146 



INTRODUCTION. 





ternal cuticle (see fig. 145), though thin, is very apparent: the internal 

 cuticle is a line in thickness, and presents a minutely wrinkled surface 

 on its outer layer. 



On the skin of the back of the same animal (fig. 146) the colouring 

 matter is abundant, not only between the internal cuticle and the corium, 

 but between the two layers of the cuticle also, giving a dark colour to the 

 surface of the body. The rete mucosum, then, is only the internal cuticle 

 imbued, during its secretion, with a coloured pigment, which may, as is 

 proved, be deposited, in the form of a separate layer of mucus, and readily 

 washed away. The demonstration of the presence of this pigment is much 

 more easy in the Negro than in the white races of mankind : indeed, in the 

 latter, many physiologists and anatomists have been disposed to doubt, if 

 not deny, its existence ; yet, if it be really to this mucous layer that the 

 colour of the skin is owing, the varieties of complexion among the white 

 races of mankind, from olive to the fairest blond, sufficiently prove its 

 presence, however delicate its tint, or slight its quantity. In many animals 

 the colour of the skin is very fugitive. The rich violet and scarlet on the 

 muzzle of the Mandrill, and the fine orange on the face of the Douc 

 Monkey, fade soon after death, scarcely a trace of the original tints being 

 left behind. The skin of many of the Monkeys, when seen through the 

 fur, as on the chest and abdomen, is blue ; but, when the skin is taken off, 

 after death, and dried, all the colour is gone. 



The corium, cutis, or true skin, is that which immediately covers the 

 muscles, fat, or cellular tissue beneath ; it is the innermost of the three 

 membranes, and varies much in thickness and density in different animals, 

 but is always flexible and elastic. It is composed of dense gelatinous 

 fibres, crossing each other in every direction, and, as it were, felted 

 together, so as to produce a compact and strong tissue, with numerous 

 perforations at given intervals. On the external surface of the skin the 

 fibrous tissue is so closely and compactly interwoven, as to exhibit 

 a smooth, continuous, membrane-like texture : on its internal, or adher- 

 ing aspect, it presents a looser structure ; and its fibrous threads merge 

 into those of the cellular, or adipose tissue, in contact with it, and over 

 which it is spread. Immersion in water, by separating the fibres of the 

 cutis, or chorion, and rendering their intervals more distinct, demon- 

 strates the arrangement of them, and of the tubular perforations, by 

 which the fibrous tissue, through the whole thickness of the cutis, is 

 penetrated, and which serve for the passage of hairs, of exhalants, and 

 of absorbents, as they come to the surface.* 



The cutis is permeated in every direction by numberless arterial 



* It is the cutis, or true skin, only, of which, by the process of tanning, leather is formed, the 

 cuticle, and all other parts, are separated previously to its immersion in the tan-pit. The structure of 

 the skin becomes impregnated with the principle called tannin. 



