462 ANATOMY AND PHYSIOLOGY OF THE HORSE^S FOOT. 
it is not possible for additional horny material to be intro- 
duced into the midst of its substance when it has reached a 
certain stage of growth. The number of tubes or fibres is 
as great at the top as the bottom of the wall, except in those 
instances which appear to me quite exceptional, where the 
anterior vascular laminae give off papillae towards the inferior 
portion of their free border ; but these may only secrete the 
projecting ridge of horn we have designated as the “ toe stay.” 
The greater compactness of the lower part of the wall seems 
to me to be due to the longer continued pressure and corne- 
ous transformation its cells have sustained, than have those 
which are recently formed ; and also, in all probability, to 
the contents of the tubes having become more solidified and 
resisting. 
The horny laminae form an integral portion of the wall, 
from which they cannot be separated by any of the artifices 
employed to disunite the sole from the wall or the frog from 
the sole and wall. Neither does the microscope or chemical 
reagents in my hands demonstrate that the horny laminae 
are secreted independently of, or have any other origin than 
from the same source as, the wall of the hoof. As shown in 
the drawings (Plate II, fig. 1), they are projected from the 
horny tissue on the inner face of the wall towards the vas- 
cular laminae, between which they form the most inti- 
mate reciprocal connection possible. Indeed, I have already 
observed, when describing the general features of the cuti- 
geral cavity, that the origin of these laminae in the wall can 
be traced by narrow lines across nearly the whole of its thick- 
ness towards the heels, but in front for a less distance, cor- 
responding, in fact, to the imprint of the coronary zone. 
And a fine transverse section of the wall, with one or more 
horny laminae, will show that both are one. If the horn be 
dark coloured, we can see the pigment-granules passing in an 
uninterrupted manner from the wall into the laminae to their 
extremity, and the polariscope testifies that they and the 
wall are indivisible. The only difference between the struc- 
ture of the wall and the laminae is the absence of tubular 
fibres. Caustic potash, by expanding and loosening the cells, 
demonstrates, in the clearest manner, that these horny leaves 
are formed by the interfibrous horizontal cells, which pass 
from between the fibres, and which appear to be arranged 
for this purpose. Before leaving the wall these cells present 
the appearance already indicated, being horizontally disposed 
and loosely aggregated one upon another; on entering be- 
tween the lamina they commence to look compressed laterally, 
and are more densely packed together, though they always 
