1082 VISUAL SENSATIONS. [BOOK in. 



(or right) visual fields, indicating failure in the central endings 

 of the right (or left) optic tract, being caused by removal of the 

 right (or left) gyrus, and destruction of both angular gyri has led 

 to total blindness, not only the hemiopia but the total blindness 

 being, however, apparently transitory. And cases have been 

 observed in which the transient blindness due to removal of the 

 occipital lobes has been succeeded by permanent hemiopia upon 

 the subsequent removal of the angular gyrus. Indeed the general, 

 but not uniform, tendency of the many experiments which have 

 been made is to connect, in the monkey, both the occipital lobe 

 and the angular gyrus with vision. 



In the dog, removal of portions of the occipital cortex have also 

 led to partial and transient blindness, or according to some to 

 permanent blindness; but the difficulties of judging of the visual 

 condition of a dog are very considerable, and his vision is so 

 different from that of man, so much less binocular, for instance, 

 than his, that it would not be profitable to relate at length the 

 results obtained in the dog, or to discuss the conclusions which 

 have been derived from them. We will only say that some 

 observers have been led to think that the lateral part of the 

 retina is connected with the lateral part of the visual occipital 

 area, the front part with the front part and so on, the retina being 

 as it were projected on to the occipital cortex ; but the facts are 

 not clear enough to make it worth while to dwell upon them here. 



In man clinical histories so far conform to the results of 

 experiments on the monkey as to associate the occipital cortex, 

 and more particularly the cuneus (see Figs. 129, 130) with vision. 

 They have however raised a point on which we have not yet 

 touched. In the experiments on the monkey, quoted above, the 

 result (putting aside transient effects due probably to 'shock') of 

 interference with one side of the brain was hemiopia; and this is 

 what we might expect from the anatomical relations ; the optic 

 tract goes straight to the tegmental masses of its own side, and the 

 optic radiation passes from those masses to the occipital cortex of 

 the same side ; there is no decussation save of the fibres of the optic 

 nerve, as they pass into the optic tract at the chiasma. Clinical 

 histories teach the same lessons as these experiments on animals ; 

 lesions limited to the occipital lobe, have for a symptom, hemiopia ; 

 and this is said to be especially the result of mischief limited to 

 the apex of the occipital lobe, that is, to the cuneus. But experi- 

 ments on monkeys have been made in which destruction of one 

 angular gyrus has produced, not hemiopia, but crossed blindness 

 or crossed amblyopia, that is to say has affected the whole of the 

 retina of one eye, and that the crossed eye, the eye of the same 

 side not being, or being supposed not to be, at all affected ; similar 

 results have also been stated to follow upon removal of one occipital 

 lobe. And a few clinical cases have been recorded in which disease, 

 especially of the angular gyrus, seemed to affect the vision of the 



