68 ANCHITHERIUM. 
be considered to belong to the same species, were it not that those of the Nebraska 
animal, which I have called Anchitherium Bairdu, are only about three-fifths the 
size of those of the former. 
The specimens which we have an opportunity to study are as follows :— 
1. The cranium proper, with a portion of the face containing on one side the last 
two and on the other the last three molars. The zygomata and post-orbital arches 
are broken away. ‘The specimen was accompanied by several fragments of a lower 
jaw, of which two contain the last two molars, and one has the coronoid process 
nearly entire. 
2. Both sides of the upper and lower jaws containing nearly all the molar teeth. 
3. Three small fragments of lower jaws of different individuals, containing teeth. 
The Anchitherium Bairdii, as indicated by the specimens, was rather more than 
half the size of the Anchitherium aurelianense. 
Description of the Head.—The cranial specimen is particularly important from its 
being the first yet discovered of the genus Anchitherium. In its form it is remark- 
ably like that of the corresponding portion of the skull of the Horse, and presents 
but few points of resemblance to the Piulacotherium, to which genus it has been 
supposed to belong. 
Lateral View.—(XI. 1.) The skull of Anchitheriwm appears relatively shorter 
than that of the Horse; as,in the specimen under examination, the molar teeth are 
much less advanced in their position than in the latter; the last of the series 
being placed below the middle of the orbit. 
The upper outline of the cranium proper, as in the Horse, is convex, and the 
temporal fossa has the same form and relative convexity ; and posteriorly it mounts 
in the same manner upon a low sagittal crest. The summit of the inion and the 
posterior boundary of the temporal fossa are relatively not quite so prominent as 
in the Horse, but as in this, the root of the zygomatic process is implanted about 
the middle of the lower border of the fossa. 
The mastoid portion of the temporal bone is relatively higher than in the Horse; 
and, as in this, impressed upon the parietal bone, there ascends from the squamous 
suture a large, deep, irregular, branched, vascular channel. 
The meatus auditorius is bounded below by a thick auditory process. 
The face is relatively of less depth than in the Horse, arising from the shortness 
of the teeth, compared with those of the latter. Below the position of the orbit 
the alveolar margin is convex antero-posteriorly, as in the Horse. 
The malar bone does not advance as much upon the face as in the latter; its 
anterior suture ascending obliquely from the position of the last molar to the ante- 
rior lachrymal suture. 
In the specimen, the orbits, at their inferior margin are broken away. When 
perfect, their entrance appears to have had almost the same form as in the Horse, 
but was relatively very much larger. They are also more deeply excavated, and 
approached each other much more. Their floor is very extensive, and at its poste- 
rior part forms a thick, obtuse margin, which is situated considerably below the 
level of the sphenoidal bodies. | 
Whether a post-orbital arch existed cannot be ascertained from the specimen, for 
