THE SKIN. 329 



mate; its general tendency being to turn dark on parts exposed 

 to the influence of tropical heat and light. 



The external surface of the skin, or that which is free, has 

 on it a great multitude of wrinkles; some of them depend upon 

 the subjacent muscles, as on the forehead and face; some are 

 caused by the flexions of the articulations, and are to be seen 

 at all of these places on the limbs; in addition to which, where 

 there is much emaciation of the parts beneath, the skin not 

 having sufficient elasticity to accommodate itself to their state, 

 is thrown into other wrinkles, and sometimes into loose folds. 

 Finer wrinkles of another description are also found on the 

 skin, arranged in various angular and spiral directions: they 

 depend on an entirely different cause, which will be treated of 

 elsewhere. 



The skin abounds in hairs, which vary in fineness and in 

 length according to the region over which they are distributed : 

 it, likewise, presents many small pits, or follicles, which are 

 the orifices of sebaceous glands. A finer description of pores, 

 which are visible only to the assisted eye, are supposed to be 

 the orifices of exhalents and of absorbents, but this is not quite 

 certain. 



The internal surface of the skin is connected to the subja- 

 cent parts by the cellular tissue, which permits a considerable 

 sliding of it backwards and forwards on most parts of the 

 body; on others, however, this is restrained, as on the cranium, 

 the palms of the hands, and the soles of the feet, by ligamen- 

 tous fibres passing to it from the fascia3 and bones below. A 

 very interesting attachment of this kind exists on the fingers, 

 where a plane of ligamentous fibres is seen passing from each 

 side of the lower end of the first phalanx, downwards, to be 

 inserted into the skin, half an inch or an inch off. 



Since the first observation of Malpighi, on the tongue of a 

 bullock, whereby he ascertained that its integuments consisted 

 in three layers, and the discovery of a similar arrangement on 

 other portions of the integuments by Ruysch,* anatomists have, 

 for tho most part, admitted the skin to consist of three lamince, 

 the Cuiis Vera, the Rete Mucosum, and the Cuticula. 



* Thesaurus, Anat. IX. 

 28* 



