PISCES. 
circumstance which proves that their brain does 
not grow in the same proportion as the rest of 
the body; indeed Cuvier found the dimen- 
sions of the brain nearly similar in individua!s 
of the same species, though one might be 
double the size of the other. 
Fig. 526. 
Brain of Perch, upper surface. (After Cuvier. ) 
a, cerebellum; b, hollow (cerebral) lobes ; ¢, ol- 
factory lobes; other letters as in the two following 
figures. 
The encephalon consists of a series of lobes 
situated one behind the other (fig. 526), con- 
cerning the precise analogies of which no two 
authors seem to be agreed. In the following 
account of its general structure we shall there- 
fore closely adhere to Cuvier’s masterly analysis 
of the organization of the brain of the Perch, at 
the same time, however, noticing the opinions 
of anatomists, and the principal variations, ob- 
servable in other Fishes, from the form of brain 
selected for special description. 
The anterior pair of lobes (figs. 526, 527, c,c ) 
invariably give origin to the olfactory nerves, and 
consequently are very generally called the olfac- 
tory lobes of the brain. Their surface is most 
frequently smooth, but occasionally marked, as 
for example in the Cod, with slight sulci. 
Their relative size varies very much, but they 
are generally, but not always, smaller than the 
succeeding pair of lobes (6,6). They are con- 
nected with each other inferiorly by a commis- 
sure, which is sometimes double, and the in- 
ternal fibres of the medulla oblongata may be 
distinctly traced into their substance. 
In front of these olfactory lobes there are gene - 
rally one and sometimes two pairs of ganglia 
(figs. 526, 527, 528, i, 7) connected with the 
origins of the olfactory nerves, which, when very 
large, might be mistaken for additional lobes of 
the brain. They are, however, never connected 
by commissural fibres to their fellows of the 
opposite side, and the olfactory nerve can be 
traced along their under surface as far as the 
roper anterior lobes of the encephalon (c, c ). 
nternally they frequently present a ventricular 
cavity, which communicates beneath the ante- 
rior commissure with that of the cerebral masses 
next to be described. 
The second pair of cerebral lobes (figs. 526, 
527, 528, b, b) are of an oval form, and are re- 
markable from the circumstance that they enclose 
a wide cavity or ventricle, whence they have been 
designated by some anatomists the hollow lobes 
(fig. 527, b). They consist, like the cerebral 
lobes of the higher Vertebrata, of two layers, 
which are generally easily separable ; the outer 
layer consisting of grey or cineritious matter, the 
inner layer of the white or fibrous substance of 
the brain, the fibres of the latter running trans- 
VOL. III. 
- 
993 
versely so as to line the roof of the ventricular 
cavity, which is common to both sides of the 
brain; for although the hollow lobes are united 
to each other superiorly along the median line so 
as to form a kind of corpus collosum with a me- 
dian raphé, there is no septum between the two 
sides. The fibres lining the ventricular cavity 
seem to emerge from two semicircular bands of 
grey matter (fig. 527, h, kh.) situated upon the 
floor of the ventricle. 
Brain of Perch, with the ‘« hollow lobes” laid open, 
and the cerebellum turned to the right side. ( After 
Cuvier. ) 
Letters a, b, c, as in last figure ; g, supplementary 
cerebellic lobes; A, fibres lining the ventricular 
cavity. 
At the bottom of the ventricular cavity there 
are likewise, in osseous Fishes, two or four 
tubercles of grey substance placed in front of 
the base of the cerebellum, and arching over 
the canal which leads from the large cavity 
contained in the hollow lobes into the ventricle 
behind the cerebellum, which it is impossible 
to consider as anything else but the representa- 
tive of the fourth ventricle of the superior classes 
of animals, and the canal of communication as 
the “ iter a tertio ad quartum ventriculum” of 
the human anatomist, the tubercles themselves 
being evidently the homologues of the tubercula 
quadrigemina. 
The external fibres of the medulla oblongata 
are easily traceable into the lobes we are now 
considering, which, moreover, are connected 
with each other by a broad commissure exactly 
corresponding in situation with the anterior 
commissure of the human brain. There can, 
therefore, be no reasonable doubt that the 
“ hollow lobes” of the Fish’s brain represent 
the cerebral hemispheres of the encephalon of 
Reptiles, Birds, and Quadrupeds, and, with 
the data above given before us, it is not difficult 
to point out the analogies of the remaining parts 
not displayed in the figure. Thus, immedi- 
ately behind the commissure is a passage 
leading into the cavity, which corresponds to 
the third ventricle, and which leads as usual to 
the infundibulum and towards the pituitary 
body that occupies its usual situation at the 
base of the brain. 
The internal fibres of the medulla oblongata 
may be traced forwards into these hollow cere- 
bral lobes, in which they spread out as in the 
higher animals. 
At the inferior surface of the brain, beneath 
the “ hollow lobes” just described, are two oval 
protuberances ( fig. 528, e, e), which are desig- 
nated by Cuvier the inferior lobes, between the 
anterior extremities of which is situated the 
3s 
