394 ANATOMY FOR NURSES [Chap. XIX 



of the body involved in the convulsion or loss of function. In this 

 connection it must be remembered that the fibres extending from 

 the brain into the cord, and from the cord into the brain, decussate 

 or cross in the medulla. 



Sense areas. — The term " sense areas " is used to designate those 

 parts of the brain to which sensation is due, and which control 

 vision, hearing, smell, and taste. The visual area is situated in 

 part of the occipital lobe ; the auditory area in the superior part 

 of the temporal lobe ; and the olfactory and gustatory areas are 

 in the anterior part of the temporal lobe. 



Location of speech areas. — " The speech areas, four in number 

 and in kind, are in the left hemisphere in right-handed persons and 

 in tlie right in left-handed persons. There are two types of aphasia, 

 which is the loss of the power of speech, known as motor and sen- 

 sory aphasia. The motor speech centre lies in the posterior part 

 of the third frontal convolution just in front of the centre of the 

 muscles of speech. A lesion of the motor speech centre causes 

 motor aphasia, in which there is a loss of the word-forming power, 

 although the tongue is movable and the patient may understand 

 spoken and written language and knows what he wants to say. 

 It is as if memory of the motor combinations essential to produce 

 speech were lost. 



The power of writing is usually lost with motor speech. The 

 probable location of its cortical centre is in the posterior two-thirds 

 of the first, and perhaps in the second, temporal convolution. A 

 lesion here causes ' word deafness,' a sensory aphasia in which the 

 memory of the sounds of words is lost so that they are not under- 

 stood, though hearing may be normal. 



Word-blindness (alexia), or the loss of memory of printed or 

 written language, is caused by a lesion in the occipital lobe, 

 though sight itself may be normal. 



"Thus the basis of language is a series of memory pictures: 

 (1) of the sound of words; (2) of their appearance; (3) of the 

 effort necessary to enunciate them ; and (4) to write their sjTnbols. 

 As these memory pictures are connected with each other and with 

 others that make up the concept by subcortical association fibres 

 passing between them, a lesion in any of these association tracts 



