362 
ANATOMY OF THE HORSE. 
culated or serrated. Into this circular groove or canal is received 
the terminating margin of the cutis ; the cuticulo-horny layer of 
the hoof, in front of it, having every appearance of being a con¬ 
tinuation of the cuticle. 
Situation — Dimension. —The coronary substance occupies the 
concavity formed upon the inside of the superior or coronary bor¬ 
der of the wall of the hoof: it is the part constituting the basis 
of the circular prominence commonly distinguished in the living 
animal as the coronet. It is broadest around the toe of the wall, 
diminishing in breadth towards the quarters and heels, and 
be in o' somewhat broader around the outer than the inner side. 
o 
It is thickest in substance around its middle and most promi¬ 
nent parts, growing gradually thinner both above and below. 
Connexion. —Externally, the coronary substance is connected 
with the hoof; and the connexion appears to be principally, if 
not entirely, of a vascular nature: the surface of the wall pre¬ 
senting a porous honeycomb-like texture, and the villi or ves¬ 
sels issuing from the coronary substance entering the pores, and 
thus establishing an intimate and extensive vascular union be¬ 
tween these organic and inorganic parts. Internally, the coro¬ 
nary substance is connected with the coffin-bone, the extensor 
tendon, and the cartilages, by a fine, dense, copious cellular tis¬ 
sue, which at the same time forms a bed for the assemblage and 
ramification of the bloodvessels concerned in the secretion of the 
wall of the hoof. Superiorly, its union with the skin is so in¬ 
timate and complete, that one has been thought to be a conti¬ 
nuation of the other ; and, so far as meets the eye of a common 
observer, they might be taken as such: but, when we come to 
examine them by anatomical tests, we not only find a line of 
external demarcation between them, but discover such difference 
of internal structure as forbids the adoption of this delusive no¬ 
tion. As it descends upon the coffin-bone, the coronary substance 
not only grows thinner, but in growing attenuated becomes im¬ 
perceptibly gathered or puckered into numerous points from 
which issue a like number of plaits or folds, which afterwards 
form the sensitive laminae. It is worthy of remark, that the part 
of the bone upon which this transformation takes place is smaller 
in circumference than the coronet; consequently the same mea¬ 
sure of coronary substance which but tensely and smoothly 
covered the latter, admitted of being disposed in gathers or folds 
so soon as it reached the former. Posteriorly, the coronary sub¬ 
stance forms a junction, and becomes continuous in substance 
with the heels of the sensitive frog. 
Structure. —The coronary substance discloses three different 
parts in its composition :—1. A Jibro-cartilaginous circling band , 
