Microscopic Anatomy of the Skin of the Horse

SUMMARY Thirteen normal horses 2 to 17 years old were killed, and skin specimens from 49 areas were immediately collected. The skin surface contained grooves and ridges. The hairs erupted in the grooves. The average thickness of the general body skin was 3.8 mm.; of the skin near the body openings, 3.3 mm.; and of the skin from which the permanent hairs (mane and tail) originated, 6.2 mm. The epidermis consisted of 4 layers: stratum basale, stratum spinosum, stratum granulosum, and stratum comeum. The stratum lucidum was absent. Keratohyalin granules and dendritic melanocytes were in the stratum spinosum and stratum granulosum. Basal processes of the cells of the stratum basale anchored the epidermis to the underlying tissue. The dermis consisted of two well-demarcated layers: the superficial or papillary layer containing fine, loosely arranged collagenous fibers and the deep or reticular layer with organized compact collagenous fiber bundles. An extensive network of elastic and reticular fibers was seen throughout the dermis, but was more prominent in the superficial layer. The dermis of the lumbar, sacral, and gluteal regions was modified by the presence of a third layer of collagenous fibers interwoven with fine elastic and reticular fibers. Hairs occurred singly, and the large rectangular cells of the medulla were characteristic. The larger hair follicles contained follicular folds below the openings of the sebaceous glands. The density of the coat and the size of the individual hairs varied. In thin skin, the angle of the hair was more acute. Usually two sebaceous glands were associated with each hair follicle. Generally the skin near the body openings contained large, branched sebaceous glands. Sweat glands were the apocrine type.