618 
primitive fibres or tubes, and com alto- 
gether of isolated cells, arranged in a linear 
direction only towards the middle of the cord, 
can transmit influences in any given direction ; 
and more especially how the tract of black or 
grey matter, if it exercises any liar fune- 
tion (excito-motory) communicates with the 
origin of the nerves. The nerves, also, are 
remarkable, originating in single roots, and 
containing in their composition one kind only 
of primitive fibres (cylindrical).”’] 
Fig. 351. 
a, first cerebral mass 
or olfactory tubercle. 6, 
olfactory tubercle sliced, 
showing its solid struc- 
ture. c, second cerebral 
mass or optic lobe, of large 
relative size. d, optic 
lobe, cut open to shew 
the internal cavity. e, 
tubercles in the cavity. 
J, third cerebral mass or 
cerebellum, tongue-sha- 
ped. g, spinal cord. h, 
posterior longitudinal fis- 
sure of spinal cord. 4, 
central canal of spinal 
cord. _ k, olfactory nerves. 
l, optic nerves. m, fifth 
pair of nerves, m, acons- 
tic nerve. 0, glossopha- 
ryngeal nerve of Cuvier. 
p» eighth pair—par va- 
gum. gq, bristle passed 
under the cerebellum and 
along the fourth ventricle, 
‘shewing the communica- 
tion of this latter with the 
cavity of the optic lobes 
or third ventricle. 
Brain and portion of spinal marrow of Gadus morhua 
( Cod-fish ), about natural size. 
The brain, especially in the lowest of the 
fishes, presents quite the appearance of a series 
of ganglia developed on the superior surface of 
the cords of the spinal marrow (fig. 351, a, b, 
c). In many species it is extremely small, and 
by no means fills the cranial cavity; in the 
mackarel, the volume of the brain and of the 
cavity destined to receive it are nearly equal. 
Its very small size is at once evident by com- 
paring its weight with that of the whole body 
of the animal: thus in a chub, weighing 842 
scruples, the brain weighed only one scruple, 
the proportions being as 100 : 84200; ina 
carp, weighing 11280 grains, the brain weighed 
only fourteen grains, the proportions being as 
100:80600 ; in a roach, weighing 5030 grains, 
the brain weighed only nine grains and a half, 
the proportions being as 100: 52,900; and, as 
before observed, in a lamprey weighing 570 
grains, the brain weighed only four-tenths of a 
in, the proportions being as 100 : 142,500. 
In Leuret’s table a discrepancy still more 
striking oe be observed. is author gives 
as a mean the proportion 1: 5668.7] We thus 
observe how small is the proportion which the 
size of the brain bears to that of the rest of the 
body, and consequently how imperfect is as yet 
the developement of the encephalic mass. 
* Systéme nerveux, t.i. p. 153, 
NERVOUS SYSTEM. (Comparative Awatomy.) a 
On taking a general review of the con- 
formation of the cerebral masses forming the 
brain of fishes, we find it to consist of a suite 
of ganglia arranged behind each other—tw 
pairs and a single one: ist, there are two gan 
glia or lobes, situated the most anteriorly, the 
olfactory lobes; immediately behind h ar 
two others, generally of larger size, the 
lobes; and behind these, in, is a sing 
ganglion or lobe, situated in the median line 
the cerebellum. On the inferior surface, im 
mediately underneath the optic lobes, are tw 
more ganglia. The names thas haste el iv 
to these parts are extremely various; and r 
specting the relations and ies which 
bear to the brain of the higher animals, 
wane of opinion exists. ‘on _ 
ist. The olfactory tubercles, or cerebr 
mass (figs. 351 and 352, a, a), which, wil 
Arasky,* Serres,+ Desmouli Carus,§ an 
Tiedemann, ||and contrary to Collins,{{ Monro, 
Camper,t+ Ebel,{} Treviranus,§§ and Cuvier, 
I consider as analogous to the cerebral het 
spheres of man, are generally of small size, a 
contain no cavity (fig. 351, 6). In the 
they consist of three pairs of ganglia, wh 
increase in comparative size from before 
behind ; in the carp and mackarel, of only ¢ 
Fig. 352. 
er 
Brain and portion of spinal marrow of L 
( Chub ), about natural poly. 
a, first cerebral mass or olfactory tube | 
second cerebral mass or optic lobe. e, thi 
bral mass or cerebellum. d, spinal marrow 
its posterior longitudinal fissure. e, fourt ' 
cle. hk, olfactory nerve. 1, tuberculous | 
ment of the olfactory nerve. 
* De piscium cerebro. a. i 
+ Anatomie Comparée du Cervean. r i 
¢ Comparative Description of the Braiz 
Four Classes of Vertebrated Animals. 
§ Anatomie Comparée. 
|| Anatomy of the Foetal Brain. s 
considers them as more particularly * 
to the corpora striata, on the external b 
which the membranous hemispheres a e 
elévated.” ay 
4] System of Anatomy. edit 
** Anat. of Fishes. : 
tt Memoir on the Ear of Fishes, 1 
tt Observationes Nevrologice ex Ani 
parata, 1788. 5 
§§ Memoir on the Brain, 1817. 
\\} Lecons d’Anatomie Comparée. 
pSTY 
