GANGLIA 



151 



within the ganglion. Nerve fibers from the sympathetic ganglia also enter 



the spinal ganglia and form pericellular arborizations about the cells 



of the second type. Dogiel 



found also that multipolar 



ganglion cells occur in the 



spinal ganglia of the adult as 



well as of the embryo. 



The more recent work of 

 Cajal (1905), Dogiel (1908), 

 and Ranson (1912) has re- 

 vealed a third distinct type 

 of cell formerly apparently 

 included under Dogiel's Type 

 I : smaller, pyriform, uni- 

 polar, cells with non-medul- 

 lated axon, rarely convoluted, 

 dividing into a central and 

 a peripheral branch, the ex- 

 act terminations of which are 

 unknown ; but having accord- 

 ing to Ranson apparently the 

 same distribution as the 

 coarser medullated fibers of 

 Type I, and probably affer- 

 ent in nature (Jour. Comp. 

 Neur., vol. 22, 1911). In 

 cat and rat Ranson esti- 

 mates the number of these 

 cells at two-thirds that of the 

 total number. These are the 

 cells which contribute the 

 bulk of the very numerous 

 non-medullated fibers of the 

 spinal nerves, only a small 

 portion of which are believed 

 to arise in sympathetic gang- type of ganglion cells. (After Dogiel.) 

 lia. 



With the exception of relatively few cells of bi- and multipolar form, 

 all of the nerve cells of the spinal ganglia are unipolar in the adult 

 condition. In the case of the larger cells, the medullated aron before 



FIG. 168. SCHEMATIC REPRESENTATION OF THE 

 RELATIONS OF THE STRUCTURES COMPOSING 

 A SPINAL GANGLION. 



A and B, ventral and dorsal spinal nerve 

 roots; Cj a spinal nerve; D and E, its ventral 

 and dorsal divisions; F, its ramus communicans. 

 a, nerve cells of the first type, whose neuraxes 

 divide and form the axis cylinder of a peripheral 

 and a central nerve fiber; 6, nerve cells of the 

 second type, whose neuraxes, n, end in a felt 

 work about the cells of the first type; s, sym- 

 pathetic nerve fibers which terminate in a bas- 

 ket work about the cell bodies of the second 



