16 
TEHTIAEY VEETEBEATA OF TJIE EAYtjM. 
'The optic nerves leave the skull far forwards, perforating the orhitosphenoids by 
two diverging ])assages, 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 
('xternal to and slightly below the level of the openings of the optic nerves there is a 
Text-fig. 
Cast of cranial cavity of Arsinoiiherium zitteli : A, from a))ove ; B, from below ; C, from left side. 
aud., auditory nerve-root ; ch., cerebellum ; f.ha., nerves passing tbrough foramen lacerum anterius ; 
h., cerebral hemispbere ; l.l., lateral lobe of cerebellum ; ol., olfactory lobe ; s., sulcus ; ii., optic cbiasma. 
g 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.). 
