46 SKIN AND MUCOUS MEMBRANES. 



membranous surfaces of the body, and which, form the 

 Epidermis, or superficial layer of the skin, and the Epithelium 

 of the internal membranes. And it will be convenient here 

 to consider the entire structure of the Skin, the Mucous 

 Membranes, and the Serous Membranes, which are complex 

 fabrics, chiefly made up of the elementary tissues already 

 described. These membranes may each be considered as 

 composed of three principal parts, namely, the superficial 

 layer or layers of cells, the basement-membrane whereon the 

 cells lie, and the subjacent texture covered by this, which 

 consists of fibrous tissue compactly interwoven and traversed 

 by blood-vessels, nerves, absorbents, and also containing 

 glands of various kinds. The Skin and Mucous Membrane 

 may, in fact, be regarded as belonging to one and the same 

 type ; for they are continuous with each other wherever one 

 of the open cavities of the body communicates with the 

 surface, as at the mouth, nostrils, and anus; and in the 

 Hydra ( 121) it has been experimentally found that the 

 membranous layer covering the body may be made to change 

 places with that which lines the stomach, without any sensible 

 disturbance in the functions of either. The difference between 

 the two essentially consists in this ; that the Skin, being 

 destined especially for the reception of sensations, and for the 

 protection of the soft parts beneath, is more copiously furnished 

 with nerves than with blood-vessels, and has its surface 

 covered by a firm, dry cuticle ; whilst the Mucous Membrane, 

 ministering especially to the organic functions, is comparatively 

 little supplied with nerves, but is abundantly furnished with 

 blood-vessels, and in certain parts with absorbents, whilst its 

 cellular layer is soft and easily permeable by liquids. Both 

 in the skin and in mucous membrane we find a multitude of 

 minute glands, for the separation of particular fluids from the 

 blood ; the nature of these differs with the locality. 



37. The fibrous mesh-work of the Cutis or True- Skin is con- 

 tinuous with that of the Areolar tissue which lies immediately 

 beneath it; so that the two textures are not separated one 

 from the other by any definite boundary (as the examination 

 of a vertical section (fig. 7) clearly proves), but are dis- 

 tinguishable only by the compactness of the one, as contrasted 

 with the looseness of the other. The outer surface of the 

 Cutis usually presents numerous minute elevations or papillce 



