MACRAUCHENIA AND ASTRAPOTHERE. 
5 61 
not the least remarkable was the so-called Macrauchenia, the typical representative 
of the suborder Litopterna. The members of this group are characterised by having 
cheek-teeth approximating in structure to those of the European palseotheres 
(p. 515), the upper molars having their outer wall divided into two distinct lobes. 
Although the long toes were arranged in the same manner as in the Odd-toed 
group of Ungulates, and were never more than three in number, the structure of 
both the wrist and ankle-joints were different. Thus, in place of the component 
bones of these joints alternating with one another, they were arranged directly one 
above another, after the so-called linear type characterising the modern elephants 
(see p. 528). The huckle-bone, or astragalus, of the ankle resembles that of the 
Odd-toed group in being grooved superiorly; but the heel-bone, or calcaneum, 
differed in having a small surface for the articulation of the fibula, or smaller bone 
of the leg, as in the Even-toed group. The long vertebrae of the neck, although 
showing the same flat terminal ends characterising the allied extinct South 
American groups, are peculiar in regard to the position of the canal for the great 
artery of the neck, and in this respect agree with the camels and llamas alone 
among living Ungulates. The thigh-bone, or femur, has a small third trochanter 
representing the larger one characteristic of the Odd-toed group. In build, the 
members of the present group were tall, slender Ungulates, with long legs, feet, 
and neck; and thus very different in appearance from the under-mentioned 
toxodonts, which were short-limbed, short-necked, and heavily-built creatures. 
The Litopterna are divisible into two families, of which the first (Macrau- 
cheniidce ) is represented by the macrauchenia and certain allied forms, and is 
characterised by the presence of forty-four teeth, forming an uninterrupted series 
in the jaws. Macrauchenia itself, which was discovered by Darwin in the super¬ 
ficial deposits of Patagonia, was an animal somewhat larger than a horse, presenting 
the remarkable peculiarity of having the aperture of the nostrils in the skull 
situated in the middle of the forehead; although during life it is probable that they 
terminated in a short trunk. In the lower, or Miocene Tertiaries of Patagonia the 
family was represented by smaller and less specialised forms (such as Oxyodonto- 
therium), in which the nostrils were more normal in position, and the crowns of 
the molar teeth lower and simpler. 
In the second family, or Proterotheriidce, represented principally in the lower 
Patagonian Tertiary deposits, the teeth were reduced in number, and formed an 
interrupted series, a pair in both the upper and lower jaw being much longer than 
the rest. In these proterotheres the molar teeth had a considerable resemblance to 
those of the palacotheres; but the feet were of the general type of those of the 
three-toed horses, or hipparions, and in some cases it appears that only the middle 
toe was functionally developed. 
The Astrapotheres and their Kin. 
Suborder Astrapotheria. 
In this second South American group, represented only in the Miocene deposits 
of Patagonia, all the species are of large size, and possess rooted cheek-teeth of a 
vol. ii.—36 
