MACRAUCHENIA AND ASTRAPOTHERE. 561 



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 (Macro n- 

 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 pakxotheres ; 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. 



Subordek 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 



