396 MUSCLES AND FASCIAE. 



more superficial portion arises from the trapezium and outer two-thirds of the 

 annular ligament; the deeper portion from the trapezoides-, os magnum, base 

 of the. third metacarpal bone, and sheath of the tendon of the Flexor Carpi 

 Radialis. The fleshy fibres unite to form a single muscle; this divides into two 

 portions, which are inserted one on either side of the base of the first phalanx 

 of the thumb, the outer portion being joined with the Abductor, and the inner 

 with the Adductor. A sesamoid bone is developed in each tendon as it passes 

 across the metacarpo-phalangeal joint. 



Relations. By its superficial surface, with the palmar fascia. By its deep 

 surface, with the Adductor Pollicis, and tendon of the Flexor Carpi Radialis. 

 By its external surface, with the Opponens Pollicis. By its internal surface, with 

 the tendon of the Flexor Longus Pollicis. 



The Adductor Pollicis (Fig. 240) is the most deeply-seated of this group of 

 muscles. It is of a triangular form, arising, by its broad base, from the whole 

 length of the metacarpal bone of the middle finger on its palmar surface ; the 

 fibres, proceeding outwards, converge, to be inserted with the innermost tendon 

 of the Flexor Brevis Pollicis, into the ulnar side of the base of the first phalanx 

 of the thumb, and into the internal sesamoid bone. 



Relations. By its superficial surface, with the Flexor Brevis Pollicis, 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. 



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 Adductor Pollicis, by 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, the Flexor Ossis Metacarpi (Opponens Pollicis), 

 the Flexor Brevis Pollicis, and the Flexor Longus Pollicis ; there is also an 

 Abductor and an Adductor. These muscles give to the thumb its extensive 

 range of motion. 



ULNAR REGION. (Fig. 244.) 

 Muscles of the Little Finger. 



Palmaris Brevis. Flexor Brevis Minimi Digiti. 



Abductor Minimi Digiti. Opponens Minimi Digiti (Flexor Ossis Metacarpi). 



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 horizontally inwards, 

 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 inti- 

 mately 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 from an expansion of the ten- 

 don of the Flexor Carpi Ulnaris; and terminates in a flat tendon, which is 

 inserted into the ulnar side of the base of the first phalanx of the little finger. 



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 

 Metacarpi. By its inner 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 



