230 PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



tively undeveloped structure, but Bolton,* on the contrary, states 

 that it has a typical structure and believes that it plays a part of 

 the greatest importance in the higher or general processes of as- 

 sociation. It is the last region of the cortex to be evolved. In 

 mental decadence or dementia it is, according to this author, the 

 first region to undergo dissolution, and in conditions of amentia it 

 is undeveloped. 



Fig. 102. Diagram to show the composition of the corpus callosum as a system of oom- 

 missural fibers, without projection fibers. (Cajal.) 



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 and the fornix. 

 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, symmetri- 

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

 the motor cortex on one side is removed, stimulation in the lon- 

 gitudinal fissure causes movements only on the side controlled 

 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 

 * Bolton, "Brain," 1910, p. 26. 



