Nos. IAND2.] ANATOMY OF SCOMBER SCOMBER. 231 



backward. The dorso-posterior part of the same canal Hes against 

 and is deeply imbedded in the lateral face of the cerebellum. The 

 posterior two fifths, or two thirds, of the united optic lobes, accord- 

 ing to the specimen examined, are overlapped dorsally, in the 

 middle line, by the anterior two thirds of the cerebellum, and they 

 themselves slightly overlap dorsally and laterally the hind end of 

 the forebrain. 



The forebrain, at its hind end, is about one half as wide and one 

 half as thick as the midbrain with its optic lobes, and lies in front 

 of the dorsal half of the latter structures. It is separated, dor- 

 sally, by a deep fissure from the optic lobes, and ventrally is con- 

 tinuous with the midbrain. The optic nerves arise immediately 

 ventro-posterior to it, from what, in lateral views, appears as the 

 ventral half of an anterior surface of the midbrain. What I take to 

 be, in Studnicka's (No. 72) terminology, the posterior lobes of the 

 forebrain, are strongly reflexed, and what are apparently simply 

 the lobi olfactorii lie immediately in front of them. The flat 

 membranous roof of the forebrain extends from the lobi pos- 

 teriores forward onto the lobi olfactorii, but its limits could not 

 be traced. In front of the lobi olfactorii the bases of the olfactory 

 nerves are always somewhat enlarged and rounded, and in all the 

 fresh, or freshly preserved, specimens this part of each olfactory 

 nerve presented strongly the external appearance of a bulbus. In 

 certain specimens this part of the nerve had even a greater diameter 

 than the lobus from which it arose. Whether this conformation 

 is due simply to the lateral pressure of the greatly enlarged orbits, 

 or represents some differentiation in the olfactory parts of the 

 brain was not investigated. 



The cerebellum, as seen in dorsal views, is oval in outline, in its 

 central part, and varies considerably in length, relatively to other 

 parts of the brain. Its anterior end projects forward and lies 

 directly upon and between the optic lobes, which it overlaps for 

 from two fifths to two thirds their length. Lateral to its posterior 

 portion there is, on each side, a pronounced swelling which is 

 apparently the homologue of what Wright (No. 80, p. 354) con- 

 siders, in ^'^jiiiiiriis, as the tuberculum acusticum. Herrick con- 

 sidered this same structure in the Siluridse, Ammrus included 

 (No. 37, p. 224), as a homologue in part of the restiform bodies. 



