THE HAIRS AND HAIR FOLLICLES. 359 



The nails, like all epidermoid tissues, are constantly being repro- 

 duced, growing in length by continual additions of new cells to their 

 posterior margins, and in thickness by like additions to their under 

 surface. When a nail is torn out, or thrown off, in consequence of 

 disease, a new and perfect nail is formed, provided the matrix is un- 

 injured. 



Fig. 68. a, transverse section of the nail, and its matrix. 6, longitudinal section of the same : both fig- 

 ures are diagrammatic. 1, the outer cuticular layer. 2, the rete Malpighianum, or mucous layer, of the 

 cuticle. 3. the cutis. 4, the nail substance. 5, the ridges of the cutis, of which the matrix or bed of the 

 nail consists. (Kolliker.) 



The hairs, like the nails, are non-vascular and insensible outgrowths 

 of the cuticle, springing from a minute sunken point of the surface of 

 the true skin, which has there no other cuticular covering. They are 

 found on all parts of the body, excepting the palms of the hands, the 

 soles of the feet, the backs of the last phalanges of the fingers and 

 toes, and the surface of the upper eyelids ; they present great varie- 

 ties in length, thickness, and color, in the male and female, at different 

 ages, and in the various races of mankind. With the exception of the 

 eyelashes, which are set perpendicularly to the surface, they are usu- 

 ally inserted obliquely into the skin. The soft swollen end of the 

 hair, which is embedded in the skin, is called its root or bulb, Fig. 69, 

 a, 5 ; the part which projects above the surface, is called the stem or 

 shaft, and the terminal extremity, the point. The shaft is usually 

 cylindrical in shape, but is often somewhat flattened, or even grooved. 

 It consists of an outer part, called the cortex, Fig. 69, a, b, c, com- 

 posed of a single layer of adherent and imbricated scales, the edges of 

 which, directed towards the point, form fine wavy transverse lines ; 

 beneath the cortex, is the so-called fibrous part of the hair, which con- 

 stitutes its bulk, and consists of fusiform cells clustered into flattened 

 fibres, which run longitudinally, and are intermixed with pigment 

 granules ; lastly, the very deepest cells, occupying the centre of the 

 shaft, and constituting the pith or medulla, are not elongated into 

 fibres, but are somewhat polyhedral, and loosely connected together, 

 containing chiefly pigment or fat granules. The pith is only found 

 in certain hairs, and does not extend so far as the point. 



The minute depression from which a hair emerges, is called the hair 

 follicle, or hair sac, a, b, 6. This, which varies from one to three lines 

 in length, is buried in the true skin, or, as in the case of the larger 

 hairs, reaches even into the subcutaneous fat : it receives, in nearly 

 all cases, the ducts of two sebaceous glands, a, 4. The sides of the 

 hair follicles are firm, and consist of two layers, an outer soft, fibrous, 

 and vascular, and an inner non-vascular homogeneous layer, both 



