(2.) The horn-secreting membrane is formed by the skin, which undergoes special development around the base of the horn and comes to resemble that of the coronary band, from which the hoof or claw is secreted. The band is about one-fifth of an inch in breadth. The papillæ of the dermis are specially developed at this point, and the epithelium which they secrete eventually forms the horn. The internal surface of the growing horn is adherent to the horn core through the medium of another tissue formed by a specially differentiated periosteum which is continuous with the periosteum covering the frontal bone. It is not a true periosteum, but a vascular tissue formed of papillary layers analogous to those of the podophyllous tissue of the ox’s claw or horse’s hoof. This keratogenous membrane receives a rich vascular supply from the arterial circle formed at the base of the horn core by a division of the external carotid, the blood conveyed by which is freely distributed to the enlarged papillæ. The great vascularity of these parts explains why lesions of the horns are often followed by such profuse bleeding. (3.) The horn secreted by the papillæ of the horn band (which is analogous to that of the coronary band of the horse) forms a cone varying in its curve in various breeds. Its base is hollow, and contains little depressions holding the papillæ from which the horn is secreted. From its base up to the end of the horn core the walls progressively increase in thickness. From this point it is solid; in a fully-grown horn the bone does not extend more than one-half or two-thirds of the entire length. In the adult, the development of the horns varies with different breeds and is affected by sex. In the bull the horns are short, but in the cow and ox long. Short and fine in animals of improved breed like the Durham, they are long and thick in breeds of working oxen. Injuries affecting the horns are of three classes, determined by the part affected. 1. Detachment of the horn or sheath. 2. Laceration:— (_a_) Of the horny sheath alone. (_b_) Of the horny sheath and of the horn core. (_c_) Of the horn core alone, the horny sheath remaining intact. 3. Fractures:— (_a_) Of the terminal half of the horn. (_b_) Of the lower half. (_c_) Of the base. DETACHMENT OF THE HORNS. When the yoke is badly fitted or padded, it is liable to cause a continual strain or a succession of shocks producing chronic inflammation of the keratogenous membrane. Should the end of the horn then be struck heavily, it is quite possible that the horn will either partially or wholly be detached. In this case it falls away without there necessarily being any important lesion of the horn core. Such accidents are not infrequently caused by the driver striking the ox on the horn with the yoke in order to keep it quiet while it is being harnessed.