16 



TEETIAET VEETEBEATA OE THE EATtTM. 



The optic nerves leave the skull far forwards, perforating the orbitosphenoids by 

 two diverging passages, the inner openings of which lie close together at the bottom 

 of a fossa (text-fig. 5, ii.) bounded anteriorly by a transverse ridge. Immediately 

 external to and slightly below the level of the openings of the optic nerves there is a 



Text-fig. 5. 



Cast of cranial cavity of Arsinoitherium zitteli : A, from above ; B, from below ; 0, from left side. 



aud,, auditory nerve-root ; cb., cerebellum ; f.l.a., nerves passing through foramen lacerum anterius ; 

 h., cerebral hemisphere ; l.l., lateral lobe of cerebellum ; ol., olfactory lobe ; s., sulcus ; ii., optic chiasma. 

 3 nat. size. 



large vertically elongated opening (represented by the projection marked f.l.a. in the 

 cast), the anterior aperture of which {foramen lacerum anterius or foramen sphenoidale) 

 is just over the alisphenoid canal, as described above (see text-fig. 4, ii. and f.l.a.). 



