50 
medium plane, with the top-level of the basi- 
occipitale. This last description is to be regard- 
ed! as an. oad to orientation : with the pre- 
sently following determinations the imaginary 
line a, 6 (eraniumbase-line) only plays a part. 
In order to determine the position of any 
plane in the eranium (e.g. a maculaplane) 
two angles must be known, viz.: 
1st. the angle, which the desired plane forms 
Pl. 1. The basi-occipitale with the medium plane, 
of the rabbit seen from 24. the angle between cranium basisline and 
above. the line of intersection of the planes men- 
tioned under 1. Thus we can first of all determine the position 
of the four macula-planes and that of the six planes of the semi- 
circular canals in the cranium. 
Moreover it is important to know the mutual position of these 
planes, i.e. we must try to find the angle: 
a, between the two planes of the posterior semicircular canals 
(Plane of posterior canal left and right PPCL and PPCR), 
8, between the two planes of the superior semicircular canals 
(PSCL and PSCR), 
y, between the two planes of the exterior semicircular canals 
(PECL and PECR). 
I &, between the planes of the superior and the exterior semi- 
circular canal on the right (PSCR and PECR). 
Il R, between tbe planes of the posterior and the exterior semi- 
circular canal on the right (PPCR and PECR). 
Ill A, between the planes of the posterior and the superior semi- 
circular canal on the right (PPCR and PSCR). 
I ZL, between the planes of the superior and the exterior semi- 
circular canal on the left (PSCL and PECL). 
II ZL, between the planes of the posterior and the exterior semi- 
circular canal on the left (PPCL and PECT). 
Ill LZ, between the planes of the posterior and the superior semi- 
circular canal on the left (PPCL and PSCT). 
UU, between the Utriculusmacula-planes (UZ and Uh). 
SS, between the Sacculusmacula-planes (SL and SR). 
SUR, between the planes of Macula utrieuli and Macula sacculi 
on the right (UR and SR). . 
SUL, between the planes of Macula sacculi and Macula utrienli 
on the left (SZ and UL). 
