ENDOCEANIAL ANATOMY OF OEEODON 297 



of the cerebrum of Oreodon was much less than that of even 

 immature specimens of Sus; and 4) that the disparity between 

 the bulk of the cerebellum in Oreodon and in Sus is not so evident 

 as that between the cerebral regions in these forms. 



Endocranial blood supply 



Arteries. The chief arterial blood supply of the cerebrum ap- 

 pears to have been derived from branches of the internal carotid 

 vessels which differ from those of modern ruminants and suUlines 

 in their relatively long, uninterrupted intracranial course. They 

 appear to enter the cranium as in the pig by the posterior lacer- 

 ated foramen and pass rostrad in well marked bony grooves be- 

 tween those for the lodgement of the ophthalmic-maxillary divi- 

 sion of the trigeminus and the pituitary fossa. Their course has 

 been described above where it has been noted that at the level 

 of the foramen lacerum anterius the grooves in question converge 

 slightly and may be traced forwards to the base of the chiasma 

 ridge (v. figure 8, p. 283). 



In modern ruminants and pigs the internal carotid arteries 

 break up into a rete mirabile beneath the inner layer of dura 

 immediately after their entrance into the cranial cavity. This 

 is also true of the arterial branches arising in common with the 

 ophthalmic artery from the internal maxillary artery in the sheep 

 (vide Owen, 25; Chauveau, 7; Sisson, 30). It is evident therefore 

 that in Oreodon the intracranial course of the internal carotid 

 artery was not interrupted by the formation of a rete mirabile 

 such as characterizes the vessel in modern artiodactyls. 



Crossing the caudo-lateral surface of the tuberculum olfac- 

 torium and the lateral surface of the pjTiform lobe about the level 

 of the trigonum Sylvii there are to be seen on every cast several 

 irregular ridges, whose outlines are not sharply cut, which corre- 

 spond to vascular grooves upon the endocranial surface of the 

 orbital wing, or the juncture of this and the temporal wing, of 

 the sphenoid. Since in modern ungulates this part of the endo- 

 cranial surface is usually sculptured more or less distinctly by 



