317 
Man. Bouvre and AnrHony have actually thought they saw this on 
the endocranial cast; but the cerebral convolutions are imprinted 
too little distinetly through the dura mater membrane, which was 
probably particularly thick, and besides the imprint is also incom- 
pletely preserved, so that even essential features remain uncertain in 
the configuration of the surface of the brain. Hence great value 
cannot be assigned to these researches. Nor is it probable that the 
proportion between the more highly and the lower organized parts 
of the brain would considerably differ from that of modern Man. 
At any rate the very large brain quantity of the Neandertal Man 
in comparison with the Apes remains a significant fact. Like modern 
Man this diluvial species possessed more than three times the brain 
volume of anthropoid Apes of. equal size (weight). If the shape of 
the Neandertal Man’s skull were a really primitive character, its 
capacity could not differ from that of an ape’s skull to that extent. 
This leads to the supposition that the pithecoid shape of the skull 
of the Neandertal Man is no primitive, inherited character, but that 
it was acquired by convergent development, an adaptation to definite 
modes of living and due to similar, mechanical causes. 
If, therefore, there is no ground to consider the flattening of the 
upper part of the cranium of Homo neandertalensis as a consequence 
of low, pithecoid brain-organization, we are naturally led to con- 
sider what mechanical factors in Anthropoid Apes can be the cause 
of, or at Jeast can have influence on the flattening and the forma- 
tion of the supra-orbital bony ridge, which we also know as the 
most striking characters of the Neandertal Man. 
We then meet with two remarkable facts. First that the skull 
of the Siamang, the only large gibbon species, is distinguished from 
all the small species by an equally great flattening and relative 
decrease of capacity of the upper cranical part together with | 
relative increase of capacity of the lower cranial part’), as the 
Neandertal Man from modern Man (Fig. 1 and Fig. 2 of bisected 
skulls). In this respect the Siamang may be called the Nean- 
dertalian among the Gibbons. This large gibbon species is, be- 
sides, distinguished from the small species in that the maxillar 
and actually the whole facial part of the skull, both as regards. 
breadth and length, is disproportionately much larger and heavier. 
Consequently the nuchal muscles must carry the head, which hangs 
forward, with the greater strength, and in conjunction with another 
muscle apparatus which will be discussed later, and an air-brake 
1) This applies both with regard to the internal a ae parts and that of 
the inion, because this occupies the same place in them. 
21 
Proceedings Royal Acad. Amsterdam. Vol. XXIV. 
