NailsThe nails, and the part upon which they lie, are essentially the same in structure as the skin in its different parts, only that the horny layer is more developed, forming the actual nail. Posteriorly, the nail is fitted into a groove; the part fitting into the recess is called the root, and the portion underlying the nail is that which represents the corium - it is, in fact, the corium; it bears, however, the name of matrix. Between the nail itself and the matrix is the rete mucosum; in fact, the bed of the nail may be described as consisting of corium with the sub-connective tissue beneath, and the rete above.
As in the case of the skin the rete dips down between the papillary projections of the corium of the nail.
The corium itself, or matrix, is divided into two parts, which are separated by a more or less convex line seen through the nail and known as the lunula. The hinder-most of these two divisions has its papillae directed forward, less distinct, and more closely seated together. The front portion is thrown into longitudinal folds, and upon these are seated the papillae. These folds are produced by the peculiar disposition of bundles of connective tissue in the structures beneath. The matrix towards the front part of the nail is covered by cells that are more and more horny, whereas over the posterior surface of the matrix (the root of the nail) these cells are softer. In fact, the part of the nail matrix behind the lunula is the spot where the nail is formed. The soft cells are directed forward, guided by the fold of the skin over the nail at its root - which fold lacks glands, and papillae on the surface applied to the nail - becoming more horny as they advance.
A correct knowledge of the anatomy of the skin is an immense aid to the right comprehension of morbid changes going on in the skin.
The epithelial stratum of the skin, made up of the horny and mucous (rete Malpighii) layers, are the special seat of a number of morbid processes. In parenchymatous inflammation as in small-pox, the first stage seems to be a great increase in the cells of the rete, and the pustule subsequently produced is formed bodily in the rete, its walls being formed by altered rete cells, stretched into fibres and enclosing pus cells. In the formation of vesicles and bullae, the rete is chiefly concerned. In some cases of non-inflammatory diseases, the epidermis cells are found to have undergone special changes, or to have been arrested in their development, as in psoriasis.
The relation of the epidermis to the papillary layer, in regard to diseased action, is a matter of no little importance.
Dr. Auspitz draws the following conclusions in regard to the production of diseases from the growth inwards of and resultant changes in the papillary layer:
- In hyperaemic and inflammatory processes occurring in the skin the papillae are found to be only succulent and slightly swollen; but no modifications of form occur, unless consecutive to secondary change in the Malpighian stratum.
- In simple and lymphatic hypertrophy of the connective tissue matrix, as well as in cellinfiltrations of the corium, the same law holds.
- In the keratoses, or horn-producing affections - ichrhyosis - there is either no change in the form or size of the papillae, or it is due only to the pressure of the hypertrophied horny layer. The prismatic and columnar forms of the latter are by no means dependent on the papillae of the cutis.
- The papillomata (warts, condylomata, epithelioma) originate essentially in an active neoplastic process taking place in the rete, which penetrates to a greater or less ex tent into the likewise hypertrophied connective tissue matrix of the corium. The papillae of the cutis, here, too, perform only a passive role, their elongation and dentritic form being occasioned by the hypertrophy of the epidermis; whilst the elevation of the surface of the skin is due to the hypertrophy of both.
- An outgrowth of the connective tissue of the skin sometimes occurs, but is never dependent on the pre-existent papillae.
- There is no essential anatomical difference between the several forms of papillomata, warts, pointed condylomata, and cauliform excrescences. The syphilitic condyloma differs from these only through the specific cell infiltration of the corium.
- Epithelioma represents exquisitely the types of the hypertrophic growth inwards of the epidermis into the connective tissue matrix.
The rete is an important pathological ground, from the fact that in most inflammatory processes there is to be found in it a great increase of the spindle-shaped or migrating corpuscles. It is now established that cutaneous cancers originate in a morbid change in the cells of the Mal-pighian layer, and by the disordered growth of these same cells in masses from their inter-papillary parts, into the corium. This is an undoubted fact and gives countenance to Dr. Auspitz's views. The corium is also the seat of very important pathological changes that originate in its substance and various alterations of its component elements. It is the essential seat, of course, of hyperaemic changes; arid according as the longitudinal plexus, or the papillary vascular loops, or both, are implicated the redness varies in aspect. The corium is, further, especially its papillary layer, the early seat of many inflammatory changes, the vessels dilating, and permitting moreover the escape of white blood cells into the corial textures, and likewise serum, which makes its way to the rete, forming vesicles, etc. Then, again, the fibrous elements of the corium furnish the migrating or fusiform cells that appear in great-numbers in chronic inflammations especially, and migrate to the rete. The corium is the chief seat, moreover, of neoplasmata other than cancerous, as in the case of syphilis and leprosy; these new growths supposedly originating from the connective tissue elements. A simple increase of the latter, too, is held to constitute certain other diseases, such as pachyderma, keloid, etc. The vacuolae and lymphatic spaces are also seats of particular changes, as in leprosy. A knowledge of the structure and peculiarities of hair follicles and sebaceous glands is hot less important in relation to the origin of many common diseases, as acne, fibroma, cancer, lichen planus. Without it the student will attain little real knowledge of the pathology and therapeutics of these frequently occurring affections.In the case of the nail, unless a student knew what was the part of the matrix at which the nail was actually formed, he would be at a loss to diagnose a syphilitic from a non-syphilitic growth, or to comprehend the difference which arises when inflammation attacks now the posterior part of the matrix (where the nail is formed), or now the anterior portion; nor would he be able to explain the predilection of parasites for the root of the nail. |
