Manual of Human Embryology Volume 1 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1910 Excerpt: ...are small and directed obliquely inwards and downwards, while in the hair cuticle they are large and directed obliquely outwards and upwards; in the fully developed follicle the two sets of scales (imbrications) fit into one another. The sheath cuticle is almost inseparable from Huxley's sheath, and the hair cuticle, similarly, from the hair; and their imbrications apparently determine the equal ascent of the hair and the hair follicle, which their disappearance promptly disturbs (Von Ebner, 1876). The hair itself arises from the large central portion of the matrix plate. It forms at first an acute cone-shaped structure, just as the sheaths do, and is covered by the cornified sheaths as with a cornucopia until it breaks through the torn sheaths in the vicinity of the hair canal. Gradually it becomes broader, and arises from the greater portion of the matrix. On the head (in the eighth to ninth fetal month) each hair arises from twentyfour to thirty of the cells seen in a greatest longitudinal section of the matrix plate (Garcia, 1891), and Stohr's figures of the lanugo hairs show about the same number. The large roundish nuclei above the matrix gradually become elongated and the cells cornify without forming trichohyalin. The cornification begins deep down, the nuclei vanishing at the level of the junction of the lower and middle thirds of the follicle (head hairs, Garcia). Between the matrix cells of the hair branched pigment cells appear, which ascend into the hair and contribute pigment granules to its other cells. According to the most recent views they take their origin from the epithelial rather than from the connective-tissue cells (see p. 253). The diameter of the hair gradually diminishes as it grows away from the papilla, and its smallest diameter...