216 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



The Corpus Callosum. The corpus callosum is the most 

 conspicuous of the bands of commissural fibers that connect one 

 cerebral hemisphere with the other. Similar tracts of the same 

 general nature are the anterior commissure, the fornix, the 

 psalterium, etc. The position and great development of the corpus 

 callosum has made it the object of experimental as well as anatomical 

 investigation. When the corpus is divided by a section along the 

 longitudinal fissure (v. Koranyi) no perceptible effect of either a 

 motor or sensory nature is observed in the animal. When it is 

 stimulated electrically (Mott and Schafer) from above symmetrical 

 movements on the two sides of the body may be obtained. If 

 the motor cortex on one side is removed stimulation in the longi- 

 tudinal fissures causes movements only on the side controlled 



Fig. 96. -Diagram to show the composition of the corpus callosum as a system of com- 

 missural fibers, without projection fibers. (Cajal.) 



by the uninjured cortex. These facts are in harmony with the 

 results of histological studies, which indicate that the fibers of the 

 corpus callosum do not enter directly into the internal capsules 

 to be distributed to underlying portions of the brain, but are truly 

 commissural and connect portions of the cortex of one hemisphere 

 with the cortex of the other side. This relation is indicated in the 

 accompanying diagram (Fig. 96). So far as the motor regions are 

 concerned, there is some evidence that the connection thus es- 

 tablished is between symmetrical parts of the cortex (Muratoff), 

 that is, between parts having similar functions, and we may per- 

 haps regard the corpus as a means by which the functional 

 activities of the two sides of the cerebrum are associated. 



The Corpora Striata and Optic Thalami. The numerous 

 masses of gray matter found in the cerebrum beneath the cortex, 



