STRUCTURE OF THE SKIN :—EPIDERMIS. 49 
‘outwards, until we arrive at layers composed entirely of dry 
flat scales, which show but little indication of ever having 
been cells. There is no doubt, however, that all these forms 
are but different stages of the existence of one and the 
‘same set of epidermic cells ; these taking their origin in the 
formative fluid exuded on the surface of the basement-mem- 
brane, and being progressively carried towards the surface by 
the successive development of new layers beneath them, 
whilst the layers above them are thrown off, or are worn 
away; and at the same time undergoing a change of form, in 
the first instance from mutual pressure, and afterwards from 
| the loss of their contained fluid. At the same time they are 
| rendered more firm in texture, by the formation of a horny 
aie in their interior ; so that the outer layers of epi- 
dermis form a consistent membrane, which is raised from the 
‘surface of the Cutis when fluid infiltrates between them (as 
‘when the hand has been long soaked in water), or is poured 
‘out by the vessels of the latter (as when a blister is applied) ; 
“whilst the soft internal layers remain in contact with the 
‘basement-membrane.—The number of layers varies greatly in 
‘different parts, being usually found to be greatest where 
‘there is most pressure or friction, as if the irritation deter- 
tmined an increased supply of blood to the spot, and thus 
favoured an augmented development of epidermic cells. 
‘Thus, on the soles of the feet, particularly at the heel and 
the ball. of the great toe, the Epidermis is extremely thick ; 
and the palms of the hands of the labouring man are 
‘distinguished by the horny hardness of their thick cuticle. 
—It was formerly supposed that a special layer of a soft 
spongy tissue, termed the rete mucosum, intervenes between 
the Cutis and the Epidermis ; and that this was the special 
‘seat of the colour ef the skin in the dark races. It is 
w well ascertained, however, that this supposed rete con- 
of nothing else than the newly-forming soft layers 
the true-epidermis; and that the colouring matter is 
; d through the epidermic cells, so as to tinge the 
ntire thickness of the cuticle, although its presence is 
articularly obvious in the deeper layers—The Nails may 
@ considered as nothing more than an altered form of 
ermis ; when examined near their origin, they are found 
consist of cells which gradually dry into scales that remain 
E 
