SEC. 5. THE STRUCTURE OF THE SKIN. 



432. The skin, like a mucous membrane, consists of an 

 epithelium resting upon a connective tissue basis ; the epithelium, 

 which is composed of many layers of cells, is called epidermis, the 

 connective tissue basis is called dermis, or corium, or cutis vera. 

 The surface of the dermis is thrown up into a number of elevations, 

 papillae, which differ in size, form, complexity and arrangement 

 in different regions of the body. Some are small, more or less 

 conical elevations, simple papillce. In others, a broader primary 

 elevation is divided at its summit into a number of secondary 

 elevations ; these are compound papillce. In many regions of the 

 skin, as for example in the palms of the hands, the papillae are 

 arranged in ridges separated by shallow furrows. The surface of 

 the skin, that is, the contour of the epidermis, does not follow the 

 papillary contour of the derrnis ; the papillae accordingly appear 

 to plunge into and to be covered up by the more even epidermis, 

 the surface of which, however, is marked by the ridges and furrows 

 spoken of above as well as by bolder creases and folds. 



The surface of the dermis is not developed into a distinct and 

 separable basement membrane, as is so often the case in a mucous 

 membrane ; but in the most superficial portions of the dermis 

 the connective tissue shews little or no fibrillation and consists of a 

 homogeneous matrix, in which are imbedded connective tissue 

 corpuscles and extremely fine elastic fibres. This superficial 

 portion of the dermis, which is especially well-developed in the 

 papillae, serves accordingly the purposes of a basement membrane, 

 and sharply defines the dermis from the overlying epidermis. 

 At a very little distance from the epidermis fibrillation makes its 

 appearance, the bundles of fibrillse interlacing in a network which, 

 very close set in the outer, more superficial layers, becomes more 

 and more open in the inner, deeper parts. The connective tissue 

 of the dermis thus passes insensibly into the sub-cutaneous con- 

 nective tissue, in which thick interwoven bundles of fibrillaa, 

 bearing in transverse section a certain resemblance to sections of 



