BRAIN 



From the primitive fore -brain are differentiated a posterior 

 diencephalon (thalamencephalon) and an anterior secondary fore- 



Ms 



FIG. 8. 



Dorsal view of the brain of Heptanchus cinercus. (From Gegenbaur, Vcrgl. Anat. Wirbcltirre.) 

 Ac, auditory nerve ; F, facial, Gp, glossopharyngeal ; H, cerebellum ; M, optic lobe ; Ms, spinal 

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

 V, fore-brain ; Vg, vagus nerve ; Z, diencephalon ; a and 5, branches of facial and trigeminal ; 

 ab, abducens ; hp, (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 



