56 DISEASES OF THE HORSE'S FOOT 



points had arisen, each to take on a function similar to the 

 epithelial process as it at first appeared. 



In the centre of the processes a few nuclei may be 

 observed, but they are scarce, and stain only faintly; they 

 have arisen from the cells of the rete Malpighii which have 

 grown into the corium. In fact, the active cells are passing 

 their daughters into the middle of the process, and these 

 pass through similar stages as those derived from the 

 ensheathing epidermis. In other words, the daughter cells 

 of the constituents of the rete Malpighii which have grown 

 into the corium pass through a degeneration precisely 

 similar to that undergone by cells shed at desquamation, 

 or those which eventually give rise by their agglutination 

 to a hair. 



This is the real origin of the horny laminae, and the 

 thickness of these is increased merely by an increase in the 

 area covered by the cells of the rete Malpighii — i. e., by the 

 development of secondary laminar ridges. If a section 

 from a foal at term be examined, the processes will be 

 found far advanced into the corium, and, occupying the 

 axis of each process, will be seen a horny plate, continuous 

 with the horn of the wall. No line of demarcation can be 

 observed between the horn so formed and the intertubular 

 material of the wall. They merge into and blend with each 

 other, with no indication of their different origins. The 

 cells that have invaded the corium have thus not lost their 

 horn-forming function. There has merely been an increase 

 in the area for horn-producing cells. The horny processes 

 are continuous w r ith the hoof proper at the point where the 

 epithelial ingrowth first commenced to invade the corium, 

 and fuses here with the horn derived from the cells of the 

 rete Malpighii which have not grown inwards, and which 

 are found between the processes in the intact foot. From 

 this it is clear that some considerable portion of the horn of 

 the wall is derived from the cells of the rete Malpighii 

 covering the corium of the foot. It becomes even more 

 clear when we remember the prompt appearance of horn in 

 cases where a portion, or the whole, of the wall has been 



