BRAIN 



209 



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

 are much more highly developed than in Cyclostomes : the pallium 



FIG. 157. BRAIN OF Scylltiun <-)ii<-nla. A, dorsal ; B, ventral ; C, lateral view. 



6.0, olfactory bulb; ep, base of epiphysis ; /. 6, telencephalon ;//, fourth ventricle ; 

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

 lobes) ; m.d, medulla oblongata ; *<-, saccus vasculosus ; th, diencephalon ; to, 

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

 the third and of the fourth ventricle has been removed, ii-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- 



