328 FISHES 



are distinguished from the remainder of the medulla oblongata, the 

 nerve of the third pair arises. 



These appear to me to be much larger in the surmullet than in any 

 other species of fish, they are excavated by a ventricle, and their sur- 

 face is furrowed. 



The name to be given to the pairs of lobes just described, and 

 which are situated in front of the cerebellum, will depend on the re- 

 lative importance that may be attributed either to the complication of 

 their structure, or to their being the origin of the optic nerve. 



If we attend to the origin of the optic nerve, it is certain that we 

 shall lind an analogy between the hollow lobes and this external pair 

 of lobes of brain in birds, to which latter the name of optic thalami 

 has been given, but which are stated by M. Gall to be the analogues 

 of the tubercula quadrigemina. 



But if we attend to the structure of the hollow lobes, to that semi- 

 circular part (A), a sort of notched body forming the internal base of 

 their envelope, and from which the tranverse fibres of their roof are 

 given off, then if we attend to the position of the third ventricle, to 

 that of the commissure (?n), placed before the opening of the ventricle, 

 and which necessarily corresponds with the anterior commissure of 

 the brain, with the small tubercles (d) hidden in their interior, and 

 which so closely resemble by their position, figure, and relations the 

 tubercula quadrigemina of the mammalia ; if all those are carefully 

 attended to, we shall not fail to recognize in them, the whole of the 

 characters that are essential to the brain of the vertebrated classes. 



This analogy will be confirmed if we make a comparison between 

 the above parts, and such of the mammalia as have the anterior por- 

 tion of their hemispheres, from which the olfactory nerve immediately 

 arises, separated from the rest by a furrow sufficiently deep, and 

 representing the anterior lobes of fishes (e, c). 



The tortoise, toad, and several other reptiles, will likewise confirm 

 this view. The olfactory lobe of their brain resembles the anterior 

 lobes of fishes, and their brain the hollow lobes of the latter. It has 

 the same bodies analogous to the notched ones, the same commissures, 

 the same entrance for the third ventricle, and for the infundibulum. 

 But in the reptiles the tubercle, analogous to the tubercula quadri- 

 gemina are large and hollow as in birds, approximated to each other 

 above as in quadrupeds, and visible externally, whilst in the fishes they 

 are at the same time, as in quadrupeds, solid, approximated to each 

 other, small and hidden, by the hemisphere which is supported behind 

 as far nearly as the cerebellum. 



It is useless to make the remark, that in the embryos of quadrupeds 

 and birds, the hemispheres are almost as small, and the tubercula qua- 

 drigemina as great, in proportion as the interior and hollow lobes of 

 fishes. The hemispheres in them are not therefore solid masses, and 

 the tubercles, although hollow, do not present in their interior, 

 notched bodies and other tubercles, still smaller. It is not under 

 them that we find the anterior commissure of the brain, nor are they 

 intercepted by the third ventricle. In the reptiles which have been 

 also collected for comparison, it is true as we have already said, that 



