No. i.] OSTEOLOGY OF PCEBROTHERIUM. 19 



edges truncate as in the camel, but do not form so much of the 

 hard palate as in that animal, on account of the more anterior 

 position of the nares : on the other hand, they have a greater 

 extension on the roof of the mouth than in Aachenia. The 

 posterior nares resemble those of Aachenia in shape and posi- 

 tion ; they are very long and narrow and with a lancet-shaped 

 anterior margin which extends as far forward as the interval 

 between the second and third molars. The canal is, however, 

 very much lower than in the existing forms. The pterygoids 

 are short and end in very small hamular processes, and the 

 pterygoid fossa is a mere shallow slit. The vomer is conspicu- 

 ous as a septum through nearly the whole length of the poste- 

 rior nares. 



The mandible has a very long and slender horizontal ramus 

 with sinuous lower border ; the symphysis is long and spout- 

 like, but is shorter than in the modern genera ; and as all of 

 the premolars are present, the edentulous portion is very much 

 shorter. The angle is prolonged into a great hook-like process 

 which is far more conspicuous, though of much less vertical 

 extent, than in the recent genera. The ascending ramus is low 

 and more sloping than in the recent forms ; the coronoid process 

 is more recurved and pointed, and the masseteric fossa is deep 

 but of small extent and situated very high up. The condyle is 

 more transversely extended and less rounded than in the camel 

 and llama, and the articular surface for the postglenoid process 

 is very small. Aside from the great production of the angle, 

 the ascending ramus of the jaw is more like that of a true rumi- 

 nant than of the llama. 



The Foramina of the skull of Pcebrothcrium are for the most 

 part like those of the modern Tylopoda. The external opening 

 of the supra-orbital canal is placed near the median line, as in 

 the camel ; the infra-orbital foramen is over the fourth premolar, 

 the position which it occupies in the existing species, but the 

 less height of the alveolus brings it nearer to the teeth. 

 The posterior palatine foramina are very far forward, opposite 

 the third premolars, and I can detect but a single pair of them. 

 The two optic foramina are placed low down and very close 

 together, though not quite in contact : the outer lip is not 

 produced into a spine. The foramen lacerum anterius and the 

 foramen rotundum have coalesced, but the opening is not so 



