ROOTS, TRUNK, BRANCHES OF VAGUS NERVE 47 



The structure of the external branch of the accessory nerve as 

 it leaves the common trunk is the same as that of the spinal root. 

 In fact, as has been seen by the study of these serial sections, 

 the spinal root maintains its individuality throughout the com- 

 mon trunk, where it runs as a well-defined bundle, and leaves 

 the common trunk as the ramus externus. The vagus and the 

 bulbar portion of the accessory have the same structure as at a 

 higher level but are less sharply separated from each other. 



Below the level of the origin of the external branch of the 

 accessory the vagus trunk, which now contams the bulbar fibers 

 of the accessory, may continue for a short distance as a single 

 trunk. It is usually, however, at once broken up again into fas- 

 cicles. Or perhaps it would be better to say that man}^ small 

 fascicles are given off which may branch and anastomose with 

 the main trunk. The complexity of this plexus formation differs 

 in different individuals. From one or more of these fascicles of 

 the vagus just above the level of the nodose ganglion the pharjTi- 

 geal branch is given off. 



In the ^'agus just below the jugular ganglion there are clear 

 areas in osmic acid preparations like those seen in the rootlets 

 of Type II. PjTidine-sih'er preparations show that these clear 

 areas are filled with non-medullated fibers. Molhant has made 

 similar observations on the structure of the vagus at this level 

 in the rabbit. 



THE VAGUS AT THE LEVEL OF THE NODOSE GANGLION 



In all cases the fascicles begin to unite into fewer bundles as 

 the nodose ganglion is approached. In some cases all of the fas- 

 cicles are united into a single trunk before the ganglion appears. 

 In others the ganglion cells appear in one or more of the still 

 separate fascicles which are then united in the ganglion. The 

 nodose ganglion presents the appearance of a fusiform swelling 

 of the nerve trunk; and apparently all the fiber bundles are 

 involved. 



In the dog the bulbar fibers of the accessory become intimately 

 mingled with the vagus fibers at or above the level of the nodose 

 ganghon. In the rabbit, according to Molhant, the fascicles 



