60 
three series. For each series the data required were first determined 
by way of descriptive, then by way of analytic geometry. The 
results thus obtained, were collected in a table (p. 59). 
With the manipulation of the 3"¢ series, Mr. H. Oort (Med. Cand.) 
gave us his greatly appreciated help; the results referring to this 
series have been determined by him. 
In the detailed article on this subject, to be published elsewhere, 
we shall enter more deeply into the discussion, to which this table 
gives rise; some main points can be stated concisely: . 
1. It appears first of all, that the angles made by the planes 
of the semicircular canals, lying on one side, do not differ greatly 
from 90°. 
The average’) value, calculated from the table, amounts to 94° 
for the angle between the superior plane and the exterior plane, 
to 90° for the posterior plane and the exterior plane and to 897/,° 
for the posterior plane and the superior plane. 
2. The planes of the exterior semicircular canals on both sides, 
make between them an average angle of 173'/,°, their line of inter- 
section forms a small angle (once 15'/,°, onee 1°) with the cranium 
base-line (which is almost conform to the clivusline). 
The planes of the two superior semicircular canals form between 
them an average angle of 82,5°, their line of intersection forms 
an angle of 82°, with the cranium base-line. The planes of the two 
posterior canals form between them an average angle of 99°; their 
line of intersection forms an angle of 58° with the craniumbase-line. 
3. The otoliths-membranes which are situated on one side form 
between them an average angle of 101°. 
4. The planes of the two utricle-otoliths-membranes form between 
them an average angle of 173°; their line of intersection forms 
with the craniumbase-line an angle of 44°. 
The planes of the two sacculus-otoliths-membranes form between them 
an average angle of 54'/,, their line of intersection forms with the 
craniumbase-line an angle of 49°. 
1!) To these average values calculated from a small number of observations, no 
great importance should be attached; therefore these numbers have not been 
mentioned in the table. 
