DR DUBOIS ON PITHECANTHROPUS ERECTUS. 51 



influencing the development of other parts of the skull, being of an 

 equal or a relatively larger size, the proportions and the form of the 

 cranium must be modified in a large degree. It appears to me 

 that some of the chief "■pithecoid''' features of the cranium of the 

 ape really are only the expression of the relative smallness of the 

 brain in comparison to the eyes and the maxillae. So for instance 

 the obliquity of the orbital surface of the frontal lobe going so far 

 as to form a real " rostrum," a foetal and a simian and also a micro- 

 cephalic character, is simply the result of a different proportion 

 between the size of the brain and that of the eye. 



There are further differences in the form of the cranium, which 

 must be taken as peculiarities of the species, as for instance the 

 characteristic height and narrowness of the cranium of the Orang- 

 utan. 



If we compare the cranial arcs of man and apes and oi PitJiec- 

 anthropiis as based on the line from the glabella to the inion, we 

 certainly can only arrive at very rough estimations of cerebral 

 development, the inion being a point determined by muscular 

 action, and the place of it pretty well independent of the size and 

 the formation of the brain. 



We obtain a better comparison of cranial arcs by taking as base 

 the line from the glabella to the upper border of the sulcus trans- 

 versus, because it more nearly represents the degree of development 

 of the cerebral hemispheres. 



However, we find that the arcs, thus obtained, by no means 

 represent the real development of the brain or of the cerebrum. 

 For even when such arcs are represented in accurate projection and 

 drawn to the same scale we do not obtain natural relations. 



After removal of the stony matter, which almost entirely filled 

 the calvaria, when I showed it at the Third International Congress 

 of Zoology at Leiden, I was able to measure exactly the capacity, 

 and to make a cast of the interior of it representing a large part of 

 the brain. This brain-cast, which I would consider as the most 

 important evidence indirectly bequeathed to us by our ancestor, is 

 now lying here before you. 



If viewed from above, in the " norma-verticalis," the most 

 peculiar feature of the brain-cast is the narrowness of the frontal 

 part of the cerebrum, whereby it differs as well from every normal 

 human brain as from all ape-brains. This narrowness of the 

 frontal lobes and the very marked convolutions are undoubtedly 

 due to the very pronounced scaphocephaly of the frontal region 

 (trigonocephaly), a peculiarity well known in man as a result from 

 the premature obliteration of the medial frontal or metopic suture 

 (the reverse of metopism, which from the researches of Anutchin 

 and of Papillault seems to be more common in the higher than in 

 the lower human races). Thereby the growth of the frontal part of 

 the cranium having been much checked in a lateral direction and a 

 certain extent of frontal cerebral cortex being necessary, the frontal 



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