102 FISHES. 



to. the corresponding parts of the brain of the Lampreys. The 



Fig. 45. — Braiu of Petromyzon. (Enlarged, after Miiller.) 

 I., Upper ; II., Lower aspect. 

 li, Medulla oblongata ; ac, nerv. acusticus ; J, corpus restiforme or rudimentary 

 cerebellum ; d, lobua ventriculi tertii ; d', entrance into tlie third ventricle ; 

 e, hypopbysis ; fa, nerv. facialis ; g, nerv. opticus ; Ti, hemisphere ; hy, 

 nerv. hypoglossua (so named by Miiller) ; i, lobus olfactorius ; Tc, sinus 

 rhomboidalis ; I, epiphysis ; m, nerv. oculo-motorius ; q, corpora quadri- 

 gemina ; tr, nerv. trigeminus ; tro, nerv. trochlearis ; o, nerv. vagus. 



foremost pair are the large olfactory tubercles, which are 

 exceedingly large in Petromyzon. They are followed by the 



