epidermal ridge

(anatomy) Any of the minute corrugations of the skin on the palmar and plantar surfaces of humans and other primates.

Minute corrugations of the skin. They compose a sculpturing, termed dermatoglyphics, which characterizes the palmar and plantar surfaces of all primates. These areas lack hair and sebaceous (oil) glands, but sweat glands are numerous. In certain kinds of monkeys, a portion of the under-surface of the tail bears similarly specialized skin.

The ridges over the human hand as a whole, in young adult males, average 0.48 mm in breadth. They are slightly narrower in females, 0.43 mm. Ridges serve two functions: (1) They increase security of contact with objects, in the manner of the milling of a tool handle. Ducts of sweat glands open on the summits of ridges, and moistening of the skin augments the security of contact. (2) They enhance the sense of touch. In passing the fingers or palm over an object for judging its texture, the slight displacement of ridges heightens stimulation of the underlying nerve endings.

The characteristics of individual ridges and their collective configurations are not ordinarily studied by direct inspection of the skin. Instead, they are examined in prints, usually impressions of the inked surface, made for the purpose of record, or natural imprints made by chance contact. See also Fingerprint.

Any of the ridges of the epidermis of the palms and soles, where the sweat pores open. Also called skin ridge.