596 THE NERVOUS SYSTEM 



prominence of the temporo-sphenoidal lobes in apes. 5. The fissure of Sylvius 

 is nearly horizontal in man, while in apes it slants considerably upward. 6. 

 The distinctness of the fissure of Rolando. 



Most of the above points are shown in the accompanying figure of the brain 

 of the orang. 



GENERAL FUNCTIONS OF THE CEREBRUM. 



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 anatomy, from pathology, and from experiments on the lower ani- 

 mals. The chief evidences regarding the functions of the cerebral hemi- 

 spheres derived from these various sources are briefly these: i. Any severe 

 injury of them, such as a general concussion, or sudden pressure as by apo- 

 plexy, 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 vertebrates and especially in man at different 

 ages, as well as in different individuals, the greater is the development of 

 the cerebral hemispheres in comparison with the rest of the cerebro-spinal 

 system. 3. No other part of the nervous system bears a corresponding 

 proportion to the development of the mental faculties. 4. Congenital and 

 other morbid defects of the cerebral hemisphere are, in general, accompanied 

 by corresponding deficiency in the range or power of the intellectual faculties 

 and the higher instincts. 5. Removal of the cerebral hemispheres in 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 of a 

 mechanism without spontaneity. 



In the case of the frog, when the cerebral lobes have been removed, the ani- 

 mal appears similarly deprived of all power of spontaneous movement. But 

 it sits up in a natural attitude and breathes quietly. When pricked it jumps 

 away. When thrown into the water it swims. When placed upon a board 

 it remains motionless, although, if the board 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 board. 



If the frog be turned on his back, he regains his normal position. If his 

 back is stroked gently he will utter the usual croaking sound. These activi- 

 ties are carried on by the normal frog. There is one striking difference, 

 however, between the brainless frog and the normal: the former, if placed 

 in a position and left undisturbed, will remain without moving for an 

 indefinite time. It has apparently lost the power to initiate movements. 

 Presumably any memory impressions or effects of former experiences have 

 been lost. Even the more elemental stimuli, which come from tissue 



