DISEASES OF THE FEET AND LEGS. 121 



on the under surface (c, fig. 4). In a healthy foot, fig. 4, 

 the heels are round, wide, and smooth (a, a), the frog 

 fully expanded, the bars or binders distinct (c, c), no 

 corns in the usual angle (J), the sole broad and concave 

 {(l). In a diseased foot, fig. 3, the heels are high, and 

 drawn together by contraction («, a), the frog narrow, 

 and filled with fissures from contraction and thrush (5), 

 corn frequently present {d\ the sole greatly shortened 

 in its transverse diameter, which is morbidly counter- 

 balanced by the increased heights in the truncated form 

 (c). When the hoof is removed, the sensible or fleshy 

 sole {li, section of foot), above which it immediately lies, 

 presents itself, covering the whole of the horny sole, 

 except so much as is taken up by the sensible frog (li). 

 This part is exquisitely sensible and vascular, and thus 

 we learn why injuries to it from puncture produce such 

 serious effect, and why very slight pressure from con- 

 traction of the hoof gives so much pain. The sensible 

 frog and the sensible sole form the insensible frog and 

 sole ; but when from pressure, too much moisture, or 

 other causes, the sensible frog, instead of forming horn, 

 secretes pus or matter as in thrush, the structure of 

 the whole becomes injured, and the frog thus losing 

 its support gradually wastes and decays. It is there- 

 fore evident that no thrush can be entirely harmless, 

 as is erroneously supposed. 



" Above the sensible frog is the great flexor tendon, 

 or back sinew, inserting itself into the vaulted arch of 

 the coffin (r<, section of foot). This important tendon, 

 arising from its parent muscle above the knee, whose 

 origin is taken from the humerus and ulna, in its pas- 

 sa2;e unites with an assistant flexor, but which latter is 

 principally distributed to the pastern bones, while the 



