42 LECTURES ON THE CENTRAL NERVOUS SYSTEM. 



passes directly into a nerve-fibre. Recent investigations have 

 shown that before passing off it gives rise to minute fibrils, 

 which form a fine net-work. This direct form of nerve-oriain 



o 



has been recognized in the great pyramidal cells of the cortex, 

 and in the cells of Purkinje in the cerebellum, in the nuclei of 

 the motor nerves in the brain and spinal cord, and in other places. 



In many other cells, however, the processes, soon after 

 leaving the cells, break up to form a fine net-work, which re- 

 ceives, also, the lateral fibrils of the axis-cylinder processes 

 before mentioned, and from this net-work the nerve takes its 

 origin. This net-work may contain the offshoots of a great 

 number of ganglion-cells. In the accompanying section through 

 the pleural ganglion of a snail you may see both methods of 

 nerve-origin taking place side by side (Fig. 24). 



AY hat part is played by the cell processes which do not 

 become connected with the nervous system Golgi calls them 

 protoplasmic processes is not yet determined. There is ground 

 for believing that they are connected with the fine net-work 

 composed partly of glia and partly of connective tissue, which 

 surrounds the blood- and lymph- vessels of the central nervous 

 system ; that is, that they bear some relation to the nutrition of 

 the cells themselves. The fact that this fine net-work, which 

 consists of all these processes of ganglion- and giia- cells, is so 

 difficult to disentangle has naturally led to other views as to its 

 composition than the one I have given you, but it is important 

 to notice that all the later authors, whatever their differences of 

 opinion in regard to the net-work (Leydig, Nassen), have ob- 

 served the double method of origin of nerve-fibres. 



It is probable that the difference in origin denotes a differ- 

 ence in function. We know that the motor roots of a peripheral 

 nerve arise directly from the axis-cylinder of the cells, and it 

 was in the sensory posterior roots that Gerlach observed the 

 breaking up of the nerves into this minute net-work. The in- 

 vestigations of His, to which I referred in the last lecture, bear 

 out the views we have adopted. 



