THE NAILS. 343 



ting a view of the circulation beneath. This is also sufficiently 

 proved by the fact, that when a nail is torn off, its lunula disap- 

 pears. The nail increases gradually in thickness from its root 

 to its free extremity. 



The nail is covered on the posterior face of its root by the 

 epidermis, which terminates there in a thin, adherent, diapha- 

 nous band: behind this band the root of the nail projects, and 

 is received into the groove of the cutis vera. The epidermis 

 also adheres to the lateral margin of the nail, and in a curved 

 line to the concave side of its anterior end. The under sur- 

 face of the nail is soft, pulpy, and has an arrangement of 

 superficial longitudinal grooves, receiving the papilla of the 

 corresponding surface of the cutis vera. As the black co- 

 lour of the negroes is sometimes seen beneath their nails, it is 

 probable, as stated, that the rete mucosum exists there also; 

 but it is not so clearly ascertained, though the observations of 

 M. Gaultier, on the rete mucosum of animals, tend to prove 

 it.* 



As the nails are entirely destitute of organization, having 

 neither vessels nor nerves, they have no power of growth nor 

 of disease in themselves, these qualities being derived exclu- 

 sively from the cutis vera. The materials of their formation 

 are, accordingly, secreted from the cutis vera, in the bottom of 

 the groove, formed by the latter for the reception of their root. 

 As these materials adhere to the preceding formation, and 

 become concrete, by adding continually to its length, they 

 shove it forward, and thereby elongate it. While this is going 

 on in the groove, the thickness of the nail is also somewhat in- 

 creased by an excretion from the skin contiguous to its con- 

 cave surface. This accounts for the nail being thicker at its 

 free extremity than at its root. 



Owing to a peculiarly morbid state of this proximate surface 

 of the true skin, it sometimes happens, that the contribution to 

 the nail from it exceeds that from the groove; the consequence 

 of which is, that the whole nail grows upwards like a horn, in- 

 stead of forwards. An example of this kind was lately exhi- 

 bited to me by a scientific friend, Dr. Charles D. Meigs, of 

 tliis city,, in a female aged about ninety. In this case one of 



* See Rete Mucosum.. 



