AND PHYSIOLOGY. 



341 



Will evidently reside in the brain (cerebrum), and re- 

 quire that this organ should be in a healthy state, since, 

 if any disease affects its whole substance, their power is 

 destroyed. Voluntary muscular movements depend on a 

 sound and healthy brain, although reflex movements, and the 

 motion necessary to sustain animal life, are often carried 

 on in some animals for a considerable time, when they are 

 born without a brain. But the whole brain does not seem to 

 be absolutely essential to life and mental operations, for many 

 instances are mentioned, where a considerable portion of the 

 brain has been removed by accident, such as a bullet or iron 

 bar being shot through the head followed by a discharge 

 of nervous matter : and yet the persons have lived for 

 years subsequent to the accident in as sound a condition as 

 ever. 



608a. Necessity of two Cerebral Hemispheres —One 

 may be injured, and not the other. — The reason of the 

 division of the brain into lobes or hemispheres is not so easily 

 understood. Perhaps it may be that so large an organ of so 

 soft a substance could not easily sustain its own weight, es- 

 pecially when reclined on one side, and at the same time 

 properly perform its functions. A more probable reason, 

 however, is this. It is a well-known fact, that one of the 

 hemispheres may be diseased or injured, so as to perform its 

 functions imperfectly, and yet the other hemisphere be in its 

 ordinary healthy state. Also one hemisphere may be so 

 much affected, that the opposite side of the whole body is 

 paralyzed in motion or sensation, or both. It then seems 

 reasonable to suppose, that, since the brain would be so liable 

 to injuries, it was made in two portions, so as to prevent the 

 entire destruction of life by an injury to one of the hemi- 

 spheres. 



60S. Where are the intellect and the will located ? What movements depend on the 

 brain ? Is the whole brain absolutely essential for intellection ? 60S a. Why are there 

 probably two hemispheres to the brain? 



