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VISION 



Figure 4 (A) Dorsal view of the nurse shark brain, with schematic of the sites of elec- 

 trode penetrations in the telencephalon (Tel). The horizontal lines are separated by 2 

 mm, and each symbol indicates a penetration site. Mediolateral symbol separations are 

 equivalent to 1 mm. The crosses on the ipsilateral (left) telencephalon indicate penetra- 

 tions where field potentials were evoked in response to optic nerve stimulation. The large 

 open circles indicate penetrations where maximum activity was obtained. The cerebellum 

 is labeled Cb. (B-F) Transverse sections through telencephalic levels indicated by leaders 

 from (A). The right half of each section is stained with cresylechtviolett to illustrate the 

 prominent central telencephalic nucleus (CT). The other abbreviations are OL, lateral 

 olfactory area; TrTT, thalamotelencephalic tract. (GT) Representative waves elicited in 

 penetrations at levels corresponding to (C), (D), and (E), respectively. Downward deflec- 

 tions indicate negativity. (Reprinted with permission from Cohen et al., Science 182:492- 

 494 (Nov. 2, 1973), Fig. 1. Copyright 1967 by the American Association for the 

 Advancement of Science.). 



