The capillaries of the skin are supplied with vasomotor nerves. Through their control, the capillary circulation largely influences the physiological functions of the skin as well as the pathological changes. A sudden dilatation of these vessels produces the common phenomenon of blushing and a sudden contraction, the equally marked blanching of the surface.
LYMPHATICS
All portions of the skin are provided with a system of lymphatic channels which aid in the important processes of absorption, and the currents of which are eventually directed to the larger vessels beneath the skin. Lymph is so abundantly supplied to the skin that Darier has aptly described the deram as a “true lymphatic sponge.” In all parts of the skin may be found juice spaces or lymphatic channels which usually lack independent walls and fail to show an absolutely free flow of lymph into the lymphatic vessels. These lymph-channels are uniformly present in the papillae of the corium and converge near the middle of the base where a lymphatic vessel usually begins. From the apices of the papillae, lymph flows into the mucous layer of the epidermis in all directions through the interepithelial spaces and between the prickle threads which unite the epithelia.
Lymph slowly returns to the corium by way of the interpapillary depressions of the epidermis through minute openings, or through the ducts of the sweat-glands which emerge at these points. Juice spaces similar to those of the epidermis exist in the hair-follicles, in the sebaceous glands, and in the ducts of the sweat-glands, and form a sheathlike covering about the connective tissue bundles, the oblique muscles and the fat-cells. The course of the lymph in the corium is slowly downward to the lymphatic vessels. The passage of lymph from the spaces of the sweat-glands and fat tissue is by slow filtration into the neighboring veins or lymphatic vessels. This anatomical peculiarity facilitates the formation of subcutaneous fat. No lymphatic vessels proper are found either in fat tissue or in subcutaneous tissue free from fat; in fact, lymphatic vessels proper are relatively few and are commonly mere appendages of the blood- vessels.
NERVES
The skin is well endowed with medullated and non-medullated sensory nerve- fibers, each in certain instances being substituted for the other, or they may be found in combination. These elements from the cerebral and spinal nerve- systems enter the skin and form horizontal bundles of nerve twigs in the subcutaneous tissue. From thence, branches pass upward with the blood-vessels through the corium, and divide into numerous ramifications in the papillary layer, some assuming a horizontal position to the surface and are disposed about the subpapillary vessels and capillaries of the papillae. Other short nerves break up near the epidermis into non-medullated fibers, which send off numerous branches, of which a smaller number end with free extremities in the connective tissue or on the endothelia of capillaries, while a large number penetrate into the epidermis between the basal cells. The nerves of the epidermis, after many divisions and, possibly, reunions to form plexuses (Unna) in the intercapillary spaces, finally send off from different points fine threads for each prickle cell, as far as the granular layer. These nerve-threads penetrate the cell protoplasm and terminate in minute bulbs on or about the nucleus. Some branches end in bulbs between the epithelia, but without any regularity of distribution. Non-medullated nerve-fibers are also supplied to the cells of the hair-sheath and the ducts of the sweat-glands. According to Krause, all sensitive nerve- filaments ultimately terminate without medullary substance and in minute enlargements. As these nerve termination are found largely and uniformly in the cells, of the epidermis up to the corneous layer, they would appear to be the transmitters of general sensation.
All nerve-fibers do not terminate as described in the last paragraph, for some especially medullated nerve-fibers end in the Pacinian corpuscles or, projecting upward to the surface, terminate in the tactile corpuscles (the corpuscles of Meissner, Wagner and Krause) and in Merkle’s touch-cells. The exact function of these various bodies is not well understood, but it is generally admitted that they are sensory organs. According to Merkle the tactile corpuscles and touch- cells are organs for finer perceptions, the bulb-corpuscles and Pacinian bodies for localization and common sensation, while the free epidermal nerve endings are for the appreciation of touch as well as temperature, and those in the hair for both touch and sensation.
Pacinian corpuscles (corpuscles of Vater) are most numerous in the subcutaneous tissue of the nipples, penis and other parts equally sensitive. Examination has revealed as many as 95 on the index finger and over 600 on an entire hand. These corpuscles are small, clearly defined, oval, grayish bodies, even visible to the naked eye in some regions, and measuring two or more millimeters in width by three or more in length. Each corpuscle consists of capsules made up of a large number of concentrically placed hyalin and connective tissue lamellae, resembling the outer structure of an onion, and enclosing a central space or core of transparent protoplasmic material, in the center of which is a single medullary nerve-fiber. The medullary sheath of the nerve is lost in the tissue of the capsules before it reaches the central space. In the central space the nerve-fiber continues to the distal end and there divides into two or more club- shaped enlargements. Ranvier claims that after supplying one corpuscle the nerve may pass on to penetrate a second or even a third. Robinson says the nerve may form a loop or loops, and then pass out at one or the other pole of the corpuscle. In such cases the nerve regains its sheath from the capsules at the point of exit.
Tactile corpuscles (corpuscles of Meissner or of Wagner) (N, Fig. 1) are found in the papillae of the corium, occupying all or the greater part of the non- vascular papillae, especially on the last phalanges of the fingers. They are rounded or oval fibrous bodies of about one-tenth the size of the Pacinian corpuscles. They consist of connective tissue cells with small nuclei interwoven into vertical or spiral rolls, which go to form one to three lobules, and are surrounded by a denser connective tissue or capsule. Each corpuscle is penetrated at one extremity by one or two medullary nerves, which lose their myeline sheaths in the fibrous substance of the corpuscle. A nerve branch passes to each lobule where it divides into delicate fibrillae, which ramify between the connective tissue cells, anastomose with each other and terminate in slight enlargements; or according to Robinson, they may penetrate the capsule at the distal extremity and emerge therefrom as one or more different nerves. Delicate nerve-threads encircle the corpuscle and pass upward with other nerves to the rete. The afferent nerve of a corpuscle may be supplied from an adjacent papillae, or one nerve may supply two or more corpuscles.
Corpuscles of Krause (bulb-corpuscles, end-bulbs) are rounded or avoid bodies with a connective tissue envelope and a non-nucleated bulb to which some fine nerve-fibers penetrate. They are observed especially about the sensory mucous membranes such as the vermilion border of the lips, the tongue, conjunctiva, glans penis and clitoris. They resemble the inner structure of the Pacinian bodies but vary somewhat in form between these and the tactile corpuscles.
Merkle’s touch-cells are oval nucleated bodies in which the medullary nerve terminates, and are situated in the epidermis and upper corium. They are found in regions where tactile corpuscles are few, such as the abdominal surface. Their exact nature and functions are still a matter of dispute, although they have been studied in the lower animals as well as in men.
MUSCLES
Both straited and smooth muscles are to be found in the skin, the former being less abundant than the latter. The straited or voluntary muscles of the skin are chiefly limited to the face and neck and arise from the subcutaneous tissue and the deep-seated muscles, and extend obliquely or vertically between the glands into the corium. To a certain extent expressions of the features can be traced to the action of these muscles in response to various physical and mental emotions. Their analogues in several of the lower animals are large and abundantly distributed.
Non-straited, smooth or involuntary muscles of the skin are very numerous and are found in the corium occupying horizontal and oblique positions in relation to the surface. The former run either in a straight or circular direction and are chiefly found in the scrotum, penis, areola and nipples of the breast, and eyelids. Contraction of these muscles forces the skin into folds and changes its external appearance. The oblique muscles are found in nearly all parts of the corium, either as minute fasciculi without attachment to the hair-follicles, or as more distinct muscular bundles with attachments to several adjacent hair- follicles below, and to the papillary layer above.
American homeopath, he directed several hospitals in New York.
Professor of dermatology.
Served as Lieut. Colonel during the 1st World War.
See his book online: American homeopathy in the world war