46 M. R. CHASE AND S. W. RANSON 



darker area in the upper right-hand corner of the drawing is the 

 bulbar portion of the accessory; the Ughter area in the lower 

 right-hand corner is the spinal portion of the accessory. The 

 spinal portion of the accessory remains unchanged and forms a 

 sharply defined zone in the common vagus-accessory trunk. At 

 no level in the series do its fibers mingle with those of the other 

 parts of the common trunk. The bulbar rootlets of the accessory 

 have fused and now form a sharply limited area wedged in be- 

 tween the spinal part of the accessory and the vagus. Thus, al- 

 though the two nerves are fused into a common trunk, it is possi- 

 ble to distinguish clearly three areas, corresponding to the spinal 

 root of the accessory, the bulbar roots of the accessory, and the 

 roots of the vagus. Each area presents the same histological 

 characteristics as the corresponding roots at a higher level. The 

 only difference is that the non-meduUated fibers are more evenly 

 distributed in the vagus at this level than they were in the roots, 

 since the fibers from the two types of vagus rootlets are now 

 thoroughly mixed. 



THE VAGUS AND ACCESSORY NERVES BETWEEN THE JUGULAR 

 AND NODOSE GANGLIA 



Below the jugular ganglion the vagus-accessory trunk may be 

 broken up into a large number of fascicles, but these are again 

 reunited into a compact trunk from which the ramus externus of 

 the accessory is given off. In one series the trunk did not break 

 up into fascicles between the jugular ganglion and the origin of 

 the external ramus. Figure 10 is a drawing from this series just 

 above the level at which the external ramus is given off. The 

 three zones seen in figure 9 are also seen in figure 10; the spinal 

 portion of the accessory to the right, the vagus to the left, and 

 the bulbar portion of the accessory in the middle. In those 

 cases in which the common trunk broke up into fascicles below 

 the jugular ganglion the fascicles again reunited to form a trunk 

 essentially like that in figure 10. The bulbar portion of the ac- 

 cessory was not so sharply separated from the vagus at this level 

 in all the nerves studied, but was in some cases scattered through 

 the vagus. 



