Donaldson, Nerve Cell Bodies in the Cottex. 143 



The average male encephalon weighs some 1360 grams/ 

 and the cortex in such a case, by estimation, weighs about 658 

 grams, a Httle less than half the total weight of the encepha- 

 lon.^ At 2^, the cell bodies found in the cortex would weigh 

 13 grams (exactly 13.16 grams), or a trifle less than \%> of 

 the total weight of the encephalon. 



Concerning this small mass of tissue representing the cell 

 bodies of the cortex, several broad statements are justified. 



In the paper by Hammarberg to which we have already 

 referred that author reports upon a number of abnormal brains 

 from persons more or less defective in intelligence. 



His observations, together with other data from pathology, 

 make it probable that, in the cases examined by him, the defec- 

 tive intelligence depended upon the defective development of 

 the cortical nerve cells. Moreover, Hammarberg shows that a 

 comparatively small deviation from the normal development of 

 these cell bodies was sufficient to reduce the intelligence to 

 moderate imbecility, such that the patient required that care and 

 protection of an asylum. 



Finally, we infer from these observations, and from the 

 fact that the dendritic branches of the cortical cells become 

 more numerous as we ascend in the vertebrate series, that the 

 principal means of increasing the physiologial complexity of the 

 cortex is represented by the dendrons of the cortical cells, to- 

 gether with the associated terminals surrounding them. As 

 those portions appear to furnish the structural basis necessary 

 to the exhibition of intelligence, variations in their number and 



' The Growth of the Brain : by Henry H. Donaldson. Walter Scott, Lon- 

 don. Charles Scribner's Sons, New York. 1895. (Volume XXIV, in The Con- 

 temporary Science Series), p. 97, Table 13. Averages for males, 2040 yrs. ; 

 Stature, 167-172 cm. Unless otherwise specified, the subsequent references are 

 all from the book above named. There the original papers are cited. 



'^ Page 204, Table 49, Case 2. Cortex given as weighing 55.3^ of the 

 weight of the hemispheres. The average weight of the hemispheres is 87.5^ 

 of the encephalon. Vide p. 99, Table 14, Males. 20-40 yrs. 87.5^ of 1360 

 (weight of encephalon) gives 1190 grms., as the weight of the hemispheres and 

 55.3% of this is the weight of the cortex, equal to 658.07 grms. 



