12 INTRODUCTION. 



racter peculiar to the brain of birds, he adds, consists in " the thin and 

 radiated septum, which shuts each anterior ventricle on the internal side. 



" The character of the brain of reptiles depends on the position of 

 the thalami behind the hemispheres. 



" The character of the brain of fishes consists in the tubercles of the 

 olfactory nerves, and the tubercles situated behind the cerebellum. 



" The three last classes, viz., birds, reptiles, and fishes, have, in com- 

 mon, the following characters of the brain, distinguishing between them 

 and Mammalia : neither corpus callosum, nor fornix, nor their depen- 

 dencies. Some tubercles, more or less numerous, situated between 

 the corpora striata and the optic thalami, the thalami containing ven- 

 tricles, and being distinct from the hemispheres. The absence of any 

 tubercle between the thalami and the cerebellum, as well as the absence 

 of the pons Varolii. 



" Fishes, in common with birds, have certain characters which do not 

 exist in the other classes, namely, the position of the optic thalami 

 under the base of the brain, and the number of the tubercles placed before 

 these thalami, which are commonly four. 



" Fishes and reptiles have, as a common character distinguishing them 

 from Mammalia and birds, the absence of the arbor vitas in the cere- 

 bellum. 



" All red-blooded animals have the following cerebral characters in 

 common: the principal division of the brain into hemispheres, optic 

 thalami, and cerebellum ; the anterior ventricles double, the third and 

 fourth single ; the aquaeductus Sylvii ; the infundibulum ; and a com- 

 munication between all their cavities. The corpora striata, and their 

 appendices, called hemispheres, in the form of a vault. The anterior 

 and posterior commissures, and the valve of the cerebrum. The bodies 

 named pineal and pituitary glands. The union of the great single 

 tubercle, or cerebellum, by two transverse crura, with the rest of the 

 brain, which gives origin to the two longitudinal crura of the medulla 

 oblongata. 



" It appears, moreover, that certain relations exist between the 

 faculties of animals and the proportions of their common parts. Thus, 

 the intelligence they possess appears more perfect, in proportion to the 

 volume of the appendix to the corpus striatum, which forms the vault 

 of the hemispheres. Man has that part greater, and more reflected, than 

 the other animals. In proportion to the descent from Man, it is observed 

 to become smaller, and smoother on the surface,* and that the parts 

 of the brain are less complicated or united with each other, but seem to 

 be unfolded, and spread out longitudinally. It even appears that certain 

 parts assume, in all classes, forms which have a relation to particular 



* In some of the Marmozet Monkeys, if not in all, it is smooth, as in the Rodentia. 



