170 
COMPARATIVE ZOOLOGY. 
forehead backward, dividing the brain into two hemi¬ 
spheres, and the spinal cord resembling two columns 
welded together; even the nerves come forth in pairs to 
the right and left. The brain is the organ of sensation 
and voluntary motion; the spinal cord is the organ of in¬ 
voluntary life and motion. The brain, above the medulla 
oblongata, may be removed, and yet the animal, though it 
cannot feel, will live for a time, showing that it is not ab¬ 
solutely essential to life; in fact, the brain does nothing 
in apoplexy and deep sleep. All of the cord, except that 
part containing the centres for respiration and circulation, 
may also be destroyed, without causing immediate death. 
The Brain is that part of the nervous system contained 
in the skull. 86 It increases in size and complexity as we 
pass from the Fishes, by the Amphibians, Reptiles, and 
Birds, to Mammals. Thus, the body of the Cod is 5000 
times heavier than its brain—in fact, the brain weighs less 
than the spinal cord; while in Man, the brain, compared 
with the body, is as 1 to 36, and is 40 times heavier than 
the spinal cord. The brains of the Cat weigh only 1 oz.; 
of the Dog, 6 oz. dr.; and of the Horse, 22 oz. 15 dr. 
The only animals whose brains outweigh Man’s are the 
Elephant and Whale—the maximum weight of the Ele¬ 
phant’s being 10 lbs., and of the Whale’s 5 lbs.; while 
the human does not exceed 4 lbs. Yet the human brain 
is heavier in proportion to the body. But quality must 
be considered as 'well as quantity, else the Donkey will 
outrank the Horse, and the Canary-bird, Man; for their 
brains are relatively heavier. 
The main parts of the brain are the cerebrum , cerebel¬ 
lum, and medulla oblongata . 
The cerebrum is a mass of white fibrous matter covered 
by a layer of gray cellular matter. In the lower Verte¬ 
brates, the exterior is smooth; but in most of the Mam¬ 
mals it is convoluted, or folded, to increase the amount of 
