DISTRIBUTION OF NON-MEDULLATED NERVE-FIBRES. 25 



easily convince ourselves that the sheath in which they are 

 enclosed represents a direct continuation of the neurilemma 

 of the small trunks. The nerves of the second order, which, 

 therefore, occur generally as a bundle of fine fibrils only, fur- 

 nished with granular swellings, divide into little bundles, 

 which constantly diminish in thickness. These — nertes of the 

 third order — are connected with each other. With higher 

 powers we are not able to recognise here any other connec- 

 tion than a plexus, namely, a simple close arrangement of 

 the constituent fibrils. A nucleus belonging to the sheath is 

 no longer to be observed. Their course is for the most part 

 sinuous, but becomes, under the epithelium, more rectilinear, 

 like the fine nerves of the cornea; only that in the nictitating 

 membrane, similar rectilinear fibres,having granules imbedded 

 in them at regular intervals, may be observed in a few places 

 in the substance, at some distance from the epithelium. 



Close under the epithelium of the posterior surface there 

 proceed from these, numerous very fine filaments, with a 

 straight course, and always distinguished by granular swell- 

 ings — nerves of the fourth order — which run always in a certain 

 place in a certain direction. They unite to form a sub- 

 epithelial network by means of small transverse threads, and 

 thence penetrate between the epithelial cells of the deep 

 layers in an oblique, or, more rarely, in a vertical direction. 

 They are likewise furnished Avith small varicosities, and 

 pursue between the cells a zigzag or abruptly winding course. 

 Between the cells of the superficial and ihe deep layer they 

 bifurcate or give off" gradually lateral horizontal branches. 

 These finally unite laterally to form an intra-epithelial net- 

 work, which in abundance of threads is not inferior to the 

 deep intra-epithelial network of the cornea of the rabbit. 



In the preceding description we have noticed the distribu- 

 tion of the non-meduUated nerve-fibres in general ; now we 

 turn to consider the relation of these to the blood-vessels and 

 glands. It is known that Kessel (30) asserts, in the case 

 of the membrana tympani, and Tomsa (31), in that of the 

 papillae of the skin, that a connection exists between the 

 fine non-medullated nerve-fibres, distinguished by their 

 nuclei, and the oblong nuclei of the capillary wall ; (Kessel 

 considers this only probable ; but Tomsa, on the other hand, 

 expresses a very decided conviction). Through the conclusions 

 which I draw from my preparations I am not only unable to 

 confirm the existence of such a connection in the capillaries 

 of tlie nictitating membrane, but I must deny it. 



In the nictitating membrane we find that numerous nerves, 

 which we have designated nerves of the second order, approach 



