338 THE SKIN. 



are covered by one or more layers of epithelium, forming the 

 cuticle or epidermis. The papillae adhere very intimately to 

 the cuticle, which is thickest in the spaces between them, but 

 tolerably level on its outer surface : hence, when stripped off 

 from the cutis, as after maceration, its internal surface presents 

 a series of pits and elevations corresponding to the papillae and 

 their interspaces, of which it thus forms a kind of mould. 

 Besides affording by its impermeability a check to undue 

 evaporation from the skin, and providing the sensitive cutis 

 with a protecting investment, the cuticle is of service in rela- 

 tion to the sense of touch. For, by being thickest in the 

 spaces between the papilla, and only thinly spread over the 

 summits of these processes, it may serve to subdivide the sen- 

 tient surface of the skin into a number of isolated points, each 

 of which is capable of receiving a distinct impression from an 

 external bodies. By covering the papillae it renders the sensa- 

 tion produced by external bodies more obtuse, and in this 

 manner also is subservient to touch : for unless the very sensi- 

 tive papillae were thus defended, the contact of substances 

 would give rise to pain, instead of the ordinary impressions of 

 touch. This is shown in the extreme sensitiveness and loss of 

 tactile power in a part of the skin when deprived of its epi- 

 dermis. If the cuticle is very thick, however, as on the heel, 

 touch becomes imperfect, or is lost, through the inability of 

 the tactile papillae to receive impressions through the dense and 

 horny layer covering them. 



Sudoriparous Glands. In the middle of each of the trans- 

 verse furrows between the papillae, and irregularly scattered 

 between the bases of the papillae in those parts of the surface 

 of the body in which there are no furrows between them, are 

 the orifices of ducts of the sudoriparous or sweat glands, by 

 which it is probable that a large portion of the aqueous and 

 gaseous materials excreted by the skin are separated. Each 

 of these glands consists of a small lobular mass, which appears 

 formed of a coil of tubular gland-duct, surrounded by blood- 

 vessels and imbedded in the subcutaneous adipose tissue (Fig. 

 112). From this mass, the duct ascends, for a short distance, in 

 a spiral manner through the deeper part of the cutis, then pass- 

 ing straight, and then sometimes again becoming spiral, it 

 passes through the cuticle and opens by an oblique valve- 

 like aperture. In the parts where the epidermis is thin, the 

 ducts themselves are thinner and more nearly straight in their 

 course (Fig. 115). The duct, which maintains nearly the same 

 diameter throughout, is lined with a layer of epithelium con- 

 tinuous with the epidermis ; while the part which passes through 

 the epidermis is composed of the latter structure only ; the 



