146 



HUMAN PHYSIOLOGY. 



FIG. 19. 



agraphic aphasia there is an inability to execute the movements necessary 

 for writing, though the mental processes are retained. In the ataxic form 

 the lesion is in the 3d frontal convolution, and in the agraphic form it is in 

 the arm centre. 



In Amnesic Aphasia there is a loss of the memory of words, the purest 

 examples of which consist of the affections known as word deafness and 

 word blindness. In word deafness the patient cannot understand vocal 

 speech, though he is capable of hearing other sounds. This condition is 

 associated with lesion of the first temporal convolution. In word blindness 



the patient cannot name a 

 letter or a word when 

 printed or written, though 

 he can see all other objects. 

 This condition is associated 

 with impairment of the visual 

 centres. 



Figure 19 will illustrate 

 the conditions in the various 

 forms of aphasia. Impres- 

 sions are constantly passing 

 from eye and ear to the 

 visual and auditory centres 

 and there registered. Com- 

 missural fibres connect these 

 centres with the arm and 

 speech centres, which in turn 

 are connected by efferent 

 fibres with the muscles of 

 the hand and vocal appa- 

 ratus. Muscular movements 

 of the eyes, hand and mouth 

 are also registered by means 

 of the afferent fibres s, s', s". 

 Sensory Centres. These 

 are the centres in which the 

 sensory impressions are co- 

 ordinated, 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 



