PAL^OSYOPS LEIDY, AND ITS ALLIES. 
329 
spicuoiLs. The vermis shows signs of transverse folds, hut the condition of the cast 
does not allow this point to be made out definitely. Two small appendages, which 
may be the Hocculi, are given off from the cerebellum, one on each side at the 
antero-inferior angle of the same. 
Medulla. — The medulla oblongata is peculiar in its great breadth, it being 
nearly as broad as the cerebellum and strongly depressed. The form of the medulla 
differs very much from this portion of the Tapir’s brain, where it is round in section 
and much narrower than the cerebellum. The brain viewed from the side shows 
no contact between the the cerebrum and cerebellum. The inferior surface of the 
brain shows the roots of the optic nerves, and posteriorly upon each side is seen 
the origin of the fifth pair of nerves ; a deep fossa between the two latter, 
bounded anteriorly by the optic nerves, is evidently the pituitary fossa. The sur- 
face of the brain posteidorly to the origin of the fifth pair is higher than the region 
of the pons Yarolii, which, together with the inferior surface of the medulla, is 
ver}’ flat and wide. Just posterior to the cerebellum and upon the lateral side of 
the medulla, are two pi’ominences which are probably the origin of the twelfth pair 
of cranial nerves. 
Co.MPARISOX OF THE BrAIN OF PaL^EOSYOPS WITH THAT OF OTHER UNGULATES. 
Comparing the brain of P. megarhimis with the lower Eocene Amblyopoda and 
Condylarthra we see a marked increase in its size and in the dimensions of the 
anterior lolies, the posterior prolongation of the latter approaching the region of 
hind brain, thus differing very much from the Wasatch forms. Although occurring 
in the same beds with Palceosyops we have the abnormally small brain of Uinta- 
theriinn, which is unusual in the diminutive size of its encephalon. In Hyrachyus 
eximuis, an animal about the “ size of a large sheepV’ we have a form with a much 
larger brain relatively than that of Palceosyops. In Hyrachyus the forebrain is 
large, with large temporal lobes. There is in the latter genus a marked difference 
in the breadth of the cerebrum as compared .with that of the cerebellum, but if the 
casts of H. eximius can be relied upon, the convolutions of its brain were not nearly 
so complicated as in Palceosyops, the gyri I'unning nearly longitudinally and par- 
allel. The general form of the prosencejihalon in Hyrachyus closely resembles that 
of the recent Carnivora. The whole bulk of the brain of P. niegarhinus compared 
with that of the Tapir, is nearly one-half less, whereas in the brain of Hyrachyus 
compared ivith that of Ovis, this difl’erence is not nearly so great. Marsh’s figures 
of the brain of Titafiothei'him indicate that the forebrain did not extend at 
all over the hind brain, although the hemisjiheres were “ richly convoluted,” 
their width and the large deA^elopment of the temporal region being greater than 
in Palceosyops. In the convoluted surface' of its hemispheres P. megarhinus 
approaches the Tapir and is much more highly developed in this respect than 
any of the Eocene forms which I have studied. The great size and breadth of 
'Tertiary Vertebrata, page (>72. 
