164 



THE ANATOMY OF VERTEBRATED ANIMALS. 



t)i the brain in osseous fishes. The posterior wall of these 

 lobes, where it passes into the cerebellum, or in the ; 

 region which nearly answers to the valve of Yieussens in 

 mammals, is thrown forwards into a deep fold which lies 

 above the crura cerebri, and divides the iter a tertio ad 

 quartwm ventriculum from the ventricle of the optic lobes 

 throiighout almost the whole extent of the latter. This fold 

 is the " fornix " of Gottsche. On each side of it the floor 



Fig. 50. 



fig. .50.— Brain of tlie Pike, viewed from above :— ^,tiie olfactory 

 nerves or lobe<!, and beneatli them the optic nerves ; B, the cerebral 

 hemispheres ; C, the optic lobes ; B, the cerebellum. 



of the ventricle of the optic lobes is raised up into one or 

 more eminences, which have the same relation to the optic 

 lobes as the corpora striata have to the prosencephalic 

 vesicle. 



The optic nerves simply cross one another, and form no 

 fhiasma. The cerebellum is usually large. 



The cephalic part of the sympathetic nerve is present, as 

 in the higher Vertebrata. 



