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UINTA SELENODONTS 



metatarsal and does not touch the second, though it is possible that a minute 

 contact with the latter is still retained. 



The metatarsus is composed of four members, two of them (iii. and iv.) 

 enlarged and functional, and two (ii. and v.) greatly reduced and filiform. 



Metatarsal ii. has undergone great reduction ; its proximal end is very 

 narrow and compressed, but has a considerable dorso-plantar thickness and is 

 so wedged in between the ento-cuneiform and mt. iii. as to be hardly visible 

 when the foot is viewed from the dorsal side. It articulates with the ento- 

 and meso-, but, so far as I can determine, not with the ecto-cuneiform. The 

 shaft rapidly tapers to a mere thread of bone, which in one specimen is pre- 

 served for a length equal to two-thirds of the large mt. iii. and is there broken. 

 It is therefore impracticable to determine whether the bone was a mere style, 

 or was furnished with a trochlea and phalanges, as in the tragulines. On the 

 whole, the former suggestion appears the more probable. 



Metatarsal iii. is relatively long and quite heavy, though it has by no 

 means attained such a proportionate degree of elongation as we find in 

 Poebrothcrium. The head is rather narrow, but very thick in the dorso- 

 plantar diameter, which is further increased by a prominent projection from 

 the plantar side. This projection and a similar one on mt. iv. are closely 

 pressed together and held in place by the ento-cuneiform and the great hook 

 of the cuboid, between which they are wedged. The head has a broad, 

 almost plane facet for the ecto-, but appears not to touch the meso-cuneiform, 

 though in Poebrotherium the latter is covered by mt. iii. and excluded from 

 contact with mt. ii. In Protylopus the pes, like the manus, is in a state transi- 

 tional to the adaptive method of reduction, a method which is fully attained in 

 Poebrothcrium. The shaft is long, slender, of nearly uniform breadth, though 

 narrowing to some extent distally, broadening and thickening again just above 

 the trochlea. In cross-section the shaft is more trihedral and less distinctly 

 quadrate than in Pocbrolhcriitm. The trochlea is shaped almost exactly as in 

 the latter ; it is narrow and low, but well rounded and provided with a 

 prominent carina, which is confined to the plantar face, and a shallow pit 

 demarcates the trochlea from the shaft. 



Metatarsal iv. is in all respects the counterpart of mt. iii., and in the best 

 specimen the two are of almost exactly equal length, their proximal ends 

 lying in the same transverse plane. Save for the proximal facet, which is quite 

 flat, this bone is not sufficiently different from mt. iii. to require a separate 

 description. 



