SINCLAIR: MARSUPIALIA OF THE SANTA CRUZ BEDS. 



345 



5. The patella is ossified in Amphiprovwerra and Protliylacynus. 

 Among living marsupials the patella is ossified only in the Peramelidae. 



6. The feet are small, with spreading toes. The degree of reduction of 

 the hallux is variable. In the recent genus it has been entirely obliterated 

 (text fig. 4, b]. In Prothylacynus a rudimentary metatarsal remains, while 

 in Amphipro'viverra the hallux is large and opposable. The loss of the 

 hallux is a cursorial adaptation, various stages in the perfection of which 

 are illustrated by the forms just mentioned. These genera, however, 

 have diverged in cranial and dental development and are not a true 

 phyletic series. A still more peculiar cursorial modification of the pes in 

 Thylacynus appears in the shifting of the ectocuneiform toward the outer 

 side of the foot until it is supported almost entirely by the cuboid (text 

 fig. 4, b]. In the Santa Cruz forms the shifting has progressed to about 

 the same extent as in Sarcophilus. The pollex is known in Amphi- 

 promverra and Cladosictis. In these genera, the phalanges of the pollex 



FIG. 4. 



Thylacynus cynoccphalus. 

 Xf 



a, right fore foot, dorsum. b, right hind foot, dorsum. Both figures 



are deflected toward the inner side of the foot as a result of the enlarge- 

 ment of the outer condyle of the metacarpal of the thumb. Indications of 

 the same structure may be observed in Thylacynus. The manus ispenta- 

 dactyl in Borhyana and Thylacynus, and probably also in Prothylacynus, 



