DR DUBOIS ON PITHECANTHROPUS ERECTUS. 9I 



different bulk (from -;- to->j and belonging to 4 orders, viz. the 



Primates, Ungulata, Carnivora, Rodentia, I found that in nearly 

 allied and equally cephalisated mammals the weight of the en- 

 cephalon is on the average proportionate to the 0"56 power of the 

 weight of the body, and that in the compared animals the calculated 

 exponent of relation only varied from about 0'54 to 0"58. 



Comparing animals of different relative cephalisation we want 

 to know the quantity of the brain independently of the size of the 

 body, i.e. the index of cephalisation, c, which can be determined 

 now from the formula 



e 

 £ = €3^^ or c = — 



In this manner I arrived at the result that Man has about four 

 times as much brain as any anthropoid ape of the same body- 

 weight. Chysothrix is the only ape of another family which comes 

 alike to the man-like apes, but Midas rosalia equals the lower Old 

 World apes. The latter do not distinctly exceed in this respect 

 the Ungulata and the Carnivora. In the Lemuridae, Nycticehis 

 and Tarsius occupy the same degree on the scale of brain de- 

 velopm.ent as measured by its quantity, about equal to that ex- 

 pressed by the lower indices in the Ungulata and the Carnivora. 

 A very low degree is taken by some Rodentia, by Manis, by the 

 Insectivora, by the Microchiroptera or insectivorous Bats and the 

 Marsupialia, but the Cetacea are ranged amongst the Ungulata. 

 Thus we obtain a very natural scale. 



Now it appears to me of great importance to arrive at an 

 estimation of the manner in which the weight of the brain in Man 

 depends on the size of his body. Certainly it must be far more 

 difficult to obtain here reliable results, because the differences of 

 the brain-weights and the body-weights are relatively very much 

 smaller. The Brown Rat is 21 times as heavy as the House- 

 Mouse, and its brain 5^ times as heavy as that of the latter animal ; 

 the weight of the body of the Lion is 36 times, and its brain 

 7 times, as much as those of the Cat. But in full-grown men of the 

 same nation differences from i^ to i in the average body-weight 

 and of IyV to i in the brain- weight are already considerable. But 

 in comparing men, it is true, we have the advantage, having at 

 command real averages from larger numbers of individuals. How- 

 ever, the material at our disposal as fit for comparison is scanty. 

 From data provided to me with very great kindness by Herr Otto 

 Ammon and from others, found in a paper of John Marshall, " On 

 the relation between the weight of the brain and the stature and 

 mass of the body in man," I was able to estimate the power of 

 relation, to which we have to raise the body-weight, in order to 

 make it proportional to the brain-weight, at about 0*25, 



E : €=8''' : /""^ or tJ~S : ^'^ 



