312 THE ANATOMY OF VERTEBRATED ANIMALS. 



in South America and one in Southwest China, I\Ialacca, and 

 Sumatra. The genus Tcqnrus has been found fossil in Europe 

 in rocks of miocene age. The closely-allied extinct genera 

 Lopliiodon (and Coryphodon?) carry the Tainridm back 

 through the eocene epoch. 



d. The Pcdceotheridm. — These are all extinct animals, the 

 remains of which are found in the older tertiary rocks ; and 

 which are closely allied, on the one hand, with the Horses and, 

 on the other, with the Tapirs. 



The type of the family, Palceotheridium, resembles the 

 Tapir in most respects, but has only three digits in the manus 

 as well as in the pes. The dental formula, however, is 



*'• "F? ^* i^ P''i^^' 4^ *^*"FT* ^^^^ diastema is smaller than in the 



Tapir, and the patterns of the grinding teeth of both jaws 

 are more like those of the Rhinoceros. 



e. The Macrauchenidoe., — The genus Macrauchenia is also 

 an extinct form, which occurs in later tertiary or quaternary 

 deposits in South America. 



The feet are tridactyle, and the dental formula is 



i. |4|- c, W p.m- ^ m. -^ The teeth are disposed in a nearly 



continuous series. The crowns of the incisors present a deep 

 fossa, as in the JEquidm. The molars are in part Equine, in 

 part Rhinocerotic in character. The skull is, on the whole, 

 Equine, but the nasal bones are very short and Tapiroid. The 

 vertebrae of the long neck are extraordinarily similar to those 

 of the Gamelidce^ and especially of the Llamas. 



2. The Artiodactyla. — The number of the dorso-lumbar 

 vertebrge in this group is always fewer than twenty-two, and 

 rarely exceeds nineteen. 



The third digit of each foot is asymmetrical in itself, and 

 usually forms a symmetrical pair with the fourth digit ; and 

 the functional toes of the hind-foot are even in number — that 

 is to say, either two or four. 



The femur is devoid of any third trochanter; the facets 

 upon the distal face of the astragalus are subequal, that for 

 the cuboid being nearly as large as that for the navicular 

 bone. The tympanic is large, and the pterygoid process of 

 the sphenoid is not perforated. 



The posterior premolar teeth usually diifer a good deal 

 from the succeeding molars, being simpler in pattern. The 

 last milk-molar in the lower jaw is trilobcd ; but this is also 

 the case in some Perissodactyla 



