152 THE SUPERIOR EXTREMITY 



proximal interphalangeal joint is placed immediately over 

 the articulation, whilst in the case of the distal inter- 

 phalangeal joints the single crease which is usually present 

 is situated immediately proximal to the articulation. On 

 the back of the hand the metacarpal bones can be readily 

 felt, whilst their distal extremities, or heads, form the promin- 

 ences known as the "knuckles." 



M. Palmaris Brevis. This small cutaneous muscle con- 

 sists of a series of fasciculi which are frequently separated 

 from one another by distinct intervals. As a whole it 

 forms a thin fleshy layer which covers the deep fascia on the 

 proximal one and a half inches of the hypothenar eminence. 

 It springs from the distal margin of the transverse carpal 

 ligament and the medial border of the strong intermediate 

 part of the palmar aponeurosis, and it is inserted into the 

 skin of the medial border of the hand. It lies superficial 

 to the ulnar artery, the superficial part of the ulnar nerve, and 

 to the deep fascia covering the muscles of the hypothenar 

 eminence. It is supplied by the superficial division of 

 the ulnar nerve. 



Dissection. Reflect the palmaris brevis to its origin from 

 the intermediate part of the palmar aponeurosis, and secure 

 the branch from the superficial division of the ulnar nerve which 

 supplies it. Remove the medial part of the palmar aponeurosis 

 from the muscles of the hypothenar eminence. Clean the ulnar 

 artery to the point where it disappears under cover of the inter- 

 mediate part of the palmar aponeurosis. Note that, as it passes 

 by the medial side of the hook of the os hamatum, it sends a 

 deep branch into the substance of the palm. Clean the ulnar 

 nerve as it lies on the medial side of the hook of the hamatum 

 and secure its two terminal branches : (i) A superficial branch, 

 which divides into the digital branch for the medial side of the 

 little finger, and a branch which divides to supply the adjacent 

 sides of the little and ring fingers ; and (2) a deep branch which 

 accompanies the deep branch of the ulnar artery into the depths 

 of the palm. Find the branches which the deep division of the 

 ulnar nerve gives to the short muscles of the little finger ; then 

 insert the handle of the scalpel into the cleft into which the deep 

 divisions of the artery and nerve pass, and carry it distally to 

 separate the abductor digiti quinti muscle, on the medial side, 

 from the flexor digiti quinti brevis and the opponens digiti quinti 

 on the lateral side. The opponens lies on a deeper plane than 

 the short flexor. 



Short Muscles of the Little Finger. There are three 

 short muscles of the little finger : the abductor, the short 

 flexor, and the opponens. They are all supplied by the deep 

 branch of the ulnar nerve. 



