48 



THE HOESE IN HEALTH AND DISEASE 



Variations in Horses' Toes. — A single-toed mare has given birth to a foal 

 which liad an extra toe on each foot. This peculiarity is known as polydactyl- 

 ism and may be hereditary. This condition is often cited as an instance of 

 reversion. There is, however, no reason to believe that this is different in 

 type from cases of polydactylism in other animals. The occurrence of super- 



Fig, ft. — Polydactylism or supernumerary digits. The abnormality involves 

 both of the carjial joints. 



n\mierary digits is not infref|uont in man and is quite common in cats. The 

 illustration (Fig. (i) is that of a horse exhibited as a freak at the Wisconsin 

 State Fair in 1913. 



The metacarpal and digif;d regions of the horse afford the best example of 

 changes due to evolution. The earliest existing horse skeleton, recognized 



