TAXEOPODA. 



377 



to the interlocking carpus. The trapezoides does not join the lunar, but 

 the unciform does so, as in Coryphodou. Professor Marsh's figure as to the 

 articulations of the magnum does not agree with his description, as it makes 

 that bone articulate with the scaphoid. The second description is however 

 correct, and the carpus is identical with that of Coryphodon. 



In the American Naturalist, June, 1882,^ I have shown that the carpus 

 of the Condylarthra is essentially like that of the Hyracoidea. 



Tarsus. — In the tarsus of the Perissodadyla and Artiodactyla it is well 



understood that the cuboid e.xtends inwards 

 so as to articulate with the astragalus, giving 

 the latter a double distal facet. It is also 

 well known that the astragalus of the Pro- 

 boscidea has but a single distal articulation, 

 that with the navicular. It is, however, true 

 that the cuboid is extended inwards, but that 

 it articulates with the distal extremity of the 

 navicular instead of that of the astragalus. It 

 was shown by Cuvier tliat the astragalus of 

 the Hyracoidea articulates with the navicular 

 only, and that the cuboid is not extended in- 

 wards so as to overlap the latter. In 1873^ 

 Marsh stated that the astragalus of the Amhly- 

 FiG. i5.-Fore leg and foot of Hy- ^^^j^, articulatcs with both cuboid and navicu- 



racotherium renticolum (original). Two- 



thirds natural size. lar. Finally I discovered in 1 88 P that the 



astragalus of the Condylarthra articulates witli the navicular only, and that 

 the cuboid articulates with the calcaneum only. In the tarsus then there 

 are four types of articulation, which are represented by the Condylarthra, the 

 Proboscidea, the Amhlypoda, and the Artiodactyla respectively. 



Orders. — From the preceding considerations we derive the following 

 definitions of the primary divisions of the Ungulata, which should be called 

 orders. In the first place I find the diversity in the structure of the carpus 

 to be greater in the relations of the magnum and scaphoides, than in the 

 relations between the unciform and the lunar. In other words the trape- 



'Page 522. 'American Journal Science and Art, January, 1S73. 'American Naturalist, 1881, p. 1017. 



