594 



TEXT-BOOK OF PHYSIOLOGY 



ith om 



The Language Zone. These different areas are connected with 

 another by association fibers, and, taken collectively, constitute the languagi 

 zone, which in people who are congenitally right-handed is located on th< 

 left side of the brain only. Their situation and relations are shown in Fig 

 253. In this figure the dotted lines coming from the eye (v) and ear (a 

 represent the visual and auditory tracts through which nerve impulses pas 

 to the visual centers (V) and the auditory (A) respectively. Similar lint 



coming from the muscles involved L 

 speech and writing might also be reprc 

 sented to indicate the paths of th 

 nerve impulses to the muscle sens 

 areas not shown in the diagram. Th 

 single continuous lines on the surface 

 of the cortex represent nerve-fiber 

 which associate the visual and audi 

 tory centers with the speech and writ 

 ing centers. The double lines assc 

 ciate the visual and the auditory area 

 with the frontal association area on th 

 one hand and the association area wit; 

 the motor speech and the motor writ 

 ing area respectively. The dotted line 

 coming from the speech and writin 

 centers represent the tracts comin 

 from the areas in the pre-central con 

 volutions, and through which nerve im 

 pulses pass to the muscle of the larym 

 tongue, mouth, and lips, and to th 

 muscles of the hand. The anatomi 

 and physiologic association of the vari 

 ous areas is essential to the registratio] 



Xf J^IS3t ^TC^ ^ tne impressions made on the ea 



^^CC---^^^ /( an d eve an d for the expression of th 

 ^ * i< ^ u -wA^ ideas evolved from them by word 



(speech) and signs (writing). Thei 

 collective action is essential to the ac 

 quisition of language. Destruction o 

 any part of this cerebral mechanisn 

 is attended by an impairment of or ; 

 total loss in either the power of ob 

 taining auditory images of words hear< 



FIG. 253. DIAGRAM SHOWING THE RE- 

 LATION OF THE CENTERS or LANGUAGE AND 

 THEIR PRINCIPAL ASSOCIATIONS. A. Audi- 

 tory center. V. Visual center. M. Motor 

 speech center. E. Motor writing center. 

 O O. Intellectual center. (A /ter Gr asset.) 



and visual images of words seen, or th 



power of expressing ideas by speech and writing. To this pathologic con 

 dition the term aphasia has been given. 



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

 in the two general divisions, motor and sensor. 



Motor aphasia may be either aphemic or agraphic. In aphemic aphasi; 

 the patient is unable to express or communicate his thoughts by spokei 

 words, owing to an inability to arrange words for outward expression am 

 hence to execute those movements of the mouth, tongue, etc., necessary fo 



