56 TEETIAET VEETEBEATA OF THE FATtM. 



These two facets are separated from one another posteriorly by a narrow groove, 

 and anteriorly by a deep fossa. There is also a deep fossa lying to the inner 

 side of the anterior part of the sustentacular facet. Anteriorly this surface joins 

 that for the cuboid {cub.), making an angle of about 100° with it. 



The cuboid surface {cub.) is about one-third of the whole distal articulation. 

 It is gently convex in all directions, and is separated from the navicular surface 

 by a slight oblique ridge. The navicular surface {nav.) occupies nearly all the 

 rest of the distal face of the bone ; it is strongly convex from side to side, and 

 slightly so from before backwards. Internally it is continuous with a small facet (? t.), 

 which may indicate the existence of a distinct tibiale such as occurs in some 

 Amblypoda. On the anterior face of the bone the lower edge of the tibial surface 

 is separated from the upper edge of the cuboid-navicular surface by an interval of 

 about 2 to 3 cm., in which the surface is concave from above downwards. 



This astragalus, though superficially similar to that of Elephas, differs from it 

 fundamentally. Among the points of diflFerence are : — (1) articulation with cuboid 

 and consequent different form of the distal surface ; (2) much larger surface for 

 fibula ; (3) presence of a large and somewhat concave surface for the internal 

 malleolus (in the early Proboscidea this seems to have been present, see below) ; 

 (4) wide difference in the form and proportions of the two calcaneal facets ; in 

 JElephas the ectal facet, in Arsinoitherium the sustentacular, is much the larger. 



The likeness to the astragalus of the Amblypoda is somewhat greater, particularly 

 in the presence of both cuboid and navicular facets. But the form of the calcaneal 

 facets is different, and the posterior notch is slightly marked, while in the Amblypoda 

 It may even be converted into a foramen. 



The calcaneum (text-fig. 32, 1 A, 1 b) is a very short stout bone somewhat like 

 that of the Dinocerata. The tuber calcis {t.c.) is very short and thick, and terminates 

 posteriorly in a great rugose mass of bone. The ventral surface is greatly swollen at 

 the sides, but in the middle line there is a deep concavity. There are two oval, 

 obliquely-arranged facets for articulation with the astragalus. Of these the ectal {ec.) 

 is concave from before backwards, while the inner (sustentacular) facet {sus.), which 

 is much the larger, is flat in front and convex behind, owing to the deflection of its 

 hinder portion. The two surfaces are separated posteriorly by a deep narrow cleft 

 which, towards the front, becomes wider and deeper. The anterior edge of the sus- 

 tentacular surface forms the upper border of a small facet lying at right angles to 

 it {\nav.), and probably indicating that there was a small articulation with the 

 navicular. The cuboid facet {cub.) is small and oval, its upper inner angle beinf 

 continuous with the small navicular facet just described. Beneath the navicular 

 and cuboid articulations is a valley bounded below by a rugose and swollen border. 

 The fibular facet {fib.) is large ; it looks outwards and upwards, and is convex 

 from before backwards, while its upper border meets the ectal facet in a sharp 



