XII 



PHYLUM CHORDATA 



353 



The spinal cord is similar in essential respects in all three 

 examples. It is a cylindrical cord of nerve matter, having 

 running along the middle of its dorsal surface a fissure, the 



Zol 



FIG. 919. Dorsal view of the brain of Scyllium canicula. The posterior division 

 of the brain is the medulla oblongata (NH), on the dorsal surface of which is 

 shown one of the central ventricles (F. rho). The large cerebellum (HH} 

 nearly covers the optic lobes (MH}. The diencephalon (ZH) shows in the 

 middle one of the central ventricles, and the place of attachment of the pineal 

 body (Gp}. The prosencephalon (VH} gives off the olfactory lobes (Tro, L. ol). 

 The following nerves are shown: optic (//), trochlear (IV}, trigeminal (V) t 

 facial (VII}, auditory (VIII}, glossopharyngeal (IX}, and vagus (X}. 

 (From Wiedersheim.) 



dorsal longitudinal fissure, and along the middle of its ven- 

 tral surface, a second fissure, the ventral longitudinal fissure. 



2A 



