114 MARINE REPTILES OF THE OXFORD CLA5T. 



forwards ; this, with the proximal articular surface of the fibula (f.) no doubt 

 articulated with the outer condyle of the femur. 



Beneath the proximal articulation the bone narrows to the middle of the shaft, 

 which, even in the uncrushed state, seems to have been somewhat compressed antero- 

 posteriorly; its inner border is concave in a longitudinal direction, the outer nearly 

 straight. Distally, the bone again widens out and bears the distal articulation for the 

 astragalus (a.f.) : this surface is narrow and strongly convex from before backwards ; 

 it is not quite at right angles to the long axis of the bone, but slopes down to the 

 preaxial border, forming a rounded projecting angle, best marked in large and fully 

 ossified specimens. 



The fibula (/'.) is a much more slender rod of bone than the tibia: it is strongly 

 compressed ; its outer face is rounded, the inner nearly flat. At its proximal end 

 it expands and terminates in an elongated convex surface for articulation with the 

 outer portion of the outer condyle of the femur. Distally (text-fig. 46, C) it is 

 expanded to a rather greater degree ; its distal extremity, which is about at right 

 angles to the long axis of the shaft, bears two articular surfaces, one on the tibial side 

 forming a strong convexity and probably articulating with the astragalus («/'.) ; the 

 other, separated from the last by an oblique groove, is a slightly concave surface 

 occupying the outer half of the bone and, no doubt, articulating with the calcaneum 



The tarsal bones (text-fig. 47), unfortunately, have never been found embedded in 

 matrix so as to show their natural relations to one another, to the tibia and fibula 

 on the one hand and to the metatarsals on the other ; consequently it is difficult to 

 make out their arrangement, a difficulty greatly increased by the circumstances that in 

 the living animal probably much cartilage persisted in this region, and that they differ 

 considerably in form from the tarsals of recent Crocodiles. This is especially true of 

 the astragalus (a., text-fig. 47), which is much narrower than in the recent forms, and 

 has scarcely any trace of the prominent process on the postaxial side which unites with 

 the fibular side of the tibia and bears on its outer side a facet for the fibula. The 

 proximal surface is occupied by a tibial facet [t.f.), which is concave in the middle, 

 but possesses rounded borders ; on the postaxial surface there is an oblique, gently 

 concave facet (f.f-), looking obliquely outwards, for union with the astragalar facet of 

 the fibula ; this corresponds to the fibular facet referred to above, as being borne on the 

 postaxial process in recent Crocodiles. The inner (preaxial) face is gently convex, with 

 a slight median depression. The distal surface is evenly convex in its preaxial two- 

 thirds ; postaxially it bears a deep pit, probably for a ligament, and behind this there 

 is a deep groove separating the outer convex portion from a narrow oblique facet for 

 union with the calcaneum ; a roughened area looking upwards and backwards 

 separates the distal and tibial surfaces posteriorly. 



The calcaneum (c, text-fig. 47) is much more similar to the corresponding bone in 



