THE CEREBRUM. 



557 



in speech and writing might also be represented to indicate the paths of the 

 nerve impulses to the motor speech (M) and the motor writing centers (E). 

 The continuous lines on the surface of the cortex represent nerve-fibers 

 which associate the auditory and visual centers with the speech and writing 

 centers and with higher psychic centers (O O) as well. The dotted lines 

 coming from the speech and writing centers represent the tracts through 

 which nerve impulses pass to the muscle of the larynx, tongue, mouth, and 

 lips, and to the muscles of the hand. The anatomic and physiologic 

 association of the various areas is 

 essential to the registration of the 

 impressions made on the ear and eye 

 and for the expression of the ideas 

 evolved from them by words (speech) 

 and signs (writing). Their collective 

 action is essential to the acquisition 

 of language. Destruction of any 

 part of this cerebral mechanism is at- 

 tended by an impairment of or a total 

 loss in either the power of obtaining 

 auditory images of words heard and 

 visual images of words seen, or the 

 power of expressing ideas by speech 

 and writing. To this pathologic con- 

 dition the term aphasia has been 

 given. 



Aphasia. It was discovered by 

 Bouillaud that a destructive lesion of 

 the third frontal convolution on the left 

 side was accompanied by a partial or 

 complete loss of the faculty of articu- 

 late speech, the power to express ideas 

 with words. To this condition the 

 term aphasia was given. Though of 

 limited application etymologically, the 

 word is now employed in a wider 

 sense to signify " partial or complete 

 loss of the power of expression or com- 

 prehension of the conventional signs 

 of language," words either spoken or 

 written, due to lesions of different por- 

 tions of the cortex, and especially on 

 the left side. 



Aphasias are of many degrees and kinds, though they may be included 

 in the two general divisions, motor and sensor. 



Motor aphasia may be either ataxic or agraphic. In atoxic aphasia the 

 patient is unable to express or communicate his thoughts by spoken words, 

 owing to an inability to execute those movements of the mouth, tongue, etc., 

 necessary for speech without there being any paralysis of these muscles, 

 the lesion is usually in the third frontal convolution and most frequently 



FIG. 255. DIAGRAM SHOWING THE RE- 

 LATION OF THE CENTERS OF LANGUAGE AND 

 THEIR PRINCIPAL ASSOCIATIONS. A. Audi- 

 tory center. V. Visual center. M. Motor 

 speech center. E. Motor writing center. 

 O. Intellectual center. (After Grasset.) 



