ANATOMY OF THE FOOT. 183 



when the arteries have been injected with 

 coloured wax or sise: it is from this part that 

 the hoof is formed. 



The bottom of the internal foot is formed 

 by the sensible trog and sole : the former per- 

 fectly resembles in shape the horny frog, to 

 the concavities of which its convexities are 

 nicely adapted. In describing the horny frog, 

 we had occasion to mention its coimection 

 with two elastic bodit's or cartilages that are 

 m great measure covered by the heels and 

 quarters of the hoof; but this connection is 

 through the medium of the seiisibk frog, 

 which is more immediately united to those 

 cartilaeos. When the former comes in con* 

 tact with the ground, and receives the pres- 

 sure of the horse's weight, the latter is forced 

 upward and rendered wider, and at the same 

 time the cartilages are forced upward and out- 

 Ivard, tending thereby to expand the heels 

 and quarters, and assisting in taking off con- 

 cussion. From the sensible frog and sole, the 

 horn which composes the external frog and 

 sole is secreted. For this purpose they are 

 supplied with numerous blood-vessels, the 

 extre.nities of vviiich may be seen upon 

 their surface, and become very conspicuous, 



