298 



ANATOMY OF VERTEBRATES. 



Blennius, Anguilla, Cyclopterus, Gasterosteus, Eperlanus, Cot- 



1(J6 tus, Trigla, Amblyopsis, 



Eclieneis, the Ganoidei, 

 and Lepidosiren. 



As the crus of the 

 rhinencephalon is formed 

 riot only of fibres con- 

 tinued from the prosen- 

 cephalon, but also, and 

 in some fishes chiefly, of 

 distinct white and grey 

 tracts, traceable along the 

 base of the mesencepha- 

 lon, in part as far back as 

 the prepyramidal bodies, 

 so the origin of the olfac- 

 tory nerve has been de- 

 scribed as characterised 

 by this complexity and 

 extent ; and it is true 

 that in some instances 

 (e. g. in the Perch), 

 where the rhinence- 

 phalon, figs. 180—182, 

 i, is in contact with the 

 prosencephalon, ib. c, a 

 small portion of the true 

 olfactory nerve may be 

 distinctly traced back- 

 ward as far as the mesen- 

 cephalon : just as we find 

 in some fishes (e. g. 

 Sturgeon) a portion of 

 the optic nerve traceable 

 as far back as the cere- 

 bellum, and in the Eel 

 to the hypoaria, and not 

 exclusively terminating 

 in the optic lobe. Most 

 of the characteristics of 



Brain and cerebral nerves of Cod-fish (Gudus morrhua). ht. • • i „„_ r ,++r-J 



orisrm and course attn- 

 bated in works of Comparative Anatomy to the olfactory nerves 

 are to be understood of the ' crura rhinencephali.' In the 



