Johnston, Forehram VfsicJe in Vertebrates. 



485 



in-pushing hypophysis remains always in front of the entoderm and 

 mesoderm except so much of the preoral entoderm as is cut off by 

 the primitive optic groove and aborted beneath the terminal ridge. 

 By stage M (Fig. 22) the hypophysis begins to be constricted off 

 from the ectoderm. It presents a shorter anterior lobe which is 



Fig. 21. Squalus ac, stage M. sagittal section, x 33. Pre- and post- 

 optic, infundibular and niammillary recesses, epiphysis and velum transversum. 

 The fibers of the optic chiasma appear in the terminal ridge. 



directed toward the optic chiasma and a longer posterior lobe which 

 is directed toward the mammillary recess. Opposite the tip of the 

 posterior lobe a special outgrowth of the brain wall represents the 

 beginning of the saccus vasculosus. Although the term infundibulum 

 scarcely applies to anything in the fish brain, yet the depression 

 from which the saccus grows out is the region which corresponds 



