ANATOMY AND PHYSIOLOGY OF THE BRAIN. 431 



as determined by its thickness and the depth of the con- 

 volutions, bear an approximation, though not constant 

 relation (see Table, page 410), to the development of the 

 intellect. In the highest fishes they are still extremely 

 rudimentary, their size not exceeding that of the corpora 

 quadrigemina (optic lobes). In reptiles, their size is rela- 

 tively much greater; and in birds, they have so much 

 increased as almost to hide the corpora quadrigemina from 

 view. Amongst quadrupeds, the dog presents himself as 

 at once possessed of considerable intelligence and a large 

 cerebral development ; but above all, in the elephant do we 

 meet with the greatest mental endowments, and, relatively 

 to the size of his body, the largest cerebral hemispheres. 

 It need scarcely be added that of all animals the human 

 subject presents the best example of a large cerebrum and 

 a correspondingly powerful intellect. 



In further confirmation of this view, it may be stated 

 that in man congenital deficiency or atrophy of the hemi- 

 spheres is usually accompanied by a corresponding defi- 

 ciency of mental power. Sudden and severe injury of the 

 hemispheres, as in apoplexy, may instantly deprive the 

 subject of all power of mind. Gradually increasing pres- 

 sure, as in the case of hydatids, in one of the hemispheres 

 produces a stupor which constantly augments with the 

 development of the cyst and the absorption of brain matter. 

 Lastly, the removal of the hemispheres leads to results of a 

 similar nature. This can be effected in birds without any 

 immediate danger to life. In the language of Dalton, 

 " the effect of this mutilation is simply to plunge the animal 

 into a state of profound stupor, in which he is almost 

 entirely inattentive to surrounding objects. The bird 

 remains sitting motionless upon his perch, or standing 

 upon the ground, with the eyes closed and the head sunk 



