THE HAND. 87 



arise all of the digital branches for the fingers, with the exception of the three furnished by the 

 arteria princeps pollicis. The convexity of the superficial palmar arch barely reaches to the 

 middle one of the three lines which diverge from the base of the index-finger to the ulnar border 

 of the hand. 



The median nerve lies upon the common sheath of the flexor tendons and passes through 

 the carpal canal in company with these structures (see page 86). It gives off seven digital branches 

 which supply the palmar surfaces of the thumb, index, middle and radial side of the ring fingers 

 and inosculate with the digital branches of the ulnar nerve. With the exception of the adductor 

 pollicis, the muscles of the thumb are also supplied by the median nerve. 



The ulnar nerve is situated to the inner side of the ulnar artery, passes into the hand to the 

 radial side of the pisiform bone, and immediately divides into a superficial palmar branch, for the 

 ulnar side of the ring finger and for both sides of the little finger, and a deep palmar branch, which 

 follows the deep branch of the ulnar artery and accompanies the deep palmar arch, supplying the 

 muscles of the hypothenar eminence, all of the interosseous muscles, and ending in the adductor 

 pollicis muscle. There are no motor nerves upon the dorsal surface of the hand. The dorsal 

 cutaneous branch of the ulnar ends in sensory filaments which supply the ulnar half of the back 

 of the hand. In this situation these filaments inosculate with the radial nerve, which furnishes 

 sensory branches for the radial half of the back of the hand (see page 84). 



In the palm of the hand there are three synovial sheaths for the tendons, in addition to a 

 small unimportant one for the terminal portion of the tendon of the flexor carpi radialis: 



1. The common large synovial sheath for the tendons of the flexor sublimis and profundus 

 digitorum. This extends about two centimeters above the anterior annular ligament (toward the 

 forearm); exudates to the proximal side of the ligament may consequently make themselves 

 manifest by the presence of a superficial swelling. 



2. The synovial sheath for the tendon of the flexor longus pollicis. This also commences 

 to the proximal side of the anterior annular ligament and envelops the tendon almost to the very 

 point of its insertion into the terminal phalanx of the thumb. It frequently communicates with 

 the common synovial sheath of the flexor tendons of the fingers beneath the anterior annular 

 ligament. 



3. The individual tendon-sheaths of the index, middle, ring, and little fingers, each one of 

 which envelops one of the superficial and one of the deep flexor tendons. As a rule, the tendon- 

 sheath of the little finger is directly continuous proximally with the common sheath of the flexor 

 tendons of the fingers. 



It follows that tenosynovitis, resulting from injuries or inflammations of the fingers, finds a 

 favorable path for its extension toward the forearm, particularly when situated in the thumb 

 and little finger. As the tendon-sheaths of the little finger and of the thumb are continuous with 

 the common synovial sheath at the wrist,* we can readily understand the occurrence of those cases 

 in which an inflammation extends through the palm from the thumb to the little finger, or in tl 

 reverse direction. Clinical observations show that the individual tendon-sheaths of the index, 

 middle, and ring fingers are occasionally also continuous with the common synovial sheath. 



As there are no tendon-sheaths upon the backs of the fingers, and since the sheaths of the 



* The sheath for the thumb is less frequently continuous than is that for the little finger. ED. 



