346 



O. C. Marsh — Recent Polydactyle Horses. 



No example of extra digits has been observed by tlie writer 

 in any wild species of existing equine mammals of the old 

 world, or their immediate descendants, although it is evident 

 that such cases are probable, and careful observation would 

 doubtless bring them to light, especially if made in the native 

 haunts of those animals. 



Figure 10. — Left fore foot of recent Tapir (Tapirus indicus, Cuvier). 

 Figure 11. — Left hind foot of same animal. One fifth natural size. 



Many examples of polydactyle feet in the recent horse, 

 preserved in museums, have been cut off below the carpus or 

 tarsus, and thus the real significance of the extra digits has 

 been lost. The whole carpal and tarsal series, and the distal 

 ends, at least, of the bones above them, may be important 

 elements in the problem to be solved, if reversion or atavism 

 is to be considered. . 



In reviewing what is now known of the extra digits in the 

 existing horse, a few points are manifest, which could not have 

 been anticipated from previous knowledge of the perissodactyle 

 foot : 



(1) The presence of a first digit in the fore foot, represented 

 by a strong, styliform metacarpal supported by a well-developed 

 trapezium, with its usual articulation, in the same foot in which 

 the fifth digit is wanting. 



(2) The frequent appearance of the second digit as a distinct, 

 free toe in one or more feet, and the large size it attains, while 

 the other digits, except the third, are aborted or wanting. 



