THE NAILS AND THE HAIR. 527 



Unstriated muscle-fibers are present in the uppermost layers of the corium, 

 principally on the extensor aspects; further, particularly on the nipple, the mam- 

 millary areola, the prepuce, the perineum, and in especial abundance in the tunica 

 dartos of the scrotum. 



The arteries of the skin in the palm of the hand and the sole of the foot, which 

 must sustain the greatest amount of pressure, possess the thickest walls for the 

 propulsion of the blood-stream. In silver- workers, the elastic fibers of the skin 

 of the hands are discolored black in places from the deposition of reduced silver, 

 and the same condition exists in cases of medicamentous argyria. 



The epidermis is a layer of pavement epithelium, from 0.08 to 0.12 mm. thick, 

 united by cement-substance. The deepest layer, the mucous layer (d), rete Mal- 

 pighii, consists of several layers of protoplasmic nucleated prickle-cells (R) , without 

 membrane, pigmented in the colored races, as well as on the scrotum and at the 

 anus, and of which the deepest are rather cylindrical and vertical. Among these 

 cells scattered lymphatic wandering cells are encountered, which convey important 

 constructive and nutrient material to the epithelial cells. On high -magnification 

 the cells are found to be provided with a fibrillar structure. The interstices 

 between the prickles serve as lymph-paths. The more superficial layers (b), 

 stratum corneum, consist of flat, horny, non-nucleated, epidermic scales (E) that 

 swell up in sodium hydrate. The division between these two layers is constituted 

 by a layer especially distinct when the epidermis is thick of bright transitional 

 forms of cells stratum lucidum (between b and d) . The uppermost layers of the 

 epidermis are being continually desquamated, while new layers of cells resulting 

 from division of the rete cells are constantly brought up from the depth. In this 

 process, the cells that are elevated 

 acquire the microscopic and 

 chemical character of the horny 

 layer, inasmuch as the nucleus un- 

 dergoes atrophy. 



Wherever pigment is present 

 in the epidermis itself and likewise 

 in the epidermoidal structures, it 

 is conveyed, in many situations, 

 from the underlying connective 

 tissue by the stellate wandering 

 cells. In this way is explained the 

 fact that pieces of epidermis trans- 

 planted from a white person to a FlG - ' TO- Cutaneous Papillae Deprived of their Epidermis 

 r^crrn cnrm Wv-nrnP rlarV TTI rpr and the Vessels Injected: a a a, tactile papillae, each con- 



taining a Meissner corpuscle. 



tain other situations, however 

 as, for instance, on the mam- 

 milla it can be shown that the pigment is formed in the deep epidermal cells 

 themselves. Finally, the pigment in connective-tissue cells is said to be derived 

 in part from that formed in the epidermal cells. 



In the layer of the epidermis in which the process of cornification takes place, 

 therefore, from the upper layers of prickle-cells down to the actual cornified 

 epidermis, the cells contain two varieties of granules the albuminoid, intracellular, 

 hyaline granules, and the fat-like, extracellular granules of eleidin, which are 

 exhibited in an analogous manner by all horny structures at the boundary of the 

 process of cornification. The granules of eleidin can be stained with henna, the 

 hyaline granules with hematoxylin. Both structures are said to be allied to 

 chitin. 



Between the prickle-cells of the epidermis, and between the laminated epithelial 

 cells of the mucous membrane, Herxheimer observed peculiar, spiral, solid fibers, 

 which appeared to consist of fibrin-like masses. The elastic fibers of the horny 

 .skin undergo hyaline swelling and scaly or granular disintegration as a phenom- 

 enon of age. 



THE NAILS AND THE HAIR. 



The nails consist of numerous layers of firmly united cornified prickly epi- 

 dermal cells, which can be isolated by caustic alkalies, and at the same time 

 undergo swelling and display a nucleus (Fig. 178, n, m). The entire inferior 

 surface of the nail rests upon the nail-bed. The posterior and the lateral borders 

 are situated in a deep groove, the nail-fold (Fig. 180, <?). The corium beneath 



