176 MAEINE EEPTILES OF THE OXFOED CLAY. 



Hind Limb (PL X. figs. 3-4). — The femur (f.) very closely resembles that of 

 Steneosaurus in its general form, but is more compressed. The convex upper border 

 of the shaft bears a narrow flattened rugose area extending throughout its length and 

 apparently intended for the attachment of powerful muscles. The trochanteric 

 roughening extends on to the ventral border of the bone instead of being confined 

 to the inner face as in Steneosaurus. The distal condyles are usually incompletely 

 ossified and, no doubt, in life were extensively covered with cartilage. The outer 

 (fibular) condyle is much the larger and is separated from the inner by a small inter- 

 condylar notch ; it articulated with the outer condyle of the tibia and the upper end 

 of the fibula. 



The tibia (tib.) and fibula {fib.) are relatively shorter than in Steneosaurus, being 

 only a little more than a third the length of the femur; both seem to have been much 

 compressed from before backwards. This compression seems to be most marked in 

 the small species in M. lave (R. 3014, PL X. fig. oj. The upper end of the tibia 

 is much thickened and its articular surface is divided by an obscure oblique concavity 

 into an inner and outer condyle, the latter, together with the upper end of the fibula, 

 articulating with the outer condyle of the femur. Beneath the widened upper 

 articular end, the shaft narrows and is compressed from before backwards to a varying 

 degree; at its distal end it again widens a little and terminates in a slightly convex 

 surface for union with the astragalus; this surface is continued on to the posterior 

 surface of the bone on its postaxial side. 



The fibula (Jib.) is a slender rod of bone : at its upper end it is considerably expanded 

 and rested against the flattened surface on the outer side of the upper end of 

 the tibia; as already noted, it articulated with part of the outer condyle of the femur. 

 At its lower end the bone terminates in a somewhat oblique and strongly convex 

 surface, the preaxial corner of which articulated with a facet ou the astragalus, the 

 remainder with the proximal surface of the calcaneum (PL X. fig. 3). 



The tarsus (PL X. figs. 3-4) consists of four elements, the astragalus (as.) and 

 calcaneum (ca.) in the proximal row, and two bones in the distal series probably repre- 

 senting the fused first to third and fourth and fifth tarsalia respectively. In the smaller 

 species, M. lave, in which the tarsals, like the other limb-bones, are much flattened, they 

 form a fairly closely fitting pavement of bones. The astragalus (as.) has on its proximal 

 border two facets, one preaxial and much the larger for articulation with the tibia, the 

 other, much smaller, gently concave and looking upwards and outwards, for union with 

 the fibula. Externally, it has a nearly straight border for union with the calcaneum 

 and distally a convex surface uniting with the fused first and second distal tarsals, and 

 in front of this apparently supporting the first metatarsal. The proximal surface of the 

 calcaneum (ca.) forms a convex facet for the fibula ; anteriorly it joins the astragalus 

 in a nearly straight border and distally it articulates with the fused fourth and fifth 

 metatarsals. Postaxially it is produced into a strong pointed talon which projects 



