560 PHYSIOLOGY OF THE NERVE CELL AND THE SPINAL CORD 



FlG- 



coarse nner 



and distinct, although both in the central and in the sympathetic nervous 

 system the end tree of one neuron may twine about the cell body of the 

 second so that the latter is brought into contact with the former neuron. 

 Any anastomosis or actual structural continuity of dendrite with end arbor- 

 ization is, therefore, emphatically denied. Every- 

 thing takes place by mere contact. 



In view of the work of Apathy and Bethe, this 

 position, however, is no longer tenable, for it appears 

 to have been definitely shown that the different nerve 

 units do unite by anastomosis. 



According to Apathy's researches chiefly on inver- 

 tebrates the nerve fibers consist of fine neurofibrils 

 which constitute independent morphological elements. 

 Within the nerve fiber they preserve their individuality 

 throughout and have no connection whatever with one 

 another. In the peripheral end organs the individual 

 fibrils split up and form an anastomosing network. 

 Likewise in the ganglion cells the fibrils which enter 

 become branched and form a network. But before 

 lion cel1 of entering the cells the delicate end twigs of the affer- 

 ^ fib - form a reticulum within the dense tangle 

 network known as the neuropile, which occupies the center oi 

 From the latter a stout the ganglion. From this neuropile very delicate fibrils 

 efferent fibril is given off emerge, penetrate the ganglion cells and there form 

 (Bethe). 1^ a peripheral network (Fig. 252), from which are 



given off in turn radial fibrils that weave about the 



cell nucleus a second network of thicker fibrils and from this finally the stout 

 efferent fibril emerges. The neurofibrils therefore represent the conducting por- 

 tion of the nervous system and through them all parts of the nervous system 

 are brought into direct communication with one another (according to Bethe). 

 In certain invertebrates at least (green crab, crawfish), but a small portion 

 of the neurofibrils pass through the nerve cells. Here, then, the fibrillar tran- 

 sition from fiber to fiber, and their intermixture must take place, for the most 

 part, in the neuropile and its reticulum. 



Bethe in particular showed that the neurofibrils are present as conducting 

 elements in the nervous system of the vertebrates also. Without any inter- 

 connection the fibrils run a separate and unbroken course to the terminal 

 arborizations of both the peripheral nerve fibers and their analogues the 

 medullated fibers of the central nervous system. They occur in the nerve 

 cells also, and almost every cell process is connected with one adjacent to 

 it by a bundle of fibrils of variable thickness. In like manner each dendritic 

 process sends some fibrils into the axis-cylinder process of the cell. 



Covering the surface of the nerve cells and of their dendritic process there 

 is found a network with polygonal meshes (Fig. 253), concerning whose real 

 nature different views have been advanced. It was first described by Golgi. 

 According to Bethe, who, however, expresses himself very cautiously in 

 this regard, this network is of a nervous character, connecting on the one 

 hand with the neurofibrils of the nerve cells, and on the other with nerve 



