4l6 PATAGONIAN EXPEDITIONS I PALEONTOLOGY. 



and heavy and shaped very much as in the latter ; the distal end is rather 

 wide, but not much thickened ; the astragalar surface is unequally divided 

 into small internal and very large external facets, with low intercondy- 

 lar ridge, which on the plantar side passes into a long and prominent 

 tongue-like process. The fibula is very slender, relatively more so than 

 in Erethizon, and its distal end is more compressed laterally and expanded 

 antero-posteriorly. 



The pes (Plate LXVI, fig. 9) is very like that of Erethizon, with longer 

 metatarsals and less reduced hallux ; certain resemblances to Coendo^^, 

 such as the presence of a second tibial sesamoid, are also to be noted. 

 The calcaneum has a short, heavy tuber, with broad and shallow tendinal 

 sulcus on the free end ; the distal, external tuberosity for the attachment 

 of the lateral ligament is a prominent ridge ; the sustentaculum is very 

 prominent and the external astragalar facet is very large and oblique, 

 facing inward more than dorsally ; the cuboid facet is oblique to the long 

 axis of the bone and but slightly concave. The astragalus is short, wide 

 and depressed, with deeply grooved and asymmetrical trochlea, the outer 

 condyle being much the larger ; the neck is very oblique and directed 

 strongly toward the tibial side, ending in a convex, somewhat depressed 

 head : on the plantar side are two large facets for the calcaneum, the exter- 

 nal one of which is continuous with the navicular surface. 



The navicular is short and narrow, with a shallow concavity for the 

 distal end of the astragalus ; distally, it rests entirely upon the meso- and 

 ectocuneiforms, the entocuneiform having only a lateral contact with it, as is 

 also the case in Coendou and Erethizon. On the tibial side of the navicular 

 is a large, thick and heavy sesamoid, which resembles that of Coendou in 

 shape and connections ; in the figure (LXVI, 9, s] its full size is not shown, 

 because it is partly overlapped and concealed by the second sesamoid (/). 

 The first sesamoid rests upon the navicular and entocuneiform, entirely 

 covering the proximal end of the latter, and on the fibular side it articu- 

 lates extensively with the astragalus, for which it has a concave facet ; on 

 the tibial and dorsal side are two small, subcircular and well-separated 

 facets for the second sesamoid. The latter, which is not present in Ere- 

 thizon, has a somewhat similar shape to that seen in Coendou, but is far 

 smaller and could have had no such functional importance ; it is a flat bone, 

 of subtriangular shape, and is connected only with the first sesamoid by 

 means of two small facets on the inner side of the plantar surface. 



