362 H. W. NORRIS AND SALLY P. HUGHES 



dorsalis. Fibers from the third ganglion together with the 

 remaining fibers from the second form the ramus lateralis of the 

 trunk. In a horizontal section through the ganglionic com- 

 plex (fig. 45) there are seen external swellings indicating these 

 three ganglia. In a sagittal section the ganglion of the supra- 

 temporal ramus is seen to be anatomically distinct from the 

 others. 



In the 22-mm. embryo Landacre finds three lateral-line ganglia 

 upon the vagus. From the first the supratemporal ramus 

 emerges connecting with three lateral-line primordia; from the 

 second ganglion a ramus, evidently ramus dorsalis, connects 

 with a large lateral-line primordium, and from the third ganglion 

 proceeds the ramus lateralis. 



In Mustelus the ganglion of the supratemporal ramus is ana- 

 tomically distinct from the other vagal ganglia, not even in con- 

 tact with them. A similar condition occurs in Raja radiata. 

 In Mustelus the ganglion is sometimes very much elongate, 

 partly intracranial and partly extracranial. 



2. The roots and ganglia of the vagus nerve proper 



The visceral sensory roots of the vagus extend for a long 

 distance posterodorsally from the origin of the lateral-line roots 

 (figs. 24 and 51). There are thirty or more of the visceral roots 

 of the vagus. The majority of them are mixed, each comprising 

 a wide sensory band and a small motor element. The poste- 

 rior six or more are exclusively motor in composition. The 

 extreme posterior three or four rootlets arise from the dorsal 

 side of the medulla. Figure 43 is of a parasagittal section 

 through the lateral wall of the medulla cutting most of the vagus 

 rootlets. It will be seen that these enter the brain in an almost 

 straight line, rising gradually from anterior to posterior. As the 

 rootlets enter the brain, the motor element in each of the mixed 

 rootlets is usually ventral in position. As they pass inward the 

 sensory elements ascend into the visceral lobe, and the motor 

 fibers turn ventrally into the lateral motor column. At the 

 brain wall there is little evidence of a segmental arrangement 



