FOREARM AND HAND 137 



are double-walled tubes. At their extremities the outer and 

 inner walls are bound together, and the space between the 

 two walls, the so-called cavity of the sheath, is thus closed. 

 The cavity of the sheath is a potential cavity only, and 

 it contains merely sufficient mucous fluid to lubricate the 

 adjacent surfaces, and facilitate their free play over one 

 another. 



The inner wall of the tube surrounds the tendon and 

 adheres to its surface. The outer wall lines the canal 

 through which the tendon passes and adheres to it. But 

 the ends of the sheaths project beyond the limits of the 

 canals which they line; therefore, as the tendons move 



Transverse carpal ligament Tendons of flexor digitorum sublimis 



Median nerve 

 Tendon of flexor pollicis longus 



Tendon of flexor 

 carpi radialis 



Tendons of flexor digitorum profundus 



FIG. 60. Diagram illustrating the relation of the Synovial Sheaths to the 

 Flexor Tendons at the level of the transverse carpal ligament. 



proximally and distally, the opposite ends of the sheaths 

 can be invaginated and evaginated, thus allowing for the 

 free play of the tendons. 



When a sheath becomes inflamed the adjacent surfaces 

 of its two walls are at first roughened, and when the tendon 

 moves, friction, which can be heard and felt, occurs and 

 pain is caused. Then the fluid between the two walls 

 increases in amount, the sheath becomes distended as if it 

 had been injected, and its position becomes apparent. At 

 the same time the friction ceases, but the distension of 

 the walls stretches the nerves, and pain is still felt. 



Some mucous sheaths, for example the mucous sheath 

 of the flexors of the fingers, are not complete tubes, but 

 merely invaginated sacs (Fig. 60). 



