avity is bounded by the front of the os
pedis, and is lined by a thin growth of horn secreted by the keratogenous
membrane covering the bone. Superiorly the cavity is quite narrow,
and extends to near the lower surface of the coronary cushion, while
inferiorly, at its open portion, it is often 1/2 inch to 1 inch wide.
Laterally it extends on each side of the toe to the commencement of the
quarters.

[Illustration: FIG. 124.--LONGITUDINAL SECTION OF A FOOT WITH LAMINITIS OF
THREE WEEKS' STANDING. On the anterior face of the cavity, in front of
the os pedis, are thickened horny laminae. Due to the sinking of the bony
column, the os pedis has perforated the horny sole.]

Exploration with a director, or with the blade of a scalpel, removes from
the opening a dry detritus. This is composed of the solid constituents
of the escaped blood, the dried remains of the inflammatory exudate, and
broken-down fragments of cheesy-looking horn. The size to which the cavity
may sometimes extend is illustrated in Fig. 124. The thickened horny laminae
forming the anterior boundary of the cavity are here depicted, together
with commencing perforation of the horny sole by the os pedis. It is this
cavity which, when opened at the bottom and discharging its mealy-looking
contents, is known as seedy-toe, for a further description of which see p.
293.

The lameness occurring with chronic laminitis does not always persist. As
time goes on the sensitive structures accommodate themselves to the altered
form and conditions of the horny box. In certain situations--namely, where
pressure is greatest--the softer structures become atrophied, and sometimes
even wholly destroyed; while in other positions the changes in form of the
hoof tend to increase in size of its interior, with a consequent diminution
of pressure upon, and increased growth of the structures within it.

_Pathological Anatomy_.--In detailing the changes to be observed in chronic
laminitis, we take up the description where we left it when dealing with
the pathological anatomy of the acute form. The alterations to be met
with are best observed by taking a foot so diseased and making of it two
sections--one longitudinal, from before backwards; the other horizontal,
and in such a position as to cut the os pedis through at its centre.

These sections will expose to view the cavity formed by the pouring out of
the exudate, and its full extent may be noticed by examining the sections
altern