100 



straight backward from the articulation. lis outer surface forms part of an 

 irregular plane with the fore part of the bone. 



The sustentaculum is thick and three-fourths the length of the bone. The 

 groove beneath for the flexor-tendons is well marked. The articular surface 

 it supports for the astragalus, is larger than that on the body of the bone. 

 The groove separating the articular surfaces for the astragalus nearly occu- 

 pies the middle of the bone. Both surfaces are flat in front, but convex back- 

 ward behind. 



No articular surface exists for the fibula. At the fore part of the bone 

 there is a small articular facet for the cuboid. The remaining portion of the 

 front surface forms a deep and wide irregular plane. 



The astragalus, of which upper and lower views are given half-size in 

 Figs. 7, 8, Plate XXVI, resembles that of the ordinary proboscideans. The 

 bone is irregularly square, with nearly equal horizontal diameters, and of less 

 thickness than these. 



The upper articular face has nearly the shape of that in a mastodon, but 

 is rather more depressed posteriorly. The fibular extension holds about the 

 same, proportion to the tibial surface as in the animal named. 



The calcaneal! articular surfaces are the reverse in their comparative size 

 to what they are in the mastodon, the inner one being the larger. Both are 

 also more concave fore and aft than in that animal. 



The navicular articular surface is proportionately deeper in comparison with 

 its width than in mastodon, and is well defined outwardly from the cuboid 

 articular facet. 



The cuboid is triangular in outline, with rounded angles, and with the 

 thickness more than half the breadth or depth. Proximally it presents a 

 double articular facet, of 'which the division for the astragalus is larger than 

 that for the calcaneum. The former division is continuous with a narrow 

 facet on the inner side for the navicular. Distally the bone also presents a 

 double articular facet, the divisions forming an obtuse angle. 



The measurements of the tarsal bones are as follows : 



Calcaneum. 



Lines. 



Length of calcaneum , 42 



Breadth at fore part 39 



Depth at fore part externally 31 



Length of tuber calcis from the outer articular facet above 20 



Breadth transversely of the outer articular facet for the astragalus 14£ 



