64 THE PROACTIVE STKUCTUKES OF THE FOOT. 



perioplic ring and coronary band, these papillce are very 

 long. The corium, however, had not always this papillated 

 appearance ; in the early stages of developmental life the 

 surface was quite plane, covered by the epidermis. During 

 the tenth week of foetal life the epidermis covering the part 

 where the hoof is to appear begins to grow into the corium 

 and dissect it up ; this ingrowth occurs at regular intervals, 

 and proceeds throughout the w^hole depth of the foot. 

 Furtheimore, a similar ingrowth takes place along the sides 

 and at the inflections of the walls known as the bars. The 

 epithelial invasions continue to advance into the corium, and 

 after a time to form on either face secondary invading points, 

 which behave in a similar fashion, though not to the same ex- 

 tent, as the original ingrowths. In this way the corium is split 

 up into a great number of plates running parallel to each other, 

 and these form the sensitive or fleshy laminae. But the epi- 

 thelial cells of the epidermis become eventually converted into 

 horn scales : such also is the fate of the epithelial cells that in- 

 vade the corium, and hence we find that occupying the axis of 

 any ingrowth is a horny plate that has resulted from the pro- 

 liferation and alteration of the cells of the epidermis. No 

 difference, therefore, is to be noted in the fate of the daughter 

 cells, save that they have cohered to form a horny plate after 

 the same fashion as their relatives, the cells producing a hair. 

 This horny plate becomes a horny lamina, and hence the horny 

 lamina comes to occupy the space between two sensitive 

 laminae. A sensitive lamina results, therefore, from two incur- 

 sions of the epidermis taking place into the corium, and its 

 depth from free edge towards its attached border represents 

 the depth of the corium of the foot. The epithelial cells cover- 

 ing the corium give rise to the horn lining the horny capsule, 

 whether it belongs to the horny laminae or to the horn 

 cementing these to the remainder of the hoof. As one proof 

 of their horn- forming function, it is to be noted that the horn 

 of the interior of the capsule is uncoloured, despite the colour 

 of the hoof, and this is to be explained by the absence of 

 pigment from the epithelial cells covering the corium in this 

 region. Again, if the hoof be partly stripped off, the epithelial 

 cells covering the soft structures speedily produce a new horny 

 pellicle. On the surface of the hoof the horn thus formed 



