Johnston, Forebrain Vesicle in Vertebrates. 483 



inferior lobes (Fig. 16). The anterior part of this is the relatively 

 deep and sharply marked primitive optic groove. The posterior 

 lx)iindary is less definitely marked by a slight projection of the brain 

 floor into the ventricle. This is the tuberculum posterius. As the 

 broad inferior lobes involve nearly the whole floor of the diencephalon, 

 neither the infundibulnm nor the mammillary bodies are to be 

 recognized at this time. Both are developed later within the general 



Fig. 19. Sqiialus ac, GO somites, parasagittal section near the middle line. 

 The mouth is open. Primitive inferior lobes, epiphysis and velum transversum. 

 X 33. 



area of the primitive inferior lobes, as specialized portions of their 

 walls. 



The mammillary bodies are indicated by a rounded caudal pro- 

 jection of the depressed floor of the diencephalon in embryos with 

 about 80 somites (Figs. 20, 21, 22). 



The infundibular recess is not found until after the completion 

 of the changes described in connection with the optic recesses. As 

 in man the infundibulnm is the funnel-shaped depression leading 

 from the floor of the tuber cinereum into the neural part of the 



