Volume 1
The physiological anatomy and physiology of man / by Robert Bentley Todd and William Bowman.
- Date:
- 1845-1856
Licence: Public Domain Mark
Credit: The physiological anatomy and physiology of man / by Robert Bentley Todd and William Bowman. Source: Wellcome Collection.
Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.
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![NAILS AND HAIRS. CHAP. XIV.] of the finger, and only to become free by a rupture of this con- nexion after birth. Thus the nail covers that portion of cutis which is without cuticle. It has been frequently discussed whether the cuticle is continued over and under the nail; but this is a ques- tion of words only, the nail Wing the same essential structure as the cuticle. The border of the root of the nail is jagged, thin, and soft, and consists of newly formed substance: the deep surface of the body is also soft, and marked by longitudinal grooves, correspond- ing to the papillary ridges on the surface of the matrix. These soft under-parts consist of nucleated particles, similar to those of the deep layers of the epidermis. The more superficial lamina* of the nail are more and more dense and fibrous; but, when treated with acetic acid, some imperfect traces of nuclei may still be detected in them. The nail grows both at the root and on the deep surface of the body ; as the substance furnished by the root advances towards the free edge, it receives accessions from the surface of the matrix. Hairs are found on all parts of the surface, except the palms of the hands and the soles of the feet, and differ much in length, thick- ness, shape, and colour, according to situation, age, sex, family, or race. We may select one of average size for a description of their structure and mode of growth. The shaft of the hair is that part which is fully formed, and which projects beyond the surface. Tracing this into the skin, we find it lodged in a follicular involution of the basement membrane (fig.87,«), which usually passes through the cutis into the subcutaneous areolar tissue. This hair-follicle is bulbous at its deepest part, like the hair which it contains. Its side* have a cuticular lining, continuous with the epidermis, and resembling the cuticle in the rounded form of its deep cells and the scaly cha- racter of the more superficial ones, which are here in contact with the outside of the hair, c. The hair grows from the bottom of the follicle, and the cells of the deepest stratum there resting on the basement membrane are very similar to those which in other parts are transformed into scales of cuticle. A gradual enlargement occurs in these cells as they mount in the soft bulb of the hair, which indeed owes its size to this circumstance. If the hair is to be coloured, the pigment grains are also here developed—for the most part in n at- tered cells, which may send out radiating processes—at other times, in a diffused manner around the nuclei of the cells generally. It frequently happens that the cell* in the axis of the bulb become loaded with pigment at one period, and not at another; so that, as they pass upwards in the shaft, a dark central tract is produced of greater or less length, often only in irregular patches, and the hair](https://iiif.wellcomecollection.org/image/b28043327_0001_0439.jp2/full/800%2C/0/default.jpg)
