( 362 ) 
Anatomy. — “On the position and displacement of the Foramen 
magnum in \he PrimatesF By Prof. L. Bolk. 
(Communicated in the meeting of June 26, 1909). 
In the Prirftates the Foramen magnum is very differently situated 
in the cranial base. Sometimes, as with Mycetes, it lies very near 
the occipital pole of the skull, so that the condition is found which 
is the rule with other mammals, sometimes, as in man, it lies about 
the middle of the cranial base. This latter circumstance has occasionally 
led to the assumption of a causal relation between the shifting of the 
Foramen magnum in a facial direction and the acquiring of an errect 
gait. But Huxley already pointed out that the amount of the shifting does 
not depend on the position which the genus occupies in the Primate 
system and it will be shown in the present communication that the 
relation between the two phenomena is certainly not such that the 
acquisition of an erect gait has been the cause of the displacement 
of the Foramen magnum. 
Together with the variations in position also the inclination of the 
plane of the Foramen magnum generally changes. This latter point, 
however, will not he dealt with in this communication, which will 
only treat of the shifting. The main points of this phenomenon have 
been known for a long time. In a certain sense the history of com¬ 
parative craniology was even inaugurated by the study of this 
displacement. As early as the year 1764, namely, a paper on this 
subject was published by Daubenton *), in which he proved the 
shifting more especially by measuring an angle which has since been 
known as Daubenton’s occipital angle, but which has the disadvantage 
that its two legs do not lie in the median plane. This angle has 
later been replaced by Broca’s occipital angle which at any rate has 
the advantage that the two legs are both in the median plane. Yet 
it seems to me that Broca’s method as well as that which the following 
investigators (Huxley, Virchow, Welcker) applied in order to express 
the displacement of the Foramen magnum numerically, may be 
replaced by a more exact one. Thfey constructed a certain angle which 
they used as a measure for the displacement. But an analysis of 
their methods shows that the value of their angle is not only deter¬ 
mined by the position of the Foramen magnum but also by different 
other factors (inclination of the plane of the Foramen magnum, 
') Differences de la situation du trou occipital dans 1’homme el dans les animal 
M&n. Acad, d. Sciences. 
