Root sheaths

The concentric sheaths surrounding the hair shaft are more clearly distin- guished in the area between the bulb and the skin surface. a. Internal root sheath. The layer closest to the hair shaft, it extends only from the bulb to the level of the sebaceous gland ducts. At this point the soft keratin-filled cells are shed into the follicular canal. There are 3 component layers: the cuticle of the internal root sheath is a layer of flat cells separated from the hair shaft cuticle only by the follicular canal; the middle layer is Huxley's layer, comprising one to 3 layers of low cuboidal cells; the outermost layer is Henle's layer, a translucent layer of flattened to cuboidal cells resembling the epidermal stratum lucidum. b. External root sheath. This surrounds the internal root sheath and is continuous with the epidermis. Above the level of the sebaceous glands, it includes all the epidermal layers. Below this level, it retains only the granulosum, spinosum, and basale. The granulosum is also lost near the follicle's base, where the spinosum and basale become continuous with the layers of the germinal matrix. c. Glassy membrane. This is the thickened basal lamina underlying the stratum basale of the external root sheath and separating it from the surrounding connective tissue sheath. d. Connective tissue sheath. A layer of condensed connective tissue, this surrounds the entire follicle, including the bulb. It extends along the follicle to the surface, where it blends into the looser papillary dermis