LOXOLOPHODON AND UINTATHERI UM. 



23 



rim and central ridge are slightly rugose for muscular attachment. The con- 

 dyles are directed obliquely downwards and set closely to the skull ; they are 

 perforated at their bases by the condylar foramina. 



The Basi-occipitals are bounded at the sides by the mastoid portion of the 

 periotic, and narrow forwards, joining the long narrow Basi-sphenoids. The 

 mastoid portion of the periotic is rough and prominent. The external auditory 

 meatus is directed sharply upwards and inwards. The post-glenoid process of 

 the Squamosal is very large and projects below the mastoid, while the glenoid 

 cavity is broad and rather shallow. The squamosal portion of the arch springs 

 well up above the level of the orbits. The Malar is rather small, forming a 

 sutural connection with the squamosal in Loxolophodon, as distinguished from 

 the smooth facet in Uintatherium. They overlap the maxillaries, but do not 

 quite extend to the orbit. The zygoma, as a whole, is arched well upwards 

 and somewhat outwards. The Alisphenoids are perforated opposite the post- 

 glenoid process by the foramen ovale. Their posterior limits are defined by the 

 foramen lacerum medium. The study of the skull is here interrupted by a 

 wide break which extends as far forwards as the palatines. 



The Loxolophodon skull in the basi-occipital region is in fair preservation, but 

 the base of another skull belonging to U. mirabile affords an opportunity for still 

 clearer interpretation of this difficult portion. The two skulls placed beside 

 each other are found to bear a close resemblance in this region ; the only dis- 

 tinctions which arise are in size and proportion. In the lateral walls of the skull, 

 behind the orbit, the skull of U. Leidianum (Plate II.) offers the best opportunity 

 for study. The description which has been given of L. Speirianum will accord- 

 ingly be continued and supplemented in greater detail by a study of the two 

 above-mentioned species of Uintathermm, and those portions only will be 

 described which are imperfect or wanting in the Loxolophodon skull. 



UINTATHERIUM LEIDIANUM. 



A full description of the skull of U. Leidianum was given in the Bulletin from 

 this Museum published in 1878. It possesses many characters in common with 

 Loxolophodon, and those which distinguish it have been outlined in the com- 

 parisons given above. They are chiefly in the palatinal region, in the propor- 

 tions of the nasals, and size and relations of the horn-cores. It is not necessary 

 to detail the lesser variations which can be found in the skull. Many of them 

 can be traced in the excellent figure given in Plate II. 



The topography of the lower side walls is one of the most difficult problems 

 met with in the study of these skulls. This is owing in part to the age of the 

 individuals, which has caused most of the sutures to become obliterated. The U. 



