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 laminez, and the 
thickness of these is increased merely by an increase in the 
area covered by the cells of the rete Malpighii—i.é., 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 with 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. 
