ANATOMY AND PHYSIOLOGY OF THE HORSE^S FOOT. 157 
front, and, with the frog, forming a complete circle that in- 
cludes the upper and posterior parts of the hoof. 
Generally, the superficial extent or width of this band is 
extremely variable, from the many causes that are in opera- 
tion tending to modify or partially destroy it in horses that 
are submitted to the usual routine of stable management 
and shoeing. It is best observed in horses whose feet are 
maintained in a natural condition. 
In describing the tegumentary appendages of the foot, 
mention was made of the ‘ perioplic ring,’ a slightly convex 
space situated between the termination of the hair and the 
coronary cushion, from which it is separated by the upper 
coronary fissure. This particular horny band arises from the 
space that constitutes the ring, and proceeding downwards 
from it in gradually diminishing width and thickness, sur- 
mounts and covers the upper external border of the wall. 
Looking at it as it passes from the hair down the hoof, it 
appears as a fine semi-transparent substance like a pellicle of 
varnish, minutely striated in the direction of the wall-fibres, 
and sometimes marked by a series of faint transverse undu- 
lations or circles, particularly towards the heels ; or some- 
times, when the hoofs are very dry, it becomes more or less 
scaly, cracks, and shows vertical or transverse fissures. Its 
inner face, on reaching the outer face of the wall, adheres 
so closely to it that it is impossible to disunite them except 
by some months 5 steeping in water. It does not adhere very 
closely, however, to the extremely thin margin of the wall 
that is lodged in the coronary fissure, and, after extending 
beyond the part of the wall whose inner face is excavated 
for the lodgment of the coronary cushion, its union with it 
becomes less intimate, and it may even exhibit traces of ex- 
foliation. Very often, however, it blends imperceptibly with 
the wall towards its lower margin, giving it a smooth shining 
appearance. At the inflections of the wall, it maintains this 
close adherence, and at this point leaves the denser portion 
of the hoof, and becomes one in substance with the branches 
of the frog. 
The periople varies in thickness in different parts of its 
extent, being thickest at the heels or glomes, thinnest at the 
quarters, and intermediate between these extremes in front. 
In this respect it resembles the wall, whose thickness depends 
upon the width of the surface from which it is secreted. 
Where the wall of the hoof is most attenuated, i. e. at its 
upper border, where it is in proximity to the skin, the periople 
is thickest. Its thickness, as a whole, may be said to 
depend upon the amount of moisture it contains ; as when 
XLIV. 12 
