FOSSIL MAMMALIA. 53 



malleolar articular smooth surface in the Palseothere there is a deep pit ; in the 

 Tapir a shallow one ; but in the Macrauchenia we observe only a smooth and 

 slightly convex triangular surface. If we compare the inner surface of the 

 astragalus in these three animals, we shall find the existing Tapir again forming 

 a transition between the two extinct genera. In the Palseothere, a round pro- 

 tuberance projects from the anterior part of this surface: in the Tapir, we 

 observe a gentle rising of the bone in the same part, while in the Macrauchene (fig. 2) 

 the surface of the bone is level at this part. The margin of the tibial malleolar 

 articular surface, which is very slightly raised in the Macrauchene, is more 

 developed in the Tapir, and still more so in the Palseothere, where it forms 

 a ridge, overhanging the rough outer side of the bone. Near the lower part 

 of this surface we observe a small but deep depression in the Palseothere; 

 there is a shallower one in the corresponding part in the Tapir; and the 

 depression is still wider and shallower in the Macrauchenia. In the Palseo- 

 there the astragalus articulates by three surfaces with the os calcis, poste- 

 riorly by a large concave surface, externally by a longitudinal sub-elliptic surface, 

 and anteriorly by a thin transverse facet : in the Macrauchene (fig. 4) two only 

 of these surfaces are present, viz. the concave and the longitudinal one, the anterior 

 transverse surface being wanting : in the Tapir, the transverse surface is present, 

 but is confluent with the longitudinal one. The posterior surface is relatively 

 larger and deeper in the Macrauchene than in the Palseothere, and approaches 

 nearer to the triangular than the oval form : the longitudinal surface is placed 

 more obliquely, and is truncated anteriorly. In the Tapir this surface is confluent 

 with the scaphoid articular surface, but it is separated therefrom by a narrow 

 strip of bone in both the Palseothere and Macrauchene. It is satisfactory to find 

 in the bone, which marks most strongly the affinity of Macrauchenia to Palceothe- 

 rium, so many easily recognizable differences, because the structure of the cervical 

 vertebrse in the latter genus is too imperfectly known, to allow us to predicate 

 confidently a distinction between it and Macrauchenia in that particular; the 

 difference, however, which they present in the condition of the bones of the 

 fore-arm and leg, forbids their being considered as generically related. 



There remains to be noticed only a single fractured metatarsal bone (fig. 1. 

 PI. XV.) This, from its bent and unsyminetrical figure, is evidently not a middle 

 one, and having the side of the proximal end, which was articulated to the adjoining 

 metatarsal in a nearly perfect state, it enables us to refer it with certainty to the hind- 

 foot, since it does not agree with any of the corresponding surfaces at the proximal 

 extremities of the metacarpal bones. It remains then to be determined, whether it is 

 an external metatarsal of the right-foot, or an internal one of the left-foot, the general 

 curvature of these being in the same direction. With neither of these bones in the 

 Tapir does our metatarsal agree, since it has but one articular facet on the lateral 



