SINCLAIR! MARSUPIALIA OF THE SANTA CRUZ BEDS. 
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5. The patella is ossified in Amphipmviverra and Prothylacynus. 
Among living marsupials the patella is ossified only in the Peramelidse. 
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 Amphiproviverra 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 
Thy lacy nus 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- 
proviverra and Cladosictis. In these genera, the phalanges of the pollex 
Fig. 4. 
Thylacynus cynocephalus. a, right fore foot, dorsum, b, right hind foot, dorsum. Both figures 
x f 
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 is penta- 
dactyl in Borhymia and Thylacynus , and probably also in Prothylacynus , 
