III.] MACRAUCHENIA. 79 



important difference, from both the Perissodactyla and Artio- 

 dactyla, occurs in the structure of the carpus (wrist) and tarsus 

 (ankle), in both of which the two rows of small component bones 

 are arranged in vertical series one above another, instead of 

 overlapping and interlocking; this so-called linear arrangement 

 being a more primitive type than the interlocking or alternating 

 arrangement characterising the two existing suborders. The 

 vertebrae of the neck are elongated, with flat terminal faces, and 

 have the vertebral artery piercing the sides of the neural arch 

 in a manner elsewhere found only in the camel family and the 

 great anteater. In the femur, or thigh-bone, the projection known 

 as the third trochanter is much less developed than in the Perisso- 

 dactyla. All the members of the group were long-limbed, long- 

 necked, and slenderly built animals, Macrauchenia itself being 

 as large as a camel, although the genera from the Santa Cruz 

 beds of Patagonia were represented by species of much smaller 

 dimensions. 



Of the typical genus Macrauchenia fossil remains occur not 

 only in the Pampean formation, but likewise in the superficial 

 deposits of both Patagonia and Bolivia. The most curious feature 

 about this remarkable animal is the position in the skull of the 

 aperture for the nostrils, which instead of being situated at the 

 extremity of the muzzle, is placed in the middle of the forehead, 

 between the eyes. Otherwise the skull is not unlike that of a 

 horse in general contour. The teeth, which are forty-four in 

 number, and form a continuous uninterrupted series, are a special- 

 ised modification of the type of those of the undermentioned 

 genus ; their crowns being taller, with a more complicated ar- 

 rangement of folds. In nearly all points of its structure, especially 

 in the number of the teeth, and the absence of large tusks, as well 

 as in the structure of the wrist- and ankle-joints, Macrauchenia 

 is a very primitive kind of animal. In the Santa Cruz beds of 

 Patagonia the family to which this genus belongs is represented 

 by several smaller animals, such as those named Oxyodonto- 

 therium, in which the aperture for the nostrils occupied a more 

 normal position in the skull, and the crowns of the molar teeth 

 were shorter and of a more simple structure. The crown-surfaces 

 of worn upper molar teeth from the right side of the jaw of both 



