﻿I860.] HUXLEY MACRAUCHENIA BOLIYIENSIS. 75 



Thus it appears that the centrum of the cervical vertebra of 

 Macrauchenia Boliviensis is far more slender than that of M. Pata- 

 chonica ; for, while the length of the former is to that of the latter 

 as 1 : Vk, the transverse diameters of the anterior faces of the centra 

 of the two species are, nearly, as 1 : 3. The cervical vertebra of the new 

 species is, absolutely, rather shorter than the fourth cervical of the 

 Vicugna ; but, relatively to its width, it is much shorter and stouter 

 than this bone in either the Guanaco or the Vicugna. There are no 

 longitudinal ridges on the surface of the vertebra below the pre- 

 zygapophyses, in which respect M. Boliviensis differs from M. Pata- 

 chonica, and approaches the Auchenioe. The anterior articular facet 

 of the centrum is concave from above downwards, in consequence of 

 the projection of the thickened and convex lower third of that face ; 

 the posterior facet is not only concave from above downwards from 

 a similar cause, but is also concave from side to side. The con- 

 cavity of both articular facets is greater than in M. Patachonica, 

 and the present species departs, in these respects, more widely than 

 the latter does from the Auchenioe. 



The astragalus (Plate VI. fig. 2). — Tbis bone is. again, quite that 

 of the Patagonian species in miniature, differing chiefly in the pro- 

 portions of its dimensions, as shown by the subjoined table : — • 



Macrauchenia Boliviensis. 

 in. 



Length 1-45 



Greatest width . . 1*2 

 Greatest depth . . '85 



M. Patachonica. Guanaco. Vicugna. 



in. in. in. 



3-3 1-6 1-3 



2-7 1-2 -85 



2-15 -95 -8 



If we take the lengths of the astragali, it will be observed that 

 their proportions in the Bolivian and Patagonian Macrauchenice are 

 not the same as those of the cervical vertebrae. The astragali bear 

 the ratio of 1 : 2^, while the cervical vertebrae gave 1 : . Further- 

 more, the proportions of length, width, and depth in the two astra- 

 gali are different. Like the cervical vertebra, the astragalus of M. 

 Boliviensis is a, relatively, stouter bone than that of the Vicugna ; 

 though instead of being shorter it is a little longer, occupying a 

 position, in point of absolute length, between the astragalus of the 

 Vicugna and that of the Guanaco. As the astragalus thus yields 

 results agreeing very well with those given by the cervical vertebra, 

 we may safely assume that not only the absolute size, but the pro- 

 portions of the body of Macrauchenia Boliviensis were nearly those 

 of the existing Llamas, and differed widely from those of the heavy 

 and huge Macrauchenia Patachonica. 



The tibia. — "What remains of the bones of the hind leg confirms 

 this view of the proportions of Macrauchenia Boliviensis. I have the 

 proximal end of the left tibia, minus the fibula, and with the outer 

 articular condyle broken away. Below this point, the outer edge 

 and surface of the fragment are uninjiu-ed, and the posterior face is 

 in good preservation, but the internal face is somewhat crushed. 

 The muscular ridges on the posterior face are as well marked as in 

 the skeleton of the Guanaco, and far more distinct than in that of 



