324 
by Arcner how muscular ‘strain, acting on the periosteum, causes 
growth of bony substance, and how pressure counteracts growth of 
bone. The formation of the torus supraorbitalis in Neandertal Man 
can then be explained by the strain of a particularly strong epicra- 
nial muscle. Strong pressure from above on the cranial vault by this 
muscle apparatus must, according to AtcHEL’s view, inhibit the 
growth on the upper surface (short sagittal suture!) in contrast with 
the sides of the skull, thus causing flattening from above. 
The flattening of the absolutely very large neurocranium can 
certainly be explained only for a small part by geometric adaptation 
to the relatively large splanchnocranium. It seems that particularly 
the mechanical action of the weck muscles and the epicranial ap- 
paratus, through strain at the periost, made the cranium extend 
backwards and frontwards (long squamous suture!) and caused it 
to be flattened. The result of this was a favourable displacement of 
the centre of gravity of the head downward. 
In this connection the fact is of great importance that in the 
Neandertal Man, in comparison with modern Man, and in the Siamang, 
in comparison with the small gibbon species, part of the contents 
of the cranium has been displaced from above downward. This in 
‘an absolute sense, for the external inion at the skull of the Neandertal 
Man does not lie higher above the internal inion than in many an 
Australian skull (24 mm. difference — maximum of Neandertalians 
— in that of La Chapelle —, 23 mm. in the Australian skull offig. 5), 
and in all the gibbon species the inion externum occupies an equal place. 
In the Frisian skulls of the islet of Marken, artificially flattened 
according to Bork «and Barer by a peculiar kind of tightly fitting 
children’s caps, this downward displacement of the contents of the 
skull is also to be found. It is of a smaller amount in proportion 
to the slighter flattening than (vertically only about a third part of) 
that in the Neandertal Man and the Siamang (in which, in com- 
parison with modern Man and the small gibbon species the contents 
of the cranium has been displaced downwards in about the same 
ratio of height — about a seventh of the total height). As was already 
mentioned above, the’ mechanical efficiency results here from the 
displacement of the centre of gravity of the head downwards, nearer 
to the supporting line lying behind the perpendicular of the centre 
of gravity, and also from the more favourable direction of the 
muscular force which pulls at the frontal bone over the cranial vault. 
In the Australian aboriginal race the head is, indeed, poised on 
the vertebral column as in all the races of Homo sapiens, but in 
consequence of the great weight of the jaws the state of. equili- 
