the lateral cartilages, the bulbs of the
plantar cushion, the pyramidal body, the anterior portion of the plantar
surface of the os pedis, and over the anterior face of the same bone. In
turn, as the human foot with its sock is covered by the boot, this is
encased by the hoof, the formation of which we shall study later.

To expose the membrane for study the hoof must be removed. This may be done
in two ways. By roasting in a fire, and afterwards dragging off the horny
structures with a pair of pincers, a knife having first been passed round
the superior edge of the horny box. Or by maceration in water for several
days, when the hoof will become loosened by the process of decomposition,
and may be easily removed by the hands. The latter method is less likely
to injure the sensitive structures, and will expose them with a fresh
appearance for observation.

For purposes of description the keratogenous membrane is divided into three
regions:

1. The Coronary Cushion.
2. The Velvety Tissue.
3. The Podophyllous Tissue, or the Sensitive laminae.

1. THE CORONARY CUSHION. In the foot stripped of the hoof the coronary
cushion is seen as a rounded structure overhanging the sensitive laminae
after the manner of a cornice. It extends from the inner to the outer bulbs
of the plantar cushion, and is bounded above by the perioplic ring, and
below by the laminae.

When _in situ_ it is accommodated by the _Cutigeral Groove_, a cavity
produced by the bevelling out of the superior portion of the inner face of
the wall of the hoof. Its superior surface is covered by numerous elongated
papillae, set so closely as to give the appearance of the 'pile' of velvet.
This is observed to the best advantage with the foot immersed in water.

_The Superior Border_ of the cushion is bounded by the _Perioplic Ring_,
the cells of which have as their function the secreting of the _Periople_,
a layer of thin horn to be noted afterwards as covering the external face
of the wall. From the perioplic ring the cushion is separated by a narrow
and shallow, though well-marked, groove.

The inferior border is bounded by the sensitive laminae.

[Illustration: FIG. 17.--THE KERATOGENOUS MEMBRANE (VIEWED FROM THE SIDE).
(THE HOOF REMOVED BY MACERATION.) 1. The sensitive laminae, or podophyllous
tissue; 2, the coronary cushion; 3, the perioplic ring; 4, portion of
plantar cushion; 5, groove separating perioplic ring from coronary cushion;
6. the sensit