THE NAILS. 439 



The Nails. 



The roots of the nails appear to originate in a fold of the 

 cutis vera, from the epidermis which lines the fold ; but the 

 bodies of the nails adhere firmly to the cutis on which they lie, 

 and appear to cover it, in the place of the cuticle. The papillaj 

 of those parts of the cutis which are covered by the nails are 

 very conspicuous when the nails are removed. It has been 

 supposed that there was no rete mucosum between the nails and 

 cutis ; but this opinion is probably erroneous, as the black pig- 

 ment is perceptible under the nails of some negroes. 



The nails can be separated from the cutis by all those pro- 

 cesses which separate the cuticle from it. When this is effected, 

 they remain connected with the cuticle, which appears to be 

 continued into them ; and on this account, as well as their 

 insensibility, and their resemblance to the horny excrescences of 

 the cuticle, they are considered as appendages of it. 



The root is opaque, and appears white. The body is trans- 

 parent, and in health shows the florid color of the cutis which it 

 covers ; but the color of this portion of the cutis depends upon 

 the state of the circulation ; and becomes livid when the blood 

 is disoxygenated, or when the circulation ceases there ; and this 

 color also appears through the nails. 



The nails are unquestionably organized, although their ultimate 

 Structure is not known. They appear to be composed of lamellae, 

 and these lamellae of fibres. They grow rapidly, and when 

 they are not pared or worn away, they sometimes acquire an 

 immense size. 



As a remarkable instance of this, it is related, that a nail of 

 the great toe was sent from Turin to the Academy of Sciences 

 at Paris, which measured four inches and a half in length. 



The growth seems to take place altogether at the roots. 



The nails, when chemically examined, appear to consist of 



membranes, the lining membrane of the mouth, pharynx, oesophagus, and the 

 vagina and cervix uteri. 2d. The cylinder epithelium, found in the remainder 

 of the alimentary canal, the ducts of the glands, and a great part of the genito- 

 urinary apparatus of the male. 3. The ciloary epithelium, found in the respira- 

 tory organs, the lachrymal passages, Eustachian and Fallopiaa tubes, etc. 

 Vide the account of these organs. 



