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



ber of non-medullated fibers in the vagus at the level of the nodose 

 ganglion proves to be real, Langley's argument would help us 

 account for this increase. It is not unreasonable to suppose that 

 the pre-ganglionic fibers of the vagus may lose their sheaths in 

 the trunk of the vagus, just as the pre-ganglionic fibers of the 

 sympathetic lose their sheaths at a distance from the cells about 

 which they end. 



THE VAGUS BELOW THE NODOSE GANGLION AND ITS RELATION 

 TO THE SYMPATHETIC TRUNK 



The vagus may remain as a single trunk throughout the nodose 

 ganglion; or toward the lower pole of the ganglion it may begin 

 to break up into fascicles with ganghon cells in one or more of 

 them. Usually the vagus is broken up into several fascicles just 

 below the ganglion. These divide and unite with one another 

 forming a complicated plexus. There is no regularity in these 

 formations. The ne/ves in different individuals present marked 

 variations. 



There is no essential change in the histology of the vagus im- 

 mediately below the nodose ganglion. The non-medullated fibers 

 are more conspicuous and appear to be present in somewhat 

 greater relative proportions. The meduUated fibers are of all 

 sizes and are rather widely separated (fig. 6). The intervening 

 tissue is unstained in osmic acid preparations, and looks like con- 

 nective tissue. But pyridine-silver preparations show that this 

 intervening tissue is filled with non-medullated axons (fig. 14). 

 They are present in astonishingly large numbers and show a 

 tendency to be grouped into bundles. 



Just before the right nerve passes over the subclavian artery 

 there is formed at one side a fascicle of large medullated fibers 

 (fig. 11). These finally leave the vagus as the recurrent nerve. 



In figure 11 is seen a cross-section of the common trunk of the 

 vagus and S3anpathetic in the neck. The sympathetic trunk is 

 flattened out on the surface of the vagus and its area in section 

 is crescentic. While the sympathetic trunk in the dog is usually 

 flattened out on the vagus at this level, it may remain throughout 



