SINUS PAEANASALES EARLY TERTIARY MAMMALS 



137 



as they are, are surpassed by the casts of these cavities made by 

 nature and preserved in fossil form. They show us the com- 

 plete form of the cavities, the blood supply, the thickness of the 

 limiting walls, and the relations of the sinuses to the nasal cavity 

 and to the brain (fig. 2). 



Ala oasis frontalis 



s ^axillaris 

 superior 



A_T V.-Smus sagittal* superior 



-Gyrus lateralis 

 -Gurus mediaUs 

 -^C?Cj/^" -Sulcus, intermedia 

 "---Confiuens smuum 



" Povoflocculus 

 Vermis cerebell 



~" Medulla spinalis 



Fig. 2 Dorsal view of the casts of the brain and the sinus paranasales of the 

 oreodont, Merycochoerus, from the White River Oligocene. The position of the 

 eyes and the location of the external auditory canal renders it probable that 

 this animal was aquatic. X f. 



The oreodont cast shown in figures 1, 2, and 3, represents a 

 member of an extinct group of artiodactyls which was so abun- 

 dant and so characteristically American in Oligocene and Mio- 

 cene times. Scott ('13) says of these animals: 



The Oreodontidae was one of the most characteristic of North 

 American artiodactyl families, and its members were exceedingly abun- 



