114 Journal of Comparative Neurology. 



III. Calculation of the percentage of the total volume of the cerebral cortex 



of man composed of functional nerve cell bodies. 



A. General method of making the calculation. 



B. The use of the formula for the cone in calculating the volume of 



cells. 



C. Calculation of the percentage of the total volume of the cortex 



filled by nerve cell bodies. 



IV. A calculation of the total number of giant cells in the cerebral cortex of 



man, and a comparison of the number of giant cells with the number of 

 pyramidal fibers passing to the spinal cord. 



A. Calculation of the number of giant cells in the cortex. 



B. Comparison of the number of giant cells with the number of pyra- 



midal fibers. 



SUMMARY. 



I. The total number of functional nerve cells in the cere- 

 bral cortex of the adult man is, in round numbers, 9200 mil- 

 lion. 



II. The proportion of the total volume of the cerebral 

 cortex of the adult man composed of functional nerve cell bod- 

 ies, is 1.37 %. 



III. The number of giant cells in the cerebral cortex of 

 man is almost the same as the number of pyramidal fibers pass- 

 ing to the spinal cord. 



I. Introduction. 



A. The most minute and careful work upon the size and 

 arrangement of the cells in the human cerebral cortex which 

 has as yet been given to the public, is that contained in a mon- 

 ograph by Karl Hammarberg, entitled " Studien iiber Klinik 

 und Pathologie der Idiotie, nebst Untersuchungen iiber die nor- 

 male Anatomie der Hirnrinde, " Upsala, 1895. The data 

 which appear in this monograph with regard to the size and 

 frequency of the functional nerve cells, and the thickness of the 

 layers in the various regions of the cerebral cortex, give oppor- 

 tunity for far greater accuracy than has before been attained in 

 the determination of two important and interesting points with 

 regard to the cortex ; first the number of nerve cells contained 

 in the cortex as a whole, and in its several parts, and second 

 the proportion of the total volume of the cortex composed of 



