494 THE MUSCLES AND FASCIA. 



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. These 

 expansions, originally figured by Albinus, have been more recently described by 

 M. Duchenne (Physiologie des Mouvements, page 29*9). 



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

 are supplied by the median nerve ; the inner head of the Flexor brevis, and the 

 Adductors, by the ulnar nerve. 



Actions. The actions of the muscles of the thumb are almost sufficiently indi- 

 cated 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 Flexor 

 ossis rnetacarpi pollicis flexes the metacarpal bone -that is, draws it inward over 

 the palm and at the same time rotates the bone, so as to turn the ball of the 

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

 Flexor brevis pollicis flexes the proximal phalanx of the thumb. The Adductores 

 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 Avill be noticed, however, that in consequence of the position of the first meta- 

 carpal bone these movements differ from the corresponding 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. 



Ulnar Region (Fig. 316). 



Palmaris brevis. 

 Muscles of the Little Finger. 



Abductor minimi digiti. Flexor brevis minimi digiti. 



Opponens (Flexor ossis metacarpi) minimi digiti. 



The Palmaris brevis is a thin quadrilateral muscle placed beneath the integu- 

 ment on the ulnar side of the hand. It arises by tendinous fasciculi from the 

 annular ligament and palmar fascia ; the fleshy fibres pass inward, to be inserted 

 into the skin on the inner border of the palm of the hand. 



Relations. By its superficial surface, with the integument, to which it is 

 intimately adherent, especially by its inner extremity ; by its deep surface, with 

 the inner portion of the palmar fascia, which separates it from the ulnar vessels 

 and nerve, and from the muscles of the ulnar side of the hand. 



The Abductor minimi digiti is situated on the ulnar border of the palm of the 

 hand. It arises from the pisiform bone, and terminates in a flat tendon which 

 divides into two slips : one passes under the lateral expansion of the extensor 

 tendon, opposite the metacarpo-phalangeal articulation, and is inserted into the 

 ulnar side of the base of the first phalanx of the little finger. The other slip 

 passes over the expansion, and is inserted into the ulnar border of the shaft of the 

 same phalanx. 



Relations. By its superficial surface, with the inner portion of the palmar 

 fascia, and the Palmaris brevis ; by its deep surface, with the Flexor ossis meta- 

 carpi minimi digiti ; by its outer border, with the Flexor brevis minimi digiti. 



The Flexor brevis minimi digiti lies on the same plane as the preceding muscle, 

 on its radial side. It arises from the tip of the unciform process of the unciform 

 bone and anterior surface of the annular ligament, and is inserted into the base 

 of the first phalanx of the little finger. It is separated from the Abductor at its 

 origin by the deep branches of the ulnar artery and nerve. This muscle is some- 

 times wanting ; the Abductor is then, usually, of large size. 



