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apparatus much more developed in the Orang utan, break the shocks 
which, arising in locomotion, might injure the skull and its contents. 
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oe eee er B 
Fig. 1. Median cross-section of the skull of 
Hylobates agilis. */s of nat. size. 
BEE 
Fig. 2. Median eross-section of the skull of Hylobates 
(Symphalangus) syndactylus. 7/3 of nat. size. 
In connection with these features the foramen magnum in the Siamang lies 
somewhat more backwards, and its plane stands up somewhat more 
steeply; also the planum nuchale of the occipital bone is steeper, 
and the bending of the cranial basis, the basi-cranial axis, is less 
pronounced than in the small gibbon species. 
These are characters of the Siamang which in the comparison of 
Apes with Man are usually considered as primitive and indicating 
a lower stage of brain organization, which however, in the comparison 
with the small gibbon species can decidedly not have such a meaning, 
but must have geometrical and mechanical causes. 
In the calculation of the mean endocranial surface dimensions 
(the two-third powers of the cranial capacities), and Kuitu’s palatal 
areas, it is found that the maxilla of the Siamang is relatively one 
and a half times as large as that of the small gibbon species, which 
is undoubtedly in connection with an important difference in the 
