File:The animals and man; an elementary textbook of zoology and human physiology (1911) (14804757353).jpg

Identifier: animansmanelemen00kell (find matches)
Title: The animans and man; an elementary textbook of zoology and human physiology
Year: 1911 (1910s)
Authors: Kellogg, Vernon L. (Vernon Lyman), 1867-1937 McCracken, Mary Isabel
Subjects: Zoology Physiology
Publisher: New York, H. Holt and company
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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covering, 2. It regulates the temperature of the body. 3. It receives the stimuli from without, by means ofwhich the body is guided in its behavior. 4. It serves as an excretory organ. Structure of the skin.- -The skin consists of two layers(fig. 178), the epidermis (a), an outer or superficial layer,and the dermis (d), a deep layer or true skin. The epidermis is composed of epithelial cells. Theouter layer consists of flattened or dead cells that are con-stantly peeling off. This is sometimes called the cuticle.The inner cells of the epidermis are live growing cells,constantly dividing and forming new cells to take the placeof those lost from the surface. The inner cells of the epi-dermis contain pigment granules which give the skin its RESPIRATION AND EXCRETION 353 color. On the palms of the hands and soles of the feetthe cuticle becomes quite horny in structure. The dermis or true skin is largely composed of connectivetissue with a mass of blood-vessels, nerves, sweat glands and a,
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FIG. 178. Section perpendicularly through skin, a, epidermis; &, pig-mentary layer of epidermis; c, papillary layer of dermis; d, dermis ortrue skin; e, fatty tissue; /, g, h, sweat glands and duct; /, k, hairwith its follicle and papilla; /, sebaceous gland. (After Brubaker.) hair follicles. This part of the skin is very sensitive owingto the numerous tactile corpuscles which are the end-organsof the nerves (fig. 183). Nails.--The nails are modified epidermal cells. Thegrowing part of the nail is embedded beneath the skin atthe base of the nail. The nail protects the ends of thefingers and renders them more useful. 354 THE ANIMALS AND MAN Hair.—Hair is similar to the nails in formation, that isit is epidermal in origin. A section of a hair shows it to bea long hollow shaft embedded at its base in a socket ofdermis called a hair follicle (fig. 178, k). The socket is linedwith an epithelial layer. The growing part of the hair isthe papilla at its base. This is supplied with blood

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