NON-MEDTJLLATED NEBVE-FIBRES. 23 



mate structure of the axis-cylinder refers to the longitudinal 

 striations. These are observed in many fibres, but they are 

 not constant. Some authors have adopted the view that 

 the markings are produced by fibrillse, analogous to the 

 fibrillse of the muscular fibres, in all the fibres, as well as in 

 those of the retina, 'Olfactory, and some of the sympathetic 

 nerves. 1 In the organs of special sense, there can be no 

 doubt of the existence of fibrillse ; but this is by no means so 

 clearly demonstrable in the general system of nerves. Still, 

 it is necessary to take into consideration, in this connection, 

 certain facts with regard to the origin of the nerve-fibres in 

 the cells and their ultimate distribution in sensitive parts. 

 In the final distribution of sensitive nerves, we shall see that 

 the fibres break up into filaments resembling fibrillee, and 

 although the fibrillated . character of the poles of the nerve- 

 cells is not unreservedly accepted by anatomists, many ob- 

 servers positively state that such is their structure. In the 

 present condition of the science, we cannot do more than 

 state that, while a fibrillated structure has perhaps been 

 shown in the nerves of some of the lower orders of animals, 

 its existence in man and the mammalia is somewhat doubtful. 

 The diameter of the axis-cylinder is about one-half or one- 

 third that of the tube in which it is contained. The various 

 appearances which the nerve-fibres present under different 

 conditions are represented in Fig. 1. 



Simple, or Non-meduUated Nerve-Flares. These fibres 

 are found very largely distributed in the nervous system. 

 In the last edition of what is perhaps the most authoritative 

 work on histology, it is stated that " the more we advance 

 in our researches, fhe more evident it becomes that, in man 

 and the higher classes of animals, nerve-fibres without the 

 white substance are very widely distributed." a However, 



1 SCHULTZE, in STRICKER, Manual of Human and Comparative Histology, 

 London, 1870, vol. i., p. 147, et seq. 



2 KOLLIKER, op. cit., p. 322. 



