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



by radicals 7, 13, 22, 23, 24, 25, 26, 28 and 29, resemble in every 

 respect the rootlets of the bulbar portion of the accessory. That 

 is to say, they are composed of many fine and fewer coarse med- 

 ullated fibers. They do not have the clear areas seen in the 

 other rootlets of the vagus. The other group. Type II, is rep- 

 resented by rootlets 8, 11,. 14, 15, 16, 17, 18, 19, 20 and 21. 

 These contain a considerable number of large and medium-sized 

 medullated fibers and a few small ones. But the characteristic 

 feature of these rootlets is the wide separation of the medullated 

 fibers by unstained tissue. A high-power drawing from one of 

 these rootlets is seen in figure 5, which represents an average field. 

 In some fields the fibers are more widely separated than in the 

 drawing; in other fields they are more closely packed. Even the 

 finest of these medullated fibers stain very sharply and their 

 sheaths are as black as those of the larger fibers. The interven- 

 ing tissue is light yellow and when highly magnified shows a 

 reticular structure. The stain of even the finest medullated fibers 

 is so perfect that there can be no suspicion of the presence of 

 unstained myelin sheaths in these light yellow areas. Other root- 

 lets, numbers 9, 10 and 12, are mixed in character. They pre- 

 sent areas in which the medullated fibers are widely separated, 

 combined with areas in which the medullated fibers, mostly small, 

 are closely packed. 



It ma^ be that radicals 7, 8, 9 and 10 correspond to Molhant 

 and Van Gehuchten's group b^ or lower vagus rootlets, and the 



Fig. 1 Diagram of the vagus nerve in the dog. 



a, vagus rootlets t.s., truncus sympathicus 



b, bulbar rootlets of the accessory nerve n.v.t.s., nervus vagus and truncus sym- 



c, spinal root of the accessory nerve pathicus 



g.j., ganglion jugulare g-c.i., ganglion cervicale inferior 



r.p., ramus pharyngeus art.s., arteria subclavia 



r.e., ramus externus n. accessorii n.r., nervus recurrens 



g.n., ganglion nodosum a.s., ansa subclavia 



n.l.s., nervus laryngeus superior g.s., ganglion stellatum 



n.v., nervus vagus r.b., rami bronchiales 



n.c.i., nervus caroticus internus p.o., plexus esophageus 

 g.c.s., ganglion cervicale superius 



The drawings were made by Katharine Hill. 



