140 PATAGONIAN EXPEDITIONS : PALEONTOLOGY. 



In Macrauchenia the navicular is very, similar, but is relatively shorter 

 proximo-distally and the step on the distal end is less distinct. 



The entocuneiform is a long, narrow, scale-like bone, convex on the 

 tibial and concave on the fibular side, and with abruptly truncated distal 

 end. Proximally, there is an oblique, concave facet for the navicular, 

 below this a small lateral facet for the mesocuneiform, and near the distal 

 end and dorsal border a small, oval surface for the second metatarsal. The 

 mesocuneiform is a relatively large, irregularly oval bone, broadest on the 

 dorsal side ; the navicular facet is slightly concave in the dorso-plantar 

 direction, and that for the second metatarsal is saddle-shaped. Other 

 facets are a small one on the tibial side, near the plantar and proximal 

 edges, for the entocuneiform, and a still smaller one on the fibular side 

 for the ectocuneiform. 



The ectocuneiform is very large ; the dorsal face is nearly square, though 

 somewhat higher than it is wide, and thence the bone narrows to a blunt 

 edge on the plantar side, which bears a small, rugose tuberosity. Proxi- 

 mally, the surface for the navicular is irregularly concave in front, convex 

 behind, while the distal facet for the third metatarsal is quite deeply con- 

 cave planto-dorsally. On the tibial side, near the distal end, are two 

 widely separated facets for the second metatarsal, a small one near the 

 dorsal and a large one near the plantar border. Articulation with the 

 cuboid is limited to a small facet on the fibular side near the proximal 

 end. 



The cuboid is a very large bone and, though widely separated from the 

 astragalus, is yet relatively high proximo-distally. The proximal surface 

 rises steeply toward the plantar side, making the height of the bone nearly 

 twice as great on this side as it is on the dorsal. On the tibial side are 

 three facets for the navicular, two near the proximal end and plantar side, 

 and the third a projection from about the middle of the tibial face, upon 

 which the navicular rests and which bears also a small facet for the ecto- 

 cuneiform. The fibular side has two prominent tubercles and, between 

 them, a tendinal sulcus. Distally, is a very large, concave surface for the 

 fourth metatarsal, and, external to this a minute facet for the vestigial fifth, 

 which is more lateral than distal in position. 



The metatarsus consists of similar elements to those of the metacarpus, 

 three functional members arranged in mesaxonic symmetry, and a vestige 

 of another, the fifth. 



