490 



THE EYE IN EVOLUTION 



Figs. 647 and 648. — The Representation of the Retina on the External 

 Geniculate Body. 



4 3 21 



Fig. 647. — In the Australian Opossum (after Packer). 



6 5 4 3 21 



Fig. 648. — In the Primate (after Le Gros Clark). 



Impulses from corresponding points (a, b) in the two retinas pass up the optic 

 tract. Uncrossed impulses (a') terminate in laminje 2 and 4 in the opossum, 

 and 2, 3 and 5 in the Primate. Crossed impulses (6') terminate in laminse 1 and 

 3 ill the opossum and 1, 4 and 6 in the Primate. These fibres terminate in a 

 rec otion unit in the lateral geniculate body which forms a band of cells 

 rac! ,_ from the hilum of the nucleus. The projection unit from the 



Iatei;i i.niculate body (c) to the visual cortex forms a band of cells involving 

 all the 1 uninse in each case. 



