EVOLUTION OF THE HORSE. 



monstrosities, like the sixth finger or toe which is some- 

 times found on the hand or foot of a human being, biit 

 are reversions to a former type. If, however, there are 

 two digits to one cannon bone, as sometimes happens 

 (Fig. 636), the abnormahty is one of dichotomy (splitting 

 into two), and not ; of reversion (or atavism). Fig. 637 

 shows a case of dichotomy in an ox, which had three. 



Fig. 635.— (4/"/«- Gaiidiy.) 

 Near fore leg of horse, 

 below the knee, with 

 second digit. 



instead of two, digits on each of its feet ; both fore and 

 hind. Professor Dunstan, M.R.C.V.S., to whom I am 

 indebted for this photograph, tells me that the abnor- 

 mality in this case appears to have been inherited, 

 because the dam had three digits on each of its fore feet. 

 The cannon bone of the ox, although it appears to be 

 only one bone, consists of the 3rd and 4th metacarpal 

 (or metatarsal) bones, which are separate during the early 



