THE SPINAL NERVES 65 



the peripheral branch of the axon breaks up within the ganglion into numerous myelinated 

 fibers, which after losing their sheaths terminate in what are apparently sensory endings. 

 The central branch runs apparently without division to the spinal cord. The cells of Type 

 XI possess, in addition to an axon, that apparently runs without division through the dorsal 

 root to the spinal cord, several processes that resemble dendrites, in that they divide re- 

 peatedly within the ganglion, but resemble axons in their appearance and in possessing 

 myelin sheaths (Fig. 40, b). These processes after repeated divisions become unmyelinated 

 and end within the ganglion and dorsal root in what appear to be sensory endings. It would 

 lead us too far afield if we should attempt to summarise Dogiel's work. It should be pointed 

 out, however, that he no longer believes in the existence of the cells which he formerly de- 

 scribed under the head of spinal ganglion cells of Type II and which find a conspicuous place 

 in most text-books. He believes that what he formerly described as the branching fibers 

 of these cells are, in reality, the dendrite-like branches of the cells of Type XI. 



Dorsal root /, 



Dorsal ramus 



Ventral root 



Ramus communicans 



Ventral ramus 



Fig. 40. Diagrammatic longitudinal section of a spinal ganglion and a spinal nerve (cervical 

 or sacral) : a, Small cells with unmyelinated axons; b, cell of Dogiel's type XI ; c, large cell possessing 

 a myelinated axon and surrounded by a pericellular plexus; d, bipolar cell. 



According to Dogiel every spinal ganglion cell is surrounded by a network of 

 fine branching and anastomosing fibers; and he believes that these are formed 

 by the ramifications of fine myelinated and unmyelinated fibers that have 

 entered the spinal ganglion from the sympathetic nervous system through the 

 rami communicantes. While the origin of these fibers is open to question, there 

 can be no doubt that such pericellular networks exist on at least a considerable 

 proportion of the cells and constitute an important element in the structure of 

 the ganglion (Fig. 40, c}. 



The fiber bundles of the ganglia are composed of both myelinated and un- 



5 



