854 



THE EYE AND VISION 



[CH. LVIII. 



of this subject in connection with cerebral localisation, the pheno- 

 mena of hemianopsia and the conjugate deviation of head and 

 eyes (pp. 736, 737). 



Fig. 542, though diagrammatic, will assist the reader in more 

 fully comprehending the paths of visual impulses, and the central 

 connections of the nerves and nerve-centres concerned in the process. 

 The fibres from the retina to the external geniculate body end 

 there by arborising around its cells, and a fresh relay of fibres from 



FIG. 542 Relations of nerve cells and fibres of visual apparatus. (Schafet) 



these cells passes in the posterior part of the internal capsule to the 

 cortex of the occipital lobe. Those to the anterior corpus quadrige- 

 minum are continued on by a fresh relay to the nuclei of the nerves 

 concerned in eye-movements (represented by the oculo-motor nucleus 

 in the diagram) ; the axons of the cortical cells pass to the tegmentum, 

 whence a fresh relay continues the impulse to the oculo-motor nucleus. 



Sherrington's observations on binocular flicker have shown that there are 

 difficulties in accepting fig. 542 as a complete anatomical basis for the psychological 

 processes involved in binocular vision, although it is probably correct so far as the 

 motor mechanisms involved are concerned. 



Visual Judgments. 



The psychical or mental processes which constitute the visual 

 sensation proper have been studied to a far greater degree than is 

 possible in connection with other forms of sensation. 



