ON THE NAVICULAR DISEASE. 29 



viz., the pulpy substance, commonly called the fatty 

 frog or elastic cushion, becomes in part absorbed. 

 The cartilaginous or reticular portion, being a , 

 harder body, remains ; therefore, it still retains its 

 form in a condensed state, and is yet an elastic sub- Absorption of 

 stance, although degenerated into a hard bed in- '^ '' ^ "^"^ 

 stead of a soft one. Thus it is that that portion of 

 the main back sinew of the leg, the flexor perforans 

 tendon, where it forms the navicular joint, is no 

 longer embedded in such an elastic medium as 

 would defy all human ingenuity to imitate, which 

 was the original and healthy condition of the fatty 

 frog. 



The dilapidated state of this spring affects the 

 elasticity of the posterior parts of the foot in other 

 ways besides the resistance it opposes to the navi- 

 cular bone in its descent ; for I believe the fatty 

 frog, as it is called, to be an organ which performs 

 several important functions, as regards elasticity 

 alone, and that there is an additional reason for the 

 larger half of this elastic mass being placed poste- 

 rior to the navicular joint, besides that of expand- 

 ing the lateral cartilages from its continuity. For^ 

 when we consider the extensive pulley-like motion 

 between the tendon and the navicular bone, and 

 that all the upper part of this pulley-like surface, 

 from the oblique position in which the bone is 

 placed, could not be benefitted by a spring imme- 

 diately under it ; and taking also into the account, 



