289 
PALyEOSYOPS LEIDY, AND ITS ALLIES. 
median keel, bordered anteriorly and laterally by prominent rugosities. Laterally 
the surface of the bone is deeply excavated in a longitudinal direction. The lateral 
extension of this region is much greater than in the Tapir’s skull. The basisjihen- 
oid is much narrower than the basioccipital and terminates on a line with the pos- 
terior opening of the alisphenoid canal. The posterior wing of the basisphenoid does 
not extend as far behind as in the Tapir’s skull, and the portion of the alisphenoid 
between the glenoid and the alisphenoid canal is broader than in the latter. 
iiGURE 2. — Comparative view of the skulls of Palxosyops and Limnohyops- 1. Limnohyops laticepa. 
S. Palxo-vjops megarhinus. S. Palseosyopspaliidosus^ 4‘ Pol^osyopslxvidens. One-sixth natural size. 
Foramina — The condyloid foramen is distinct, and situated about an inch anter- 
ior to the condyles. It is placed at the most anterior portion of the bridge of bone 
connecting the basioccipitals. The anterior border of this foi-amen is very thin and 
easily broken through to the lateral vacuity. The large lateral vacuity upon each 
side of the basal region of the skull so characteristic of the Perissodactyles is very 
largely developed in this species. It is divided by the petrous bone, but 
the latter does not unite with the basioccipital, and consequently there is a 
communication between the fr. lacerum posterius and fr. lac. medium. A 
short distance in front of the vacuity and on a line with the glenoid cavity 
is situated the separate and distinct foramen ovale. This foramen in Equus 
and Tapiriis has fused with the fr. lac. medium, although in some species of Rhi- 
noceros the anterior portion of the lateral vacuity is separated by a deeply situated 
ridge of bone, dividing the foramen ovale from the fr. lac. medium. Just in front 
of and below the foramen ovale is placed the large posterior opening of the alis- 
phenoid canal, but owing to the damaged condition of the specimen we must leave the 
description of this canal for another species. 
