THE PEKIOPLE. 79 



Secondly, because the sensitive bar insensibly fades into the 

 sensitive sole, both being marginated by the frog ; as, however, 

 the horn of the sole wears away in the same direction as that 

 of the bar, and the tw-o unite close to the lateral lacuna of the 

 frog, it is clear that no hard and fast line can be draw^n between 

 the two on this surface. 



By examining the surface of the hoof, however, first discover- 

 ing the white line between the sole and bar and following this, 

 it becomes clear that the line (figs. 45 and 46, g') never attains 

 the point of the frog, always ceasing somewhat short of it, and, 

 therefore, that the bars and sole are united into one mass a little 

 behind the point of the frog. The bars must accordingly be 

 regarded as an important means of union between the horny 

 wall and horny sole. At all other points, and over a much 

 more extensive area, the two portions of the hoof are united 

 through the medium of the white line — a much weaker and less 

 rigid method of union. This fact is not without importance in 

 connection with the physiology of the foot. 



The wall may be divided into three superposed layers, cor- 

 responding to the position of tlie epidermis from which they 

 arise. 



A. The periople is the most superficial and is formed by the 

 perioplic ring. It consists of soft horu, which in living animals 

 is yielding, very elastic, and when dry presents a glistening 

 appearance. In horses which have stood for a considerable 

 time in water, or in dead feet,, which have been macerated, this 

 horn swells up, becomes white, and exhibits a fibrillated char- 

 acter. It then forms a soft, elastic, convex strip of varying 

 breadth (fig. 44, a to cd , and fig. 48, a), which extends around 

 the foot parallel with the groove below as far as the bulbs of 

 the heel. It is somewhat broader at the toe than at the 

 quarters. At the heels it increases in. width and is prolonged 

 over the soft structures of the bulbs {ci'\ The perioplic horn 

 of either side becomes continuous at the heels, where it extends 

 upwards in a point, rising rather above the highest part of the 

 frog. When removed by maceration, it presents the appear- 

 ance of a broad strip, the inner surface of which is free above, 

 but below covers and is attached to the upper part of the wall 

 and the posterior portion of the frog, with the horn of which 

 it imperceptibly unites. Its upper (free) portion is punctated. 



