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



contain few, if any, non-niedullated fibers, and differ from the 

 rootlets of Type I only in containing a much smaller proportion 

 of fine medullated fibers. This difference is easily understood 

 when one remembers that the vagus innervates the thoracic and 

 abdominal viscera, and its efferent rootlets should contain an 

 excessive number of fine autonomic fibers. The afferent roots of 

 the spinal nerves contain, in addition to medullated fibers of all 

 sizes, large numbers of non-meduUated axons, that is, essentially 

 the same elements as are found in the vagus rootlets of Type II. 

 The proportion of non-medullated fibers is undoubtedly greater 

 in these rootlets of the vagus than in the dorsal roots of the spinal 

 nerves; but otherwise the smiilarity is complete. In view of these 

 facts it seems probable that the afferent and efferent fibers of the 

 vagus leave the medulla by separate rootlets. In the mixed 

 rootlets the areas representing each of the two types are sharply 

 marked off from each other and are formed by the fusion of one 

 or more smaller rootlets of each type. 



Fig. 10 From a section of the common vagus-accessory trunk below the level 

 of the jugular ganglion; the spinal portion of the accessory to the right, the vagus 

 to the left and the bulbar portion of the accessory in the middle. Pyridine-silver. 

 Dog. X 73. 



Fig. 11 From a section of the right common vagus-sympathetic trunk just 

 above the level of the subclavian artery. The crescentic area in the lower part 

 of the drawing is the sympathetic trunk. The bundle of large medullated fibers 

 in the upper part of the drawing represents the beginning of the recurrent nerve. 

 Pyridine-silver. Dog. X 73. 



Fig. 12 From a section of a Type II vagus rootlet. Medullated axons light, 

 myelin sheaths colorless, non-medullated fibers black. Pyridine-silver. Dog. 

 X G18. 



Fig. 13 From a section of a mixed vagus rootlet. At the left near the periph- 

 ery is an area having the structure of the Type II rootlets and containing, in 

 addition to medullated fibers of all sizes, large numbers of non-medullated axons. 

 To the right is an area having the structure of the Type I rootlets, containing 

 chiefly small medullated fibers. Pyridine-silver. Dog. X 618. 



Fig. 14 From a section of the vagus below the level of the nodose ganglion. 

 The medullated fibers are of all sizes and are widely separated by great numbers 

 of non-medullated axons. Pyridine-silver. Dog. X 618. 



Fig. 15 From a section of the superior laryngeal nerve, medullated and non- 

 medullated fibers. Pyridine-silver. Dog. X 618. 



Fig. 16 From a section of a fascicle of the esophageal plexus. Six medullated 

 and great numbers of non-medullated fibers. Pyridine-silver. Dog. X 739. 



