ROOTS, TRUNK, BRANCHES OF VAGUS NERVE 41 



neuriiim (fig. 12). These bundles of non-medullated axons corre- 

 spond to the unstained areas in the osmic acid preparations (fig. 5). 

 While these axons are evenly distributed in some portions of 

 the large root, they have a tendency to be grouped into bundles 

 of from 5 to 50 or more. 



The fiber bundles on the left hand border of the large root 

 (14) are of mixed character with the fine meduUated fibers of the 

 Type I rootlets predominating. Number 13 is also of mixed 

 character, being mostly of Type I but containing two small areas 

 of Type II. Figure 13 was drawn from this fascicle and shows 

 one of the two groups of non-medullated fibers situated at the 

 periphery of the radical. These are scattered among large and 

 medium-sized medullated fibers. Elsewhere in the drawing the 

 fine medullated fibers predominate. The two areas in figure 

 13 have the structure of the Type II and the Type I rootlets 

 respectively. 



Pyridine-silver preparations, then, correspond to the osmic acid 

 preparations so far as the number, size and distribution of the 

 medullated fibers in the \'arious rootlets are concerned. In ad- 

 dition, they show the presence in the vagus rootlets of Type II 

 of enormous numbers of non-medullated axons. These occupy 

 the areas which are unstained in osmic acid preparations. They 

 are many times more numerous than the medullated fibers in 

 the rootlets of this type. 



So far as we know, these fibers have not been observed before 

 in the roots of the vagus. JNIolhant saw them in the trunk of 

 this nerve; and Gaskell inferred then' presence here, basing his 

 inference on the unstained areas in osmic acid preparations. 

 Their presence in the rootlets is of special importance, since it 

 shows that those found in the trunk are not s>anpathetic fibers 

 as was maintained by Molhant. They belong properly to the 

 vagus nerve. 



We wish to call attention to the striking similarity between the 

 vagus rootlets of Type I and the efferent roots of the spinal 

 nerves, and between the vagus rootlets of Type II and the affer- 

 ent roots of the spinal nerves. The efferent spinal nerve roots 



