408 THE MUSCULATURE 



The opponens pollicis (fig. 377). — Origin. — From the volar surface of the transverse carpa 

 (anterior annular) ligament and from the tubercle of the greater multangular bone (trapezium). 



Structure and Insertion. — The fibre-bundles extend obliquely in a nearly parallel direction 

 to their insertion along the whole lateral border of the volar surface of the shaft and the head of 

 the first metacarpal. 



Nerve-supply. — By a branch of the first volar digital ramus of the median nerve. This 

 branch passes over or through the superficial division of the flexor brevis near the origin of the 

 muscle. One or two twigs enter the deep surface of the proximal third of the opponens near 

 its ulnar border. The nerve fibres arise from the sixth and seventh cervical nerves. 



Action. — To flex, adduct, and rotate medialward the first metacarpal bone. The volar 

 surface of the thumb is thus brought to face the volar surface of the other digits. 



Relations. — It lies beneath the thenar fascia and the abductor brevis. The flexor brevis 

 overlies its ulnar border. 



Variations. — It may be absent or it may be divided into two heads. It is usually more or 

 less fused with the short flexor. 



The flexor pollicis brevis (figs. 376, 377). — The muscle is divided by the tendon of the 

 long flexor into a superficial and a deep portion. The superficial head arises from the greater 

 multangular bone (trapezium), the adjacent part of the transverse carpal (anterior annular) 

 ligament, and the tendon sheath of the flexor carpi radialis. The fibre-bundles descend closely 

 ajjplied to the opponens, and terminate by a tendon which is attached to the lateral side of the 

 front of the base of the first phalanx. Over the joint a sesamoid bone lies in the tendon. The 

 deep head has a tendinous origin from the os multangulum minus (trapezoid) and the os capi- 

 tatum (magnum). The fibre-bundles take an oblique course, to be inserted into the tendon of 

 the superficial part. A muscle fasciculus which arises from the ulnar side of the base of the first 

 metacarpal and the neighbouring carpal ligaments and is inserted on the ulnar side of the base 

 of the first phalanx, is sometimes considered to be the deep head of the flexor brevis. It is 

 closely bound up with the carpal head of the adductor pollicis and they have a common tendon. 

 Some fibres of the medial division of the tendon may be traced into the aponeurosis of the exten- 

 sor tendon. It is probable that this portion of the muscle represents a first volar interosseous, 

 and it is so described later with the interosseous muscles. There is much dispute as to what 

 fascicuh should be included in the flexor brevis. 



Nerve-supply. — The muscle is usually supplied by twigs derived from a branch from the 

 first volar digital ramus of the median nerve as this branch passes through its substance, and 

 by twigs from the deep branch of the ulnar. Brookes found this supply in 19 out of 29 instances, 

 in 5 by the median alone, and in 5 by the ulnar alone. The nerve fibres come from the sixth 

 and seventh cervical nerves. 



Action.- — To flex, adduct, and rotate medialward the metacarpal of the thumb; flex the first 

 phalanx; and extend the second phalanx. 



Relations. — Proximally the short flexor is grooved for the tendon of the long flexor, beneath 

 which more distally the deep head of the muscle passes laterally. The superficial portion of 

 the muscle lies beneath the skin. The ulnar border of the deep head is fused proximally with 

 the adductor. 



Variations. — The deep head may be absent. Either or both heads may be double. The 

 superficial head may be fused with the abductor brevis, and is usually more or less fused with 

 the opponens. 



The adductor pollicis (fig. 377). — Origin. — By two heads. The carpal or oblique head 

 arises from the deep carpal ligaments, the capitatum and the bases of the second and third 

 metacarpals; the metacarpal or transverse head, from the crest of the third metacarpal, from 

 the suprametacarpal fascia of the third interspace, and sometimes also from that of the fourth 

 interspace and from the capsules of the second, third, and fourth metacarpo-phalangeal articu- 

 lations. 



Structure and insertion. — The fibre-bundles converge toward a tendon which is inserted 

 into the ulnar side of the front of the base of the first phalanx of the thumb. A sesamcud bone 

 lies in the tendon over the joint. 



N erve-.Hupply . — One or more twigs from the deep palmar branch of the ulnar enter the middle 

 third of the muscle on its deep surface. There may also be an anastomosing branch from the 

 median nerve. The nerve fibres come from the sixth, seventh and eighth cervical and first 

 thoracic nerves. 



Action. — To adduct and flex the first metacarpal and flex the first phalanx of the thumb. 

 When the thumb is in an extreme position of apposition, it acts as an abductor. 



'Relations. — Superficial to the muscle lie some of the tendons of the deep flexor of the fingers 

 and the first two lumbrical muscles. It extends over the two more lateral intermetacarpal 

 spaces, and is in f)art subcutaneous on the dorsal surface. The deep palmar arch extends 

 between the two heads and beneath the oblique head. The oblique head of the muscle is closely 

 united to the first volar interosseous, so that the latter by some is considered a part of the 

 adductor. 



Variations. — The extent of the attachments of origin of the muscle vary considerably. 

 The two heads of the muscle may be more or less completely separated from one another. Each 

 may be divided into separate fasciculi. 



{(1) Lumbrical Muscles 



From tlie dcop flexor tendons in the palm of the hand arise the lumbrical 

 muscles, four in numl)er, which arc atta(;hed by small tendons to the radial side of 

 the extensor tendons (fi^;s. 37;^, 375). '^I'hese luni})ri('al muscles have homologues 

 in the sole of the foot. 



