Meissner's corpuscle, skin, human, H&E ×550. seen) and its supporting cells is evident here, as is the fibrous capsule (FC) that surrounds the ending.
At the even higher magnification of this figure, the close apposition of Meissner’s corpuscle to the undersurface of the epidermis is well demonstrated throughout the entire area of the dermal papilla. The flat spiral path of the neuron (not
PLATE 46KEY D, ducts of sweat glands De, dermis Ep, epidermis FC, fibrous capsule Hy, hypodermis MC, Meissner’s corpuscles. N, nerve bundles PC, Pacinian corpuscles SG, sweat glands arrowhead, nerve fiber in center of Pacinian corpuscle
Hairs are composed of keratinized cells that develop from hair follicles. Hairs are present over almost the entire body, being conspicuously absent only from the sides and palmar surfaces of the hands, from the sides and plantar surfaces of the feet, from the lips, and from the skin around the urogenital orifices. Coloration of the hair is due to the content and type of melanin that it contains. The follicle varies in appear-ance, depending on whether it is in a growing or a resting phase; the growing follicle is the more elaborate. The skin appendages (adnexa), especially hair follicles and sweat glands, are particularly important in healing of skin wounds. They serve as the source of new epithelial cells when there is extensive loss of epidermis, as in deep abrasions and second-degree burns.
Hair follicle, skin, human, H&E ×300; inset ×440.
The growing end of a hair follicle consists of an expanded bulb of epithelial cells that is invaginated by a papilla (HP) of connective tissue. The epithelial cells surrounding the papilla at the very tip of the follicle are not yet specialized; they constitute the matrix, the region of the hair follicle where cell division occurs. As the cells leave the matrix, they form cell layers that will 524 become the shaft of the hair and the inner and outer root sheaths of the hair follicle. The cells that will develop into the shaft of the hair are seen just to the right of the expanded bulb. They constitute the cortex (C), medulla (M), and cuticle (asterisks) of the hair. The cells of the cortex become keratinized. This layer will come to constitute most of the hair shaft as a thick cylinder. The medulla forms the centrally located axis of the hair shaft; it does not always extend through the entire length of the hair and is absent from some hairs. The cuticle consists of overlapping cells that ultimately lose their nuclei and become filled with keratin. The cuticle covers the hair shaft like a layer of overlapping shingles.
The root sheath (RS) has two parts: the outer root sheath, which is continuous with the epidermis of the skin, and the inner root sheath, which extends only as far as the level at which sebaceous glands enter the hair follicle. The inner root sheath is further divided into three layers: Henle’s layer, Huxley’s layer, and the cuticle of the inner root sheath. These layers are seen in the growing hair follicle and are shown at higher magnification in the inset with numbers 1 to 5: 1, cells of the outer root sheath; 2, Henle’s layer; 3, Huxley’s layer; 4, cuticle of the inner root sheath; and 5, future  cuticle of the hair.
Many of the cells of the growing hair follicle contain pigment that contributes to the color of the hair. Most of this pigment is inside the cell (inset); however, in very dark hair some pigment is also extracellular.
The connective tissue surrounding the hair follicle forms a distinct layer referred to as the sheath, or dermal sheath (DS), of the hair follicle.
Nail, skin, human, H&E ×12.