5 10 



TEXT-BOOK OF PHYSIOLOGY. 



the dotted lines coming from the ear (a) and the eye (v) represent 

 the auditory and visual tracts through which nerve impulses pass 

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

 lines coming from the muscles involved 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 center (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 

 attended by an impairment 

 or a total loss either in the 

 power of obtaining auditory 

 images of words heard and 

 visual images of words seen, 

 or in the power of expressing 

 ideas by speech and writing. 

 To this pathologic condition 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 accom- 

 panied by a partial or complete loss of the faculty of articulate speech, 



FIG. 228. DIAGRAM SHOWING THE 

 RELATION OF THE CENTERS OF 

 LANGUAGE AND THEIR PRINCIPAL 

 ASSOCIATIONS. A. Auditory center. 

 V. Visual center. M. Motor speech 

 center. E. Motor writing center. 

 O O. Intellectual center. (After 

 Grasset.) 



