ROOTS, TRUNK, BRANCHES OF VAGUS NERVE 45 



STRUCTURE OF THE VAGUS AND ACCESSORY NERVES AT THE 

 LEVEL OF THE JUGULAR GANGLION 



Traced distally, the roots described in the preceding section 

 converge toward the jugular foramen. The rootlets of the vagus 

 fuse into a single trunk; and the bulbar rootlets of the accessory 

 one after another join the spinal root of that nerve. All these 

 bulbar rootlets join the same side of the spinal root on the sur- 

 face of which they form a crescentic field. The fibers in this 

 bulbar area do not mix with those of the spinal portion. 



After this fusion has taken place, there are two trunks, the 

 vagus and accessory nerves, running side by side. Shortly after 

 the vagus rootlets have united into a single trunk the jugular 

 ganglion appears. It first is seen as a group of cells in the con- 

 nective tissue at one side of the nerve (fig. 9) . In the succeeding 

 sections groups of ganglion cells appear within the fascicles of 

 the nerve trunk ; and for some distance downward columns of gan- 

 glion cells are seen in the nerve. Kolliker ('96) says that, whereas 

 in man the vagus goes with all its roots into the jugular ganglion, 

 in the dog a small part of the nerve remains separate from the 

 ganglion. Macroscopically this might seem to be the case, but 

 microscopic sections show cells of the jugular ganglion at some 

 level in practically all parts of the trunk. It is impossible to say 

 that any bundle of nerve fibers is entirely free from nerve cells. 

 The jugular ganglion is, then, represented in the dog by an accu- 

 mulation of cells on one side of the nerve and by cells scattered 

 more or less diffusely through it. 



Bundles of nerve fibers can be seen passing from the laterally- 

 placed accumulation of ganglion cells into the nerve trunk. In 

 these bundles one sees some non-medullated fibers. This indi- 

 cates that some of the non-medullated fibers seen in the roots 

 arise from cells in the jugular ganglion, just as the non-medullated 

 fibers in the dorsal roots arise from cells of the spinal ganglia. 



In tracing the roots distally in the serial sections, one sees that, 

 at a level slightly below the beginning of the jugular ganglion, 

 the vagus and accessory nerves unite to form a single trunk. 

 The accessory nerve is shown in the right third of figure 9. The 



