v] ExjH'rhiH'iitul Kridcncc r<'<jar<li IKJ Function 133 



Now since accounts of the recorded experiments on the cortical localisation of vision 

 cover familiar pages of all text-books of neurology, it will be unnecessary for me to discuss 

 them at any length. Suffice it to say that while Hitzig is to be credited with first 

 having indicated the probability of the existence of the visual centre in the hinder part of 

 the cerebrum, Munk was the first to attempt to locate it by experiment. The majority 

 of Munk's operations were performed on dogs, but he also employed some monkeys ; and 

 the conclusions he arrived at concerning the location of the visual sense in the occipital 

 lobe were either wholly or partially substantiated by Schafer, Horsley, Vitzou, Sanger- Brown, 

 and other observers who repeated his experiments. One point gathered from these experi- 

 ments has a special bearing on the present research. It is that, in the case of the ape, 

 Munk and Schafer agree in stating that, in order to produce blindness, it is necessary to 

 extend the field of ablation on to the lateral surface of the hemisphere and as far forward 

 as the " Affenspalte." This statement is of particular interest to me, because it agrees with 

 my statement that, in the anthropoid, the type of cortex to which I have assigned visual 

 characters has a similarly wide distribution, and on looking through the literature for con- 

 firmation of this anatomical truth, I find that Schlapp, in the case of the lower apes, has 

 subdivided the cerebral cortex into three types, the posterior of which corresponds ap- 

 proximately with Hunk and Schafer's field, and his observations coupled with mine must 

 be accepted as very strong proof of the accuracy of the broad results of these particular 

 experiments. 



Ferrier, whose researches are so well known in this country, combatted Munk's views 

 and extended the visual area to the angular gyrus, and in doing so received support from 

 Lannegrace, but now it is believed almost universally that the blindness which Ferrier pro- 

 duced by destruction of the angular gyrus was due to severance of or interference with the 

 occipito-thalamic fibres which underlie this region and which are bound to suffer in such an 

 ablation. In like manner the temporary interference with vision recorded by Goltz and 

 Hitzig, after ablation of the frontal lobe in dogs, is more reasonably ascribed to accidental 

 disturbance of the vascular apparatus of the optic nerve, or of the primary visual centres, 

 than to a direct association between the frontal lobes and the visual sense; although it 

 is to be remembered in this connection that Sherrington and Grunbaurn figure a somewhat 

 extensive area on the lateral surface of the frontal lobes of the higher apes, faradisation 

 of which yielded conjugate movements of the eyeballs, an area spatially separated from the 

 Rolandic " motor " area by a field of inexcitable cortex. 



And concerning the effects of cortical stimulation, it is further to be observed that 

 movements of the eyeballs attend faradisation of other parts of the cortex; thus Ferrier 

 obtained lateral movements of the eye (and also of the head?) towards the opposite side 

 by stimulation of the angular gyrus. Schafer produced associated movements of the eyes 

 from stimulation of all parts of the occipital lobe, viz., movements downward and to the 

 opposite side from the upper part, upward movements from the posterior part, and pure 

 lateral movements from the middle part. In reference to the last-mentioned result, it is to 

 be noted that Muuk and Obregia obtained fixation of the eyes in the middle line, plus 

 slight convergence, by stimulation of the corresponding area. 



Gerwer writing in 1899 states that, in the ape, eye movements are obtainable by stimu- 

 lation of three areas, the posterior portion of the frontal lobe, the occipital lobe, and the 

 angular gyrus ; and that while extirpation of the first-named area is followed by lateral 



