150 PHILOSOPHY OF ZOOLOGY. 
“5, The three last classes have, in common, the follow- 
ing characters by which they are distinguished from the first. 
‘© a, Neither corpus callosum, nor fornix, nor their de- 
pendencies. 
“* ®. Some tubercles, more or less numerous, situated be- 
tween the corpora striata, and the optic thalaini. 
c. The thalami containing ventricles, and being distinct 
from the hemispheres. 
“‘d. The absence of any tubercle between the thalami 
and the cerebellum, as well as the absence of the 
pons Varolii. 
“<6. Fishes have certain characters in common with birds, 
which are not to be found in the other classes. ‘These are, 
** a. The position of the optic thalami under the base of 
the brain. 
‘*‘ b, The number of the tubercles placed before these tha- 
lami, which are commonly four. 
«7. Fishes and reptiles have, for a common character, 
distinguishing them from the two first classes, the absence 
of the arbor vite in the cerebellum. 
‘¢ 8. All red-blooded animals have the following charac- 
ters in common. 
“‘ qa. The principal division into hemispheres, optic thala- 
mi, and cerebellum. 
“, The anterior ventricles double ; the third and fourth 
single; the aqueeductus Sylvii ; the mfundibulum ; 
and a communication between all their cavities. 
‘“‘¢. The corpora striata, and their appendices, in the 
form of a vault, called hemispheres. 
«‘d. The anterior and posterior commissures, and the 
valve of the cerebrum. 
“¢ ¢. The bodies named Pineal and Pituitary Glands. 
“« f. The union of the great single tubercle or cerebellum, 
by two transverse crura, with the rest of the brain, 
