COMPARATIVE ANATOMY. 
raeter of animals, have derived their name the largest brain in proportion to his body, 
from that circumstance, afford to our obser- Some more modern physiologists, however, 
vation a more clear and manifest gradation, 
from the most simple to the most com- 
pound structure, than any others in the ani- 
mal economy. 
In some of the most simple animals of 
the class vermes, particularly among what 
are called zoophytes, little or no distinction 
of similar parts (or structures) can be dis- 
cerned, and we are unable to recognize any 
thing as a particular nervous system, or 
even as a part of such a system. The power 
of sensation and voluntary motion which 
these possess, as well as any other order or 
class of the animal kingdom, proves that the 
nervous matter must be uniformly spread 
throughout their homogeneous substance. 
The almost transparent polypps (hydra), 
which are often found with a body of an 
inch in length, and arms or tentacula of a 
proportionate size, appear to consist, when 
surveyed in the best light by the strongest 
magnifying powers, of nothing but a granu- 
lar’sti’ucture connected into a definite form 
by a gelatinous substance. 
In many other vermes, and in insects, 
particular nerves can be distinguished, 
arising in general from a chord running the 
whole lengtli of tlie body, and called the 
spinal marrow, the superior extremity of 
which part, slightly enlarged, constitutes 
the brain. The latter organ, however, in 
both classes of cold and red-blooded ani- 
mals, and still more in those which have 
warm blood, has a much more complicated 
structure, and a far greater relative magni- 
tude : all animals are however exceeded in 
both these points by the human subject, 
which, according to the ingenious observa- 
tion of the learned Soramerring, possesses 
by far the largest brain in proportion to the 
size of the nerves which arise from it. 
The vast superiority of man over all other 
animals in the faculties of the rnind,.which 
may be truly considered as a generic dis- 
tinction of the human subject, led physiolo- 
gists at a very early period to seek for 
some corresponding difference in the brains 
of man and amimals. They naturally inves- 
tigated the subject in the first instance, by 
comparing the proportion which the mass- 
of tlie brain hears to the whole body; and 
tlm result of this comparison in the more 
common and domestic animals was so satis- 
factory, that they, pvosecuted. the inquiry no 
further, hut laid down the general proposi- 
tion, which has been universally received 
since the time of Aristotle, that man has 
in following up this comparative view in a 
greater number of animalSj discovered seve^ 
ral exceptions to the general position. They 
found that the proportion of the brain to 
the body in some birds exceeds that of 
man; and that several mammalia (some 
quadrumana, and some animals of the mouse 
kind) equal the human subject . in this 
respect. 
As these latter observations entirely over- 
turned the conclusion which had been be- 
fore generally admitted, Sommening has 
furnished us with anotlier point of compari- 
son, that has hitherto held good in every in- 
stance: viz. that of the ratio, which the 
mass of the brain bears to the nerves arising 
from it. 
Let us divide the brain into two parts ; 
that which is immediately connected with 
the sensorial extremities of the nerves, 
which receives their impressions, and is 
therefore devoted to the purposes of animal 
existence. The second division will include 
the rest of the brain, which may be consi- 
dered as connecting the functions of the 
nerves with the faculties of the mind. In 
proportion then as any animal possesses a 
larger share of the latter and more noble 
part; that is, in proportion as the organ of 
reflection exceeds that of the external senses, 
may we expect to find the powers of the 
mind more vigorous and more clearly deve- 
loped. In tliis point of view man is decid- 
edly pre-eminent : here he excels all otlier 
animals that have hitherto been investigated. 
All the simiae, says Sdramei ing, are placed 
far behind man in this respect. Although 
the brain in some instances, particularly 
among the smaller kinds, which have pre- 
hensile tails, is larger in proportion to their 
body than that of the human subject ; yet a 
very large share of that brain is required 
for the immense nerves which supply tlieir 
organs of sense and mastication. Let ns 
remove that portion of the brain, and a very 
small quantity will remain. 
The researches of the same author on 
animals in general have led him to conclude, 
that- the quantity of brain, over and above 
that which is necessary for a mere animal 
ejf-istence ; that part, in short, which is de- 
voted to the faculties of the mind, bears a 
direct ratio to the docility of tlie animal, to 
the rank which it would hold in a compa- 
rative scale of mental powers. 
The largest brain, wliich Siimmerring has 
found iiiiji horse, weighed Mb. ioz. and fee 
