ENDOCRANIAL ANATOMY OF OREODON 299 



occipital sinuses. A medium sized sinus ridge situated on the 

 lateral surface of the caudal part of the pyriform lobe has been 

 termed in the foregoing description the infero-lateral sinus. It 

 drains into the posterior lacerated foramen which is also con- 

 nected in its caudal part with the occipital sinuses. 



Endocranial foramina 



The cribriform laminae in Oreodon are large and occupy the 

 rostral end of each olfactory fossa. No details as to the arrange- 

 ment of the fenestrae cribrosae have been ascertained on any of 

 the specimens. 



The optic foramina open into the endocranial cavity by a 

 single dorso-ventrally depressed canal in a manner somewhat 

 similar to that obtaining in Ovis, and due to the presence of a 

 shelf of bone extending backwards from the orbitosphenoid. 

 The canal is somewhat dumbbell-shaped in cross section as the 

 result of moulding of the bone around the optic nerves. 



In proportion to the optic foramen, the foramen lacerum ante- 

 rius is somewhat smaller in Oreodon than in Sus. In section it 

 is roughly quadrangular with the shortest axis laterally directed. 

 It gives exit to the ophthalmic and maxillary divisions of the 

 trigeminus and probably also the Nerves III, IV and VI as in 

 modern artiodactyls. The two foramina are separated from one 

 another by a distance relatively much greater than obtains in 

 Ovis and Sus. As in modern artiodactyls, the foramen rotundum 

 is not present as a separate entity. Thus in all these forms the 

 primitive arrangement for the exit of the maxillary trigeminal 

 division by way of the foramen lacerum anterius has been 

 retained (v. Gregory, 16). 



The foramen ovale opens downwards and outwards into a 

 short canal which is separated by a stout bony bar from the 

 foramen lacerum posterius. The endocranial aperture of this 

 foramen is somewhat larger than the ensuing bony canal through 

 which passed the mandibular division of the trigeminus. In 

 modern Bovidae the internal carotid artery is also transmitted 



