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 



w 



Zol 



Fig. 219. — 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 (//J, trochlear {IV), trfgeminal (F), 

 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 



