150 I'JIII.OSOI'HY 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. 



" b. Some tubercles, more or less numerous, situated be- 

 tween the corpora striata, and the optic thalami. 



" 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. 



" I. 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 vita3 in the cerebellum. 



" 8. All red-blooded animals have the following charac- 

 ters in common. 



" a. The principal division into hemispheres, optic thala- 

 mi, and cerebellum. 



" b. The anterior ventricles double ; the third and fourth 

 single ; the aquaeductus Sylvii ; the infundibulum ; 

 and a communication between all their cavities. 



" c. 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. 



" e- The bodies named Pineal and Pituitary Glands. 



M f. The union of the great single tubercle or cerebellum, 

 by two transverse crura. with the rest of the brain, 



