STBTJCTUBE OF THE ENCEPHALON. 655 



arachnoid cavity, such as exists in Man. It has been remarked that the 

 interval between the cranium and the brain is considerably less in young 

 than in mature fishes a fact which sufficiently proves that in them the 

 brain does not grow in the same proportion as the rest of the body ; and, 



Fig. 319. 



Brain and cerebral nerves of the Perch (after Cuvier): c, the cerebellum; b, cerebrum; 

 c, olfactory ganglia ; i, bulbous commencement of the olfactory nerve ; o o, olfactory nerve, ter- 

 minating in the nasal capsule; , optic nerve ; p, q, third, fourth, and sixth pairs of nerves, 

 appropriated, as in Man, to the muscles of the eyeball ; a, ophthalmic branch of the fifth 

 pair ; , superior maxillary branch of ditto ; 6, inferior maxillary branch of ditto ; ft, opercular 

 branch ; f, branch of the fifth pair, mounting upwards to join 6, a branch from the eighth pair, 

 running to supply the dorsal region of the body ; s s, auditory nerve ; 1 1', nerves belonging to 

 the eighth pair ; w, z, nerves answering to the spinal recurrent. 



indeed, the size of the brain is nearly equal in individuals of the same 

 species, even although the body of one be twice as large as that of the 

 other*. 



(1801.) In these, the lowest forms of Vertebrata, the brain consists 

 of several masses placed one behind the other, either in pairs or singly ; 

 these masses, in fact, may be regarded as so many distinct ganglia, the 

 complexity and perfection of which we must expect to become gradually 

 increased as we proceed upwards towards mammiferous quadrupeds. 



(1802.) The anterior pair of ganglia (figs. 319, c ; 320 ; 322, a) 

 invariably give origin to the olfactory nerves, and consequently may 

 be justly looked upon as presiding over the sense of smell. These 

 ganglia are, in fact, the representatives of those masses which in Man 

 are erroneously called the " olfactory nerves ; " for even in the human 

 subject, although their real nature is obscured by the enormous develop- 

 ment of other parts of the encephalon, the so-called nerves are not 

 nerves at all, but really lobes of the brain from which the true nerves 

 emanate. 



* Cuv. et Val. op. cit. 



