182 THE STEUCTUEE OP THE HOESE 



fatty cushion of the bulb at the end of the human 

 finger (fig 24, 17). 



In the horse this c plantar cushion ' is of great size 

 and importance. It is wedge-shaped; the narrow, 

 pointed end, which is turned forwards and reaches to 

 the middle of the under surface of the foot, causes the 

 median triangular prominence called the ' frog.' Pos- 

 teriorly in the middle line is a deep depression (the 

 ' median lacuna '), bounded on each side by the 

 i branches of the frog,' which end in rounded projections, 

 the i glomes of the frog ' forming the lower part of the 

 heels. Blood-vessels, nerves, lymphatics, and connec- 

 tive tissue make up the rest of the structure of the toe, 

 and the whole is encased in a prolongation of the 

 ordinary skin of the limb, which, however, has under- 

 gone some very considerable modifications. At a sharply- 

 defined line (the 1 coronet ') which runs all round the 

 foot, highest in front and becoming lower behind, where 

 it drops rather below the most prominent part of the 

 heels and dips into the lacuna, the hairy covering 

 altogether ceases, and a very thick epidermis takes its 

 place, completely encasing the whole terminal part of 

 the digit, as a thimble upon the end of a finger. In 

 order to provide for the nutrition and continuous growth 

 of this abundant epidermic covering, the derm has 

 acquired a greatly modified condition, being very thick 

 and vascular, and its surface is everywhere immensely 



