sitive sole. _a_, papillae, with
horn-cells surrounding them; _b_, interpapillary or intertubular horn;
_c_, hollow spaces in the intertubular material filled with blood; _d_, a
papilla and its surrounding horn-cells filled with blood.]

Ordinarily, this ecchymosis of the horny sole is due to injury of the
sensitive sole _immediately beneath_ it. It may, however, proceed from
injury to the vessels of the laminae either of the bars or of the wall. In
this case the ecchymosis of the horny sole may be explained by the fact
that the escaped blood tends to _gravitate_ to that position.

When the corn is of long standing, or is due to _repeated_ injuries on the
same spot, the horn adjacent to the lesion becomes hard and dry, and often
abnormally brittle, simply on account of the inflammatory changes thus kept
in continuation. This is often seen when attempts are made to _pare out_
the corn with the knife.

Should the injury be seated in the sensitive laminae, then the brittle
nature of the horn secreted by the injured tissues makes itself apparent by
the appearance of cracks in the wall of the quarter. Why this should occur
will be readily understood by a reference to Fig. 100.

[Illustration: FIG. 100.--INNER SURFACE OF THE WALL OF THE QUARTER, SHOWING
CHANGES IN THE HORNY LAMINAE BROUGHT ABOUT BY CHRONIC CORN.]

It will here be seen that the injury to the keratogenous membrane has led
to great interference with the secretion of horn from the sensitive laminae.
As a result, the regularly leaf-like arrangement of the horny laminae has
been largely broken up. Certain of the laminae are altogether wanting,
while others are broken in their length and rendered incomplete. With this
condition there is always more or less contraction of the quarter.

Microscopic examination of the structures involved in such a case reveals
the fact that with the contraction is an alteration in the normal direction
of the horny and sensitive laminae.

They become bent backward, and, instead of the regular and normal
arrangement depicted in Fig. 32, show the distorted appearance given in
Fig. 101.

From the appearances and characters of the blood-stain in the horny sole
we are able to deduce evidence relative to the duration and nature of the
injury.

[ILLUSTRATION: FIG. 101.--PERPENDICULAR SECTION OF THE WALL OF A CONTRACTED
QUARTER IN A CASE OF CHRONIC CORN. Both the sensitive and horny laminae
are bent backwards, and haemorrhages have tak