The Anatomy of the Skin

In order to correctly understand the nature of the mor­bid changes that go on in the skin, and to comprehend correctly how and where these changes begin, it is neces­sary to have an accurate knowledge of the healthy skin in its different parts.

The healthy skin is, of course, the standard of com­parison for all changes in the skin, and without the clear­est perception of what that standard is the student can, of course, only fall into error from the inability to distin­guish between what is normal and what is abnormal.

The skin 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 cutis vera, dermis, or corium. 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 papillae. In others, a broader primary elevation is divided at its sum­mit into a number of secondary elevations; these are compound papillae. 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 dermis; the papillae accordingly appear to plunge into and 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 shows 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 fibrillae interlacing in a network which, very closely 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 subcutaneous connective tissue, in which thick interwoven bundles of fibrillae, bearing in transverse section a certain resem­blance to sections of tendon bundles, form a tough open network, the larger spaces of which are frequently occu­pied by masses of fat cells of the subcutaneous adipose tissues. Elastic fibres are very abundant in the dermis proper, being very fine immediately beneath the epider­mis and becoming coarser in the deeper parts; they are present also, though to a less extent, in the subcutaneous connective tissue. The skin, as a whole, is a very elastic structure.