xm PHYLUM CHORDATA 453 



are usually absent or vestigial. The femur has no third trochanter. 

 The tibial surface of the astragalus is flat, the distal surface 

 articulates largely with the cuboid, and the calcaneum has a flat 

 articular surface for the fibula. The pre-molars are smaller than 

 the molars. The stomach is almost always complex, and the 

 coscum is small. The teats are few and situated in the groin, or 

 numerous and extending along the abdomen. The placenta is 

 diffuse or cotyledonary. 



This sub-order includes the Ruminants, such as the Camels 

 (Camelidce), Oxen (Bowdce), Sheep (Ovis), Goats (Capra), Antelopes, 

 Giraffes (Giraffa), and Deer (Cervidce), and the Non-Ruminants, 

 viz., the Pigs (Sus), Peccaries (Dicotylcs), and Hippopotami 

 (Hippopotamus). 



Sub-order c. Litopterna. 



Extinct Ungulates with the digits of the manus and pes (which 

 are never more than three in each) elongate, and of the Perisso- 

 dactyle type. The astragalus has a pulley-shaped articular surface 

 for the tibia as in the Perissodactyla, while the calcaneum has a 

 small facet for the fibula as in the Artiodactyla. The bones of the 

 carpus and tarsus do not interlock as in existing Ungulata vera, 

 but are arranged in vertical series. A third trochanter is present, 

 but is smaller than in .the Perissodactyla. 



This sub-order includes Macrauchenia and other genera, the 

 remains of which have only been found in the Tertiary deposits of 

 Patagonia and Bolivia. 



Sub-order d. Astrap other ia. 



Extinct Ungulates with the digits of the manus and pes, of 

 which there were probably five in each, comparatively short. The 

 astragalus has a flat articular surface for the tibia. The carpal 

 and tarsal bones do not interlock. Sometimes there is a pair of 

 large tusks in each jaw. The molar teeth have a more or less 

 marked resemblance to those of the Rhinoceroses. 



This sub-order includes only two genera Astrapotherium and 

 Homalodontotherium both confined to the Tertiary deposits of 

 Patagonia. 



SECTION 2. SUBUXGULATA. 



Ungulata in which the feet may be plantigrade and there may 

 be five functional digits. The magnum of the carpus does not 

 articulate with the scaphoid, at least in living forms. 



Sub-order a. Hyracoidea. 



Small Subungulata with furry 'integument, with four completely 

 ormed digits in the fore-foot (the pollex being vestigial), and 



