368 ROY L. MOODIE 
nothing of importance to Osborn’s (’88, p. 87) description, his 
words, copied herewith, will apply. 
Mesohippus had a large and well-convoluted brain. The length and 
breadth indicate that it weighed about one-third as much as the brain 
of the recent horse, while if we estimate the body weights of the fossil 
and recent animals by the relative size of the humeri, the brain of the 
Miocene species was proportionally heavier. The cerebrum of the 
horse is, however, much more highly convoluted, and the frontal 
lobes are relatively broader. The Mesohippus brain is distinguished 
in a marked manner by the longitudinal direction of the parietal and 
occipital sulci, and by the transverse frontal sulci, from the oblique 
sulci of all recent ungulates. In fact, in this respect it bears a marked 
general resemblance to the brain type of recent Carnivora, and con- 
forms with the higher Ungulata of the Eocene. To this may be added 
that the hemispheres are narrower and less capacious in the fossil, and 
as in all the lower members of the ungulate series, they taper much 
anteriorly. This brain shows in the parietal and occipital region very 
close agreement with the principal fissures of the equine brain as 
figured by Krueg, but in the frontal region the agreement is much less 
close, owing to the transverse direction of the frontal sulci. 
The high degree of cerebral development indicated by the 
cast of Mesohippus (fig. 24), by Osborn’s (’88) discussion and 
figures of the endocranial cast, by Scott’s (91) description of 
the brain case of Mesohippus, and by Cope’s (see Matthew 715) 
figures of the brain cast of Merychippus is strikingly at variance 
with the other Oligocene Mammalia studied. Mesohippus, an 
Oligocene tridactyl horse, exhibits in its cerebral pattern a much 
closer approach to the brain of the modern horse than the brain 
of Daphaenus, for instance, does to the cerebral pattern of the 
modern Canidae. This is an interesting example of accelerated 
development of cerebral pattern in the equine group. The 
brain of the Oligocene horse had already attained a high degree 
of complexity and, while still somewhat primitive, it is remark- 
ably modern in its development. 
