512 L. BOLK 
Some years ago I published an extensive investigation upon 
the normal obliteration of the sutures in Primates. The re- 
sults of this inquiry were based upon the examination of more 
than 800 skulls of platyrrhine and catarrhine monkeys and a 
considerable number of skulls of anthropoid apes, all present 
in the anatomical museum of the University of Amsterdam. 
As to the problem interesting us in the present paper, we may 
limit ourselves to the conclusions relative to the anthropoid 
skulls. 
There are striking differences in the process of obliteration 
between man and apes. These differences concern the age in 
which normal obliteration takes place and the order of suc- 
cession in Which the closure in the different sutures begins. 
In man, as a rule, the principal sutures persist for a longer or 
shorter time after the complete formation of the skull. The 
same happens in some genera of American monkeys; but in 
apes the sutures can close immediately after the skull is 
full grown. At this moment the general growth of the 
individual is not yet finished, and though it is, for reasons near 
at hand, impossible to know the age in which the obliteration 
begins, it is sure that the process commences, and perhaps in 
some sutures is even finished, before the animal has attained its 
adult state. 
The significance of this premature synostosis of the skull 
bones in apes may be found in the strong development of the 
muscles of mastication, arising from almost the whole surface 
of the braincase, and moreover in Gorilla and male Orangs from 
strong crests developing exactly in the line of union of the parietal 
and occipital bones. 
Now it is obvious that in the apes, as well as in man, there 
exists- a relation between the growth of the brain and the brain- 
case. In apes, as a rule, the different bones of the skull can- 
not unite together before the brain has attained its final volume. 
This is so clear and simple that it is altogether unnecessary to 
enlarge upon it. As it is, the conclusion lies close at hand that 
the sutures in the braincase of apes disappear immediately 
after their physiological function is finished. The physiological 
