298 DAVIDSON BLACK 



the middle cerebral artery, the grooves in question are to be con- 

 sidered as corresponding to analogous vessels in Oreodon. They 

 cannot be traced above a level corresponding approximately to 

 the rhinal fissure either in Oreodon or in modern forms. 



Large and small branches of the middle meningeal artery are 

 evident as sharply defined ridges on the caudo-lateral surface of 

 all the casts. These ridges may be distinguished readily from 

 those corresponding to the middle cerebral artery by the follow- 

 ing characters: 1) the middle meningeal arterial ridges are 

 sharply cut and have the appearance of being pasted on the cast ; 

 2) the origin of the larger ridges is always abrupt and presents 

 a broken surface on the cast since in the lower part of their course 

 these arteries are for the most part enclosed in a bony canal; 

 and 3) their topographical relations on the cast are dissimilar. 

 Only the larger vessels of this nature have been indicated on the 

 drawings of the casts. The difference between middle cerebral 

 and middle meningeal arterial ridges is especially clear in Speci- 

 men IV (fig. 16). 



In one cast (Specimen II) two small arterial grooves caudad 

 of the pituitary fossa may indicate the presence of posterior com- 

 municating arteries. In Specimen V attention has been drawn 

 to the curious elongated prominence situated in front of the 

 chiasma ridge and between the olfactory tubercles. It is pos- 

 sible that this corresponds to a groove upon the orbito-sphenoid 

 caused by one of the anterior cerebral arteries, since I have ob- 

 served a similar groove corresponding to a large anterior cerebral 

 artery in this relation in one specimen of Canis. 



Veins. The groove for the superior sagittal sinus is well 

 marked on all the casts. Caudally this sinus bifurcates at the 

 confluens. The resulting branches, forming the so-called lateral 

 sinuses, may show considerable inequality in their size and they 

 diverge from one another at an angle much more acute than is 

 the rule in Sus and Ovis. The lateral sinuses appear to drain 

 chiefly into the parieto-temporal canals. The latter are also 

 connected with large venous channels which ascend from the 

 medulla along the lateral borders of the paramedian lobules of 

 the cerebellum and which apparently represent the ungulate 



