No. i.] OSTEOLOGY OF PCEBROTHERIUM. 39 



aspect of the head, and is shorter, shallower, and nearer the 

 border of the head than in the llama. The bridge connecting: 

 the head and the great trochanter is narrower, shorter, and less 

 rugose, and the great trochanter rises higher above it, producing 

 a decided notch. Though the great trochanter is higher than in 

 the recent forms, it is much less massive and thickened antero- 

 posteriorly, and in consequence the digital fossa is much shal- 

 lower. The second trochanter is also less developed, especially 

 in the vertical direction, than in the llama, though relatively 

 larger than in Camelus, and forms a small conical protuberance. 

 The shaft is long, slender, and arched forward, and except for 

 its greater slenderness, very similar to the proportions found in 

 the recent species. With the length of the humerus taken as 

 100, that of the femur in Pcebrotherium is 125, in Camelus 127, 

 and in Auchenia 134. The rotular trochlea is broad and shal- 

 low, with sharp external and thickened internal lip, the latter 

 being also somewhat the higher of the two — a more decided 

 difference than occurs in either of the modern genera. The 

 condyles are smaller, less strongly projecting, and less widely 

 separated than in the latter. The trochlea rises higher upon the 

 shaft, is less strongly arched, and less oblique to the transverse 

 axis of the distal end of the bone, than in the recent genera. 

 The external condyle is somewhat larger than the internal, and 

 there is no such decided notch above the latter as occurs in 

 Auchenia. Pcebrotherium agrees with most of the true rumi- 

 nants, and differs from the Camelidce in the presence of a dis- 

 tinct pit for the insertion of the plantaris muscle above the 

 external condyle. 



It is clear from the foregoing that the femur of Pcebrotherium 

 departs but little from the cameline type, and that such diver- 

 gences as are observable are in the direction of the more gen- 

 eralized artiodactyls. 



The tibia (PI. Ill, Figs. 40-42), like all the other limb bones, 

 is long and slender ; longer as compared with the humerus than 

 in either of the existing genera, its length being 141, as com- 

 pared with 130 in Auchenia, and 1 1 1 in Camelus. The facets for 

 the femoral condyles are large and nearly flat, and separated by 

 a prominent bifid spine ; the external facet is considerably larger 

 than the internal, but shows no tendency to assume the peculiar 

 recurvature which occurs in the camel. The cnemial crest is 



