THE MAMMALIA OP THE DEEP KlVEIi BEDS. 157 



separated by a rather deep groove. The shaft is strongly arched forward and proxi- 

 mally is broad and trihedral; below, it becomes more and more compressed, and in 

 the middle of its course is of almost rectangular section. The distal end is slightly 

 contracted, both transversely and antero-posteriorly, and is almost concealed from 

 view by the radius when seen from the front. The cuneiform- facet is simply convex 

 and has its long axis placed nearly in the fore-and-aft direction. The radius retains 

 the family peculiarities in a very marked degree. The head is not greatly expanded 

 and displays the usual three facets for the humeral trochlea. The shaft becomes 

 more and more slender until the middle of its course is reached and then gradually 

 broadens to the distal end. This form of shaft is highlj- characteristic of the oreo- 

 donts and is in marked contrast to the broad shaft of oval section which is found 

 among the true ruminants. The distal end of the radius is broad, thick and rugose, 

 contracting somewhat suddenly to form the carpal facets ; there are no well-marked 

 sulci for the extensor tendons. The surfaces for the scaphoid and lunar are connected 

 in front by a sort of bridge, but for the rest of their extent they are separated by a 

 wide and deep cleft. The scaphoid facet is somewhat oblique in position, is strongly 

 concave from side to side, and is reflected far -up upon the postero-internal angle of 

 the bone. The lunar facet is wider and of a saddle shape, being somewhat convex 

 transversely and concave antero-posteriorly. 



The carpus of M. montanus presents some differences from that of the species 

 from the upper Loup Fork, which I have elsewhere described under the name of M. 

 ccenopus (No. 32, p. 346). The scaphoid is large in all its dimensions, but compared 

 with that of the true ruminants, its most striking feature is its great vertical height. 

 The radial surface is rather curiously shaped ; the anterior ridge is narrow, but the 

 articular surface descends far down upon the anterior face of the bone and the pos- 

 terior concavity is extended in both directions. The antero-external angle of the 

 proximal end is drawn out into a spur which occupies the " bridge " on the radius 

 mentioned above. The inferior facet for the lunar is very large, both antero-poste- 

 riorly and (near the dorsal side) vertically as well ; this facet is but slightly concave. 

 The distal surface is very unequally divided between the facets for the trapezoid and 

 magnum, that for the former being of nearly the same dorso-palmar depth, but much 

 narrower transversely than the latter. There is no articular surface for the trapezium. 



The lunar is a very curious bone ; its radial surface is so warped as to be both 

 convex and concave in both directions ; the anterior border rises steeply towards the 

 ulnar side, where it forms a narrow projection for the cuneiform. The proximal con- 

 tact of the two bones is limited to this small facet, and behind it the upper portion 

 of the lunar is much contracted. On the radial side there is no superior facet for the 



