sect. 49-] EPIDERMIS. 93 



continues, may be called growth. The deepest layers of cells arc 

 undoubtedly concerned in this regeneration, in forming new cells 

 by often repeated divisions. 



In the deep fold of the skin which surrounds the giant penis and the clitoris, 

 a constant throwing off and reproduction of the epidermic scales, which are 

 here soft and nucleated, takes place, by which a peculiar secretion, the 

 smegma 'praputii, is occasioned, in the formation of which, at least in the 

 male sex, the secretion of the sehaceous follicles of the prepuce (see posted) 

 takes part. A casting-off, or desquamation of the entire horny layer of the 

 epidermis in a more extensive degree, as occurs in the embryo and in many 

 animals, is not met with in after life, except in certain diseases. On the other 

 hand, its capability of regeneration is exhibited in other ways besides that 

 above described. When portions of the epidermis are cut out, they are easily 

 and speedily restored, provided the corium is not injured. This does not take 

 place by means of the deposition of epidermis immediately from the corium 

 in the seat of the wound, but by an up-growthof the whole epidermis from below; 

 and this undoubtedly does not take place by a new formation of cells, but by the 

 increase of the remaining cells of the Malpighian layer, probably by means of 

 cell-division. If the corium be injured as well, an epidermis is formed upon 

 the substance of the cicatrix, but without the original depressions and eleva- 

 tions, because the new cutis possesses no papillce or ridges. If the epidermis 

 be raised into vesicles by means of certain irritating substances, as tartrate 

 of antimony, or by scorching, scalding, etc., the raised portion, which consists 

 of the horny layer and part of the mucous layer, never again becomes 

 attached ; but a new horny layer is gradually formed from the main portion 

 of the mucous layer, which generally remains adherent to the papillae. 



§ 49. Development of the Epidermis. — The first layers of the 

 epidermis arise, in the mammalia, from the metamorphosis of the 

 most superficial formative cells which originally compose the 

 voting embrvo. When the first foundations of the mucous and 

 liornv layers are laid down, the former continually increases in 

 thickness by the multiplication of its elements ; while the horny 

 layer recruits itself therefrom, in order to its own increase and the 

 repair of loss by desquamation, just in the same manner as in the 

 adult. As regards the horizontal extension of the epidermis, it 

 would seem to be, only in a very slight degree, owing to the en- 

 largement of the elements, as Harting (Becherches Micrometry 

 p. 47) justly infers from the fact, that the epidermic scales of the 

 foetus and of the adult differ very little in superficial extent. Accord- 

 ingly, from the great horizontal growth of the cutis and rete Mal- 

 pighii, and the small capability of extension of the strata of the 

 horny layer, we are constrained to assume that a series of desqua- 

 mations of the latter occur, which, if this opinion be correct, must 

 be demonstrable after birth. 



