3^ Dr Treviranus on the Cochlea of the 
to be 73° 40'. An acute rhomboid. Fig. 3. PI. III., of this mea- 
surement may, therefore, be considered as the primitive. The 
other planes in the figure are marked with the signs designating 
the laws of decrements which produce them. In the present 
case, ail these signs may be obtained without measurement, on 
account of the parallelism of the edges of combination. Thus, 
the face P is parallel to the edge of intersection of two of the 
faces belonging to the sa,me summit ; is parallel to the su- 
perior edge of the primitive, and is parallel to the superior 
edge of the rhomboid The faces d} and the two six- 
sided prisms are also determined by the parallelisms they offer, 
and their relative positions. The sign of this form, according to 
the method of designation of Haliy, is therefore Pa^ e^ e^ (P. 
According to Mohs, the same modifications would respectively 
be designated by 
r, r — QO , r— -2, r-j-1, r + go , r- — 1, P -f- oo , 
I have calculated the incidences of the secondary faces from 
their signs, and the angle 73° 40' of the primitive. They ar^ 
as follow, and agree within ten minutes with observation. 
p,r^ 
IP = 
73° 
96 
e^ 
d\ d^ 
= 63 
= 19.6 
40' 
15 
59 
44 
P, = 112° 33' 
h\ 129 34 
= 101 40 
120 
120 
a% a' 
148 49 
90 
d\a'^= 90 
Art. IX . — On the Cochlea of the Internal Ear qf Birds, By 
Dr G. R. Treviranus, Professor of Medicine, Bremen, 
Communicated by the Author 
structure of the cochlea of the internal ear of birds has 
been hitherto principally known by the description of Professor 
Scarpa, from which it appears so simple, that it is rather diffi- 
cult to comprehend how a class of animals, in which many spe- 
cies display an acuter sense of melody and of articulate tones 
than most of the Mammalia, should, in respect to the perfection 
of this organ, which certainly is principally intended for the re- 
ception of the different modifications of audible impressions, be 
* Eead before the Wernerian Society, December 18, 1824, 
