THE CEREBRUM. 509 



pictures are therefore separate, a fact which has led to a division of 

 the visual area into a lower and a higher area. 



It was stated in a previous paragraph that electric stimulation of 

 the sensor areas of the monkey brain is attended by certain motor 

 reactions which vary with the area stimulated. Corresponding areas 

 are believed to be present in the human brain and that their stimula- 

 tion would be followed by similar motor reactions. Their location is 

 shown in Figs. 226 and 227, and named visual, auditory, olfactory, 

 and gustatory motor. 



The stereo gnostic area or area of stereognostic perception, by which 

 objects are recognized through their form independent of vision and 

 by the sense of touch alone, has been located in the superior parietal 

 convolution and the precuneus (Mills). The existence of such an 

 area is rendered probable by the fact that cases have been recorded 

 in which there was a loss of this power (astereognosis) unaccompanied 

 by either sensor or motor disturbances. Postmortem investigations 

 showed that in these cases there was a destruction of the superior 

 parietal convolution. 



Equilibratory, intonation, and orientation areas have been pre- 

 viously located in the sphenotemporal lobe. 



Language. The succession of motor acts by which ideas are 

 expressed, is known as language, which may be divided into (i) 

 articulate or spoken, and (2) written. 



The expression of ideas both by words and signs depends primarily 

 on the power of reviving the images or memories of words and letters 

 heard and seen; and secondarily on the power of reviving the images 

 or memories of the muscle movements which were previously em- 

 ployed in an effort to imitate or reproduce the words (speech) or 

 the verbal signs (writing). 



Clinico-pathologic investigations have shown that words and 

 letters heard and seen have areas of representation in the cortex, the 

 former in the general auditory area, the latter in the supra-marginal 

 convolution and angular gyrus (Fig. 226). Destruction of these 

 areas is followed by word-deafness and word-blindness respectively. 

 The same methods of investigation have shown that the muscle 

 movements employed to reproduce the words and the verbal signs 

 also have areas of representation in the cortex; the former in the 

 third frontal convolution (Fig. 227), and probably in the adjacent 

 region, the island of Reil, on the left side in the great majority of 

 people ; the latter in front of the arm region of the general motor area. 

 Destruction of these areas is followed in the first instance by a loss 

 of the power of executing the movements of the muscles employed 

 in speech, and in the second instance, of those employed in writing. 



These different areas are connected with one another by associa- 

 tion fibers, and, taken collectively, constitute the language zone. 

 Their situation and relations are shown in Fig. 228. In this figure 



