228 GENERAL ANATOMY. 



sides there is, behind, a disposition analogous to that at the 

 root, and before, to that of its free extremity. 



The nails have no connections besides those just described. 

 It is from want of observation that some anatomists have 

 admitted them to have others with the periosteum and the 

 tendons. 



331. Some have admitted, with Blaucardi, that the nails 

 are formed of agglutinated hairs; others, that they result from 

 the super-position of scales or horny lamina, the uppermost 

 of which is the whole length of the nail, while the others suc- 

 cessively diminish in length, which occasions a regularlj 

 increasing thickness from the root to the free extremity. 

 These are rather ways of accounting for the mode of the forma- 

 tion of the nails, than results of observation, which in fact dis- 

 covers in the nails a horny substance only, hard and dry ex- 

 ternally, and mucous in the interior. Neither vessels nor 

 nerves are to be found in them. They consist in a thick and 

 horny layer of the mucous body of the skin. 



332. The nails are diaphanous, flexible, and elastic; they 

 may be torn crosswise, notwithstanding their fibrous appear- 

 ance in another direction. Their chemical properties are those 

 of coagulated albumen; they appear also to contain a little 

 phosphate of lime; they are very similar to horn. They are 

 totally deprived of irritability and sensibility. The force of 

 formation or a continual growth by a sort of vegetation, is the 

 only organic and vital phenomenon observed in them; even 

 this is foreign to them. The materials of which they are 

 formed, are continually and proportionably secreted and ex- 

 creted by the dermis: this matter applied to the extremity 

 and adhering face of the nail, like that of the secretion of the 

 silk-worm, concreting as fast as it is excreted, and being con- 

 tinually added to that which has preceded it, pushes it before 

 it, and thus lengthens the nail by juxta-position, and not by 

 intus-susception. It is then a true excretion, whose materials, 

 once deposited, are never absorbed. The nails arm, support 

 and protect the extremity of the fingers and toes. 



333. The nails begin to appear about the middle of the 

 foetal, term: even at birth they are still very imperfect. In 



