RADIO-DORSAL DIVISION 387 



On the volar side of the forearm for some distance above the wrist the tendons of the 

 flexor carpi radiahs, the pahnaris longus, and the flexor carpi idnaris run between two layers of 

 the fascia. The fascia is much strengthened at the wrist bj' transverse fibres which give rise 

 to the volar ligament of the carpus. Beneath it lies the transverse ligament of the carpus 

 (anterior annular ligament). This dense band is broader than the volar ligament but like it 

 extends from the pisiform bone and the hamulus of the hamatum (unciform) to the tuberosity 

 of the navicular and the tuberosity of the greater multangular (trapezium). It serves to 

 complete an osteo-fibrous canal through which pass the flexor tendons of the fingers. Between 

 the two ligaments which are partially fused with one another run the ulnar artery and nerve. 



On the palm of the hand the ensheathing fascia presents tliree distinct areas — a central, 

 a lateral, and a medial. 



The central portion, the palmar aponeurosis, is composed chiefly of bundles of fibrous 

 tissue which radiate superficially toward the fingers from the tendon of the palmaris longus or 

 from a corresponding region of the forearm fascia when this muscle is absent. Between these 

 bundles are others which arise from the transverse hgament. The deep surface of the fascia is 

 composed of a thin incomplete layer of transverse fibres which continue the transverse fibres of 

 the forearm fascia. Near the capitula of the metacarpals this layer becomes much stronger 

 and constitutes a ligamentous band (superficial transverse ligament of Poirier) . Near the bases 

 of the digits bundles of transverse fibres (fasciculi transversij lie in the webs of the fingers and 

 constitute an incomplete transverse ligament separated by a distinct interval from the super- 

 ficial transverse ligament. 



From the palmar aponeurosis processes are sent in toward the deeper structures. Of these, 

 the most important are those continued into a fibrous sheath which surrounds the space con- 

 taining the long flexor tendons and the lumbrical muscles. This dense fibrous sheath is united 

 by fibrous processes to the third, fourth, and fifth metacarpals. As the flexor tendons diverge 

 and the ends of the metacarpals are approached, numerous processes descend from the palmar 

 aponeurosis to the transverse capitular ligament. These hold the tendons in place. On the 

 volar surface of the fingers the fascia serves to complete osteo-fibrous canals for the long flexor 

 tendons. The ventral surface of the first and second phalanges of each finger is slightly grooved. 

 The fascia is firmly united on each side to the margin of the groove, and over the groove forms 

 a semicylindrical, strong, fibrous sheath, the vaginal ligament of the finger. This sheath is 

 strengthened by transverse bands over the bases of the first and second phalanges (annular 

 ligaments) and by cruciate bands over the shafts of the phalanges (cruciate ligaments). Over 

 the interphalangeal joints the sheath is thin, but is strengthened by crucial bands which permit 

 of freedom of motion. 



The thenar fascia is a thin membrane covering the short muscles of the thumb. It is con- 

 tinued above into the fascia of the forearm, medially is fused with the tendon of the palmaris 

 longus and the palmar aponeurosis, and extends as a septum to be attached to the third meta- 

 carpal. Laterally it is attached to the first metacarpal and is continued into the dorsal fascia 

 of the hand. It is fused with an aponeurosis from the tendon of the abductor pollicis longus. 

 Distally it is continued into the vaginal ligament of the long flexor of the thumb. Superficialh' 

 it is closely adherent to the skin. 



The hypothenar fascia invests the palmar muscles of the little finger. It is continued 

 from the ulnar margin of the fifth metacarpal over the muscles of the little finger to the palmar 

 aponeurosis, and, by means of a septum, to the radial side of the fifth metacarpal. Proximally, 

 it is attached to the hamatum (unciform; and extends into the fascia of the forearm, distally, 

 it extends into the vaginal ligament of the tendon of the fifth digit. 



A deeply seated suprametacarpal fascial layer, or deep palmar fascia, covers the inter- 

 osseous muscles and is attached to the volar surface of the metacarpal bones. 



In addition to the fasciae mentioned, intermuscular septa serve to separate nure or less 

 completely the various intrinsic muscles of the hand. 



MUSCLES 

 1. Radio-Dorsal Division 



The muscles of this group lie in two chief layers, a superficial and a deep. 



a. Superficial Layer 

 (Figs. 367, 370, 371) 



The muscles of this layer, closely associated at their origins, extend from the 

 radial side of the distal end of the humerus to the distal extremity of the radius, 

 the carpus, and the fingers. They are divisible into a radial, an intermediate, 

 and an ulnar set. 



Radial set. — To this belong three muscles, the brachio-radialis, extensor carpi 

 radialis longus and brevis. The brachio-radialis (fig. 370), a forearm flexor, is a 

 superficial fusiform muscle which arises from the lateral epicondylar ridge of the 

 humerus and is inserted into the base of the styloid process of the radius. The 

 extensor carpi radialis longus (fig. 371) is a narrow, fusiform muscle which extends 



