THE CEREBRUM. 127 



thalami, but if the lesion encroaches upon the white matter of 

 the internal capsule or crura cerebri, the effect is to cause more 

 or less paralysis, depending upon the severity of the lesion and 

 its position. 



What are the functions of the cerebrum ? 



The motor and sensory functions which have been seen to belong 

 to other nuclei of gray matter are centred here, but infinitely 

 broadened, for the cells in the convolutions of the cerebrum can 

 originate the efferent and perceive the afferent nerve-impulses. 

 In fact, it is in this portion of the brain that the intelligence is 

 centred: it is the organ of the mind. Memory, reason, emotions, 

 and all the other attributes of the mind are dependent upon its 

 functional power. 



What is the effect upon animals of the removal of the hemi- 

 spheres ? 



In some of the lower animals the cerebrum may be entirely 

 removed without killing them. When this is done, for example, 

 in the case of a pigeon, the bird remains quiet in one position, and 

 is not disturbed by noises, or if thrown from its perch it flies and 

 alights in a nearly normal manner. If a foot be pinched, it with- 

 draws it and perhaps changes its position. The bird is capable 

 of reflex actions of various complicated kinds, but there is no 

 spontaneous exercise of volition : all its movements are excited 

 by the nerve-stimuli of the moment. There is no perception of 

 stimuli ; the intelligence is gone. 



What is unilateral action of the brain ? 



There are instances in which the injury or disease of one-half of 

 the brain has left the intellectual faculties not gravely impaired. 

 From a consideration of such cases it has been held that the action 

 of one of the hemispheres was sufficient for the purposes of the 

 mind. There is, however, an absolute dependence for motor and 

 sensory functions upon the integrity of both sides, for the one side 

 cannot act for the other in these functions. As a rule, it is safe 

 to assume that the two hemispheres act in unison. 



Are the functions of the brain localized ? 



While the brain is regarded as an organ of the mind, it is prob- 

 able that the various functions may be regarded as belonging to 

 definite portions of the convolutions which arc appropriated for that 



