( 525 ) 
Anatomy. — “On the slope of the Foramen magnum in Primates". 
By Prof L. Bolk. 
(2 nd Paper on the Comparative Craniology of Primates). 
In the first paper on the anatomy of the Primate-skull, the 
position and shifting of the occipital Foramen in Primates was treated. 
This paper will be devoted more especially to the consideration of 
the inclination of this plane. 
All the writers who have dealt with this subject have pointed out 
that these two features: position and inclination, stand in a certain 
relationship to each other, in so far as the closer the Foramen lies 
to the occipital pole the more vertical a position does it assume, 
while as it gradually approaches the middle of the cranial base the 
tendency is towards a horizontal position. This variation in the slope, 
like the shifting, has been connected with the erect gait of the human 
body. In the typical quadruped, where the skull more or less hangs 
from the spinal column, the Foramen lies at the occipital pole of 
the skull, and the plane is vertical; in human beings, where the 
longitudinal axis of the body runs vertically, the occipital Foramen 
lies in the middle of the cranial base, while the plane is almost 
horizontal. Thus it is seen that this plane is disposed to take up a 
position perpendicular to the longitudinal axis of the body. Another 
point of view, first fully developed by Huxley, concerns the connection 
which is said to exist between the slope of the plane of the Foramen 
magnum and the degree of prognathism 1 ). The more pronounced 
the prognathism — i. e. the longer the face-skull — the more per¬ 
pendicular would the Foramen magnum stand. If now a rough 
comparison be made of an animal’s skull with a human skull, the 
parallelism between these two features is at once noticeable. Huxley, 
however, believed he could show it even in the skulls of different 
races of men. From the superposition of the mediagrams of the 
highly prognathous skulls of an Australian and a Negro on the 
skull of a Tartar, it was seen that “the plane of the occipital 
Foramen forms a somewhat smaller angle with the basiscranial axis 
in those particular prognathous skulls than in the orthognathous . 
Welcker holds a somewhat similar opinion, though he does not 
express it as being a connection between prognathism and the slope 
of the Foramen magnum, but between prognathism and the position 
i) T. Huxley, On some fossil remains of man. Collected Essays. VII, p. 198. 
*> H. Welcker, Untersuchungen iiber Wachsthum und Ban des menschlichen 
Schadels. Leipzig 1862. 
