54 



NOBUHARU SUITSU 



Cameron ('17) says that in the lower orders of callosal mam- 

 mals, where the surface of the cerebral hemisphere is smooth 

 and free from convolutions, the corpus callosum is feebly devel- 

 oped, whereas in the higher orders, where the hemispheres show 

 a progressive increase in the amount of the convoluting of gray 

 matter, there is a concomitant increase in the size of the corpus 

 callosum. 



To make this comparison between man and the rat, table 7 

 has been prepared. According to the data there presented, the 

 area of the cross-section of the callosum in man is 4.43 per cent 



TABLE 7 

 Giving a comparison of the relations between the area of the total brain and the 

 callosal area in man and in the albino rat. The data in columns A, B, C, D, 

 are derived from Spitzka ('07) and the data in columns F, G, H, I, are derived 

 from the records in table S 



of the computed area of the brain, while in the rat it is only 

 3.29 per cent. These figures show a clear difference in this 

 relation, although the difference is perhaps not so large as w'e 

 might have expected. Nevertheless, it may correspond in a 

 general way to the relative proportions of the area of the cortex 

 in the two species. 



From my own studies on the ontogeny of the callosum I can 

 conclude that there is also a progressive increase in the area of 

 the corpus callosum with increasing body weight and age. The 

 calloiml area continues to grow until late in life, and in associa- 

 tion with the increase of psychical activity, also to become 

 more mature. I have already stated that from the twentieth 



