192 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



Fig. 274. — The superficial layer of the muscles of the flexor surface of the forearm together with the 



brachioradialis, seen from in front. 

 Fig. 275. — The superficial layer of the muscles of the flexor surface of the forearm after removal of the 



palmaris longus and the flexor carpi radialis, seen from in front and slightly from 



the radial side. 

 The brachioradialis is drawn outward to show the supinator and the insertion of the tendon of the biceps. 



The flexor digitorum sublimis (Figs. 274 to 276) is concealed at its origin by the palmaris 

 longus and the flexor carpi radialis, and the greater portion of its ulnar border is covered by the 

 flexor carpi ulnaris. The main origin of the muscle, the humeral head, forms the deepest portion 

 of the common tendon arising from the internal epicondyle, while the second head, the radial 

 head, arises by a fiat tendon from the volar surface and border of the radius below the insertion 

 of the supinator. The two heads are connected by a tendinous arch beneath which passes the 

 median nerve, and unite to form a broad and strong muscular belly which is usually composed 

 of two distinct portions, a superficial and a deep. The deep portion receives the oblique fibers 

 from the radius and soon gives off the tendons for the index and little fingers, while the tendons for 

 the middle and ring fingers proceed from the superficial portion. The four tendons, which 

 frequently do not become independent until near the wrist- joint, run through a synovial sheath 

 together with the tendons of the deep flexor and pass beneath the transverse carpal ligament 

 to the middle phalanges of the second to the fifth fingers (see page 205). 



The flexor digitorum sublimis is exclusively supplied by the median nerve. It flexes the middle phalanges of the 

 four fingers. 



The flexor carpi ulnaris (ulnaris internus) (Figs. 274 and 276) is the innermost and the 

 most posterior muscle of the group. Its posterior border is in relation with the anconeus and 

 the superficial extensors, being separated from the latter by the dorsal border of the ulna. In 

 addition to a humeral head the muscle also possesses an ulnar head from the anterior surface 

 of the olecranon, the ulnar nerve passing between the two heads. An additional origin is 

 furnished by the antibrachial fascia, which is adherent to the upper two-thirds of the ulnar 

 border of the muscle and by means of which the muscle arises from the volar border of the ulna. 

 The muscle is distinctly semipenniform in structure, since a tendon is formed in its inner border 

 at the middle of the forearm, into which muscular fibers radiate almost as far down as the 

 wrist-joint. This tendon is inserted into the pisiform bone and the insertion is thence prolonged 

 to the metacarpus by the ligaments of the pisiform bone (see page 125). 



The muscle is supplied by the ulnar nerve. When acting with the flexor carpi radialis it effects volar flexion; 

 together with the extensor carpi ulnaris it produces ulnar flexion. 



THE DEEP LAYER. 



The deep layer of the muscles of the flexor surface consists of the two deep flexors of the 

 digits and of the pronator quadratus. It is almost entirely concealed by the superficial layer. 



The flexor digitorum profundus (Figs. 275 and 277) is a broad, strong, thick muscle 

 which arises from the volar surface of the ulna from the coronoid process to the junction of the 



