1919] Merriam: Tertiary Mammalian Faunas of Mohave Desert 497 



The length of the skull is a 

 I'.ttle greater than the measure- 

 ments of Merychippus material 

 from the Great Plains region 

 available for comparison, and is 

 greater than in a specimen of 

 Protohippus sejuncttts (no. 8291, 

 Am. Mus. Nat. Hist.). 



The brain case is large, wide, 

 and strongly arched anteroposter- 

 iorly in the median line (fig. 60). 

 The anterior slope of the dorsal 

 surface extends downward to the 

 wide, flat or slightly concave 

 frontal area, producing in speci- 

 men no. 20039 a peculiar convex 

 form in the parietal region. 



The rostral region is rather 

 narrow anterior to the cheek- 

 teeth. Very large lateral or lach- 

 rymal fossae originate imme- 

 diately anterior to the orbits and 

 extend forward as very marked 

 depressions almost to a point 

 opposite P 3 . In less marked form 

 they may reach almost to the 

 anterior end of the cheek-tooth 

 series. The long narrow nasal 

 elements extend forward over the 

 nasal openings to a point some- 

 what in advance of the superior 

 canines. 



The anterior ends of the large 

 oval orbits are situated above the 

 posterior region of M 3 . The zygo- 

 matic arch and postorbital bar 

 are rather slender. The post- 

 glenoid process is of moderate 

 length. The paroccipital process 

 is long and slender. 



