COMPARATIVE ANATOMY, 
smallest, which he has seen in an adult nian, 
was %lh. S^oz. Yet the nerves arising 
from the former brain were at least ten 
times larger than those of the latter. 
Generally speaking small animals have a 
larger brain in proportion to their body 
than larger ones. The pachydennata have 
it very small ; and in red-blooded animats, 
its size is very trifling when compared with 
the body. 
It forms in man from ^ to ^ of the body. 
33 
2I 
461 
In some simi® 
the IMole 
Bear 
Dog 
Cat 
Hare 
Rat 
Mouse.. . 
Elephant 
Dig 
Horse.... 
Dolphin 
Eagle 
Sparrow 
Chaffinch . . . 
Redbreast.. 
Blackbird .. 
Caiiai-y-bird 
Cock 
Duck 
Goose 
Tortoise 
Turtle 
Coluber natrix 
Erog 
Shark 
Pike 
Carp 
Many mammalia possess a bony tentori- 
um cerebelli. It is difficult to give a physio- 
logical explanation of the use of this bony 
tentorium. The opinion which has been 
generally adopted by anatomi.sts, that the 
structure in question belongs to such ani- 
mals only as jump far, or run with great 
velocity, and tliat it serves the purpose of 
protecting the cerebellum from the pressure 
of the cerebrum in these quick motions is 
obviously unsatisfactory. It exists in the 
bear, which is not distinguished for its acti- 
vity ; while several animals which excel in 
jumping or s]>ringing do not possess it ; v-iz. 
the wild goat, (capra ibex). Cheselden as- 
cribes it to predacious animals only (“ Anat. 
of the Bones,” cap. 8); but it exists in se- 
veral others. 
We have given these remarks on the gene- 
rally assigned use of the bony tentorium, 
because a similar mechanical explanation 
has been assigned of the falx and the tento- 
rium of the human subject; viz. that the 
former protects tire hemispheres from mu- 
tual pressure when the person lies with his 
head resting on one side ; and that the latter 
provides against the compression of the 
cerebellum by the superincumbent cere- 
brum. These explanations are assigned in 
the present day by anatomists of such dis- 
tinguished reputation as Sommeriing and 
Cuvier (“ de Corporis Humani Fabrica,” 
VO], 4, p. 27'. “ Logons d’Anat. compar." 
tom. 2, p. 178). If the futility of this piece 
of physiology were not sufficiently proved 
94 
by considering that the cranium is accurate- 
• ly filled, and that there is consequently no 
room for its contents to fall from one side 
to the other ; it must immediately be ren- 
dered manifest by Mr, Carlisle’s case; in 
672 
which the falx was entirely absent, and the 
two hemispheres united throughout in one 
T02 
mass, without any perceptible inconveni- 
ence during the patient’s life. (“ Transact 
... 2b 
tions of a Society for the Improvement of 
Medical and Chii'urgical Knowledgej’’ voL 
32 
ii. p. 212). We have met with four instances 
in which the anterior half of the felx was 
deficient. This production of the dura 
mater commenced in a narrow form about 
the middle of the sagittal suture ; and gi as 
dually expanding, had acquired the usual 
• 2243 
breadth at its termination in the tentorium. 
'* b688 
The two hemispheres adhered by the pia 
.. 7^ 
mater covering their opposed plane surfaces, 
'• 172 
but were formed naturally in other respects. 
'• 
A want of the falx has also been recorded 
L 
• 1305 
by Garengeot (« Splanchnologie,” tom. ii. 
p. 24.) 
The brain of the mammalia wants the 
digital cavity of the lateral ventricle, and in 
general the acervulus of the pineal gland. 
Its anterior lobes are elongated into a pro- 
cess called the mamillary, giving rise to the 
olfactory nerves. In birds, reptiles, and 
fishes, there is a successive and gradual 
change towards a more simple structure; 
the braitr in these classes consisting merely 
of tubercular eminences. In the lower or- 
ders the brain seems to be really wanting. 
A nervous chord runs along the body, and 
possesses ganglia at different distances, from 
which the nerves arise. Itt insects and 
vermes the upper ganglion of the nervous 
chord, which represents the brain, is placed 
near tire rrrouth, or oesophagus, and very 
generally surrounds that tube by a kind of 
colter. 
