332 



MANUAL OF HISTOLOGY. 



structures imbedded in the epithelium, in which the nerve fibres ter- 

 minate. These are known as Langerhans' cells. A few more points may 

 be mentioned in regard to these views. 



A few years ago an excellent observer, Hensen, stated that in the tail 

 of the tadpole the terminal filaments penetrated into the nucleoli of the 

 epithelial cells. His observations gained greatly in interest through the 

 further investigations of Frarikenhauser and Arnold ( 183). But these 

 statements have not since been confirmed, and must now be declared 

 incorrect : this we maintain against Lipmann, who asserts that very 

 delicate nerve fibrillse may be seen to terminate in the nucleoli of the 

 posterior epithelial cells -of the cornea. 



We must also confess our disbelief in Joseph's theories with regard 

 to a similar ending of the nerves in the cells of bone, and to Lavdowskijs 

 with respect to those of the cornea. 



But, on the other hand, we have since learned from the beautiful inves- 

 tigations of Hoyer and Cohnheim, that very fine nerve-fibres or primitive 

 fibrillse do terminate in the epithelium of the corneal conjunctiva. Of this 

 there can be no doubt. 



The cornea possesses several distinct plexuses of these nerve fibres. 

 From the most superficial, which lies close under the lamina elastica 

 anterior (fig. 318), and which consists of bundles of delicate primitive 



fibrilloe, there arise at inter- 

 vals isolated twigs (e), which 

 perforate this anterior boun- 

 dary layer of the cornea per- 

 pendicularly. Arrived at the 

 external surface of the latter, 

 they break up into a tassel of 

 primitive fibrillse, and form 

 a " sub-epithelial plexus " of 

 the most delicate threads 

 (6, below), with elongated 

 meshes radiating from the 

 centre of the cornea (Guinea 



Pig); 



From this horizontal end- 

 plexus a number of primi- 

 tive fibrillse are given off as 

 side branches, which ascend 

 vertically in the epithelium, sending out twigs in various directions, and 

 terminating as such in the superficial epithelial layers. The same arrange- 

 ment almost is to be seen in the human cornea. 



According to Klein, two very dense webs of the most delicate nerve 

 fibres are to be found in the epithelium, a deep and a terminal, which is 

 very superficial, only covered by about two layers of cells. 



In the year 1868 Langerhans pointed out fine non-medullated nerve 

 fibres passing in between the cells of the rete Malpighii, partly uniting here 

 with elongated oval cells measuring 0-0088-0-0033 mm,, and partly pass- 

 ing on farther upwards with subdivision. This arrangement was con- 

 firmed as existing in the cornea of the rabbit by Podcopaew. 



A similar arrangement of terminal nerve filaments had, however, been 

 found before this in the mucous membrane of the tongue by Freyfeldl- 

 Szabadfrtdy ; and Luschka made the same discovery in regard to the lining 



Fig. 318. The cornea cf a rabbit in vertical section after 

 treatment with chloride of gold, o, the older; ft, the 

 younger epithelial cells of the anterior surface ; r, corneal 

 tissue; d, a nerve twig; (, finest filaments or primitive 

 fibrillae; /, their splitting up and termination in the epi- 

 thelium. 



