348 0. C. Marsh — Recent Polydactyle Horses. 



in the hind foot of the same animal oifer another point of interest, 

 especially in connection with the corresponding carpal series. 



The hoofs of the extra digits of the modern horse vary 

 much in size and form at birth, and are subsequently affected 

 by the surroundings of the animal, and the care it receives. 

 If these hooflets are low enough to reach the ground, their 

 growth is checked by wear, like the large hoof, although in 

 less degree. As the main hoofs will become of abnormal 

 length, and more or less twisted, if the animal is confined to 

 soft, boggy ground, so the extra hoofs having no wear, and 

 receiving no pruning, often become much elongated and 

 curved, or by trimming may assume the form of a spur or 

 horn. The " horned horse from Texas," shown in outline in 

 figure 7, probably received some attention of this kind, as the 

 hooflets are much more pointed than any examined personally 

 by the writer. 



The cleft seen in the last phalanges, or hoof bones, of 

 Orqkvppus and other fossil equines, and occasionally present in 

 the coffin bone of the modern horse, is interesting, but of no 

 special significance. It certainly does not represent the union 

 of two digits, as frequently supposed, and sometimes asserted 

 by scientific writers. 



The tapir has the most primitive feet of existing peris- 

 sodactyles, and most like those of the early predecessors of the 

 horse. The feet of the Middle Eocene Orohipjms were, in 

 fact, very similar in structure, as will be seen by comparing the 

 man us and pes of each as shown in figures 10-11, and 16-17. 

 The living rhinoceros has feet of the same general type, but 

 less primitive (figures 12-13), while the modern horse, when 

 normal, has the extreme specialization of the monodactyle foot. 

 The frequent reversion to extra digits indicates a polydactyle 

 ancestry, which is now demonstrated by actual discovery. 



The terms Perissodactyla (odd-toed) and Artiodactyla (even- 

 toed) proposed by Owen, and now in general use to distinguish 

 two great groups of hoofed mammals, are misleading, and a 

 stumbling block to the lay reader, as well as to many popular 

 writers on science. The horse, tapir, and rhinoceros are the 

 only recent examples of the so-called perissodactyles, or odd- 

 toed ungulates, and the pig and peccary are certainly typical 

 artiodactyles. The tapir, however, has four toes in the front 

 foot, while the peccary has three only behind, and these 

 exceptions do not prove the rule, for the number of toes alone 

 has nothing to do with the profound distinctions separating 

 the two groups, at least in all recent forms. 



