40 



E. M. MUSEUM MEMOIRS. 



wholly on the postero-external face of the shaft, with an expanded distal 

 extremity articulating by a narrow facet with the rim of the distal face of the 

 radius, and forming a wide external malleolus. This bone seems to have a 

 narrow articular facet for the astragalus, but does not touch the calcaneum. 



Marsh ' has pointed out clearly the characters of the hind-foot from the fine 

 specimens in his possession. Our collection of foot-bones is not quite complete. 

 The Astragalus, with a slightly concave upper surface, showing no groove, 

 articulates below with both the navicular and cuboid. The Calcaneum is small 

 with a short tuber-calcis directed inwards ; it has two subquadrate facets for the 

 astragalus. It has a narrow anterior face for the cuboid. Marsh states that it 

 does not meet the navicular. The metatarsals are shorter and stouter than the 

 metacarpals. The hallux is complete, but very small ; the remaining digits are 

 well developed. 



Proboscidian and Perissodactyle Affinities of the Appendicular 



Skeleton. 



The Fore-limb. The proboscidian characters of the axial skeleton of Uinta- 

 therium have been considered above. In the appendicular skeleton the following 

 distinctions and homologies are observed. The fore-limb : (i) The upper borders 

 of the scapulse resemble each other; the spine is less recurved. (2) The supina- 

 tor ridge of Uintatheriiim is a low rugose line ; in Elephas it is a stout crest. (3) 

 The radius of Uintatherium is proportionally much larger and crosses the ulna 

 less obliquely and the distal ends of the ulna and radius are sub-equal in size, while 

 in Elephas that of the ulna is much greater. In both the ulna has a narrow artic- 

 ulation with the lunar. The arrangement of the manus is similar in the two gen- 

 era, with the exception that in Uintatherium (4) the unciform articulates broadly 

 both with the lunar and cuneiform. In the reduction of the radius, which is evi- 

 dently advancing in the Dinocerata, is seen a divergence towards the proboscidian 

 rather than the perissodactyle, type of fore-arm ; for in the latter group, where 

 there is a reduction of either bone, it is the radius which develops at the expense 

 of the ulna, the distal end of the latter bone being reduced in the tapir and 

 disappearing entirely in the horse. 



The fore-limb of Rhinocerus differs in the narrow, high ungulate type of 

 scapula. The humerus offers contrast with that of Uintatherium in its salient 

 deltoid ridge. The ulna is in process of reduction at its lower end, but, as in 

 the Dinocerata, covers the entire proximal surface of the cuneiform. The two 

 ends of the radius are sub-equal, the lower occupying a postero-external position 

 in relation to the ulna. The unciform articulates, as in the Dinocerata, with 

 both lunar and cuneiform. 



' Am. Journ. Science and Arts, 3d series, Vol. XI. p. 168. 



