520 ANIMAL PHYSIOLOGY. — 
some seem to pass directly downward through the internal cap- 
sule. It is held by many that the fibers passing through the 
posterior portion of the internal capsule are derived from the 
posterior lobe of the cerebrum, and are the paths of sensory im- 
pulses upward; while the rest of the internal capsule is made 
up of fibers from the anterior, and especially the middle portion 
of the cerebral cortex (motor area), and these fibers are the 
‘paths of motor (efferent) impulses. 
It now becomes clearer that the brain is constituted a whole 
by such connections; and that, apart from the multiplicity of 
cells with different functions to perform, situated in different 
areas, the complexity and at the same time the unity of the 
_ encephalon becomes increasingly evident, merely upon anatomi- 
‘eal grounds; but we shall find such a view still further strength- . 
ened by study of the functions of the various parts. While the 
tracts enumerated are anatomical and have been clearly traced, 
there can be little doubt that many others yet remain to be 
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MIDDLE commissure! ¥ 
OPTIC THALAMUS! SQ’ /soP Be. 
3° NERVE 
AQUEDUCT OF SYLVIUS. 
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Fic. 380.—Median longitudinal section of human brain, semi-diagrammatic (after Flint). 
marked out; and that, apart from such collections of fibers, we 
must recognize functional paths by the neuroglia, and possibly 
