. Chordate anatomy. Chordata; Anatomy, Comparative. THE INTEGUMENTARY SYSTEM I 2- parts of the body. But finally growth ceases, the hair dies, and is shed. If the hair papilla retains its stratum germinativum, a new hair grows. Each hair column, in addition to producing a hair, may form as lateral outgrowths one or more sweat or sebaceous glands. Muscle cells devel- oped from the mesenchyma of the corium attach themselves to the hair- roots and become arrectores pilorum. The human foetus before birth has a hairy covering, the ''lanugo," which is shed shortly before or soon after birth. Th
. Chordate anatomy. Chordata; Anatomy, Comparative. THE INTEGUMENTARY SYSTEM I 2- parts of the body. But finally growth ceases, the hair dies, and is shed. If the hair papilla retains its stratum germinativum, a new hair grows. Each hair column, in addition to producing a hair, may form as lateral outgrowths one or more sweat or sebaceous glands. Muscle cells devel- oped from the mesenchyma of the corium attach themselves to the hair- roots and become arrectores pilorum. The human foetus before birth has a hairy covering, the ''lanugo," which is shed shortly before or soon after birth. The coat persists,. SEBACEOUS GLAND EPITHELIAL BED ROOT OF HAIR Fig. ii6.—A vertical section of skin of a five month human embryo, showing four early stages in the development of a hair. The growth of a hair is initiated by the forma- tion of an epidermal papilla projecting (down) into the underlying corium. (Redrawn from Bremer after Stohr.) however, in certain types of "hairy ; The evolution theory affords the only rational explanation of the lanugo. PIGMENT Skin color in man is due in part to the blood in the capillaries of the corium. In addition, there are two pigments in the skin and hair, a brown, sometimes darkened to a black, both in granules; and a yellow, that may strengthen to a red, both diffused in the tissues. All are prod- ucts of cell metaboUsm.^ The pigments of the hair are confined to the cortex. The epidermis and the outer parts of the corium are both pigmented. Not until shortly after birth do pigment granules appear in the stratum germinativum, so that even Negroes are born white. Moles and freckles involve excessive local pigmentation. Freckles are small local patches of excess pigmentation, which are more likely to occur in light-skinned individuals who have been exposed to strong sun- light. A mole or nevus is an elevation of the skin due to local prolifera-. Please note that these images are extracted from scanned page images that may hav
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Keywords: ., bookcentury1900, bookpublisherphi, booksubjectanatomycomparative
