68 Journal of Comparative Neurology. 



cause numerous small branches are given off and received all 

 along the short distance between its ganglion and its ramus 

 communicans, and for the reason that, owing to its large size, 

 it is penetrated by osmic acid with great difficulty. 



The Xth, unlike the other nerves, passes out of the spinal 

 canal through a long foramen in th.e iirostyle (canalis coccygeus). 

 This position renders its necessary exposure to the reagent and 

 its removal without injury very difficult and justified its exclu- 

 sion at this time also. 



V. The Number and Arrangement of the Nerve Fibers 



IN the Dorsal and Ventral Roots and in the 

 Beginning Nerve Trunk. 



1. The examination of the roots consisted in counting the 

 fibers in sections taken from two or three different levels of each 

 root; i. e., the fibers of each root were counted at different dis- 

 tances from their cells of origin. The points at which the sec- 

 tions were taken are indicated by the numbers i, 2 and 3, Plate 



VI. The Plate shows also that in case of the longer roots three 

 counts were made, while for the shorter, for obvious reasons, 

 two counts were thought sufficient. 



2. Counts were made of a section of the trunk taken im- 

 mediately distal to the spinal ganglion and of a section of the dor- 

 sal branches made as close up to the ganglion as possible. (Sec- 

 tions 4 and 6, Plate VI), 



3. Another enumeration was made of the fibers contained 

 in the trunk at a point just central to its junction with the ra- 

 mus communicans. (Section 5, Plate VI). 



The results of such enumerations are presented in Tables 

 I and II. These tables contain results obtained from two differ- 

 ent specimens. They show (i) that, as indicated in the col- 

 umns A, B and c, the number of fibers in the ventral root re- 

 mains constant or decreases in the course of the root from the 

 spinal cord towards the dorsal root ganglion ; (2) that the num- 

 ber of fibers in the dorsal root remains constant or decreases in 

 the course of the root from the ganglion towards the spinal 

 cord. Leaving the roots and turning to the trunk, the tables 



