head about the middle of the forearm terminates in large part 

 on the volar surface of the dense tendinous band above mentioned. From this in turn two 

 muscle bellies arise. One of these is inserted in a bipenniform manner on a tendon going to 

 the index finger, the other on a tendon going to the little finger. A muscle fasciculus also usually 

 passes from the region of the tendon band to that portion of the superficial fasciculus which 

 terminates on the tendon of the ring finger. 



The four tendons pass together through the carpal canal under the transverse carpal 

 (anterior annular) Ugament, those to the middle and ring fingers lying at first superficial to the 

 other two. The tendons then diverge, and each tendon, together with and above a tendon of 

 the flexor profundus, passes over the metacarpo-phalangeal joint into an osteo-fibrous canal on 

 the palmar surface of the first phalanx of the finger for which it is destined. Here the tendon 

 becomes flattened about the round tendon of the flexor profundus. Opposite the middle of the 

 phalanx the tendon divides into two slips, between which the tendon of the flexor profundus 

 passes. The divided halves of the sublimis tendon fold about the profundus tendon so that their 

 lateral edges come to meet in the mid-line beneath this tendon opposite the phalangeal joint 

 (figs. 375, 376). Thev then again separate, extend distally, and are attached one on each side 

 into a ridge at the middle of the lateral border of the second phalanx. The tendons are also 

 attached bj^ vincula tendinum, a ligamentum breve, between the tendon and the head of the 

 first phalanx and the joint, and a ligamentum longum, between the tendon and the volar surface 

 of the first phalanx. 



Nerve-supply. — Before the median nerve passes between the two heads of the pronator 

 teres a branch arises which accompanies the nerve through the pronator and sends several 

 branches into the proximal third of the ulnar head of the muscle. As the median nerve pa,sses 

 beneath the muscle, one or more branches are given to the radial head, and a long branch is given 

 to the fasciculus of the second and from this one to that of the fifth digit. Occasionally, the 

 median nerve in the distal third of the forearm gives rise to branches for these fascicuU. The 

 nerve fibres arise from the seventh and eighth cervical and first thoracic nerves. 



Action. — Chiefly to flex the second phalanx of each finger on the first; secondarily, to flex 

 the fingers on the hand and the hand on the forearm. 



