626 NERVOUS SYSTEM. 
portional is as 100: 256. In the sheep, 
as 100: 232. In the deer, as 100:233. The 
lateral lobes are very evident in all, and con- 
volutions are observable on the external sur- 
face, ly in the horse. In the cat its 
proportional length is as 100: 200; in the 
Stoat as 100 ; 228. The external convolutions 
in both are numerous: in the monkey (fig. 
359, 1), the proportional length is as 100 : 305 ; 
lamine are numerous and small, thus ap- 
proaching very much the characters of the same 
in man. 
The following is a table, shewing the actual 
and relative lengths of the cerebral hemispheres 
and the cerebellum in the Mammalia :— 
Length of 
Animal. | Cerebral of Proportions, 
Hemisphere |Cerebellum 
Bat....} 2} lines. | 2 lines.| As 100: 125 
Rabbit 144 — | 7 — 100 : 207 
Rat....| 7} — | 4} 100 : 166 
Mouse .| 4 — | 23 — 100 : 160 
Horse. ./64 — |25 — 100 : 256 
Sheep../36 — |15} — 100 : 232 
Deer.../42 — [18 — 100 : 233 
Stoat...}8 — | 3} — 100 : 228 
Cat..../18 — | 9 — 100 : 200 
Monkey/30} — [10 — 100 : 305 
On cutting into its substance in many of 
these animals, the appearance of the arbor vite 
is more or less distinct, similar to the human 
cerebellum. On its inferior surface is situated 
its great commissure, the pons Varolii, which 
first makes its appearance in this class of ani- 
mals, and, with the exception of the transverse 
fibres forming it being thinner and fewer in 
number, particularly in those lower orders of 
Mammalia where the cerebral hemispheres 
were small, it presents but little differences from 
the same part in the human adult brain. This 
latter remark will equally apply to the fourth 
ventricle, which has been an object of consi- 
derable interest, and which, from being at first 
an open exposed cavity, is now shut in and 
concealed. 
[On the peculiarities of the brains of the 
implacental class of Mammalia, see the ar- 
ticles Marsupratia and Monorremata.] 
On reviewing these statements of the nervous 
system in the Mammalia, we observe that the 
brain now preponderates greatly in bulk over 
the spinal marrow ; this latter is also shorter, 
and terminates by a true cauda equina. The 
Jirst cerebral mass has now acquired its maxi- 
mum of developement as regards size ; the two 
portions of which it is composed are united by 
a large commissure; their exterior surface is 
convoluted. The second cerebral mass is divi- 
ded into two pairs of ia, in which the 
cavities are obliterated. onthe third cerebral 
mass has lateral hemispheres developed, strie 
and convolutions on their exterior surface, and 
an important commissure, the pons Varolii, on 
its inferior surface. 
Having thus completed the investigations 
proposed at the commencement of this. paper, 
(Comparative Anatomy.) 
it may not in conclusion be without i 
and utility to take a very rapid review te : 
developement of the nervous system in the five” 
large groups of animals in the system i 
rapgement, as follows :— é 
a. The nervous s (perhaps) first e 
an molecaler fre > that is, me made u 
globules dispersed throughout the homoger : 
texture of the animal, oo. in, the Acta 
won Entozoa, &c. 
b. This nervous matter arranged in a 
gitudinal direction forms filaments. The d d 
rection which they assume is that of a raj 
nerve, and a central point, or 3 he 
latter communicate with each comm 
sures, which unite them in the e form of a 
This ring is situated around the ae orifice ¢ 
the animal; it takes the name of 
nervous ring; and from it issue filaments 
a radiated manner, as in the E . 
¢. This oral nervous ring becom 
more complicated in itself; sraglons are . 
developed on its lateral and inferior pc 
from which nerves off in a longitud 
direction, as in ees lower Mollusca, a 
secondly on its superior surface, as bak 
higher animals of this class: a sup 
ganglion is at first proporti 
in fo the Gasteropoda, but afterwards large, 
sometimes very large, as in the Cephalope 
It is the analogue of the tubercula quadrigemil 
of the higher animals. 
d. This nervous ring, in its me 
highly pam yen y Fs now becomes repeat 
several times in the body of the animal 5 J 
in an undetermined number, as in the E 
thoid Articulata; secondly. in a detern 
number, as in the Entomoid Articulata. _ 
nervous rings are united by poet 
missures, and the most anterior one always. 
a highly developed ganglion on its supe 
surface. The uniting commissures posse 
two distinct nervous tracts ; 
sympathetic nerves exist, as in the In 
e. These primary nervous rings es 
become ganglia (brain); the uniting ¢ 
sures are become primary nervous rings 
marrow). First, the ganglia and theis e 
sures are neatly equally sero, 
horizontal, as in the lower Vertebrata ; r 7 ) 
the ganglionic formation predomina te 
direction, with regard to the comm 
comes more that of a right anges _ 
higher Vertebrata; thirdly, the pi r 
of the ganglionic formation is ¥ 
creased, and its relative direction is 1 
complete right angle, as in the human 5) 
es. 
(John Andet 
NERVOUS CENTRES. 
tomy).—A nervous centre ma po os bad s 
mass composed of grey mm 
matter with which nerves are intim ratel 
nected. Ina physiological ig balls. i 
a centre of nervous action, as nerve 
to conduct to it as well as from it. 
The nervous centres in the human § 
are the GANGLIONS, the SPINAL CORD, 2 
BRAIN. 
hinodermata. 
ESP Ory 
ecta. 
