EVEN-TOED UNGULATES 



(ARTIODACTYLA). 



Ungulates of very variable size, almost always with an even number of toes, which are arranged about two parallel 

 axes running through the middle line of the second and fourth digits. The thigh-bone has no third trochanter. 

 The stomach shows a tendency to subdivision. The originally complete dentition gets gradually specialized 

 and reduced. The teats are abdominal and inguinal. Placenta diffuse. 



This order, now the most numerous after 

 the Rodents, presents similar phenomena to 

 those which we have observed in the previous 

 one. In it, if we consider only the members 

 now living, we in fact recognize two pretty 

 different series of forms, which would neces- 

 sitate a division into two orders, the rumi- 

 nants on the one hand, and the pigs or 

 many- toed ungulates on the other; but when 

 we enter into the details of the organization, 

 and especially also into those of fossil forms, 

 then we must acknowledge that the lines 

 of demarcation fall away one after the other, 

 and that even among the living forms these 

 limits are not so complete as those which 

 separate the tapirs and rhinoceroses from the 

 horses. Among the palaeontological remains 

 we find proofs of an evolution similar to that 

 which we have traced in the perissodactyles. 

 Out of the originally clumsy and heavy forms 

 with a complete dentition and at least four 

 toes touching the earth have at last arisen 

 slender, shapely forms with elegant limbs, 

 in which the toes are reduced to two and the 

 dentition is no longer complete. The many- 

 toed forms with complete dentition of our 

 present fauna approach more closely to the 

 ancestral stem-forms, from which have sprung, 

 as palaeontology proves, the two-toed forms 



with incomplete dentition, those, namely, 

 which have been called the Ruminants, on 

 account of a special function, while the others 

 may be called the Many-toed (Polydactyla). 



The predominant character of the Artio- 

 dactyla is that which is presented by the 

 structure of the feet, which always have the 

 toes clothed with hoofs, and which are 

 adapted only for locomotion. All these ani- 

 mals "divide the hoof," as the Bible says; in 

 other words, the toes are arranged in pairs, 

 and there are two equivalent widely separate 

 axes formed by the third and fourth digits. 

 The first or innermost digit is wanting even 

 in the ancestral forms, which have four almost 

 equal toes, with the corresponding meta- 

 carpal and metatarsal bones quite separate; 

 while both bones of the lower fore-limb and 

 hind-limb, that is, the radius and ulna in the 

 one case, and the tibia and fibula in the other 

 case, are likewise separate and attain an equal 

 degree of development. This structure of 

 the limbs has been preserved in the hippo- 

 potamus. The two lateral digits, the second 

 and the fourth, then get steadily reduced in 

 size in the general evolution of the group. 

 The two middle toes alone touch the ground ; 

 the two lateral ones are shorter, but still carry 

 false or accessory hoofs ; the two middle toes 



