Pigmentation of the greater part of the skin, in the white race, is slight and limited to a uniform pigmentary deposit in the lower rete cells. The deeper colored portions of the skin of the white race such as the scrotum and areolar of the nipple, and the general integument of the colored races, are produced by a wider or deeper pigment staining and deposit in the prickle cells and their nuclei. In the negro pigmentation ascends to the granular layer and a dark coloration of the skin results. There is never any real pigmentation of the corneous layer of the epidermis and only in abnormal conditions is it found in the corium. The source of the pigment in the skin is undetermined, but it is probable that the pigment is derived from the subepidermal structures and in some way is originally obtained from the blood itself.
(Coil-glands; Sudoriparous glands; Glandulae sudoriferae; Glandulae glomiformes)
Coil-glands (T, Fig. 1) may be observed in the fifth month of fetal life and originate from in growing of the rete cells in the form of conic epithelial processes into the corium. In the course of development the central part liquifies forming a tube. These glands are present in great numbers in all parts of the skin except the colored border of the lips, glans penis, inner surface of the prepuce and the clitoris. They are most numerous in the palms and soles, where, according to Krause, they number nearly 3,000 to the square inch. They vary in size according to location being largest in the axillary and anal regions. The average length of a straightened tube is about a quarter of an inch, and it is estimated that the total length of these tubes in the normal adult skin is upward of nine miles.
Sweat-glands originate in the subcutaneous tissue and consist of a simple tube coiled several times upon itself forming an avoid convoluted body with a blind end in the central or outer part of the coil, and an excretory duct. The latter is simply a continuation of the lower tube somewhat altered. It traverses the corium straight upward between the papillae, passes through the rete in a less regular manner and through the corneous layer in a wavy or spiral manner and opens upon the surface in a funnel shaped aperture, the so-called sweat-pore. Unna believes that the true duct ends at the surface of the corium and the remaining portion of the tube outward is a common outlet for exudations from the interstices of the epidermis and for the sweat. The sudoriparous glands are simple in structure. The outer coat is continuous with the basement membrane of the corium; the middle or epithelial coat is continuous with the deeper layers of the stratum mucosum; the inner coat or lining is a delicate cuticle. The sweat-glands are each surrounded by a sheath of connective tissue and fat cells, which support and hold the tubes in position.
(Oil-glands; Hair-follicle glands; Glandulae sebaceae; Glandulae sebiferae)
Sebaceous glands (S, Fig.1) are first noted in the third or fourth months of fetal life, appearing as buddings from the external root-sheath of the hair- follicle. These projections consist of epithelial cells which by multiplication and further downward growth, form the gland. They are richly supplied with blood-vessels, being surrounded by a network of capillaries. They appear first in the skin of the eyebrows and forehead, like the hairs, thence spread over the trunk, finally reaching the extremities. Oil-glands are simple or complex, racemose structures lined with round-cell epithelia. By a process of slow fatty degeneration and rupture of the cells lining each acinus, their secretion called sebum is produced. The ducts leading from these glands are short and end in the hair-follicles, or open directly on the surface. These glands are to be found in the corium of almost any part of the body surface except the palms, soles and dorsum of the third phalanges. According to their distribution they are divided into three groups.