No. i.] OSTEOLOGY OF PCEBROTHERIUM. 6 1 



presence of an articular surface on the anterior edge of the 

 inferior arch. The odontoid process of the axis is somewhat 

 more concave on its superior surface than in Paebrotheriitm, 

 much less so than in the recent forms. The other cervicals are 

 relatively smaller than in the llama, the transverse processes 

 more expanded and less completely separated into anterior and 

 posterior portions, and there are no neural spines. As in the 

 recent genera, the third and fourth vertebras are of nearly equal 

 length, while in Pcebrotlierium the third is considerably the 

 longer. 



The dorsal vertebrae of Procamelus are imperfectly known, 

 but the character of the spines agrees best with that of the 

 recent genera, except that they are rather longer. 



The lumbar vertebrae have in the anterior region an inferior 

 angulate keel, while in the posterior ones there is an angle on 

 each side of the median one. The episphenial processes of the 

 zygapophyses are quite distinct and much better developed than 

 in Pcebrotlierium. 



The ribs of Procamelus, so far as they are known, agree best 

 with those of the recent species, being much broader and more 

 flattened than in Pcebrotlierium. They appear, however, to be 

 more simply and regularly curved than in the camel. 



V. The Fore Limb. 



The fore limb is entirely unknown in Pantolestes ; and with 

 regard to Homacodon, we know only that the manus contains 

 four digits. Of Leptotragulus, fragments of the fore limb are 

 preserved which throw some welcome light upon the questions 

 at issue. 



The glenoid cavity of the scapula is oval in shape, the antero- 

 posterior diameter exceeding the transverse, and is placed some- 

 what obliquely to the vertical axis of the bone ; the coracoid is 

 much less prominent than in the later genera, and is not at all 

 rugose, and but little recurved at the tip. The spine is placed 

 nearly in the median line, but not quite, so that the postscapular 

 fossa is slightly larger than the prescapular. 



The distal end of the humerus is narrow; the internal epi- 

 condyle is pushed to the posterior angle ; the outer condyle of 

 the trochlea is narrow, the inner somewhat broader, and the 



