404 THE MUSCULATURE 



The ulnar nerve supplies the muscles of the little finger, the interossei, the 

 medial lumbrical muscles, and two of the muscles of the thumb; the median 

 nerve supplies most of the muscles of the thenar region and the lateral lumbrical 

 muscles. 



(a) Subcutaneous Muscle 

 (Fig. 375) 



The palmaris brevis is a small, trapezoid sheet situated between the hypothe- 

 nar fascia and the skin. It arises at the lateral edge of the palmar aponeurosis 

 from tendinous slips which maj^ be traced through the aponeurosis to the navicular 

 and greater multangular. It is composed of nearly parallel fibre-bundles, and ex- 

 tends into the deep surface of the skin along the ulnar border of the palm. It is 

 generally taken to be a subcutaneous muscle like the superficial muscles of the 

 head and neck. It has, however, been suggested that it represents the remnants 

 of a short flexor of the digits corresponding with the flexor digitorum brevis of the 

 foot. 



Nerve-supply. — The superficial branch of the palmar division of the ulnar nerve gives rise 

 to a twig which enters the deep surface of the muscle. The fibres come from the (seventh and) 

 eighth cervical and first thoracic nerves. 



Action. — The action of the muscle is to draw the skin of the ulnar side of the hand toward 

 the centre of the palm. It is said that it thus helps to form a cup-shaped hollow when the hand 

 conveys fluid to the mouth. The contraction of the muscle by raising a ridge over the ulnar 

 nerve and artery when an object is grasped hard serves, according to Henle, to protect these 

 structures. 



Variations. — It varies in size. In about 2 per cent, of bodies it is absent (Le Double). 

 It may send tendinous slips to the pisiform bone. (For a thenar subcutaneous muscle, see 

 variations of the abductor pollicis brevis.) 



(b) Muscles of the Lillle Finger 

 (Figs. 375, 376, 377) 



In the hypothenar eminence are three muscles, the abductor, the flexor brevis, 

 and the opponens digiti quinti. The abductor digiti quinti is a flat, fusiform 

 muscle which arises from the pisiform and is inserted into the ulnar border of the 

 first phalanx and into the dorsal aponeurosis through which it helps to flex the 

 first and extend the second and third phalanges of the little finger. The fusiform 

 flexor brevis arises from the hamatum (unciform) and adjacent part of the trans- 

 verse carpal (anterior annular) ligament and is inserted into the ulnar side of the 

 base of the first phalanx. The triangular opponens likewise arises from the hama- 

 tum (unciform) and the transverse (anterior annular) ligament. It is inserted 

 into the ulnar border and the head of the fifth metacarpal. 



The abductor of the little finger corresponds with that of the little toe. A part of the oppo- 

 nens beneath the ulnar nerve corresponds with that of the little toe, while the more superficial 

 portion is unrepre.sented in the foot. The flexor brevis of the little toe corresponds with a part 

 of the deep portion of the opponens of the little finger. The flexor brevis of the httle finger 

 is unrepresented in the foot. (Cunningham.) 



The abductor digiti quinti (figs. 375, 37G). — Origin. — From the distal half of the pisiform, 

 the ligaments between this and the hamatum, the tendon of the flexor carpi ulnaris, and often 

 from the transverse carpal (anterior annular) ligament. 



Structure and insertion. — The fibre-bundles descend verti(!ally, at first increasing in number 

 and then concentrated, toward two short tendons one of which is inserted into the ulnar border 

 of the first phalanx of the little finger and the other into the aponeurosis of the extensor tendon 

 of the little finger. 



Ne.rve-sup])ly. — From the deep palmar division of the ulnar nerve before it passes through 

 the opponens, or froin the superficial palmar branch, arise one or more twigs which enter the 

 radial side of the muscle on its dcej) surface in the proximal third. The nerve fibres arise from 

 the (seventh and) eighth cervicid and first thoracic nerves. 



Action. — To abduct the little finger, flex flie first i)halanx, and extend the last two. 



Relations. — It f)verlies the oj)p(in(>iis and flexor brevis. Superficially it is covered by fascia 

 and the palmaris brevis musclc!. Along the proximal part of its ratlial margin run the deep 

 palmar branches of the ulnar artery and nerve. 



Variations. — It may be missing or doubled. It may be fused with the short flexor or 

 receive fasciculi from the palinaris longus, the ulnar flexor, the fascia of the forearm, etc. 



The flexor digiti quinti brevis (figs. 376, 377). — Origin. — By a short tendon from the hook of 

 the hamatum (unciform) ami from the; adjacent parts of the transver.se carpal (anterior annular) 

 ligament. 



Structure and insertion. — The fibre-bundles take a nearly parallel course and are inserted 



