1038 
origin from much less projecting zygomatic arches, than in Homo 
neandertalensis, strongly diverged from each other downward, which 
must have gone together with peculiarly strong divergence in that 
direction of the musculi pterygoidei interni. Jointly with the musculi 
temporales and pterygoidei interni, the masseters drew, in their 
principal action, not only the lower jaw upward at the angles, but 
at the same time the two angles towards each other, through which 
its arch was greatly strained, most at the symphysis, where the 
curvature of the arch is greatest, and caused thereon the outside 
of the lower jaw very considerable stretching strains. In general in 
Homo sapiens the resulting contraction direction of all the muscles 
of mastication is converging upward, and stretching strains arise of 
this nature. 
In the mandibular type of Homo neandertalensis, on the contrary, 
strong strains must have arisen in the mandibular arch on the 
inside of the symphysis, in consequence of the convergence of 
the two musculi masseteres, which was still increased by the pecu- 
liar projection of the zygomatic arches — the considerable phaenozygy. 
The same we find in the Apes, for also those Anthropoids in which 
the ramus mandibulae is not directed obliquely to the sagittal plane 
from above outside to below inside, yet present convergence of the 
two musculi masseteres in consequence of the projecting far beyond 
the sides of the skull of the zygomatic arches, from which these 
muscles take their origin; the phaenozygy is here still more con- 
siderable than in Homo neandertalensis. 
It will remain WatLkuHorr’s great merit that he was the first to 
draw attention to muscular action as an explanation of the chin of 
Homo sapiens. In his conception Homo neandertalensis and Homo 
heidelbergensis must have been almost or entirely speechless, which, 
taking the great brain-capacity of the Neandertal Man into consider- 
ation, is very doubtful. But Vax pen BROEK is justly of opinion that 
other muscles than those which are directly active in speech, namely 
the facial (mimic) muscles and the muscles of mastication, may have 
given rise to the particular form of the chin of modern Man. He 
chiefly thinks of the facial (mimic) muscles *). Here stress may be 
laid on the action of the muscles of mastication, by the side of 
whose strength, which acts not less continually than the facial 
muscles and which is to be measured by more than a hundred 
kilograms even in Europeans, the power of the lingual and hyoid 
1) A. J. P. van DEN Brork, Ueber Muskelinsertionen und Ursprünge am Unter- 
kiefer; ein Beitrag zur Kinnfrage. Zeitschrift fiir Morphologie und Anthropologie. 
Band 21, p. 227. Stuttgart 1920. 
