54 DISEASES OF THE HORSE’S FOOT 
tissue. Each point of the ingrowing lines of the échelon 
has usually one cell further advanced into the corium than 
its neighbours, and may be termed the apical cell. The 
fine basement membrane separating epithelium from cortum 
is still clearly evident. This epidermal irruption of the 
corium takes place at definite points right round the foot. 
It is extremely probable, however, that it commences first 
at the toe and spreads laterally. 
As yet, these cellular ingrowths (which are destined to be 
Fic. 28.—SecrTion From CaLF Empryo. 
The epithelial ingrowths hang down from the epidermis into the corium like 
the teeth of a comb (Mettam). 
the horny lamine, and cut up the corium into sensitive 
lamine) are free from irregularities or secondary laminz. 
Before these are to be observed other changes in connection 
with the ingrowths are to be noticed. 
The first is merely that of elongation of the epithelial 
processes into the connective tissue, until the rete Malpighii 
gives one the impression that it has hanging to its under- 
neath surface and into the corium a number of thorn-like 
processes. These extend all round the front of the foot, 
and even in great part behind. Accompanying this elonga- 
