THE BRAIN. 495 



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 connec- 

 tions 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 cms 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. (&.) 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 

 (tegmentum) to the optic thalamus of each side and onward 

 to the temporo-sphenoidal lobes, forming the posterior com- 

 missure. 



3. Fibers connecting different parts of the cerebral convolu- 

 tions on the same side. These are exceedingly numerous and 

 belong to such tracts as the "arcuate fibers," passing from one 

 gyrus to another; "collateral fibers," forming distant convo- 

 lutions ; fibers of the fornix between the uncinate gyrus, hip- 

 pocampus major, and optic thalamus ; longitudinal fibers of the 

 corpus callosum; fibers of the taenia semicircularis, uncinate 

 fasciculus, etc. 



4. Fibers forming the cerebrum and the spinal cord. Ac- 

 cording as they pass downward or upward do they converge or 

 diverge, and the most important seem to pass through the in- 

 ternal capsule ; and while the majority do perhaps form some 

 connection either with the corpora striata and optic thalami, 

 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 



