50 
TiarriAliY VERTEinJATA OE THE EAYlJM. 
'J'hese two facets are separated from one anotlier posteriorly by a narrow groove, 
and anteiiorly by a deep fossa. There is also a deep fossa lying to the inner 
side of the anterior })ait of tlte sustentacnlar facet. Anteriorly tliis surface joins 
that for the cuboid (cub.), making an angle of about 100° with it, 
d'he cuboid surface (cub.) is about one-third of the wdiole distal articulation. 
It is gently convex in all directions, and is separated from the navicular surface 
l)y a slight obli(pie ridge. The navicular surface (uav.) occupies nearly all the 
rest of the distal face of the bone ; it is sti'ongly convex from side to side, and 
slightly so from before backwards. Internally it is continuous wuth 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 surftce 
is separated from the upper edge of the cuboid-navicular surface by an interval of 
about 2 to d cm., in which the surface is concave from above downwards. 
This astragalus, though superficially similar to that of £lephas, differs from it 
fundamentally. Among the points of difference are ; — (1) articidation with cuboid 
and consequent different form of the distal surface ; (2) much larger surface for 
fibula ; (d) presence of a large and somewdiat concave surface for the internal 
malleolus (iu the early Proboscidea this seems to have been present, see below) ; 
(4) wide difference in fbe form and proportions of the two calcaneal facets; in 
Elepitas the ectal facet, in Arsinoitherium the sustentacnlar, 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 calcaneuiii (text-fig. d2, 1 a, 1 b) is a very short stout bone somewhat like 
that of the Diuoccrata. The tuber culcis (t.c.) is very short and thick, and terminates 
posteriorly in a great rugose mass of bone. Tlie 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 back^vards, while the inner (sustentacnlar) facet (sus.), which 
is much the larger, is flat in front and convex behind, owing to tin' deflection of its 
hinder portion. The two surfaces are se[)arated posteriorly by a deep narrow cleft 
which, towards the front, becomes wider and deeper. 4'he anterior edge of the sus- 
tentacular surface forms the uj)per border of a small facet lying at right angles to 
it (Vnav.), and ])robably indicating that there was a small articulation with the 
navicular. The cuboid facet (cub.) is small and oval, its upper inner angle being- 
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 u[)wards, and is convex 
from before backwards, while its upper border meets the ectal facet in a sharp 
