1140 GENERAL ANATOMY OB HISTOLOGY. 



body, and the anterior extremity tliefree edge. The nail has a very firm adhesidn 

 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. Corresponding to 

 the body of the nail, the matrix is thick, and raised into a series of longitudinal 



Nail groove. 



FIG. 681. Transverse section through human nail and its sulcus. (From Bohm and Davidoff 'B His- 

 tology.) 



ridges, which are very vascular, and the color 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, and here the tissue of the nail is somewhat more opaque ; 

 hence this portion is of a whiter color, and is called the lunula on account of its shape. 



The cuticle, as it passes forward on the dorsal surface of the finger or toe, is 

 attached to the surface of the nail, a little in advance of its root ; at the extremity 

 of the finger it is connected with the under surface of the nail a little behind its free 

 edge. The cuticle and horny substance of the nail (both epidermic structures) are 

 thus directly continuous with each other. The nails consist of a greatly thick- 

 ened stratum lucidum, the stratum corneum forming merely the thin cuticular 

 fold (eponychimii) which overlaps the lunula. The cells have a laminated arrange- 

 ment, and are essentially similar to those composing the epidermis. The deepest 

 layer of cells, which lie in contact with the papillae of the matrix, are columnar in 

 form and arranged perpendicularly to the surface ; those which succeed them are 

 of a rounded or polygonal form, the more superficial ones becoming broad, thin, 

 and flattened, and so closely compacted 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 forward and maintains a due thickness, 

 while, 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 ones, they 

 assume a flattened form, and finally become closely compacted together into a firm, 

 dense, horny texture. In chemical composition the nails resemble the upper layers 

 of the epidermis. According to Mulder, they contain a somewhat 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, soles of the feet, and 

 the glans penis. They vary much in length, thickness, and color in different 

 parts of the body and in different races of mankind. In some parts, as in the 

 skin of the eyelids, they are so short as not to project beyond the follicles con- 

 taining them ; in others, as upon the scalp, they are of considerable length : again, 

 in other parts, as the eyelashes, the hairs of the pubic region, and the whiskers and 

 beard, they are remarkable for their thickness. Straight hairs are stronger than 

 curly hairs, and present on transverse section a cylindrical or oval outline ; curly 

 hairs, on the other hand, are flattened. 



A hair consists of a root, the part implanted in the skin ; the shaft or stem, the 

 portion projecting from its surface ; and the point. 



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

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

 involution of the epidermis called the hair-follicle (Fig. 679). When the hair is 



