No. I.] SYMPATHETIC GANGLIA OF VERTEBRATES. 71 



however, come in contact with the cell bodies of the sympa- 

 thetic cells, but are separated from them by their capsule. 



Dogiel (40) has further described a " general peripheral 

 plexus," situated under the fibrous capsule of the ganglion. In 

 the formation of this kind of plexus, dendrites from nearly all 

 the cells of the smaller ganglia and many of the cells of the 

 larger ganglia take part, the dendrites from the cells situated 

 more centrally in the ganglia winding their way out until the 

 plexus is reached. 



Neiiraxis. — It is now very generally conceded that the sympa- 

 thetic neurons of Mammalia possess one neuraxis — axis-cylin- 

 der. This may arise from the cell body or from a dendrite at 

 a variable distance from the cell body. In making the latter 

 statement I have been guided largely by observations made 

 by others, as in sections where, as a rule, only relatively short 

 segments of the axis-cylinder are met with, it is often exceed- 

 ingly difficult to classify the processes of any particular sympa- 

 thetic cell. In most preparations the axis-cylinder branches 

 are not stained in any way characteristically. Sometimes, 

 however, as may be seen in PI. V, Fig. 26, they stain a deeper 

 and more purple shade of blue, which color differentiation may 

 aid in making out which one of the several processes of a sym- 

 pathetic cell is the axis-cylinder. In such sections I have been 

 able to coniirm the statements made above. Near the cell 

 body the neuraxes of the sympathetic cells of Mammalia have 

 a very regular contour and maintain about the same size ; and 

 Dogiel (40) has described a very delicate longitudinal striation, 

 caused by a deeper staining of the ultimate fibrillae of the 

 axis-cylinder. 



Kolliker (32), who has for many years paid especial attention 

 to the structure of the neuraxes of sympathetic cells, has quite 

 recently summarized his observations as follows : 



i) The sympathetic nerve fibers (axis-cylinder processes of 

 sympathetic cells) are in many cases surrounded by a very deli- 

 cate sheath of myelin. 



2) In some of these fibers the sheath of myelin accompa- 

 nies the neuraxis to its periphery — nerve fibers from the ciliary 

 ganglion and the pilo-motor nerves of the cat. 



