306 Illinois State Lahoratory of Natural History. ^ 



The auditory (eighth) is a stroDg nerve which arises- 

 just behind the facial and on a level with it, but is com- 

 pletely independent. It divides into two branches at 

 once, and these subdivide before being distributed to the 

 ear. 



A considerable space separates the ninth nerve (glosso- 

 pharyngeal) flora the eighth. It is slender in Polyodon, 

 and extends backward parallel with the spinal cord at 

 first, lying beneath the tenth nerve (vagus), so that it is 

 not visible from above. A short distance posterior to 

 the medulla it turns outward and then becomes distin- 

 guishable. 



A slender nerve arises above the ninth and extends 

 back over it to the side of the tenth with which it joins 

 and mi^rges, though not entirely losing its identity as 

 far as followed. I take this to be the lateral line nerve. 

 Near its origin it exchanges fibers with the ninth. 



One of the largest cranial nerves in Polyodon is the 

 vagus, although it is not as large as in A. "rnbicundus. 

 It arises well back on the side of the medulla, on a level 

 with the nerves just mentioned. Its fibers separate into 

 bundles where it joins the medulla, of which I count 

 eleven, the two hindmost being smallest and turning 

 abruptly out of the general course to join the medulla. 



The sixth nerve (abduoens) I have not studied in Poly- 

 odon. In A. rubicundiis it is very small, and arises by 

 two roots near the ventral middle line, about midway 

 between the eighth and ninth nerves. 



Further explanation may be left to the figures accom- 

 panying these notes. 



Looking at the brain of Polyodon as a whole, and as 

 compared with that of the sturgeon and other fishes, 

 it may be said that it impresses one as that of a fish 

 of inferior rank, although the yjeculiar snout and other 

 features of the anatomy speak of a somewhat special de- 

 velopment. The large relative size of the medulla oblon- 

 gata and the undivided and poorly developed fore- and 



