CEREBRAL LOCALIZATION OF FUNCTION. 145 



tion of which causes " opening of the eyes, dilatation of the pupils and 

 turning of the head to the opposite side with conjugate deviation of the 

 eyes to that side." 



The centres of origin of the nerves for the ocular muscles lie in 

 the gray matter of the aqueduct of Sylvius. Destruction of the gray 

 matter at these points is followed by paralysis of the muscles of the 

 opposite side of the body, and morbid growths, hemorrhages or thrombi of 

 the vessels of the parts, result in abnormal stimulation or interference of the 

 functions corresponding to the nature and extent of the lesion. Cerebral or 

 Jacksonian epilepsy is a result of local cortical disease. 



Centre for Speech. Pathological investigations have demonstrated 

 that the left third frontal convolution is of essential importance for speech. 



FIG. 18. 



DIAGRAM OF THE MOTOR AREAS ON THE MARGINAL CONVOLUTION OF A MONKEY'S 



BRAIN. Horsley and Schafer. 



Adjoining this convolution are the centres controlling the motility of the 

 lips, tongue, etc. In the majority of the cases the speech centres are on the 

 left side of the brain, though in exceptional cases it is on the right side, 

 especially in left-handed people. In deaf-mutes this convolution is very 

 imperfectly developed, while in monkeys it is quite rudimentary. 



Lesions of the third frontal convolution on the left side, if the patient be 

 right-handed, produce the various forms of aphasia or the partial or com- 

 plete loss of the power of articulate speech. 



Aphasia is of many degrees and kinds. In ataxic aphasia the patient is 

 unable to communicate his thoughts by words, there being an inability to 

 execute the movements of the mouth, etc., necessary for speech. In 



