198 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



Fig. 281. — Tendons and muscles (interossei dorsales) of the dorsum of the hand. 

 The dorsal carpal ligament is retained, the rest of the dorsal fascia being removed. 



Fig. 282. — The palmar aponeurosis and the palmaris brevis. 

 The thenar and hypothenar muscles are shown covered by the fascia. 



long, slender, muscular belly which passes downward to the wrist-joint beside the extensor 

 digitorum communis. Just before reaching the wrist it terminates in a tendon which passes 

 through a special compartment in the dorsal carpal ligament (Fig. 289), crosses* the tendons 

 of the extensores carpi radiales immediately before their insertion, and is attached to the ungual 

 phalanx of the thumb, being partly adherent to the tendon of the extensor pollicis brevis. 



This muscle is also supplied from the radial nerve. It extends the ungual phalanx of the thumb and assists the action 

 of the abductor. 



The extensor indicis proprius (the indicator) (Figs. 279, 280, and 289) is a long slender 

 muscle situated to the ulnar side of the extensor pollicis longus. It arises chiefly from the dorsal 

 surface of the ulna, receiving additional fibers from the interosseous membrane, is completely 

 concealed by the extensor digitorum communis, and passes through the dorsal carpal liga- 

 ment in the same compartment with the latter muscle (Fig. 289). Just above the wrist- joint 

 it terminates in a tendon which runs on the dorsum of the hand alongside of the tendon of the 

 communis for the index-finger and forms with this tendon the dorsal aponeurosis of that finger. 



It is supplied from the radial nerve. It aids in the extension of the index-finger. 



THE MUSCLES OF THE HAND. 



The thenar and hypothenar eminences occupy respectively the radial and ulnar bor- 

 ders of the hand, but the flexor tendons and lumbricales, running in the middle of the palm, are 

 covered by a strong aponeurosis which is usually a direct radiation of the tendon of the palmaris 

 longus (see page 193) and is known as the palmar aponeurosis (Fig. 284) (the palmar fascia). 

 This aponeurosis is always connected with the transverse carpal ligament and gradually fades 

 away upon either side into the fascia of the thenar and hypothenar eminences. It is narrow at 

 the transverse carpal ligament and becomes broader as it passes downward toward the fingers, 

 and its longitudinal fasciculi, which gradually disappear in the integument over the bases of the 

 proximal phalanges of the second to the fifth fingers, are united in the distal portion of the palm 

 by transverse fasciculi, which close in the interspaces lying between the longitudinal fasciculi 

 passing to the individual lingers. These spaces give passage to the vessels and nerves for the 

 margins of the fingers, and beneath them are situated the lumbricales. 



The ulnar margin of the denser central portion of the palmar aponeurosis and the transverse 

 carpal ligament give origin to a muscle which passes over the muscles of the hypothenar emi- 

 nence and the ulnar vessels to the integument at the ulnar border of the hand. This muscle is 

 situated entirely within the superficial fascia of the palm, varies in its development in different 

 individuals, and is termed the palmaris brevis (Fig. 282). 



* This crossing occurs within the dorsal carpal ligament, so that the tendon-sheaths also cross each other (see the 

 description of the tendon-sheaths of the hand, page 203). 



