BRAIN 



209 



istic of, and confined to, the group, though the particular regions 

 are much more highly developed than in Cyclostomes : the pallium 



Fn;. 157. BRAIN OF ScyUium canicula. A, dorsal ; B, ventral ; C, lateral view. 



6.0, olfactory bulb; ep, base of epiphysis ; /./*, telencephalon ;fr, fourth ventricle ; 

 h. 6, cerebellum ; h.p, hypophysis ; if, lobi inferiores ; m.b; mid-brain (optic 

 lobes) ; m.d, medulla oblongata ; sr, saccus vasculosus ; th, diencephalon ; to, 

 olfactory tract (very short in Scyllutm). The epithelial and vascular roof of 

 the, third and of the fourth ventricle has been removed, it-x, cerebral nerves 

 (the ventral vagus roots are omitted in B). 



is almost exclusively nervous. According to its external form, two 

 main types can be distinguished. Thus in Spinax, Scymnus, Noti- 



