1 6 Bulletin American Museum of Natural History. [Vol. XIV, 



Creodonts, and is separated by a slight angle from the fibulo-cal- 

 canear facet. The trochlea of the astragalus is very shallow, the 

 foramen ' is present, and the notch for the flexor digitorum wide 

 though not very deep. The head of the astragalus is consider- 

 ably flattened, about as much as in Ursidse or Felidae. The 

 cuboid has a rather narrow astragalar facet, concave, and sepa- 

 rated by an angle from the rather flat calcanear facet. The 

 corresponding facet on the astragalus is not separable from the 

 navicular facet. The entocuneiform is large and metatarsal I short, 

 stout, and divergent, though with less play than the correspond- 

 ing metacarpal. The other four metatarsals are of about equal 

 length, the second being wedged in proximally between the 

 ecto- and ento-cuneiforms. 



Comparisons. 



The union of the centrale with the scaphoid is an interesting 

 stage in the consolidation of the carpus. The position and size 

 of the centrale are peculiar. In Mesonyx it lies entirely beneath 

 the scaphoid (Scott, '87, p. 161, pi. VII, fig. i). In Dissacus 

 (Osborn and Earle, '95, p. 33, fig. 9) it is less completely so, but 

 the shape is rhombic instead of rectangular. In Hycenodon (Scott, 

 '87, p. 182, pi. VII, fig. 5) the centrale lies partly under the lunar, 

 but is small and triangular, hardly touching the magnum, while 

 the trapezoid is very large, and the unciform has no lunar facet. 

 In Oxycena the carpus is less strongly interlocking, the centrale 

 smaller and rhombic, trapezoid larger, trapezium different in 

 shape. In Viverravus the carpus is narrower, foot probably 

 slenderer — little is known as to the arrangement of the carpals. 

 Comparing this carpus with the various primitive Creodonts, Con- 

 dylarths and Amblypods, shows a great deal of similarity among 

 them all. The progressive characters in Clc£nodo7i seem to be : 



1. Union of centrale with scaphoid ; ? large size of centrale, almost excluding 

 magnum from lunar on upper surface ; sharp keel of magnum. 



2. Grooving and inward facing of distal facet of trapezium. 



3. Stout semi-opposable first metapodial, and length of fifth. 



* The use of this foramen seems to be unknown. Prof. Osborn has suggested that it may 

 have held an extension of the interosseous ligament,which lies between the two astragalo- 

 calcanear facets and connects the astragalus with the calcaneum. If this ligament originally 

 passed up to the tibia, its disappearance would be directly connected with the keeling of the 

 proximal and flattening of the distal end of the astragalus, all being due to the transference of 

 the main ankle-joint from the distal to the proximal end of the astragalus, i. e., the evolution 

 of the mammal from the reptilian stage of development in this character. 



