No. i.] OSTEOLOGY OF PCEBROTHERIUM. I J 



face than in either of the living genera, and there is a marked 

 rugosity for the attachment of the masseter muscle. The lach- 

 rymal is rather small, but extends more on the face than in the 

 camel, and articulates with the frontal, maxillary, and jugal, but 

 not with the nasal, from which it is separated by a process of 

 the maxillary. There is, however, no such vacuity at this point, 

 as occurs in the llama and to a less extent in the camel. The 

 lachrymal foramen is double, and is situated within the rim of 

 the orbit. 



The frontals are broad but short ; they are widest just above 

 the orbits, and from this point they taper in posteriorly and are 

 received into a deep notch formed by the diverging parietals. 

 From the anterior end of the sagittal crest distinctly marked 

 supra-orbital ridges diverge, and curving forward and outward, 

 terminate in the long and rugose postorbital processes. Near 

 the front of the upper rim of the orbits there is a deep and 

 widely open notch. Anteriorly the frontals terminate little if 

 any in advance of the front of the orbits. There are consider- 

 able frontal sinuses, but they do not produce any bulging of the 

 skull. The frontal zone of the cranium is less developed than 

 even in the camel, and has hardly any share in roofing over the 

 cerebral hemispheres. The orbits are very large and situated 

 low down in the face ; they are much farther back than in the 

 camel, the anterior rim being over the second molar, and in 

 some specimens over the third. This is a decided advance over 

 the condition found in the primitive selenodonts generally. 

 The alveolus of the third molar makes a hardly noticeable pro- 

 jection into the antero-inferior portion of the orbit. The orbits 

 are also remarkable for their depth, which is so great that a 

 veritable interorbital septum is formed as in the tragulines. In 

 existing tylopodans there is no such appearance. 



The nasals are very different from those of either of the 

 recent genera, especially in their greater length. At their junc- 

 tion with the frontals they are quite broad, but rapidly taper, 

 and for most of their length they are extremely narrow : ante- 

 riorly they extend nearly to the tips of the premaxillaries. 



The maxillaries are long and low; the alveolar portion is 

 especially low, in correspondence with the brachyodont condi- 

 tion of the molars, and thus the inferior rim of the orbit is sepa- 

 rated from the teeth by a much narrower space than in the 



