56 
Pl. 6 shows part of the top section shown in Pl. 5. The circles 
A and B are the sections of the bored canals. Line P, P, connecting 
the centres of these circles is the line of intersection of Plane 3 
with the plane of the direction of the cut, while line P,P, shows 
the line of intersection of Plane 1 with the plane of the direction 
of the cut. If point a (pl. 6) is a point of definition of a semicircular 
canal, the ordinates of this point aa, and aa, can be easily deter- 
mined, viz. by direct measuring. The ordinate aa, depends on the 
number of the section in the series, its size is determined by the 
thickness of the sections and the degree of enlargement. (See PI. 5). 
It will be easy to understand now, that in this way, not only 
from a point a, but also from 18 points, being 6 X 3 points of 
definition of six planes of semicircular canals, the ordinates, with 
regard to the planes P,,P, and P, which are used as planes of 
projection, can be determined. 
By means of the projections of these 18 points 6 planes can be 
construed, according to the method of descriptive geometry and the 
angles between those planes can be measured, conformable to the 
description given above. 
B. The planes of the otoliths. 
In order to determine the position of the planes of the semi- 
circular canals, it has proved necessary to neglect one property viz. 
“the swaying’. Similarly when determining the position of the 
planes of the otoliths, it must be kept in view, that these planes 
do not exactly answer to the membranes of the otoliths. A factor 
of curvature is neglected here as well, the sacculus- and the utriculus- 
otolith-membranes viz. both forming curved planes, which are hard 
to represent in our calculation. What has been described as the 
otolith-membrane here, is consequently a simplified “flattened-out” 
otolith-membrane. The mistake arising out of this is very small as 
regards the utricule otolith-membrane, as this membrane almost 
answers to a level plane. It is different with the saccule otolith- 
membrane of which the greater distal part is almost entirely level 
as well; the proximal part however is bent fairly strongly to the 
lateral side. 
As is Known the otolith-membranes have more or less the form 
of an ellipse, of which the long axis runs from proximal to distal. 
The beginning and the end of this long axis can be determined 
in our series, by examining the section in which the said otolith- 
membrane comes first, and that in which it comes last. 
