518 ANIMAL PHYSIOLOGY. 
vidual elements, especially of the cortical cells, both as the re- 
sult of innate, inherited powers, and as altered by education, 
is, of course, a matter of great importance. By education we 
mean all those influences that have been brought to bear upon 
these cells from without, of whatever kind. Apart, too, from 
all these considerations, it must be clear that what any set of 
cells can accomplish, be they brain-cells or other, must depend 
largely upon their capacity to appropriate nourishment, which 
will in turn be modified by blood-supply, the behavior of ex- 
creting organs, etc. In a word, the intellectual achievements 
are dependent on a great variety of factors. The brain and 
other parts are so mutually dependent that they can not be un- 
‘derstood by any isolated consideration of the one or the other. 
_It is not to be supposed that an individual with a poor respir- 
atory, circulatory, and digestive system, no.matter what the 
possibilities of his cerebrum, can ever rank with an organism 
admirably balanced in these respects. 
The Connection of one Part of the Brain with another.—Though 
it has long been known that the different parts of the brain 
were connected by bridges of fibers (commissures, etc.), the 
physiological significance of the fact seems to have been largely 
ignored, and even at the present day is too little considered. 
1. Cerebral fibers pass between the convolutions of this part of 
the brain and the cerebellum; between the former and the main 
basal ganglia; between the gray matter of the convolutions on 
the same side, and between the latter and those on the opposite 
halves; between the gray matter of the cortex and the internal 
capsule, the corpora striata, optic thalami, pons Varolii, the 
medulla oblongata, and so to the spinal cord. The course of 
the latter tracts of fibers have been, especially by the help of 
pathology, definitely followed. Some of these connections are 
given in more detail below: 
1. Cerebro-cerebellar fibers. (a.) From the cortical cells of 
the anterior cerebral lobe to the pons Varolii, passing through 
the internal capsule and thence through the lower and outer 
part of the crus cerebri (crusta). (b.) Fibers from the occipital 
and temporo-sphenoidal lobes, passing by the crusta, reach the 
upper surface of the cerebellum. 
2. Fibers bridging the two sides of the cerebrum. (a.) By 
means of the corpus callosum chiefly, passing from the gray 
matter in the first instance. (b.) From the temporo-sphenoidal 
lobe on each side through the corpora striata and anterior com- 
missure. (c¢.) Fibers from the upper part of the crus cerebri 
