No. i.] OSTEOLOGY OF PCEBROTHERIUM. 1 1 



I. The Dentition (PI. I, Figs. 8 and g). 



A. Upper Jaw. — I have not seen any specimens of the supe- 

 rior incisors, but there can be no doubt that they were present 

 in the typical number. The canine is short, compressed, and 

 trenchant, and is relatively much smaller than in the recent 

 genera. There is, however, not a sufficient number of speci- 

 mens available to determine accurately whether or not this small 

 size of the canine is a sexual characteristic. The first premolar 

 is isolated by a diastema, both in front of and behind it ; it is 

 implanted by two fangs, and has a very simple, compressed, and 

 trenchant crown, which is remarkable for its antero-posterior 

 elongation. Pm. 2 and 3 are similar in general character, but 

 are even more elongated ; on the outer side they exhibit a 

 prominent median ridge with anterior and posterior depressions. 

 Some specimens show a well-marked antero-external buttress 

 on pm. 3 ; in others this is but feebly developed. A very small 

 internal festoon is shown on the posterior half of the crown in 

 some individuals ; others have no trace of it. Pm. 4 is much 

 less elongate (antero-posteriorly) than the anterior premolars, 

 and resembles the corresponding tooth in the ruminants gener- 

 ally in being made up of two crescents, an external and an 

 internal one. 



The true molars are all brachyodont, and are not strongly 

 extended antero-posteriorly, the true molar series but slightly 

 exceeding the premolar in length. M. 1 is the smallest of the 

 three in both dimensions. M. 2 is slightly longer and narrower 

 than m. 3. In each of them the crown is composed of four 

 crescents, no trace of the unpaired fifth lobe ever appearing ; 

 the valleys are very narrow and rather shallow, so that they are 

 obliterated at a comparatively early stage of wear. The outer 

 wall of the crown has a distinct, though very much compressed, 

 median buttress, and a much less prominent anterior buttress : 

 each crescent has a well-defined median ridge. In the recent 

 genera, and especially in Camelus, the posterior half of m. 3 is 

 decidedly narrower than the anterior half ; in Pccbrotherium this 

 difference is indicated but slightly. The presence of internal 

 basal pillars is subject to much variation. In one specimen I 

 find a minute trace of such a structure on m. 1 and 2, and; a 

 fairly well developed pillar on m. 3 ; a second specimen shows 



