108 PHYSIOLOGY. 



Animals from whom the hemispheres were removed, had constantly 

 the appearance of deep sleep, and when irritated resembled in their 

 motions an animal just awaking. M. Flourens likens them to an 

 animal condemned to perpetual sleep, but deprived even of the faculty 

 of dreaming. A hen, in which Hertwig had cut away the hemi- 

 spheres nearly to the base of the brain, was found to be deprived of 

 sight, hearing, taste, and smell ; it sat constantly in one spot, and 

 was as if dead, until strongly roused^, when it moved a few steps; it 

 neither fed itself, nor drank, nor attempted to avoid danger. It is 

 evident from these experiments, and from the effects of pressure on 

 the cerebral hemispheres in man, that they are the seat of the 'menial 

 functions ; that in them resides the power of directing the mind to 

 particular sensorial impressions, — thQ faculty of attention. 



The portions of the cerebral hemispheres that possess these 

 elevated functions are the convolutions. The complexity of the 

 convolutions in the animal scale is in the direct ratio of the advance 

 of intelligence. In infancy they are imperfectly developed, and 

 their increase in size goes on simultaneously with the advance of 

 mental power. If their growth be arrested, the mental powers are 

 of the feeblest kind. In idiots the brain is not only small, but the 

 convolutions are exceedingly limited. The object of these convolu- 

 tions is to afford as extensive a surface of the gray or vesicular 

 matter, in as small a space as possible. By this arrangement also, 

 a more ready access is permitted to the blood-vessels on the one side, 

 and a more free communication on the other with'the vast number 

 of fibres by which its influence is to be propagated. 



It is evident, that if the surface of the gray did not exceed that of 

 the white matter, folds or convolutions would not be necessary, but 

 a simple expanse of the former would suffice to cover the surface 

 of the latter. The existence of convolutions on the surface of the 

 hemispheres affords evidence of a large relative amount of the 

 dynamic or vesicular nervous matter, and their number or com- 

 plexity is a measure of the extent to which the vesicular surface is 

 increased. Of two brains, equal in bulk, the one that has most con- 

 volutions has most vesicular matter, and is, physiologically, the 

 more potential. It has been calculated that the entire surface of the 

 human cerebrum, when the convolutions are unfolded, is equal to 

 about 670 square inches. 



The weight of the entire encephalon in the adult male usually 

 ranges between 46 and 53 ounces ; in the female, from 41 to 47 

 ounces. The maximum is about 64 ounces or ^«/- jt?ow?2^5 / the 

 minimum about 31 ounces, or rather less than two 'pounds. In the idiot 

 it is often much below this, as for instance 20 ounces. The cerebral 

 hemispheres alone weigh zkiowifour ti'mes as much as the rest of the 

 cerebro-spinal mass. 



The brain is abundantly supplied with blood by the vertebrals and 



