494 C. JUDSON HERRICK 



and secondary terminal nuclei of the sensory nerves of the medulla 

 oblongata, in higher vertebrates progressively more complex 

 correlation tissue is added to the olfactory association centers 

 and the hemispheres assume their definitive form as the centers 

 for the highest forms of neural function. 



In lower vertebrates, particularly some elasmobranchs, the 

 walls of the telencephalon medium are greatly elongated and con- 

 tain correlation tissue which is incorporated into the hemispheres 

 of higher forms. The nucleus preopticus is the remnant of this 

 unevaginated tissue which is most constantly preserved. This 

 nucleus is continuous rostrally in lower vertebrates with the basal 

 grey of the rhinencephalon of the hemispheres. In teleosts and 

 some ganoid fishes the telencephalon is atypically developed and 

 the hemispheres are very imperfect!}' differentiated. The lamina 

 terminalis, tela chorioidea and ventriculus impar of the telen- 

 cephalon are thrust far forward so that the actual evagination 

 includes little but the olfactory bulbs, while the massive correla- 

 tion tissue which corresponds morphologically and functionally 

 with the greater part of the walls of the hemispheres of some sela- 

 chians, dipnoans and amphibians lies in the floor of the telenceph- 

 alon medium. 



In view of the data presented in the body of this memoir I 

 would modify Johnston's suggestions as follows: 

 Mesencephalon 



Pars ventralis — pedunculus cerebri 



Pars dorsalis — corpora quadrigemina 

 Diencephalon 



Epithalamus 



Hypothalamus 



Thalamus 



Pars dorsalis 

 Pars ventralis 

 Telencephalon 



Telencephalon medium 



Ventriculus tertius pars telencephalica (or ventriculus 



impar telencephali) 

 Lamina terminalis 



