378 ROY L. MOODIE 
Fig. 24 Partial endocranial cast identified as representing the cerebrum 
of Mesohippus, the early Tertiary three-toed horse. a, Dorsal view of cast; 
b, Left lateral view of same cast. 
The fundamental equine cerebral pattern is already laid down in this early 
Tertiary horse, from which the cerebrum of Equus differs only in size and com- 
plexity of pattern. Length of cast, 60 mm. 
Fig. 25 Comparative sizes of the ancient mammalian endocranial casts de- 
scribed. Projection drawings representing cross-sections through the widest 
parts of the cerebrum, made by viewing the casts from directly in front. All 
two-thirds natural size. 
a, Oligocene rodent, uncertain. 
b. Small specimen of Ictops, Oligocene hedgehog. 
c, Larger specimen of Ictops, Oligocene hedgehog. 
d, Dinictis, primitive Oligocene cat. 
e, Hoplophoneus (?), Oligocene machairodont. 
f, Smilodon (reconstructed), giant saber-tooth cat. 
g, Daphaenus, Oligocene bear-dog. 
h, Aenocyon, giant Pleistocene wolf. 
i, Oreodon, the common Oligocene pig-like ruminant. 
j, Oreodon gracilis Leidy. 
k, Mesohippus, the three-toed horse (reconstructed). The prominence of the 
temporal lobes is due to the imperfect nature of the cast. 
