words: during the post/oetal development of the. skull the foramen 
magnum is shifted occipitally. I had not expected this result. A priori 
I should have expected the opposite, namely that the individual deve¬ 
lopment would reflect the phylogenetic. I shall first show the stated 
for the ape skulls, and then for human skulls. 
The direct proof of this shifting is obtained by comparing the basal 
indices. But also in another manner 1 will give a striking proof, 
namely by superposing the mediagrams of youthful and adult skulls. 
Of the Siamanga I made sections of two juvenile skulls, the youngest 
of which possessed all the milk teeth, while no permanent tooth had 
yet appeared. The basal index of this skull was 62, i. e. eleven units 
less than the lowest basal index of an adult siamanga skull. The 
second possessed a mixed set of teeth, the permanent canines, the 
first premolars and the third molar had not yet come through. Of 
this skull the basal index was 70. Hence a considerable backward 
shifting of the Foramen magnum had taken place already, which 
evidently had not been completed yet. 
The difference of position of the Foramen magnum which is 
indicated by these different values of the basal index, is very clearly 
shown in fig. 2. - 
Tig. 2. Mediagrams of an adult and an infantile Siamanga skull. 
In this figure the full line is the mediagram through an adult 
•aroanga skull with a basal index of 76, the dotted one is the 
mediagram of the young Siamanga with the milk teeth and a basal 
! n ex 658. The absolute length of G was in the adult gkull 80 mm., 
1 young one 72 mm. The mediagram of the juvenile skull has 
accordingly been enlarged in the ratio 80 to 72. If now the base 
^nes are made to coincide, so that the fronton and bccipiton of the 
skulls are the same, a figure is obtained from which it may be 
at a glance what deformations the skull undergoes when 
'coping from the juvenile to the adult form. In my communications 
