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6l 



UINTA SELENODONTS 



The tibia (No. 1 1,223) '^ shorter, more slender, and in every way- smaller 

 than that of Protylopus, from which it may immediately be distinguished 

 by the far less prominent development of the cnemial crest. The condyles 

 for the femur are narrow, but well extended from before backward, and of 

 nearly equal size. Despite their extension, these condyles do not project so far 

 back of the plane of the shaft as in Proiylopns. The proximal portion of the 

 shaft is stout and trihedral ; beneath the cnemial crest it becomes much more 

 slender and assumes an oval section, expanding in both dimensions at the 

 distal end. As already mentioned, the cnemial process is far less conspicuous 

 than in Protylopus, a difference which especially affects its antero-posterior 

 breadth, for in length there is little difference; distally, it dies away much less 

 abruptly upon the shaft. The distal end of the tibia exhibits no noteworthy 

 difference from that of the last-named genus, except that the malleolar process 

 is somewhat longer and heavier. 



In none of the specimens is the fibula quite complete, but there can be no 

 doubt that it was uninterrupted and entirely free from the tibia. The proxi- 

 mal end is very narrow and compressed, though it has considerable antero- 

 posterior extension ; the shaft is much reduced and very slender, and though 

 it has not attained the thread-like proportions found in Protylopus, j'et it is far 

 more slender than in any of the known oreodonts. The distal end is a narrow 

 but thick external malleolus, which is deeply channelled on the outer side by 

 the sulcus for the peroneal tendons, and which has shifted partly beneath the 

 edge of the tibia. 



The pes (Plate II., fig. 14) (No. 11,223) 's of very considerable interest. 

 The tarsus is of the same structural type as in Protylopus, but may readily 

 be distinguished from the latter by the smaller proximo-distal height of its 

 members, especially of the cuboid. In size, shape, and general appearance 

 the astragalus resembles that of the last-named genus, with a few differ- 

 ences in relatively unimportant details. The tibial trochlea is quite deeply 

 grooved and somewhat more asymmetrical than in Protylopus, the outer 

 condyle exceeding the inner one more in width, thus bringing the deepest 

 part of the groove nearer to the internal side. On the distal trochlea the 

 cuboid facet is conspicuously narrow. The sustentacular facet is broad, 

 extending to the tibial border of the bone. 



The calcaneum is relatively long and slender; its actual length is almost 

 the same as in Protylopus, and thus the bone is proportionately longer, as 

 compared with the rest of the limbs and feet. On the other hand, the tuber 



