60 VARIATION 



but also as regards their articulation with the small bones above. 

 This foot is now on the road to becoming indifferently either a 

 two-toed or a one-toed form, depending upon whether n and v 

 reduce together or whether in takes the lead. 



In this connection certain intermediate or stranded forms are 

 of no little interest. For example, the elephant has five toes in 

 front, with four and sometimes three behind. The rhinoceros has 

 three both before and behind, but the extinct form often had 

 four. The tapir, which is also regarded as a remnant of ancient 

 life preserved until the present, has generally three toes, though 

 sometimes four and occasionally two. In any case, however, digit 

 in is largest and symmetrical in itself, showing affinity with the 

 line of descent that has developed the single-toed forms. 



The camel has two toes, while the nearly related chevrotain 

 has four, two being reduced. The hippopotamus has four short 

 toes, all down, all hoofed and partly webbed, showing affinity 

 with two-toed forms in that the symmetry is about a line drawn 

 between digits in and iv. This is the same plan as that of the 

 pig, except that in the latter the foot is more contracted, the 

 toes being flattened on the inside and the second pair not touch- 

 ing the ground. 



The kangaroo is anomalous, having five toes in front and in 

 general four behind, of which iv is much the largest ; v is small, 

 and ii and in are much reduced and incased in a common 

 integument. 



With this brief survey of specific differences in respect to 

 digits, certain individual deviations will have an added meaning. 

 Bateson gives us the following : 1 



1. Horse having supernumerary toe on inside of right fore foot, presum- 

 ably digit ir. It articulated with an extra bone in the lower row of the 

 carpus and was provided with a hoof, " convex both sides, resembling the 

 hoof of an ass" (see Fig. 1 1). 



2. Foal having two toes on each fore foot, otherwise normal. The car- 

 pus was in this case normal, but the extra toes were again borne on the 

 inside and were provided with a small hoof. 



3. Horse having a rudimentary digit on inside of left hind foot. This 

 again results from a slight development of digit n, which is the most com- 

 mon cause of polydactylism among horses. 



1 For variation in the feet of the horse, see Bateson, Materials, etc., pp. 360-372. 



