Textbook of normal histology: including an account of the development of the tissues and of the organs . and are so intimatelyunited that the boundaries of the individ-ual elements under ordinary circumstancesare not distinguishable. On the root thecells are broader, less horny, and assumemore and more the character of the ele-ments of the stratum mucosum as the prox-imal end of the hair-bulb is approached;immediately around the papilla the-cells of the cortical substance become con-tinuous with the extension of the stratum mucosum, the outer root-sheath. The medulla, or pith, occupies the cen
Textbook of normal histology: including an account of the development of the tissues and of the organs . and are so intimatelyunited that the boundaries of the individ-ual elements under ordinary circumstancesare not distinguishable. On the root thecells are broader, less horny, and assumemore and more the character of the ele-ments of the stratum mucosum as the prox-imal end of the hair-bulb is approached;immediately around the papilla the-cells of the cortical substance become con-tinuous with the extension of the stratum mucosum, the outer root-sheath. The medulla, or pith, occupies the central tract of the hair-shaft,and extends in favorable examples from near the hair-bulb almost tothe extremity of the hair. Many hairs possess no pith, this partbeing usually wanting in the fine hairs of the general body-surfaceand the colored hairs of the head, as well as in the hairs of chil-dren under four or five years of age. In the thick short and in therobust long hairs, likewise in most white scalp-hairs, the medulla ispresent, and constitutes sometimes one-third of the diameter of the A, human hair; the upper halfof the figure represents the super-ficial homy cells (h) constituting thecuticle, the lower half, the fibrousstructure of the cortical substanceand the medulla; B, isolated ele-ments of the hair; a, cuticularscales ; 5, thin fibre-cells of corticalsubstance. THE SKIN AND ITS APPENDAGES. 269 Fig. 305. The medulla is composed of rows of irregular cuboidal orspherical cells, 15-20 ij. in diameter, filled with dark granules, whichreally are minute air-vesicles ; by reflected light the pith appearssilvery-white, while by transmitted light it is dark and opaque. Theair gains access to the medulla in consequence of the partial dryingout of the soft protoplasm of the cells. In many animals the medulla-cells form a conspicuous and relatively large portion of the hair, andpresent characteristic details sufficiently dis-tinctive to determine the kind of animal from
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Keywords: ., bookauthorpiersolgeorgeageorgea, bookcentury1800, bookdecade1890
