FUNCTIONS OF THE CEREBRUM. 



209 



284. As might be expected, the Brain of Man bears by far the highest 

 proportion ; but this proportion is not so large in the transverse and vertical 

 diameters, as in the antero-posterior ; in fact, in the proportion of the vertical 

 diameter, the brain of Man is equaled by that of the Dolphin, and nearly so 

 in that of the transverse diameter. In the complexity of the convolutions, 

 however, and in the thickness of the gray matter, the Cerebrum of Man far 

 surpasses that of this Cetaceous animal. In these respects the higher Q,uad- 

 rumana present the nearest approach to it ; but their brain is much inferior 

 in size. In descending the scale of Mammalia, there may be observed a 

 gradual simplification in the general structure of the Brain, depending upon 

 a great diminution in the amount of commissural fibres ; until in the Marsu- 

 pialia the Brain presents nearly the same condition which it offers in Birds 

 ( 218). These animals manifest a much lower degree of intelligence than 

 many Birds evidently possess ; and it is interesting to remark, that their cere- 

 bral hemispheres are proportionably smaller than those which we find in 

 many Birds : the diminution in their relative size not being counterbalanced 

 (as it is in some other instances) by increased complexity of structure. In 

 the class of Birds we observe that the Vulture and the Falcon, whose preda- 

 ceous instincts give them a considerable amount of general energy, are much 

 inferior in the size of their brains to the Insessorial Birds, which are more 

 intelligent ; and that of all, there is none in which the brain is so proportion- 

 ally large, as it is in the Parrot tribe, the educability of which is familiar to 

 every one ; whilst the easily domesticable, but unintelligent Turkey, has a 

 brain of scarcely half the proportional size. The' very small size of the Cere- 

 brum in Reptiles and Fishes, completely harmonizes with the same view ; 

 these animals presenting for the most part but feeble indications of intelli- 

 gence. Among Reptiles, the Tortoise has a Cerebrum comparable in length 



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