144 THE HUMAN BODY. 



vision may be equally good in both eyes, although one hemi- 

 sphere may be atrophied, or may have suffered, as from 

 wounds, a great loss of substance. It is, on the contrary, 

 exclusively in the cerebral lobes that the perception of sen- 

 sations lies, and that the ideas are formed which these sensa- 

 tions create. It is also from the hemispheres that the im- 

 pulse emanates, which results in voluntary motion. Some 

 physiologists have referred this impulsion to the white, and 

 others to the gray substance of the brain. Wherever may 

 be the seat of the motor principle, we know that the brain 

 exercises a cross action on the muscles; that is, the left hemi- 

 sphere induces the movements of the right side, and the 

 right hemisphere those of the left. But in certain cases the 

 action is direct notwithstanding; this has been explained by 

 an exceptional incompleteness of the crossing of the cerebral 

 fibres. Physiologists have sought in vain to localize the 

 source of motion in the brain, and the difference of opinion 

 on this point does not permit us to consider it a settled 

 question. 



The encephalon controls the intellectual phenomena, and 

 most authors consider the cerebral lobes the seat of the soul. 

 In the superior animals the most complete development of 

 the brain proper coincides, in fact, with the greatest degree 

 of intelligence, and the proportions of the brain of man 

 unite with his intellect in placing an immense interval between 

 him and animals the most gifted in this respect. And lastly, 

 the encephalon in idiots is specially characterized by atrophy 

 of the cerebral lobes, of their convolutions, and of the gray 

 or cortical substance. Several authors, from repeated observa- 

 tion of this latter fact, have considered the gray substance 

 as the seat of the intellectual faculties. 



We have already stated, in speaking of the skull, that Gall 

 and his school have placed the intellectual faculties in the 

 anterior lobes of the brain, the moral qualities or tendencies 

 of the mind in the middle lobes, and the animal faculties or 

 instinctive propensities in the posterior lobes. This doctrine 

 seems to be the rational consequence of that which recog- 

 nizes one portion of the encephalon as specially designed for 

 the functions of the intellect; but if we admit the possible 



