CEREBRAL LOCALIZATION OF FUNCTION. 129 



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. Cere- 

 bral or Jacksonian epilepsy is a result of local cortical disease. 



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 

 complete loss of the power of articulate speech. In deaf mutes this con- 

 volution is very imperfectly developed. 



Aphasia is of many degrees and kinds ; ataxic, when there is inability to 

 execute the movements of the mouth, etc., necessary to speech; agraphic, 

 if there be loss of the power of writing ; amnesic, when there is loss of 

 memory of words ; paraphasic, if there is loss of the power to connect rightly 

 the ideas with the proper use of words, etc. In word blindness the person 

 cannot name a letter or a word when printed or written ; and in ivord 

 deafness the patient hears sounds but does not hear words. Conditions 

 of these kinds are apt to coexist with hemiplegia. 



Sensory Centres. These are the centres in which the sensory im- 

 pressions are coordinated, and in which they probably become parts of our 

 consciousness. The most important are : 



The Visual Centre, located in the occipital lobe and especially in the 

 cuneus. Unilateral destruction of this area results in hemianopsia, or 

 blindness of the corresponding halves of the two retinae. Destruction of 

 both occipital lobes in man results in total blindness. Stimulation or irri- 

 tation of the visual centre causes photopsia, or hallucinations of sight, in 

 corresponding halves of the retinae. There have been instances of injury of 

 these parts when sensations of color were abolished with preservation of 

 those of space and light, thus showing a special localization of the color 

 centre. Late experiments show that the centres of the two hemipheres are 

 united, as ocular fatigue of a non-used eye was proportional to the fatigue 

 of the exercised one. 



The Auditory Centres are located in the temporo-sphenoidal lobes. 

 Word deafness is associated with softening of these parts, and their com- 

 plete removal results in deafness. 



The Gustatory and Olfactory Centres are located in the uncinate gyrus, 

 on the inner side of the temporo-sphenoidal lobes. There does not seem 

 to be any differentiation, up to this time, of these two centres. 

 " The Superior and Middle Frontal convolutions appear to be the seat of 

 the reason, intelligence and will. Destruction of these parts is followed by 

 proportional hebetude, without any impairment of sensation or motion. 



