54 



ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 



surface of its proximal end, while the outer metatarsal of the right-foot of the 

 Tapir, with which, in other respects, it most closely corresponds, has two articular 

 surfaces. In the cast of a hind-foot of a Palaeothere, I find that the outer meta- 

 tarsal bone closely agrees with this metatarsal bone of the Macrauchene, in the 

 structure just alluded to : the articulation with the middle metatarsal being by a 

 single sub-oval facet, which stands out a little way from the surface of the bone : 

 the articular surface in the Macrauchene presents a similar form and condition, 

 and is similarly situated to that in the Palseothere, being at the posterior part of 

 the lateral surface, and a little below the superior or tarsal articular surface. 

 The bone expands towards its distal end, which corresponds in structure with 

 those of the two lateral metatarsals in the fore-foot, in being completely divided 

 into two trochlear surfaces by a well- developed median ridge, and in having the 

 posterior half of this ridge suddenly produced, so as to project about two lines 

 further from the trochlear surface than the anterior part of the same ridge. In 

 both the Tapir and Palseothere this anterior part of the ridge is wholly sup- 

 pressed, and the posterior is much more feebly developed than in the Macrauchenia. 

 The metatarsal bone here described is of exactly the same length with the internal 

 metacarpal bone, and proves, in conjunction with the proportions of the astralagus, 

 that the fore and hind feet of the Macrauchenia were of equal size. 



Thus then we obtain evidence, from a few mutilated bones of the trunk and 

 extremities of a single representative of its race, that there once existed in South 

 America a Pachydermatous quadruped, not proboscidian, which equalled in 

 stature the Rhinoceroses and Hippopotamuses of the old world. But this, though 

 an interesting and hitherto unsuspected fact, is far from being the sum of the 

 information which is yielded by these fossils. We have seen 

 ungueal phalanx bespeaks a quadruped of the great series of Ungulata, and 

 this indication is corroborated by the condition of the radius and ulna, which are 

 fixed immoveably in the prone position. Now in the Ungulated series there are 

 but two known genera, — the Rhinoceros and Palaeotherium, — which, like the 

 quadruped in question, have only three toes on the fore-foot. Again, in referring 



* 



the Macrauchenia to the Tridactyle family of Pachyderms, we find, towards the 

 close of our analysis, and by a detailed comparison of individual bones, that the 

 Macrauchenia has the closest affinity to the Palaeotherium. 



But the Palaeotherium, like the Rhinoceros and Tapir, has the ulna distinct 

 from the radius, and the fibula from the tibia : so that even if the Parisian Pachy- 

 derm had actually presented the same peculiarities of the cervical vertebras as the 

 Patagonian one, it would have been hazardous, to say the least, while ignorant 

 of the dentition of the latter, to refer it to the genus P alee other turn. 



Most interesting, indeed will be the knowledge, whenever the means of ob- 

 taining it may arrive, of the structure of the skull and teeth in the Macrauchenia. 



that the single 



