50 



/r 



attached to the dorsal surface of the prosencephalou , its point of 

 attachment being visible from above. Just in front of the brain, it 

 bears a filiform ganglion (gfw), and then runs forward like a delicate 

 thread along the side of the tractus. Passing over the bulbus from 

 behind, it dips into the fissure separating the two divisions of the ol- 

 factory nerve. But widening the fissure, the slender nerve can be 

 readily followed to the base of the olfactory cup. In the specimen 

 sketched, the membranous envelope was trimmed close to the base of 

 the olfactory cup, in order to expose the bundles of the fila olfactoria, 

 where they are united with the bulbus. 



I have also dissected the nerve in Squatina fimbriata in which 

 form, both the brain and the anatomy of this nerve are strikingly 



similar to those of 

 Squatina angelus. 



In Raja sps. 

 — I have observed 

 this nerve in several 

 species of Raja (aste- 

 rias, clavata, erinacea, 

 laevis, macrorhynchus 

 etc.). It is connec- 

 ted by two slender 

 roots with the an- 

 terior dorsal surface 

 of the prosencephalon 

 (Fig. 15), and bears 

 an inconspicuous gan- 

 glion (not represented 

 in the figure). 



The ganglion of 

 R. clavata although 

 small is well defined. 

 It lies in contact with 

 the surface of the brain, near the point where the roots penetrate the 

 brain-wall. It is, however, not freely exposed but must be dissected 

 free from connective tissue and blood vessels. There is also another 

 smaller enlargement, containing ganglion cells, in the angle between 

 the brain and the olfactorius tractus. In R. asterias and R. laevis, 

 the long slender ganglion, near the union of the olfactory tractus and 

 brain, is easily overlooked. 



In front of the gangUon the nerve passes along the inner margin 



n npl 



msence. 



Fig. 15. Brain of an adult Eaja sp., )x( 1, 



