572 ZOOLOGY SECT. 



which Halitherium is the best known member. These were 

 characterised by the possession of upper incisors, of enamelled 

 pre-molars and molars, of a milk-dentition, and of small vestiges- 

 of femora. The family of the Dugongs is represented by a form 

 nearly allied to the existing genus in the Pliocene of France, 

 and probably by another genus in the Tertiary of California. 

 The family of the Manatees is not known to be represented by 

 any fossil forms. Of doubtful position in the order are certain 

 genera that have been described from European and Australian- 

 Tertiary formations. 



The Tertiary Ungulata comprise an immense number of forms,, 

 including a considerable number of extinct families, into an account 

 of which it would be going beyond the scope of the present work 

 to enter. In the Artiodactyle series there is to be traced a pro- 

 gressive union and coalescence of the third and fourth metacarpals 

 to form the cannon-bone, a progressive reduction of the lateral 

 digits, and a progressive development of horns or of tusks absent 

 or rudimentary in the earlier representatives of the sub-order. In. 

 the Perissodactyle series the reduction of the lateral toes reaches 

 its maximum in the existing genus Equus. The history of this 

 reduction, together with the development of other characteristic- 

 features, can be traced from pentadactyle forms with simple 

 molars through a long series of gradations to the monodactyle 

 Horses with their complexly folded molars. Similar genealogies, 

 though not always so complete, can be traced for the Tapirs and 

 Rhinoceroses, and for the Deer, Camels, and Pigs. 



The order Proboscidea was represented in Tertiary and Pleisto- 

 cene times, not only by forms allied to those now living, though 

 sometimes, as in the Mammoths, of much greater size, but by an 

 extinct family, the Dinotheridce (Fig. 1166) (Miocene and Pliocene 

 of Europe and India), which possess a pair of downwardly-directed, 

 tusks in the lower jaw. 



A separate sub-order, the Condylarthra, has been established, 

 for a number of Eocene Ungulates, which differ somewhat widely 

 from all the other members of that group, and approach the 

 Carnivora in some respects, though having certain resemblances to 

 the Hyracoidea. The pre-molars and molars are short and usually 

 bunodont, the pre-molars being simpler than the molars, the fatter 

 sometimes tritubercular, like those of many of the Carnivora ; the 

 incisors and canines also sometimes resemble those of the Carni- 

 vora. The humerus differs from that of the other Ungulata, 

 and resembles that of the Carnivora in the presence of a foramen 

 over the inner condyle. As in the Hyracoidea the scaphoid 

 articulates with the trapezoid and not with the magnum, and the 

 femur has a third brochanter. The limbs are usually penta- 

 dactyle, with pointed ungual phalanges. The astragalus has r 

 as in the Carnivora, a uniformly rounded distal articular surface.. 



