REPTILIA: VARANOSAURUS 107 



antero-posterior plane. It is broader above and more convex on 

 the anterior side. The outer articular surface, for the calcaneum, 

 is divided by a deep transverse groove near its lower third, which 

 in apposition with a similar but less deep groove on the inner side 

 of the calcaneum forms the canal for the perforating artery, whose 

 posterior orifice is almost wholly within the astragalus. Below 

 the groove there is only a narrow surface for union with the calca- 

 neum. The distal surface is divided into two facets, the outer 

 oblique one for articulation with the fourth tarsale, the inner or 

 longer one for articulation with the centrale or its cartilaginous rep- 

 resentative. These surfaces are nearly flat. 



The calcaneum or fibulare (Plate IV, Figs. 6, 7) is as broad as 

 long, somewhat wider, but no longer than the astragalus. The 

 proximal border on the inner side forms, with the astragalus, the 

 articulation for the fibula, rather more on this bone than on the 

 astragalus. The articular surface on the inner side for the astrag- 

 alus is grooved, as already described, for the perforating canal; 

 it has an angular process on the back side projecting into the 

 emargination of the astragalus at the place of the groove. The 

 distal articulation for union with the fourth and fifth tarsalia 

 forms an angle with the distal surface of the astragalus. The 

 outer border, that between the fibular and tarsal surfaces, com- 

 prises about one-third of a circle and is relatively thin, much 

 more so on the lower part. 



Of the tarsalia, the fifth and the second are small, the fourth 

 the largest, the third and first subequal in size. Each bone sup- 

 ports exclusively its own metatarsal. The fifth articulates with 

 the calcaneum, and for a considerable extent the outer articular 

 facet of the fourth; the first tarsale articulates with the 

 centrale and the second tarsale; the fourth joins broadly the 

 calcaneum, and for a considerable extent the outer articular facet 

 of the astragalus; the third tarsale articulates with its adjacent 

 tarsalia and with the centrale or possibly the astragalus. The 

 second tarsale, of which only a small oval facet is seen from in 

 front, articulates proximally with the centrale, and laterally with 

 the adjacent tarsalia; the first tarsale is flattened and thinned, 

 and evidentlv has much freedom of movement, since it is invariably 



