GENERAL OBSERVATIONS 55 
tion of the processes is a condensation of the epithelial 
cells immediately above the rete Malpighii, with a partial 
or total loss of their nuclei. This is the first appearance 
of true horn, and its commencement is almost coincident 
with the first stages of ossification of the os pedis. 
With the appearance of horn comes difficulty of sectioning. 
The last specimen that Professor Mettam was able to satis- 
Bite 
9” ™ 
a 
i a 
Fig. 29.—Sgction oF AN EpirHeLiaL INGROWTH FROM AN EQUINE 
Fervus. 
It shows commencing secondary laminar ridges. In the centre are epithelial 
cells which are undergoing change into horny elements to form the horn- 
core, or ‘ horny lamine’ (Mettam). 
factorily cut upon the microtome was from a foetus between 
three and four months old. In this the secondary laminar 
ridges were clearly indicated, and the active layer of the 
rete Malpighii could be traced without a break from one 
ingrowing epithelial process to the next, and around this, 
following all the irregularities of its outline, and covering 
the branches of the nascent lamine. The lamine mostly 
show this branching as if a number of different growing 
