BRAIN OF MAMMALIA. 13 



qualities of animals : for example, the anterior tubercula quadrigemina 

 of the Carp tribe, the most feeble and least carnivorous of ordinary 

 fishes, are proportionably larger than in the other genera, in the same 

 manner as they are in the herbivorous quadrupeds. By following these 

 inquiries, we may hope to obtain some knowledge of the particular uses 

 of each of the parts of which the brain consists." (See Anat. Comp. 

 vol. ix. p. 8.) 



It appears, for instance, that, in the herbivorous Mammalia, the ante- 

 rior lobes of the corpora quadrigemina exceed the posterior, while the 

 reverse obtains among the Carnivora ; in Man and the Simise they are 

 nearly equal. In the lower Mammalia, as the Rodentia and Marsupialia, 

 the cerebral hemispheres present the lowest grade of development among 

 mammals, being not only the smallest, but being, also, destitute, or nearly 

 so, of those convolutions by which the superficies of the brain, in the 

 ./higher orders, is actually increased. The Pachydermata and the Rumi- 

 nantia occupy an intermediate station, in this respect, between the Rodentia 

 and the Carnivora, the Simiae and Man, in which latter groups we find 

 the convolutions of the cerebral hemispheres deep and symmetrical, and 

 also the cerebellic laminae numerous. In proportion to the development 

 of the cerebral hemispheres, is that of the optic thalami and the corpora 

 striata ; while the magnitude of the olfactory tubercles, and the depth of 

 their cineritious investment, increase in an equal degree with the degrada- 

 tion of the cerebrum, as is remarkably exemplified in the Marsupialia. It 

 may, further, be regarded as a rule, that where the cerebrum, in the Mam- 

 malia, is least expanded, the spinal chord increases in comparative circum- 

 ference, as is found in the herbivorous races generally ; whereas, in the 

 higher groups, as the Carnivora, not only the cerebral and the cerebellic 

 hemispheres, but the great commissure between the two cerebral hemi- 

 spheres the crura prolonged from them, and also the pons Varolii are 

 relatively larger. 



With respect to the spinal chord, compared with the cerebral mass, 

 it is smaller in Man than in other Mammalia ; but is continued com- 

 pletely down the spinal canal.* From the spinal chord are given off 

 the nerves of sensation and motion; the former from the posterior, the 

 latter from the anterior columns, and the motor roots and anterior 

 columns are smaller than the sensitive : in Man, the sensitive roots of the 

 spinal nerves are larger than in other Mammalia. It is, however, when 

 the brain of the Mammalia, generally, is compared with that of the lower 

 classes, that its superiority becomes manifest. In the Mammalia it is, that 

 the central axis, to which the nervous system converges, is most developed, 

 and has its parts most intimately united, so as to form a perfect and com- 



* In many Mammalia the spinal chord divides, before it has reached the termination of the vertebral 

 canal. In the Hedgehog, indeed, it is remarkable that the chord does not pass, in an undivided condi- 

 tion, beyond the extent of two-thirds down the canal. 



