394 ANATOMY AND PHYSIOLOGY OF THE HORSE*S FOOT. 
end of the villus we not unfrequently observe them to he 
loosely and irregularly disposed, wide spaces often occurring 
between their clusters, but as the fibre passes downwards, 
they become more densely aggregated, and towards the lower 
or ground extremity of the tube are moderately compressed, 
probably owing to the concussion arising from the foot 
striking the ground. They generally exhibit a nucleus, and 
as a rule minute white granules are mixed among them. 
Their white colour, visible to the unaided eye, is due, I 
think, to the presence of air among them in a minute state of 
division, as a very weak solution of any alkaline substance is 
sufficient to expel it, and then the chalky -looking appearance 
vanishes. 
The peculiar loose arrangement of the medullary cells and 
their form, accounts, I am led to imagine, for the notable 
hygroscopic properties of the horn composing the hoof ; 
moisture readily passing up among them from the lower ends 
of the fibres, even to the villous prolongations they contain at 
their upper extremities. No membrane, so far as I have 
been able to ascertain, lines this canal. In withdrawing the 
villi from their canals in the horn, it is frequently observed 
that they carry a number of epidermic cells with them, and 
that these are laid flat, one upon another, on the sides of the 
villi — a circumstance which not only goes to prove the vertical 
arrangement of the cells in the horn fibres, but also the 
absence of any intra-tubular membrane, which was supposed 
to line and support these canals. 
Professor Chauveau* was of opinion that the cavity of the 
fibre was occupied by an amorphous matter of a different 
character to anything else in the hoof; that this material — 
which he considered as the third histologic element entering 
into the composition of the foot cover — was also dispersed in 
the concentric lamellae of the fibres, and even in the inter- 
tubular substance, and that it played an important part in 
endowing the horn with its cohesive properties. This is pal- 
pably an error. 
It may be remarked that in the hoof of the ox and sheep, 
the fibres of the wall are thin and wide apart, though the 
arrangement of the cells is the same. 
The colour of the horn of the wall, sole, and frog, when 
other than white, is due to the presence of pigment granules , 
minute specks of irregular shape, closely and thickly dis- 
seminated among the epidermic cells in proportion to the 
depth and extent of the tint. 
I have very rarely been able to trace the presence of pig- 
* ‘Journal de Med. Veterinaire,’ Lyons, 1853. 
