OF THE NAILS. 229 



the coloured races, the colour is subjacent to the nail. In 

 many animals, on the contrary, the coloured layer of the mu- 

 cous body is confounded with the horny layer in the compo- 

 sition of the nails and similar parts. The parts most analo- 

 gous to the nails of man are the claws of the carnivora, &c., 

 which surround the dorsal face and the sides of the last pha- 

 lanx, and are curved towards the sole; and the hoofs of the 

 ruminantia, &c., which envelop the whole extremity of the 

 last phalanx. The nails of the human foot have sometimes a 

 considerable growth, and assume a direction that approximates 

 them to claws. 



334. The alterations* attributed to the nails, are, in fact, 

 utterly foreign to them, and depend wholly on the skin that 

 produces them. It is the same with respect to accidental 

 horny productions: it is in the subjacent tissue, that we must 

 seek for their origin. 



When a nail has been torn by violence, or detached by dis- 

 ease from the subjacent skin, it grows again slowly, and differs 

 more or less from the primitive one, just as the affection of 

 the skin continues more or less, at the time of its second 

 growth. 



Horny laminae, more or less analogous to the nails, are 

 formed upon cicatrices, the ends of the toes and other places 

 exposed to pressure or violent and reiterated friction, such 

 are callosities, &c. Simple ichthyosis, differs from them only 

 in its extent and our ignorance of its cause. 



Corns also consist of round, hard, small, accidental horny, 

 productions, which by the compression they transmit, irritate, 

 inflame and sometimes pierce the skin, and even affect the 

 bones and subjacent articulations. 



Horns or horny conoid productions more or less elongated, 

 have been very often observed from the earliest ages on al- 

 most all parts of the skin. Sometimes a single one of these 

 excrescences exist on an individual and is developed on a ci- 

 catrix, in a sebaceous follicle, or on some point of the skin, 

 that has been previously altered, or even without any thing 



* Plenck, de marbis unguium, in dodrind de rnorbis cutancis. 



