134 THE SUPERIOR EXTREMITY 



ligament and investigate its course and direction with the aid of 

 a blunt probe. 



If the sheath of the flexor pollicis longus has not already 

 been distended by the air or fluid thrown into the common 

 flexor sheath, pull the tendon of the flexor carpi radialis medially, 

 find the tendon of the flexor pollicis longus which lies behind 

 it, and either distend its sheath in the manner indicated or 

 examine it with a probe. It extends from one inch above the 

 transverse carpal ligament to the base of the terminal phalanx 

 of the thumb. 



Now turn to the middle finger and make a small longitudinal 

 incision through the flexor sheath opposite the middle of the 

 second phalanx. A blunt probe introduced through the incision 

 can be passed distally to the base of the terminal phalanx and 

 proximally to the level of the head of the metacarpal bone. The 

 conditions are the same in the cases of the index and ring fingers, 

 therefore the digital sheaths of the index, middle, and ring fingers 

 dp not communicate with the common flexor sheath. If the 

 digital sheath of the little finger is opened in a similar manner 

 no difficulty will be experienced in passing a probe along it into the 

 common flexor sheath, and if the digital sheath of the thumb is 

 opened and a little care exercised a probe can be passed along it, 

 and behind the transverse carpal ligament, to the proximal limit 

 of the mucous sheath of the flexor pollicis longus tendon. 



Mucous Sheaths of the Flexor Tendons. As the tendons 

 of the flexor digitorum sublimis, the flexor digitorum 

 profundus, and the flexor pollicis longus pass behind the 

 transverse carpal ligament they are accompanied by the 

 median nerve and they are enveloped in two mucous 

 sheaths (Fig. 58). One sheath surrounds the flexor pollicis 

 longus,- the other surrounds the tendons of both the flexor 

 sublimis and the flexor profundus, and it may enclose 

 also the median nerved The sheaths, therefore, line a 

 "carpal tunnel" which is bounded superficially by the 

 transverse carpal ligament and dorsally by the carpal bones, 

 and they greatly facilitate the free play of the tendons between 

 the transverse carpal ligament and the carpus. As already 

 stated, the sheaths are two in number. Both sheaths are pro- 

 longed proximally, into the forearm, for 25 mm. (one inch) or 

 more, and both are carried distally into the palm in the form 

 of diverticula upon the diverging tendons. The diverticula in 

 relation to the tendons which go to the index, middle, and ring 

 fingers end near the middle of the palm. Those upon the 

 tendons of the thumb and little finger, however, are prolonged 

 distally into the digits, and line the fibrous sheaths which 

 confine the tendons upon the volar aspects of the phalanges 

 (Fig- 57)- 



