BRAIN 



J5 



From the primitive fore -brain are differentiated a posterior 

 diencephalon (thalamencephalon) and an anterior secondary fore- 



S" „ 



Ms 



Fig. 



Dorsal view of the brain of Heptanchus cinereus. (FromGegenbaur, Vergl. Anat'JVirbeltiere.) 



Ac, auditory nerve ; F, facial, (^.glossopharyngeal; H, cerebellum ; M, optic lobe ; Ms, spinal 

 cord ; N, medulla, also nasal sac ; 0, optic nerve ; Po, olfactory tract ; Tr, trigeminal nerve ; 

 V, fore-brain ; Vg, vagus nerve ; Z, diencephalon ; a and b, branches of facial and trigeminal ; 

 ab, abducens ; ftp, (hypoglossal) occipito-spinals ; I, olfactory lobe ; om, oculomotor ; v, origin 

 of vagus roots. 



brain, the telencephalon. The diencephalon, bounded behind by the 

 posterior commissure, is crossed above by the superior commissure 



