NAILS. 



417 



less closely arranged, and terminate in branched extremities as in other parts of the epidermis. 

 In the snout of the pig the branched axis cylinders pass partly into concavo-convex enlarge- 

 ments between the deeper epithelium cells (tactile menisci of Ranvier, see p. 335). 



Merkel has described the nerves of the epidermis as ending in pyriform cells (tactile cells) 

 placed between the ordinary epithelial cells ; and Langerhans thought that the nerves could be 

 traced to stellate cells in the interstitial spaces, but improved methods of staining with chlo- 

 ride of gold, which have been employed in the investigation, would seem to render it probable 

 that the termination of the nerve-fibrils in the cuticle is free as above described, and between 

 the cells, not actually within them. 



Nerves are supplied in very different proportions to different regions of the true 

 skin. They pass upwards towards the papillary surface, where they form plexuses, 

 of which the meshes become closer as they approach the surface, and the con- 

 stituent branches finer. From the most superficial or subepithelial plexus, which 



Fig. 475. SECTION OP SKIN SHOWING TWO 



PAPILLJB AND DEEPER LAYERS OF KPI- 



DERMIS. (Biesiadecki.) 



a, Vascular papilla with capillary loop 

 passing from subjacent vessel c ; b, nerve 

 papilla with tactile corpuscle, t. The latter 

 exhibits transverse 'fibrous markings : three 

 nerve-fibres, d, are represented as passing up 

 to it : at // these are seen in optical section. 



lies immediately under the epithe- 

 lium, delicate non-medullated fibrils 

 pass upwards amongst the cells of 

 the Malpighian layer of the epi- 

 dermis, where they end, as we have /| 

 seen, in free extremities. A large 6 i. 

 share of the nerves of the cutis vera 

 is distributed to the hair-follicles, 

 whilst some terminate in end-bulbs,, 

 tactile corpuscles, and Paciuian 

 bodies, the last-named being seated 

 in the subcutaneous tissue. The 



tactile corpuscles of the skin are found most numerously in certain papillae of 

 the palm and sole, more sparingly in those of the back of the hand and foot, the 

 palmar surface of the fore-arm, and the nipple. Such papillae commonly contain 

 no blood-vessels, and are named " tactile " (fig. 475, b), as distinguished from 

 the " vascular " papillae (#). The structure of these different terminal corpuscles 

 has been already described (pp. 332 to 344). Many of the nerve-fibres, probably 

 chiefly the non-medullated, are supplied to the plain muscular tissue of the minute 

 hair-muscles, and to that of the blood-vessels. 



NAILS AND HAIKS. 



The nails and hairs are growths of the epidermis, agreeing essentially in nature 

 with that membrane. 



Nails. The posterior part of the nail, which is concealed in a groove of the skin, 

 is named its " root," the uncovered part is the "body," which terminates in front by 

 the " free edge." A small portion of the nail near the root, named from its shape 

 the lunula, is whiter than the rest. This appearance is due to the substance of the 

 nail at this point possessing a greater degree of opacity in consequence of its being 

 covered with a thick layer of the rete mucosum, the cells of which are in active 

 process of division (Toldt). 



