GENERAL FUNCTIONS OF THE CEREBRUM 575 



(rostrum) between the olfactory bulbs. 4. The much greater 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 animals. 

 The chief evidences regarding the functions of the cerebral hemispheres de- 

 rived from these various sources are briefly these: i, Any severe injury of 

 them, such as a general concussion, or sudden pressure as 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 vertebrates and especially in man at different ages, as well as 

 in different individuals, the greater is the development of the cerebral hemi- 

 spheres 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, Re- 

 moval of the cerebral hemispheres in the lower animals produces effects cor- 

 responding with what might be anticipated 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 activities 

 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 quietly 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 hunger and thirst, 

 apparently do not affect the brainless frog. In other words, the oper- 



