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



;iii(l ])yii(liiu>-sil\or ])i'oi):ii-ali()ns <>;ivo mutually supplementary 

 pictures. Ijiirg-o and inodiuin-sizcMl inedullated axons are easily 

 recogiiizod in the silvei- preparations by the clear" unstained rings 

 of myelin which surround them. In order to make sure of the 

 differentiation between the finest medullated and the non-med- 

 ullated fibers, it is necessary to supplement the silver prepara- 

 tions by those stained with osmic acid. 



In hgure 3 is shown a drawing of the roots of the vagus and ac- 

 cessory nerves taken at about the same level as figure 2. The 

 relative position of the individual rootlets is much the same in 

 the two figures. Pyi'idine-silver preparations confirm the find- 

 ings in those stained with osmic acid, in so far as the medullated 

 fibers are concerned. 



The light yellow axons of the large medullated fibers, sur- 

 rounded by thick unstained rings of myelin, give the spinal root 

 of the accessory nerve (c) a light color. The bulbar rootlets of 

 the accessory (h) are stained more darkly, because the small 

 medullated axons of which the roots are chiefly composed stain a 

 dark brown. In these preparations one can readily recognize 

 the thin clear rings of myelin surrounding the finest of the med- 

 ullated fibers. There are few, if any, non-medullated fibers in 

 the roots of the accessory nerve. 



The two types of vagus rootlets are clearly differentiated in 

 pyridine-silver preparations. Those of Type I (Nos. 1 to 7 and 

 11) have the same structure as the bulbar rootlets of the 

 accessory, and contain many small and fewer large medullated 

 fibers and very few, if any, non-medullated axons. It will be 

 seen that these rootlets are arranged somewhat differently than 

 in figure 2. 



The large root, 14, came off the medulla as a single trunk. The 

 fiber bundles on its left hand border are of mixed character. 

 But the rest of the large root 14 and the rootlets 8, 9, 10 and 12 

 are of Type II. In these the medullated fibers are of all sizes 

 rather widely separated from each other. In the areas left \'a- 

 cant by the medullated fibers are seen enormous numbers of 

 axons stained black and imbedded in the light yellow endo- 



