GENERAL OBSEEYATIONS 



55 



tion of the processes is a condensation of the epithehal 

 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- 



FiG. "29. — Section of an Epithelial Ingrowth fk(>3i an Equine 



FCETUS. 



It shows commencing secondary laminar ridges. In the centre are epithelial 

 cells which are undergoing change into horny elements to form the hom- 

 core, or ' horny laminfe ' (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 laminae. The laminse mostly 

 show this branching as if a number of different growing 



