52 



TEETIAEY VEETEBEATA OE THE EATtTM. 



portion of the inner facet the surface of the bone slopes strongly downwards 

 towards the not very prominent but massive cnemial crest (en.). Immediately 

 beneath the postero-external angle of the proximal end of the bone is a broad 

 facet (/.) for union with the upper end of the fibula. Beneath the cnemial crest 

 the shaft is trihedral ; its posterior face is nearly flat, the antero-external first 

 concave, then towards the middle of the bone flat, the antero-internal rounded. 

 The distal end of the bone is expanded laterally, so that it is nearly twice as wide 

 in that direction as from before backwards. The greater portion of the distal 



cn 



Eight tibia of Arsinoithenum zitteli: A, from front ; B, from back ; C, proximal end ; D, distal end. 



ast., surface for astragalus ; en., cnemial crest ; /., surface for proximal end of fibula ; /.', surface for distal 

 end of fibula ; i., inner surface for femur ; i.m., internal malleolus ; o., outer surface for femur. 



I nat. size. 



end is occupied by the slightly concave surface for the astragalus (ast.). This is 

 produced somewhat downwards into a point posteriorly and much more strongly 

 internally, where it runs down on to the face of the blunt internal malleolus (i.m.). 

 External to the astragalar surface, and separated from it by a slight ridge, is a 

 roughly semicircular facet (/.') looking downwards and outwards, for union with the 

 expanded lower end of the fibula. 



The tibia is extremely like that of the Dinocerata (except that the femoral facets 

 are more unequal in size), and diff"ers from that of Elejyhas in being shorter and 



