dd 
The construction of the angles a, B and y, made us find the lines 
of intersection of conformable planes of semicircular canals, lying 
in the mediumplane, on the left and on the right. In order to find 
the angle mentioned under 2°¢, the construction must still be made, 
leading to the measuring of the angle formed by those two lines ; 
thus making this question a simple problem of descriptive geometry. 
But now comes the question: how to get our planes of projection. 
Before entering upon this subject it will be necessary, to mention 
some technical details about the treatment of the objects. 
The material examined consisted of three rabbits, treated in the 
following way : 
The recently killed animal was rinsed from the aorta with MOLLER’s 
liquid. : 
The back part of the cranium (including the hypophyse; the 
cranium-roof remained intact, the brains were removed) was then 
treated according to Wurtmaack’s method’), but this exception 
that the bone was decalcinated after the impregnation in celloidine. 
The decalcination in the celloidine offers the advantage, that no 
removal of the labyrinths with regard to each other can take place. 
In first decaleinating and consequent enclosing, mistakes caused by 
removal may take place. The celloidine-block was consequently 
fastened on the microtome, in such way as to make the direction 
of the cut an almost frontal one. The sections made at the first 
beginning do not contain the object yet. 
Before the object appears in the sections, a plane has been formed 
on the celloidine-block, being the plane of the direction of the cut, 
which remains the same all through the further manipulation. Round 
canals were bored perpendicularly in the celloidine-block on this 
plane, which canals appear as round holes in every section. This 
was obtained by placing a brass block bored by canals, on the 
plane of the direction of the cut. A hollow needle pierced through 
these canals into the celloidine-block gets the direction of the canals 
in the brass block, these canals being made in such a way, as to 
cause them to stand perpendicularly on the base, in other words 
the canals made in the celloidine-block stand perpendicularly on 
the plane of the direction of the cut. 
Pl. 5 schematically sketches six sections lying on top of each 
other, e.g. 25 enlarged. P, is a plane through the axis of two 
bored canals. P, is the plane on which the sections lie (the plane 
of the direction of the cut) P, is a plane standing perpendicularly 
on? and ee 
1) Zeitschrift für Ohrenheilkunde. Bd. 51. bldz 148. 
