No abstract

SUMMARY To most authors the study of nerve terminations in mammalian skin has been an exercise in descriptive morphology. A single histological technique was usually considered adequate and presumably impeccable, for observations resulting from different techniques were not compared and the possibility of artefacts was not considered. The literature is thus excessively large and full of controversies over histological minutiae. It also contains theories concerning the organization of the nervous system which are at variance with the results of physiological observations. The work of a few authors is in striking contrast, but their observations have either been ignored or discounted. The recent discovery that nerve fibres can be seen in fresh specimens of cornea under phase‐contrast conditions has led to the development of new neuro‐histological techniques. These display nerve fibres and their terminals selectively in skin. They appear in an undistorted state and are virtually free from artefacts. The use of new techniques has shown that it is characteristic of all nerves entering mammalian skin to terminate in an arborization of fine (< 1μ in diameter), naked, axoplasmic filaments which probably end freely. Ensheathed stem fibres give rise to unencapsulated nerve endings in all skin strata, and terminals from neighbouring stem fibres overlap and interdigitate extensively. Axoplasmic filaments terminate in the cellular layers of the epidermis and in the dermis but in no specific relation to the capillaries. They are found in relation to the myoepithelial and gland cells of sweat glands, and in relation to the adventitia and media of blood vessels. In hairy skin there are in addition to the unencapsulated nerve endings nerves which end specifically in relation to hair follicles. Ensheathed myelinated stem axons give rise to two distinct and separate series of arborizations of fine, naked, axoplasmic filaments which lie at right angles one within the other. The outer series encircle the hair lying among the cells of the middle layer of the dermal coat. The inner series lie among the cells of the outer root sheath parallel to the hair shaft. No encapsulated nerve endings are seen in hairy skin. In glabrous skin and mucous membranes, such as the lip, anus and glans penis, there are, in addition to the unencapsulated nerve endings, numerous encapsulated nerve endings. They are of different sizes and shapes, and the ensheathed myelinated stem fibre or fibres which enter the capsule pursue a more or less tortuous course. They then give rise in all cases to an arborization of fine, naked, axoplasmic filaments which end freely among the capsular cells in planes roughly parallel to the surface layer of cells. In the light of these findings a re‐analysis of the observations and, in particular, the diagrams in the literature, forces one to the conclusion that the actual facts which have been reported by various authors have more in common than would have been supposed from a perusal of their summaries and conclusions. As th...

No abstract

V ARIABILITY in the pattern of plexus formation and in the distribution of peripheral nerves are well recognized factors responsible for producing deviations from the form representing the "idealised" or "normal" dermatome pattern of innervation of the skin. Schwartz s has recently described the presence of anastomoses between the cervical posterior rootlets of the spinal cord and considers them to be a further potential factor in causing deviations from the "normal" dermatome pattern in the areas innervated by the cervical posterior roots. Moreover, he has shown clinical evidence that such anastomotic connections which he found in the cervical region were of surgical significance in the operation of posterior rhizotomy for the relief of pain. Schwartz confined his observations to the cervical region and proposed that there is embryological predilection for the production of such rootlet anastomoses there. It appears desirable, however, to extend the study of rootlet anastomoses to include the other regions of the spinal cord as well. Fifty human spinal cords, obtained post mortem, were carefully dissected and searched throughout their length for posterior rootlet anastomoses. A dissecting microscope was employed to facilitate the search. In 10 instances the anastomotic connections found were excised and prepared for examination alternatively by Flemming's method for myelinated nerves and the Romanes silver method for axons.

Pacinian corpuscles in the mesentery of adult cats were fixed with either glutaraldehyde, osmium tetroxide or permanganate solutions by close intra-arterial injection through the mesenteric artery, and were processed, after electron staining and Epon embedding, for electron microscopy . Better resolution of the corpuscle's ultrastructure was obtained than available heretofore . The myelinated segment of the corpuscle contains blood vessels separated from the axon by collagen fibers and 3 to 4 layers of lamellae . No blood vessels are found in the central core, though access from the vessels is afforded by diffusion through the "cleft" of the inner core . Two cell types are discernible in the inner core hemilamellae ; the "clear cells" in which pinocytotic vesicles and organelles abound and reflect the greater metabolic activity of these cells, in contrast to the "dark cells ." The ultraterminal is ellipsoidal in form with projections into the "cleft" which give this portion an irregular appearance in section . The terminal and ultraterminal are packed with mitochondria, and "synaptic" vesicles are seen in the ultraterminal . The innermost laminae of the inner core cells are in close apposition to the terminal and break their regular pattern of hemilamellation to surround the small ultraterminal projections at the apical part of the corpuscle .