892 THE SENSE ORGANS AND SKIN OF THE HORSE 
is the densest part of the hoof. Its horn tubes run in a straight direction from the 
coronary to the basal border. In dark hoofs it is pigmented except in its deep part. 
The laminar layer (Stratum lamellatum) is internal; it consists of the horny 
lamine (Lamelle cornee), and is non-pigmented. The primary lamin are narrow 
and thin at their origin at the lower margin of the coronary groove, but become wider 
and thicker distally. At the junction of the wall and sole they are united by inter- 
laminar horn to form the white line. Only the central part of the lamine becomes 
fully keratinized. They are composed of non-tubular horn in the normal state. 
The sole consists of tubular and intertubular horn. The tubes run parallel 
with those of the wall and vary much in size. 
The frog is composed of relatively soft horn, which is much more elastic than 
that of the wall or sole, and is not fully keratimized. The horn tubes in it are slightly 
flexuous. 
The hoof is non-vascular and receives its nutrition from the corium. It is 
also destitute of nerves. 
THE CORIUM OF THE HOOF 
The corium of the hoof or pododerm (Corium ungule) is the specially modified 
and highly vascular part of the corium of the common integument which furnishes 
nutrition to the hoof. It is convenient to divide it into five parts which nourish 
corresponding parts of the hoof.! 
1. The perioplic corium or ring (Corium limitans) is a band 5 to 6 mm. in 
width which lies in a groove between the periople and the coronary border of 
the wall. It is continuous above with the cortum of the skin, and is marked off by 
a groove from the coronary corium. At the heels it widens and blends with the 
corium of the frog. It bears very fine, short papillee which curve downward and 
are received in depressions of the periople, to which it supplies nutrition. 
2. The coronary corium (Corium coronarium) is the thick part of the coritum 
which occupies the coronary groove, and furnishes nutrition to the bulk of the wall. 
It diminishes in width and thickness posteriorly, and along the upper border of the 
bar it is not clearly defined from the corium of the frog. The convex superficial 
surface is thickly covered with filiform papille 4 to 6 mm. in length, which are re- 
ceived into the funnel-like openings of the coronary groove. At the heels and along 
the bars the papillae are arranged in rows, separated by fine furrows. The deep 
surface is attached to the extensor tendon and the cartilages of the third phalanx 
by an abundant subcutis which contains many elastic fibers and a rich venous 
plexus. 
3. The laminar corium (Corium lamellatum) bears primary and secondary 
laminze which are interleaved with the horny laminze of the wall and bars in the 
natural state.2 It is attached to the dorsal surface of the third phalanx by a modi- 
fied periosteum (Stratum periosteale) which contains a close-meshed network of 
vessels, and to the lower part of the cartilages by a subcutis which contains a rich 
venous plexus. The lamin are small at their origin above, become wider below, 
and end in several papillze 4 to 5mm. in length. They supply nutrition to the horny 
lamin and to the interlaminar horn of the white line. 
4. The corium of the sole (Corium soleare)—also termed the sensitive sole— 
corresponds to the horny sole, to which it supplies nutrition. It is often more or 
less pigmented and bears long papillse, which are specially large along the convex 
1TIn some veterinary works the statement is made that the various parts of the corium “‘se- 
crete” corresponding parts of the hoof. The statement is, of course, ludicrous, as the relationship 
here, both anatomically and physiologically, is the same as in the case of the corium and epidermis 
of the skin. Hence the terms ‘‘keratogenous membrane” and ‘‘matrix’’ should be dropped. 
2 The laminze of the corium are commonly termed “sensitive” lamin to distinguish them 
from the “horny”’ lamin, which are, of course, insensitive. 
