752 



THE CEREBRAL CORTEX. 



produced from the temporal and occipital regions. 1 The extra cell or 

 cells through which they operate must probably, therefore, be looked 

 for in lower centres (thalamus 2 or superior corpora quadrigemina ?). 

 It may therefore be concluded that the disposition of the tracts by 

 which the nervous impulses which produce motion operate, is different 

 in the case of the Eolandic areas and of the areas connected with visual 

 and auditory sensations a conclusion which has a far-reaching effect in 

 connection with the question of the supposed sensory functions of the 

 Eolandic cortex. It also militates against the hypothesis of Flechsig, 3 

 that each sensory sphere is like the cortex of the Eolandic region, in 

 having its own special mechanism for producing movements of the 

 particular peripheral sense organ, and only of this one, and that each 

 such sphere is therefore a motor area in the same sense as is the cortex 

 of the Eolandic region. 



We may next proceed to consider more in detail the several 



sensory areas which have been men- 

 tioned. 



Visual area. The parts com- 

 prised within this area are, in the 

 monkey, the occipital lobe and the 

 immediately adjacent portions of the 

 temporal lobe, including the cuneus, 

 lingual lobule, and posterior parts 

 of the temporal convolutions upon 

 the inner and under surfaces. 



Terrier was the first to describe 

 in various animals (dog, jackal, cat, 

 rabbit, monkey) the existence of an 

 excitable zone in the posterior part 

 of the hemisphere, stimulation of 

 which causes movement of the eyes 

 to the opposite side. In carnivora 

 he placed this zone on the posterior 

 part of the second convolution, in 

 the monkey on the angular gyrus ; 

 and both alone and in conjunction 

 with G. F. Yeo he subsequently 

 found destruction of the angular gyrus to produce loss of vision in the 

 opposite eye, and of both angular gyri complete blindness in both eyes. 

 Hitzig described blindness of the opposite eye as the result of removal 

 of the cortex of one occipital lobe in dogs, 4 but later was led to con- 

 clude that a similar result might follow lesions of the anterior part of 

 the brain also. 5 On the other hand, Luciani and Tamburini 6 asserted 



1 Schafer, Internal. Monthly Journ. Anat. and Physiol., "Leipzig, 1888, vol. v. This 

 has been confirmed by other investigators, e.g. Danillo, Rosenbach, Steiner and Obregia 

 (Arch. f. Physiol. , Leipzig, 1890, S. 260). The last observer also found that extirpation 

 of the occipital lobes had no effect on the movements obtained from the excitation of the 

 frontal lobes. 



2 Various observers have described centrifugally conducting fibres as passing from the 

 cortex of the occipital lobe, and terminating in the thalamus. 



3 Neurol. CcntralU., Leipzig. 1894, Bd. xiii. S. 674. 



4 Centralbl. f. d. med. Wissensch., Berlin, 1874, S. 548. 



5 Arch.f. Psychiat., Berlin, 1883, Bd. xv. S. 270. 



6 " Sui centri psico-sensori corticali," Reggio- Emilia, 1879. See also on the effects of abla- 

 tion of the occipital lobes in dogs, Yitzou, Arch, dephysiol. norm, eipaih. , Paris, 1893, p. 678. 



FIG. 343. Brain of a monkey from which 

 one occipital lobe had been entirely re- 

 moved but the angular gyrus left intact. 

 This animal was rendered permanently 

 hemiopic. 



