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



larger group of radicals, 11 to 29, corresponds to their group 1)', 

 or higher vagus rootlets. If this be so, their groups b^ and b^ 

 would both contain some of each of our two types of rootlets. 



The rootlets of Type II are more closely grouped together 

 than those of Type I and may come off from the medulla as a 

 single large root. Those of Type I are more widely separated 

 from each other and from those of Type II. 



To sum up the findings in osmic acid preparations of the roots 

 of the ^^agus and accessory nerves, the following statements con- 

 cerning their content of medullated fibers may be made. The 

 spinal root of the accessory nerve is composed almost wholly of 

 large fibers of uniform size. The bulbar portion of the same nerve 

 is composed largely of those of the smallest size, with some large 

 ones, and fewer of medium size. The vagus rootlets are of two 

 kinds : those of Type I have the same structure as the bulbar por- 

 tion of the accessory; those of Type II contain medullated fibers 

 of all sizes, with a predominance of the medium-sized, separated 

 by a large amount of unstained tissue. 



Pyridine-silver preparations. The pyridine-silver method stains 

 only the axons of the nerve fibers. These vary from black in the 

 non-medullated to light yellow in the large medullated fibers. 

 The connective tissue is also stained a hght yellow. Osmic acid 



Fig. 4 From a section of a bulbar rootlet of the accessory nerve stained with 

 osmic acid. Dog. X 515. 



Fig. 5 From a section of a Type II rootlet of the vagus nerve stained with 

 osmic acid. Dog. X 515. 



Fig. 6 From a section of the vagus nerve below the nodose ganglion stained 

 with osmic acid. Dog. X 618. 



Fig. 7 From a section of the superior laryngeal nerve stained with osmic acid. 

 Dog. X 618. 



Fig. 8 From a section of the recurrent nerve stained by the pyridine-silver 

 technique: a, area of large medullated fibers for the larynx; b, area of small med- 

 ullated fibers for esophagus, trachea, and heart; c, area of sympathetic fibers. 

 Dog. X 176. 



Fig. 9 From a section of the common vagus-accessory trunk at the level of 

 the jugular ganglion; the accessory nerve at the right, the jugular ganglion at the 

 left, the vagus in the middle. The section of the accessory nerve shows two well 

 defined areas: the lower, lighter area corresponds to the spinal root; the upper, 

 darker area corresponds to the bulbar rootlets. Pyridine-silver. Dog. X 73. 



