NERVOUS SYSTEM. VERTEBRATA. 



285 



almost as broad in front as it is behind " (Mivart, op. cit.) . 

 These illuminating remarks of Mivart will be seen to have 

 a much wider application than even their author intended, 

 for the resemblance between the plan of the sulci in Otaria 

 and Ursus is so very striking, even in the arrangement of 

 small and apparently unimportant features, that there can 

 be no question as to the identity of the two series of sulci. 



The olfactory bulb [lacking in this specimen] is large 

 for a Pinniped Carnivore [compare the cast of the cranial 

 cavity, D. 371]. It is borne on a long peduncle, which 

 extends from the region of the tuberculum olfactorium 

 forward on the base and then upward on the anterior surface 

 almost to the antero-dors.il angle or apex of the hemisphere 

 (fig. 160). It is lodged in a deep sagittal olfactory sulcus. 



Fig. 160. 



SULC.SUPRAS 



Parallel to and coextensive with the latter there is an 

 orbital (presylvian) sulcus, which does not join the rhinal 

 fissure (fig. 160). A comparison of this with the human 

 orbital (so-called triradiate) will make clear to the reader 

 why the term " orbital " has been employed in these notes 

 throughout the whole mammalian series in place of the 

 more customary " presylvian." 



The " Sylvian fissure " is distinctly Ursine. It begins 

 on the ventral surface of the brain in a distinct vallecula 

 Sylvii caused by the flexure of the small pyrifonn lobe 

 (fig. 160) : it ascends with a slight inclination backward. 



The clue to the complete understanding of the brain of 

 the Seals is afforded by the study of the Bear's brain. It 



