a NERVOUS CENTRES OF FISHES. 365° 
ing from it, are largest in those animals in which the 
rain is smallest. , 
453. It is in Fisues that we find the brain least developed, 
the cerebral hemispheres bearing the smallest proportion 
0 the other parts. On opening the skull, we usually observe 
nervous masses (three of them in pairs) lying, one in 
¢ of the other, nearly in the same line with the spinal 
sord. Those of the first pair are olfactory ganglia, or the 
lia of the nerves of smell (fig. 192 4,02). In the Shark, 
d some other Fishes, these are separated from the rest by 
uncles or foot-stalks (B, ol); a = of much interest, as 
laining the arrangement B 
which we find in Man (§ 458). 
dehind these is a pair of gan- 
jlionic masses (¢ h), of which 
he relative size varies con- 
iderably in different fishes 
thus in the Cod they are 
buch smaller than those » 
hich succeed them, whilst 
n the Shark they are much 
rger) ; these are the cerebral sp\\ 
emispheres. Behind these, 
gain, are two large masses - 
op), the optic gangli a, in Fig. 192.—Braiys oF FIsHes. 
vhich the optic nerves termi- +> Rods: By ee 
fee Awd af the back of these, overlying the top of the 
pinal cord, is a single mass, the cerebellum (ce) ; this is seen 
| be much larger in the active rapacious Shark, the variety 
whose movements is very great, than in the less energetic 
jd. The spinal cord (sp) is seen to be divided at the top by 
fissure, which is most wide and deep beneath the cerebellum, 
here there is a complete opening between its two halves. 
bis opening corresponds to that through which the cesophagus 
sses in the Invertebrata ; but, as the whole nervous mass of 
ertebrated animals is above the alimentary canal (§ 74), it 
.0es not serve the same purpose in them ; and in the higher 
lasses the fissure is almost entirely closed by the union of the 
) halves of the cord on the central line. 
454. In Reprites we do not observe any considerable 
dvance in the character of the brain, beyond that of Fishes ; 
