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of the astragalus, as in Man and Quadrumana, but it is more produced 

 and supported on a longer neck, which is also more oblique than in the 

 Quadrumana, where the astragalus already begins to recede, in this cha- 

 racter, from the Human type. In the Seals the upper surface of the 

 astragalus somewhat resembles the present fossil in the meeting of the 

 tibial and fibular facets at an obtuse angle formed by a longitudinal rising, 

 but the fibular surface is rather the wider of the two, and the tibial one 

 is divided by a broad rough tract from the scaphoidal prominence ; and 

 in addition to this anterior production of the bone there is also another 

 process from its posterior part, which, as Cuvier remarks, gives the astra- 

 galus of the Seal the aspect of a calcaneum. By some of the remarkable 

 peculiarities which the astragalus presents in the Order Brula, it ap- 

 proaches the Australian fossil under consideration ; as in the Mylodon, 

 for example, where the surface for the calcaneum is single and undivided. 

 But in this great extinct leaf-eating quadruped the calcaneal facet is con- 

 tinued into the navicular facet, which, on the other hand, is separated by 

 a rough tract from the tibial articulation, as in all the Edentata, recent 

 and fossil. The latter character likewise distinguishes the astragalus of 

 the Rodentia from the fossil astragalus under consideration. 



In the Ornithorhynchus the astragalus has a deep depression on 

 its inner side for the reception of the incurved malleolus of the tibia, 

 and in both the Ornithorhynchus and Echidna the tibial surface is more 

 convex than in the present fossil. 



Amongst the existing Marsupialia, the astragalus in the largest her- 

 bivorous species, as the Kangaroos, oilers very great differences from the 

 present Australian fossil : the broad and shallow trochlea for the tibia is 

 continued upon the inner side of the bone into a cavity which receives 

 the internal malleolus ; whilst the fibular facet is long and narrow, and 

 situated almost vertically upon the outer side of the bone. The sca- 

 phoidal surface is unusually small, and convex only in the vertical direc- 

 tion ; and is divided by a vertical ridge into two surfaces, the outer one 

 being applied to the os calcis. The inferior and proper calcaneal articu- 

 lation is divided into two small distinct surfaces, the outer one concave, 

 the inner one concavo-convex. 



2 T 



