chiefly on the question whether the points, joined by the base line 
are really homotopic. 
In the present paper this method, which was also followed by 
Aeby, although his base line was in my opinion wrongly chosen *), 
will be first applied for determining the position of the Foramen 
magnum. This can be done in a very simple manner. If namely 
from the anterior edge of the foramen magnum — the basion — a 
perpendicular is raised on the base line, this latter is divided into 
an anterior and a posterior part (See fig. 1). The anterior part will 
in future be indicated by A, the posterior by B. In my gradually 
to be developed craniometrical system these letters will always have 
the same meaning. 
The base line itself will be indicated by G, so that A is the part 
of G, situated before the projection point of the basion, while B is 
‘the part of G behind it. Now A becomes greater the further the 
basion and hence the foramen magnum lies backward. If now we 
put G 100, in order to become independent from absolute measures 
and to be able to make direct comparisons, then by determining 
A and G in absolute measure in the mediagram, the ratio of A and 
(t may be directly expressed by a number which will be larger as A 
itself becomes larger. This ratio number will in future be called the 
“basal index” of the skull. It is found by the formula 
lOOA _ r 
4 — Index basalis. 
1 ). T [j e chief err0r in Aeby’s base line is that he placed it between two ‘ana¬ 
tomical-’ points; he derived it from the “structure” of the skull, whereas the base 
line I have rhosen, is determined by its “form”. 
