194 THE STRUCTURE OF THE HORSE. 



size and importance. It is wedge-shaped ; the nar- 

 row, 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." Posteriorly in the middle line is a deep 

 depression (the " median lacuna"), bounded on each 

 side by the ''branches of the frog," which end in 

 rounded projections, the "glomes of the frog" form- 

 ing the lower part of the heels. Blood-vessels, 

 nerves, lymphatics, and connective tissue make up 

 the rest of the structure of the toe, and the whole is 

 incased in a prolongation of the ordinary skin of the 

 limb, which, however, has undergone some very con- 

 siderable modifications. At a sharply defined hue 

 (the " coronet ") which runs all round the foot, high- 

 est 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 incasing the whole terminal 

 part of the digit, as a thimble upon the end of a fin- 

 ger. In order to provide for the nutrition and con- 

 tinuous 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 increased by folds, ridges, 

 papilla?, or villi. This vascular and sensitive struct- 



