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 laminæ. 1. THE CORONARY CUSHION. In the foot stripped of the hoof the coronary cushion is seen as a rounded structure overhanging the sensitive laminæ 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 laminæ. 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 papillæ, 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 laminæ. [Illustration: FIG. 17.--THE KERATOGENOUS MEMBRANE (VIEWED FROM THE SIDE). (THE HOOF REMOVED BY MACERATION.) 1. The sensitive laminæ, 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 sensitive sole.] The upper portions of the laminæ, those in contact with the cushion, are pale in contrast with the portions immediately below, and thus there is given the appearance of a white zone adjoining the inferior border of the cushion. Widest at its centre, the cushion narrows towards its extremities, which, arriving at the bulbs of the plantar cushion, bend downwards into the lateral lacunæ of the pyramidal body, where they merge into the velvety tissue of the sole and frog. The papillæ of the coronary cushion secrete the horn tubules forming the wall, and the papillæ of the perioplic ring secrete the varnish-like veneer of thin horn covering the outside surface of the hoof.