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THE ANTIQUITY OF MAN 
turned more upwards, and holds such a relationship to 
the whole skull that the strains and stresses arising 
during mastication are transmitted, not to the forehead, 
as in the chimpanzee, but to the skull as a whole. There 
is no need in the orang for a frontal scaffolding of bone. 
The retrogression of the supra-orbital ridges in the orang 
is apparently secondary. The gorilla and chimpanzee 
appear to retain the original form — the form found in the 
oldest and most primitive of anthropoid apes, the gibbon. 
On the other hand, the divided or bipartite condition of 
CHIMPANZEE 
OCCIP CONDYLE 
Fig. 48. — The skull of an orang superimposed on that of a chimpanzee to 
show the presence of a torus supra-orbitalis in the latter. 
the supra-orbital ridge seen in modern human races 
(fig. 46) is also met with amongst old-world monkeys.^ 
If we suppose that the old-world monkeys are still more 
ancient and primitive than the anthropoids, then it might 
be argued that it is modern man that has retained the 
primitive or original form of supra-orbital ridge, and that 
the torus shape, seen in the gorilla, chimpanzee, and 
Neanderthal man, has been evolved at a more recent date. 
I am discussing at some length the development of the 
^ D. J. Cunningham, " The Evolution of the Eyebrow Region of the 
Forehead," Trans. Roy. Soc. Edin., 1908, vol. xlvi. p. 283 
