134 Visuo-Sensory and Visuo-Psychic Areas [CHAP. 



deviation of the eye and paralysis of lateral movements, no paralysis attends destructive 

 interference with the other areas. Accordingly he looks upon these excitation eye movements, 

 those obtainable from stimulation of the frontal lobe excepted, as reflex. 



Sherrington and Griinbaum, in their experiments on the higher apes, did not find 

 that the angular gyrus responded in any way to electrical excitation ; and with regard to 

 the occipital lobe, it was only at the extreme posterior apex and along the calcarine region 

 that faradisation yielded any result, and then not easily. 



Interesting as it undoubtedly is that electrical stimulation of different parts should 

 excite such ocular movements, the value of the observations from the localisation standpoint 

 is admittedly doubtful. 



Having determined within rough limits the topography of the visual area in the oc- 

 cipital lobe, experimenters next devoted themselves to the elucidation of other points bearing 

 upon the subject ; in this way, the correlation between various parts of the retina and 

 various districts of the visual area, the possible amount of recovery of function after oc- 

 cipital ablations, and the degree of blindness resulting from operative interference in turn 

 received attention, but as might have been expected, on none of these points has unanimity 

 been arrived at. 



Regarding the question of definite retinal localisation in the occipital lobe, it seems 

 patent when three authorities such as Munk, Schafer, and von Monakow all uphold different 

 views, that the subject must be hedged in with difficulty, and that a solution is hardly 

 to be expected from experimental observation ; hence I can gain nothing by pursuing tin- 

 question here. 



In the next place, concerning the question of the degree of blindness which has at- 

 tended operations on the area of cortex in the occipital region which is believed to stand 

 in relation to the visual function ; the first general result of such operations to be men- 

 tioned is the well-known truth that destruction of that area on one side gives rise to 

 crossed hemianopsia. In like manner, extension of the destructive process to both occipital 

 lobes apparently results in total blindness, at least that is the view held by Munk, Schafer, 

 and most experimenters, for it must be mentioned that the totality of the blindness is 

 denied by Goltz, who believes that a monkey or a dog deprived of its cortical visual aiva 

 still can orientate its position in space, to a certain extent, by means of the retina. But 

 it is a question whether the slight amount of vision which may remain in such cases is 

 not due to the unimpaired activity of what German writers call the " primary optic centres," 

 viz., the corpora quadrigemina anteriora vel colliculi superiores, the corpora geniculata lateralia, 

 and the pulvinaria. Concerning these centres, there exists an abundance of anatomical and 

 pathological evidence to some of which I shall have occasion to refer later -proving that 

 they stand in the closest relation with the optic nerves, and from the phylogenetic point 

 of view it is interesting to recall the facts emphasised by Edinger and others, that in forms 

 low in the animal scale, such as fishes, the corpora quadrigemina or optic lobes are the 

 chief visual organs, sight not being represented in the cerebral cortex. But in higher 

 animals, the external geniculate bodies and pulvinaria progressively assume the upper hand 

 over the quadrigeminal bodies and act as way-stations in the visual track from the retina 

 to the occipital cortex. And the deduction follows that certainly in the frog and pigeon, 

 animals which when completely decerebrated still show signs of being able to see, probably 

 in the rabbit, cat, dog, and ape, and possibly in man, any trace of the power of vision 



