1410 ON CUTANEOUS AND [BOOK in. 



occur in the nipple of the breast, on the under, volar, surface of 

 the fore arm, being here however exceedingly scanty, at the edge 

 of the eyelids and lips, and on the genital organs. From the 

 greater part of the surface of the body they appear to be wholly 

 absent. 



873. We may now turn to the second kind of ending of 

 nerve fibres in the skin, that in which fibrils pass into the very 

 epidermis. It will be useful to begin with the nerves of the cornea, 

 the examination of which is relatively easy. 



The medullated nerve fibres, which enter into the body of the 

 cornea at its circumference, soon lose their medulla and subse- 

 quently their neurilemma. The axis cylinders dividing form 

 towards the front of the cornea a plexus called the 'primary 

 plexus,' at the nodal points of which, as also occasionally on the 

 bars of which, nuclei are seen. From this primary plexus bundles 

 of fibrillse form other plexuses in the substance of the cornea, espe- 

 cially in front, where beneath the anterior elastic lamina ( 716) 

 a plexus called the "sub-basal plexus" may sometimes be found. 

 From this plexus, or directly from the primary plexus, bundles of 

 fibrillse, or divisions of axis cylinders, of some little thickness, run 

 straight outwards to the epithelium, piercing the anterior elastic 

 lamina, and hence called rami perforantes. Reaching the base of 

 the lowermost, vertical tier of cells, each ramus breaks up into a 

 pencil of delicate fibrils, which taking a direction at right angles 

 to that of the ramus itself, and converging towards the centre of 

 the cornea, form between the upper surface of the elastic lamina 

 and the base of the lowermost tier of cells, a close-set horizontal 

 plexus of delicate fibrils, the subepithelial plexus. From this 

 subepithelial plexus still more delicate fibrils run upwards into 

 the epithelium, forming between the cells an intraepithelial plexus', 

 and from this or directly from the subepithelial plexus, extremely 

 fine fibrillse pass upwards towards the surface of the epithelium. 

 It has been asserted that these project beyond the surface, the 

 free ends swollen into tiny knobs waving freely in the fluid which 

 always covers the surface of the cornea. This however has been 

 doubted; but in any case the nerves of the cornea send off 

 branches which end in the manner described, quite close to the 

 surface of the cornea as free fibrils, not directly connected with 

 any cells. It need hardly be said that the detection of these fine 

 endings requires special preparation ; they can be seen only with 

 the gold chloride method. 



874. A similar mode of ending also occurs in the skin. In 

 all parts of the skin medullated nerve fibres are present, assuming 

 more or less a plexiform arrangement in the dermis close beneath 

 the epidermis, the fibres being more numerous and their arrange- 

 ment more intricate in some regions of the body than in others. 

 These medullated fibres give off fibres which, losing their medulla, 

 penetrate into the epidermis, and there forming a more or less 



