THE NERVOUS SYSTEM. 
167 
half of the spinal cord is diseased, one side of the body is 
paralyzed. 
may be removed, and yet the 
anunal, though it can not feel, 
will live for a time, showing 
that it is not absolutely essential 
to life; in fact, the brain does 
nothing in apoplexy and deep 
sleep. But if the spinal cord be 
destroyed, the animal dies, for 
it can neither move nor breathe, 
as all the afferent and efferent 
nerves terminate in the cord. 
The Brain is that part of the 
nervous system contained in the 
skull.” It increases in size and 
complexity as we pass from the 
Fishes, by the 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, com- 
pared 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 0z.; of the 
Dog, 6 oz. 54 dr.; and of the 
Horse, 22 oz. 15 dr. The only 
animals whose brains outweigh 
Man’s are the Elephant and 
Whale; the maximum weiglit 
The brain is the organ of sensation; the spi- 
nal cord is the organ of mere life and motion. 
The brain 
Fie. 135.—Human Brain and Spinal 
Cord, one-fifth natural size: a, 
great longitudinal fissure; b, an- 
terior lobe; ec, middle lobe; 4, 
medulla oblongata; e, cerebel- 
lum; J, first spinal nerve; g, 
‘brachial plexus of nerves supply- 
ing the arms; h, dorsal nerves; 7, 
Inmbay nerves; k, sacral plexus 
of nerves for the limbs, J, canda 
equina: the figures indicate the 
twelve pairs of cranial nerves, of 
which 1 is olfactory, 2 are optic, 
and § auditory. 
of the Elephant’s being 10 lbs.; and of the Whale’s, 5 Ibs. ; 
while the human does not exceed 4 lbs. 
Yet the human 
