INTEROSSEOUS MUSCLES 



409 



The lumbricales (figs. 375, 376). — Origin. — The two lateral arise from the radial side of 

 the volar aspect of the first and second tendons of the flexor digit orum profundus; the two 

 medial arise from the adjacent sides of the second and third and third and fourth tendons. 



Structure and insertion. — The fibre-bundles of each muscle arise directly from the flexor 

 tendons near the distal border of the transverse carpal (anterior annular) ligament. They 

 converge as far as the metacarpo-phalangeal joint, upon a small tendon which begins about the 

 middle of the muscle. The tendon passes out between the palmar aponeurosis and the trans- 

 verse capitular ligament, winds about the metacarpo-phalangeal joint, expands, and is attached 

 along the side of the first phalanx to the radial border of the tendon of the extensor digitorum 

 communis. 



Nerve-supply. — Branches from the median nerve enter the middle third of the radial border 

 of the first two or three lumbrical muscles. The last one or two are supplied by branches from 

 the deep volar branch of the ulnar nerve, which enter the middle third of the deep surface. The 

 third lumbrical and sometimes one or more of the others may receive a branch from both nerves. 

 The nerve fibres come from the eighth cervical and first thoracic nerves. 



Action. — Together with the interosseous muscles they flex the basal phalanges on the meta- 

 carpal bones and extend the terminal and middle phalanges. They also adduct the fingers 

 toward the thumb. 



Relations. — The muscles run between the tendons of the flexor profundus and beneath the 

 palmar aponeurosis. They lie upon the fascia covering the interosseous muscles, the capitular 

 ligaments, and the septum' over the adductor and deep head of the flexor poUicis brevis. 



Variations. — These are very frequent, especially in case of the third and fourth. Each 

 may be doubled or missing. They may arise from the tendons of the flexor sublimis or from 

 the belly of the deep flexor. The first lumbrical may come from the tendon of the long flexor, 

 from the opponens, or the metacarpal of the thumb. The tendon of insertion may go to the 

 ulnar side of the base of the digit opposite that to which the tendon is usually attached, or the 

 tendon may divide and go to the adjacent sides of two fingers. Kopsch has found that in 110 

 bodies all four lumbricals were inserted on the radial side of their respective digits in 39 per cent. 

 In 35 per cent, the first, second, and fourth were so inserted, while the third sent shps to the 

 adjacent sides of the middle and ring fingers. An accessory fasciculus has been found to arise 

 from the tendon of the flexor poUicis longus and go to the base of the index finger. 



(e) Interosseous Muscles (figs. 377, 378, 379) 



These muscles lie between the metacarpal bones and are covered dorsally and 

 ventrally by fascise attached to the metacarpals. In each interspace are two mus- 

 cles, a dorsal and a palmar. The volar interossei are inserted into all the fingers 



Fig. 378. — The Volar Interossei. 



except the middle finger, and are adductors toward an axis passing through the 

 middle finger; the dorsal interossei are inserted into both sides of the middle finger 

 and into the radial side of the second and the ulnar side of the fourth finger, and 

 are abductors. All also serve as flexors of the first row of phalanges and extensors 

 of the second and third. In the foot the axis to and from which the interosseous 

 muscles adduct and abduct the toes passes through the second toe. 



The interossei volares arise from the sides toward the middle finger and the front of the 

 shafts of the first, second, fourth, and fifth metacarpals. The first arises from near the base, the 



