C34 HANDBOOK OF PHYSIOLOGY. 



of the faculties of judgment, understanding, memory, reflection, induc- 

 tion, imagination and the like. 



Evidence regarding the physiology of the cerebral hemispheres, has 

 been obtained, as in the case of other parts of the nervous system, from 

 the study of Comparative Anatomy, from Pathology, and from Experi- 

 ments on the lower animals. The chief evidences regarding the func- 

 tions of the cerebral hemispheres derived from these various sources, are 

 briefly these: 1. Any severe injury of them, such as a general concus- 

 sion, or sudden pressure by apoplexy, may instantly deprive a man of all 

 power of manifesting externally any mental faculty. 2. In the same 

 general proportion as the higher mental faculties are developed in the 

 Vertebrate animals, and in man at different ages and in different indi- 

 viduals, the more is the size of the cerebral hemispheres developed in 

 comparison with the rest of the cerebro-spinal system. 3. No other part 

 of the nervous system bears a corresponding proportion to the develop- 

 ment of the mental faculties. 4. Congenital and other morbid defects 

 of the cerebral hemisphere are, in general, accompanied by correspond- 

 ing deficiency in the range or power of the intellectual faculties and the 

 higher instincts. 5. Eemoval of the cerebral hemispheres in one of the 

 lower animals produces effects corresponding with what might be antici- 

 pated from the foregoing facts. 



Effects of the Removal of the Cerebrum. The removal of the cere- 

 brum in the lower animals appears to reduce them to the condition r.f a 

 mechanism without spontaneity. 



In the case of thefroy, when the cerebral lobes have been removed, 

 the animal appears similarly deprived of all power of spontaneous move- 

 ment. But it sits up in a natural attitude, breathing quietly; when 

 pricked it jumps away; when thrown into the water it swims; when 

 placed upon the palm of the hand it remains motionless, although, if 

 the hand be gradually tilted over till the frog is on the point of losing 

 his balance, he will crawl up till he regains his equilibrium, and comes 

 to be perched quite on the edge of the hand. This condition contrasts 

 with that resulting from the removal of the entire brain, leaving only 

 the spinal cord; in this case only the simpler reflex actions can take 

 place. The frog does not breathe, he lies flat on the table instead of 

 sitting up ; when thrown into a vessel of water he sinks to the bottom ; 

 when his legs are pinched he kicks out, but does not leap away. 



A pigeon from which the cerebrum has been removed will remain 

 motionless and apparently unconscious unless disturbed. When dis- 

 turbed in any way it soon recovers its former position ; when thrown 

 into the air it flies. 



In mammals it is difficult to remove the cerebral hemispheres, but in 

 those animals in which the operation has been carried out, as for example 



