82 GENERAL ANATOMY. 



the dorsal surface of the terminal phalanges of the fingers and toes. Each nail 

 is convex on its outer surface, concave within, and is implanted by a portion 

 called the root into a groove of the skin; the exposed portion is called the body, 

 and the anterior extremity the free edge. The nail has a very firm adhesion to 

 the cutis, being accurately moulded upon its surface, as the epidermis is in other 

 parts. The part of the cutis beneath the body and root of the nail is called 

 the matrix, because it is the part from which the nail is produced. Correspond- 

 ing to the body of the nail, the matrix is thick, and covered with large, highly 

 vascular papillae, arranged in longitudinal rows, the color of which is seen 

 through the transparent tissue. Behind this, near the root of the nail, the 

 papillae are small, less vascular, and have no regular arrangement; hence, the 

 portion of the nail corresponding to this part is of a whiter color, and called 

 lunula, from its form. 



The cuticle, as it passes forwards on the dorsal surface of the finger, is at- 

 tached to the surface of the nail, a little in advance of its root. At the ex- 

 tremity of the finger it is connected with the under surface of the nail, a little 

 behind its free edge. The cuticle and horny structure of the nail (both epi- 

 dermic structures), are thus directly continuous with each other. The nails, in 

 structure, consist of cells having a laminated arrangement, and these are essen- 

 tially similar to those composing the epidermis. The deepest layer of cells 

 which lie in contact with the papillae at the root and under surface of the nail, 

 are of elongated form, arranged perpendicularly to the surface, and provided 

 with nuclei; those which succeed these are of a rounded or polygonal form, the 

 more superficial ones becoming broad, thin, and flattened, and so closely com- 

 pacted together as to make the limits of each cell very indistinct. 



It is by the successive growth of new cells at the root and under surface of 

 the body of the nail, that it advances forwards, and maintains a due thickness, 

 whilst, at the same time, the growth of the nail in the proper direction is 

 secured. As these cells in their turn become displaced by the growth of new 

 cells, they assume a flattened form, lose their nuclei, and finally become closely 

 compacted together into a firm, dense, horny texture. In chemical composition, 

 the nails resemble the epidermis. According to Mulder, they contain a some- 

 what larger proportion of carbon and sulphur. 



The Hairs are peculiar modifications of the epidermis, and consist essentially 

 of the same structure as that membrane. They are found on nearly every part 

 of the surface of the. body, excepting the palms of the hands and soles of the 

 feet, and vary much in length, thickness, and color, in different parts of the 

 body, and in different races of mankind. In some parts they are so short as 

 not to project beyond the follicles containing them; in other parts, as upon the 

 scalp, they are of considerable length; along the margin of the eyelids and 

 upon the face, they are remarkable for their thickness. A hair consists of a 

 root, the part implanted in the skin; the shaft, the portion projecting from its 

 surface, and the point. They generally present a cylindrical or more or less 

 flattened form, and a reniform outline upon a transverse section (Fig. 42). 



The root of the hair presents at its extremity a bulbous enlargement, which is 

 whiter in color, and softer in texture than the stem, and is lodged in a follicular 

 involution of the epidermis, called the hair-follicle. When the hair is of con- 

 siderable length, the follicle extends into the subcutaneous cellular tissue. The 

 hair-follicle is bulbous at its deep extremity, like the hair which it contains, 

 and has opening into it, near its free extremity, the orifices of the ducts of one 

 or more sebaceous glands. In structure, the hair-follicle consists of two coats 

 an outer or dermic, and an inner or cuticular. The outer coat is formed 

 mainly of areolar tissue; it is continuous with the corium, is highly vascular, 

 and supplied by numerous minute nervous filaments. The inner or cuticular 

 lining is continuous with the epidermis, and, at the bottom of the hair-follicle, 

 with the root of the hair; this cuticular lining resembles the epidermis in the 

 peculiar rounded form and soft character of those cells which lie in contact 



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