Fan-.] l'^2 [May 15, 



broken away so that all its characters cannot be determined. The bor- 

 der of bone above the acetabulum is rounded and not sharp. The 

 ischia turn upward slightly posteriorly and form more of a plate poste- 

 rior to the obturator foramen posteriorly than in the smaller species. The 

 sacrum has five vertebrae entering into its formation. The spines of the 

 lumbars are still very high, but they have a more considerable antero- 

 posterior extent proportionately than in M. hairdi. The femur has a 

 massive proximal end, the great trochanter being lower and more mas- 

 sive than we usually see it in Mesohippus, but this may in part be due 

 to the fact that our skeleton is of a young animal.* The tibia of M. inter- 

 medins is somewhat stouter in proportion to its length than that of M. 

 hairdi. The cnemial crest is strong and well developed. As usual, 

 there is a large fossa external to the cnemial crest. The fibula is still 

 complete and is distinct from tibia. The proximal end is quite small 

 and the shaft is very much reduced, while the distal end is quite large, 

 forming the external malleolus to articulate with astragalus and with 

 calcaneum in extreme extension. Both proximal and distal ends, as well 

 as the shaft, are closely applied to the tibia, but are not coossified with 

 it. The tarsus of M. intermedins is more modern than that of 31. bairdi 

 in that the tarsus is wider and lower, which is a step in the direction of 

 the modern horse. The calcaneum is very long, the tuber proportion- 

 ately longer than in M. bairdi, and is quite stout with an expanded free 

 end. The cuboidal facet is long and narrow, almost crescentic in shape 

 and extends downward and inward to the sustentaculum. There is 

 quite a large fibular facet. The astragalus is broader and the trochlea is 

 not so deeply incised as in M. bairdi, though it is distinctly equine in 

 pattern. The two condyles of the astragalus are very unequal in size. 

 The inner almost always overlaps the navicular facet, while the external 

 is separated from it by a long interval. In M. bairdi the internal con- 

 dyle never reaches the navicular surftice. The navicular is much flatter 

 and lower, as is also the ecto-cuneiform, than in 31. bairdi. The cuboid 

 is also shortened, just equaling the height of the two contiguous bones, 

 metatarsal iii extends over on cuboid. 



This is another modernization. There is a distinct facet on the cal- 

 caneum for the navicular. There is a much more complete interlocking 

 of the tarsal bones in 3f. interinedius than in any other White River 

 horse. The ento-cuneiform as usual is high, extending both above and 

 below the meso-cuneiform which is still not so deep as the ecto-cunei- 

 form. On its posterior surface it bears a distinct facet for the cuboid 

 with which it unites in forming the small facet for M. iv. Metatarsal iv 

 is usually less reduced proximally than M. ii, but tapers to about the 

 same size distally. This demonstrates the manner in which the reduc- 

 tion of digits takes place in the family. We know froni 31. bairdi that 

 M. i first disappeared and afterward M. v. The condition in 31. inter- 

 medins indicates that M. ii would next become rudimentary, and then 

 M. iv. In the horse where the lateral metapodials are mere splint 



* This may also account for the fact that fibula is not coossified with tibia. 



