316 



HISTOLOGY. 



is stated on page 46. It is probable that the epidermal pigment arises 

 in the cells in which it occurs. The origin of the granules found between 

 the epithelial cells is obscure. 



NAILS. 



The nails are areas of modified skin consisting of corium and epi- 

 thelium. The corium consists of fibrous and elastic tissue, the bundles 



Nail. 



Corium. 



Stratum 

 germinativum. 



Nail wall. 



Xail groove. 



Bone of third 

 phalanx. 



FIG. 363. -DORSAL HALF OP A CROSS SECTION OP THE THIRD PHALANX OF A CHILD. 

 The ridges of the nail bed in cross section appear Hke papillae. 



Eponychfum. 



X 15. 



of which in part extend vertically from the periosteum of the phalanx 

 to the epithelium, and in part run lengthwise of the finger. In place of 

 papillae the corium of the nail forms narrow longitudinal ridges which 

 are low near the root of the nail but increase in height toward its free 

 distal border; there they abruptly give place to the papillae of the skin. 

 At the proximal end or root of the nail the corium has tall papillae. 



The epithelium consists of a stratum germinativum and a stratum 

 corneum, but the latter corresponds with a thick stra- 

 tum lucidum. In the embryo the horny substance is 

 entirely covered by a looser layer, the eponychium, 

 and this name is applied in the adult to the skin-like 

 tissue which overlaps the root and sides of the nail 

 (Fig. 363). The eponychium is the stratum corneum 

 of the adjoining skin. Although the nail cells are 



FIG. 364. CELLS OF J 



x 2 ^o MAN NAIL ' f rme d by the entire underlying stratum germinati- 

 vum, as is shown by the increasing thickness of the 

 nail toward its distal edge, yet the principal production is at its proxi- 

 mal root beneath the crescentic white area, the lunula. The opacity of 

 the nail at the lunula has been attributed to keratohyalin; an imper- 

 fect stratum granulosum occurs there. The pink color of the outer por- 

 tion is due to blood beneath, which is seen through the transparent stra- 

 tum lucidum. The cells of the nail may be separated by heating to 



