POSTERIOR PART OF LOWER EXTREMITY. 391 



Ligamenta Vaginales. These are the fibrous sheaths of deep fascia that 

 cover the flexor tendons. They are formed by the deep fascia, in a modified 

 form. Above, they are continuous with the plantar fascia. They are attached 

 on the sides to the margins of the grooves on the plantar surface of the 

 phalanges. 



The Theca and Thecal Culs-de-sac. The vaginal synovial membrane, con- 

 sisting of a visceral and a parietal layer, is called theca. The point in conjunction 

 between the two layers about the middle of the metatarsal bones forms a cul- 



Peroneua longus 



Plantar interossei 



Dorsal interossei 



FIG. 275. FOURTH LAYER OF THE MUSCLES OK THE SOLE. 



de-sac. -Pus forming below in the cavity of the tlicca could burrow to this point. 

 Note the difference in the fingers. 



Normally, the thecal cul-de-sac is found as above described in each toe, thus 

 making five in number. The homologous structures of the fingers are described 

 as three, the thumb and little finger having none, since the thecal synovial mem- 

 brane corresponding to these two members is continuous above with the two 

 bursae under the annular ligament. My experience is, however, that in the 

 majority of cases no communication will be found between the thecal sacs of the 

 thumb and little finger, and the bursse under the anterior annular ligament at 

 the wrist. 



The Vincula. These are small silvery cords that extend from the bottom of 



