61 



the lateral and penetrates the brain-wall in a median depression near 

 the optic chiasma. The lateral root connects with the brain-wall naore 

 anteriorly and laterally. 



The ganglion varies in position and size, it is usually near the 

 bulbus, with the roots joined to it by a single stem, but sometimes 

 it lies on the base of 

 the brain with the roots 

 divided to the ganglion 

 as shown in D. In front 

 of the ganglion, the 

 nerve divides into three 

 branches (two principal 

 ones) which join the di- 

 visions of the olfactory 

 nerve. 



The two divisions 

 of the olfactory nerve 

 are separated by a very 

 distinct fissure, and the 

 bundles of the fila ol- 

 factoria comprising these 

 divisions, are also se- 

 parated, and lie like 

 cords on the olfactory 

 cup. This is the only 

 form in which this con- 

 dition has been observed. 



In Carcharias 

 lit tor alls. — Of all 



the selachians I have Fig. 24. a, brain of adult Pristiurus melano- 



examined the new nerve stomus. B, slightly enlarged view of the olfactory cups 



' and new nerve. C, partly diagramatic view of the same 



is most readily seen in the froiü^ below. D, two ganglia of the same with their roots. 



sand ♦ shark , Carcharias 



littoralis. It is always more or less difficult to see this nerve before 

 the brain has been stained, but in Carcharias [Fig. 25) the nerve can 

 readily be detected before staining. It is connected with the ventral 

 surface of the brain as in Mustelus, considerably in front of the optic 

 nerve. The course of the nerve from its ventral connection, is nearly 

 in a straight line to the olfactory cup. It runs obliquely towards the 

 long slender tractus and, after reaching it, runs for a part of its course 

 directly upon the tractus. The result is that the nerve enters the 



