282 CHEMICAL SENSES 



represented in Figure 11. The lateral ventricles form hollow spaces whose 

 dorsal walls constitute the pallium. 



Until recently the available evidence indicated that the lateral olfactory 

 tract in sharks carries the extensively processed olfactory information to 

 most regions of the telencephalon, which therefore seemed to be mainly 

 concerned with olfactory and gustatory function (the "olfactory brain": 

 Edinger 1980; Ariens Kappers 1909; Ariens Kappers et al. 1936; 

 Nieuwenhuys 1967). This interpretation of old standing had to be drastically 

 reviewed as a result of recent findings which demonstrated that the olfactory 

 tract projects onto only a small zone of the lateral wall of the telencephalon 

 in the nurse shark (Figure 12) (Ebbesson and Heimer 1968, 1970; Veselkin 

 and Kovacevic 1973), whereas higher order olfactory areas do not seem to 

 have extensive projections to the hemispheres either (Ebbesson 1972). 



This raised phylogenetically important question of what the functions of 

 those large telencephalic regions that apparently do not receive olfactory 

 information could be (Schroeder and Ebbesson 1974). Earlier (Ebbesson and 

 Schroeder 1971) it was shown that the telencephalon in the nurse shark 

 receives optic afferent nerves; this suggests that the forebrain may have 

 become a sensory integration center early in phylogeny. Bruckmoser (1973) 

 has suggested that such an integrative function may play a role in migratory 

 and homing behavior in lower vertebrates. Furthermore, Ebbesson and his 

 collaborators demonstrated that the retina (Ebbesson and Ramsey 1968), 

 cerebellum (Ebbesson and Campbell 1973), spinal cord, and tectum (Ebbes- 

 son et al. 1972) send axons to the dorsal thalamus, which may therefore 

 function as a relay for sensory information to the nonolfactory telencephalic 

 areas. The pathways of some of the nonolfactory afferents were recently 



ped.ol. 



tub. ol. 



Figure 11 Transverse hemisection through the telen- 

 cephalon of Scyliorhinus: pallium (pal), pedunculus 

 olfactorius (ped. ol.), corpus striatum (c. str.), tuber- 

 culum olfactorium (tub. ol.) and septum (sep.). From 

 Nieuwenhuys (1967). 



