THE ULNAR REGION 493 



The Adductor obliquus pollicis (m. adductor pollicis) (Figs. 368 and 369) 

 arises by several slips from the os magnum, the bases of the second and third 

 metacarpal bones, the anterior carpal ligaments, and the sheath of the tendon 

 of the Flexor carpi radialis. From this origin the greater number of fibres pass 

 obliquely downward and converge to a tendon, which, uniting, with the tendons 

 of the deeper portion of the Flexor brevis pollicis and the Adductor transversus, 

 is inserted into the inner side of the base of the first phalanx of the thumb, a sesa- 

 moid bone being developed in the tendon of insertion. A considerable fasciculus, 

 however, passes more obliquely outward beneath the tendon of the long Flexor 

 to join the superficial portion of the short Flexor and the Abductor pollicis. 1 



Relations. By its superficial surface, with the Flexor longus pollicis and the superficial head 

 of the Flexor brevis pollicis. Its deep surface is in relation with the deep palmar arch, which 

 passes between the two Adductors. 



The Adductor transversus pollicis (m. adductor transversus pollicis) (Figs. 

 368 and 369) is the most deeply seated of this group of muscles. It is of a tri- 

 angular form, arising, by its broad base, from the lower two-thirds of the meta- 

 carpal bone of the middle finger on its palmar surface; the fibres, proceeding 

 outward, converge to be inserted, with the inner part of the Flexor brevis pollicis, 

 and the Adductor obliquus pollicis, into the ulnar side of the base of the first 

 phalanx of the thumb. From the common tendon of insertion a slip is prolonged 

 to the Extensor longus pollicis. 



Relations. By its superficial surface, with the tendons of the Flexor profundus and the 

 Lumbricales. Its deep surface covers the first two interosseous spaces, from which it is separated 

 by a strong aponeurosis. 



Three of these muscles of the thumb, the Abductor, the Adductor transversus, and the Flexor 

 brevis pollicis, at their insertions give off fibrous expansions which join the tendon of the Extensor 

 longus pollicis. This permits of flexion of the proximal phalanx and extension of the terminal 

 phalanx at the same time. 



Nerves. The Abductor, Opponens, and superficial head of the Flexor brevis pollicis are 

 supplied by the sixth cervical through the median nerve; the deep head of the Flexor brevis, and 

 the Adductors, by the eighth cervical through the ulnar nerve. 



Actions. The actions of the muscles of the thumb are almost sufficiently indicated by 

 their names. This segment of the hand is provided with three Extensors an Extensor of the 

 metacarpal bone, an Extensor of the first, and an Extensor of the second phalanx; these occupy 

 the dorsal surface of the forearm and hand. There are also three Flexors on the palmar surface 

 a Flexor of the metacarpal bone, a Flexor of the proximal, and a Flexor of the terminal phalanx; 

 there is also an Abductor and two Adductors. The Abductor pollicis moves the metacarpal 

 bone of the thumb outward; that is, away from the index finger. The Opponens pollicis 

 flexes the metacarpal bones that is, draws it inward over the palm so as to turn the ball of 

 the thumb toward the fingers, thus producing the movement of opposition. The Flexor brevis 

 pollicis flexes and adducts the proximal phalanx of the thumb. The Adductords pollicis move 

 the metacarpal bone of the thumb inward; that is, toward the index finger. These muscles 

 give to the thumb its extensive range of motion. It will be noticed, however, that in conse- 

 quence of the position of the first metacarpal bone, these movements differ from the corre- 

 sponding movements of the metacarpal bones of the other fingers. Thus extension of the 

 thumb more nearly corresponds to the motion of abduction in the other fingers, and flexion 

 to adduction. 



12. The Ulnar Region (Fig. 369). 



Palmaris brevis. Flexor brevis minimi digiti. 



Abductor minimi digiti. Opponens minimi digiti. 



The Palmaris brevis (m. palmaris brevis) is a thin quadrilateral muscle placed 

 beneath the integument on the ulnar side of the hand. It arises by tendinous 



' This muscle is described by some as the deep portion of tjie Flexor brevis pollicis. 



