G8 ANCHITIIERIUM. 



be considered to belong to the same species, were it not that those of the Nebraska 

 animal, which I have called Anchltlierium Bairdii, 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 zj'gomata 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 Anchifhermm Bairdii, as indicated by the specimens, was rather more than 



half the size of the Anchitherium aurclianense. 



Description of the Head. — The cranial specimen is particularly important fi'om its 

 being the first j'et discovered of the genus Anchitheriian. 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 Palaeotherium, to which genus it has been 

 supposed to belong. 



Lateral View. — (XI. 1.) The skull of Anchitherium 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 230steriorly 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 pi'ocess 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 ascei'tained from the specimen, for 



