322 



Amongst the gradatorial and pedimanous Marsupials, and herein more 

 especially the Wombat, we at length find a form of astragalus which 

 repeats most closely the characters of the extraordinary fossil under con- 

 sideration : in the astragalus of the Wombat the fibular facet, of a sub- 

 triangular form, almost as broad as it is long, slightly slopes at a very 

 open angle from the ridge which divides it from the tibial surface : this 

 surface, gently concave from side to side, and more gently convex from 

 behind forwards, repeats the more striking character of being directly 

 continued by its inner and anterior angle with the large and transversely 

 extended convexity for the os scaphoides. The calcaneal surface below 

 is single and continued uninterruptedly from the back to the fore-part of 

 the outer half of the under surface ; and its outermost part is produced 

 into an angle, which is received into a depression at the outer side of the 

 upper articular surface of the calcaneum. Thus all the essential cha- 

 racters of the fossil are repeated in the astragalus of the Wombat. The 

 differences are of minor import, but are sufficiently recognizable ; thus, 

 in the Wombat, the single calcaneal surface is directly continued into the 

 cuboido-scaphoidal convexity, instead of being separated from it by a 

 narrow rough tract, as in the fossil ; the calcaneal surface is also narrower 

 than in the fossil, and the outer angle is less produced : the division of the 

 tibial trochlea for the inner malleolus is better defined in the Wombat, 

 and the depression round which the continuous smooth surface between 

 the tibial and scaphoid surfaces winds is less deep in the Wombat ; the 

 scaphoidal convexity is also less developed in the vertical direction in the 

 Wombat. 



We thus find that the great fossil astragalus from Australia, viewed in 

 reference to the general characters of that bone in the mammalian class, 

 offers great and remarkable peculiarities ; and we further find that these 

 are exclusively, but most closely repeated in certain Australian genera of 

 Marsupialia, and especially in the bulkiest of the existing vegetable 

 feeders, which are not saltatorial. The inference can hardly be resisted, 

 that the rest of the essential peculiarities of the marsupial organization 

 were likewise present in that still more bulky quadruped of which the 

 fossil under consideration once formed part. 



