454 



Bulletin American Museum of Natural History. [XoX. XXVII, 



part of the back and not separated from the navicular facet. The navicular 

 facet, in correlation with the spreading character of the pes extends up on the 

 inner side of the neck. The tuber of the calcaneum is pointed downward 

 as well as backward and the foot is entirely plantigrade. In Pha-s-colomys, 

 representing the Diprotodontia, the ectal, sustentacular and navicular facets 

 are quite continuous, and the sustentacular is still near the outer border of 

 the back (Fig. 30, B) . Just internal to the ectal-sustentacular facet is a deep 

 groove;^ a similar groove in Edoconus, Patriofelis, etc., lies between the ectal 

 and sustentacular facets and terminates in the astragalar foramen. In an 



//. Didelphis 



B. Phascolomys C Ectoconus 



cub) (rta-vf 



D Patriofelis E Castoroides 



Fig. 30. Morphology of the astragalus in Marsupials etc. From specimens in the American 

 Museum. Scale various. 

 {tb.), tibial facet. 

 (/6.), fibular " 



tib. mall., surface for malleolar portion of tibia. 

 {ecf.), ectal facet, 

 (sws.), sustentacular facet. 

 (nav.), navicular " 



(c6.), cuboid " 



(ses), facet for tibial sesamoid. 

 f.astr., astragalar foramen. 



astragalus of Edoconus (Amer. INIus. No. 3036) a Periptychid, wrongly 

 ascribed by Cope to the Basal Eocene Pohjmastodon (p. 169), we find a clear 

 foreshadowing of the Placental type, in so far as regards the better develop- 

 ment of the trochlear ridges, the separation of the neck from the trochlea, 

 the angulation of the internal inferior region of the neck, the presence of an 

 astragalar foramen, the beginning of the separation of the sustentacular and 

 navicular facets, and the more central j^osition of the sustentacular facet. 



The most distinctive features of the primitive Marsupial astragalus thus 

 appear to be: 



' Possibly lodging a brancli of the peroneal artery (Matthew, 1909, p. 451). 



