[Illustration: FIG. 99.--HORIZONTAL SECTION OF A CORN. The section cut at about the base of the papillæ of the sensitive sole. _a_, papillæ, 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 laminæ 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 laminæ, 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 LAMINÆ 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 laminæ. As a result, the regularly leaf-like arrangement of the horny laminæ has been largely broken up. Certain of the laminæ 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 laminæ. 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 laminæ are bent backwards, and hæmorrhages have taken place at the base of the sensitive laminæ.] When, for instance, the stain is not to be found in the superficial layers of the sole, but is only discoverable by deep paring, then the injury is a recent one.