376 ROY L. MOODIE 
aT 
Sinilat.-- tit 
Fig. 17 Endocranial cast with casts of nasal cavity (C. n.) and paranasal 
sinuses (Sin. maz., Sin. f., Sin. max. sup.) of a large semi-aquatic oreodont, 
Merycochoerus, from the White River Oligocene. The entire brain cast measures 
80 mm. in length. 
Fig. 18 Dorsal view of an endocranial cast of a small oreodont, possibly 
Oreodon gracilis Leidy, from the Lower Oligocene of South Dakota. The entire 
endocranial cast measures 60 mm. in length and displaces 20 cc. of water. 
Fig. 19 Base of same cast. 
Fig. 20 Left lateral view of same endocranial cast. The long sulcus (S. 
pseud.) is correlated with the same sulcus in Oreodon culbertsoni Leidy, as figured 
by Black (’20, fig. 23). 
Fig. 21 Relation of cerebral cast to paranasal sinuses in Oreodon gracilis 
Leidy. The entire cast as figured, measures 98 mm. in length; the cerebrum has 
a length of 40 mm. from the base of the olfactory bulbs. It will be noted that 
the form of the cerebrum is more robust in this specimen of Oredon gracilis than 
in the one shown in figures 18, 19, and 20. The cerebral pattern is the same in 
the two forms, though the sulci are more deeply cut in the smaller cast. 
