1 66 THE SUPERIOR EXTREMITY 



intervals between the tendons as they approach the roots of 

 the fingers. 



In the fingers the two flexor tendons run distally, upon 

 the volar aspects of the phalanges, and are held in position 

 by the flexor sheaths, which have already been studied. 



The tendon of ti\e flexor pollicis longus occupies the lateral 

 part of the tunnel, and, gaming the palm, turns laterally to 

 reach the terminal phalanx of the thumb. 



Tendon of the Flexor Pollicis Longus. The tendon of 

 the long flexor of the thumb proceeds distally, in the interval 

 between two of the short muscles of the thumb (viz., the 

 superficial head of the flexor pollicis brevis and the oblique 

 part of the adductor pollicis), and also in the interval between 

 the two sesamoid bones which play upon the head of the 

 metacarpal bone. At the base of the proximal phalanx it 

 enters a fibrous flexor sheath constructed upon a similar 

 plan to those of the fingers, and passes along it to the base 

 of the terminal phalanx, into which it is inserted. The 

 mucous sheath which surrounds the tendon during its 

 passage through the carpal tunnel is continuous with the 

 sheath which invests the tendon in front of the phalanges. 



Mm. Lumbricales. The lumbrical muscles are four slender 

 fleshy bellies which arise from the tendons of the flexor 

 digitorum profundus as they traverse the palm. The first 

 lumbrical arises from the lateral side of the tendon for the 

 index finger ; the second lumbrical springs from the lateral 

 border of the tendon for the middle finger ; whilst the third 

 and fourth lumbricals take origin from the adjacent sides of 

 the tendons between which they lie (viz., the tendons for 

 the middle, ring, and little fingers). The little muscles pass 

 distally, and end in delicate tendons on the lateral sides of 

 the fingers. Each tendon is inserted into the lateral margin 

 of the expansion of the extensor tendon, which lies upon the 

 dorsal aspect of the proximal phalanx. 



Dissection. Divide the flexor digitorum profundus in the 

 forearm, and turn the distal part towards the fingers. As the 

 tendons and the lumbrical muscles which are attached to them 

 are raised, secure the fine twigs of supply which pass to the 

 medial two lumbricals from the deep division of the ulnar nerve. 

 They are easily found if ordinary caution is observed. The 

 deep volar arch and the deep division of the ulnar nerve are now 

 exposed. Clean both the arch and the nerve, and trace the 

 branches of the nerve to the interossei muscles and to the adductor 

 pollicis and the deep head of the flexor pollicis brevis. Then 



