162 AN ATTEMPT TO DESCRIBE THE ANIMALS THAT MADE 



feet to the ground, and by a sort of double hop, which produces a 

 series of tracks of a very dubious character. 



The regular alternation of the right and left foot, on each side 

 of the line of direction, is a most decisive indication of the biped 

 origin of a row of tracks. And usually the right and left foot can 

 be readily distinguished. In the pachydactylous tracks, the two 

 protuberances of the inner toe, while the outer one has four, settle 

 this point. When a fourth toe points backward, we know which 

 foot made the impression, because that toe is always on the inside. 

 So it is where it proceeds from a long heel. If the toes are curved, 

 the curvature of the middle toe is generally inward in bipeds ; that 

 is, when the toes curve to the left, it is the right foot, and vice 

 versa ; and, finally, a less certain mark to guide us is the relative 

 length of the toes, since the inner toe is almost always shortest. 

 This is less certain only because we cannot always determine which 

 toe is the shortest. 



The regular movement of a quadruped in walking or running, 

 not leaping, produces two nearly parallel rows of tracks, of the 

 character represented on Plate 19, fig. 1. Here, as the fore 

 foot is lifted up to advance, the hind foot is brought up nearly 

 to the same place ; and hence it is, that we have put unequal 

 intervals between the tracks. But some animals — the cat, for 

 instance — are frequently in the habit of bringing the hind foot 

 so exactly into the place just vacated by the fore one, that it 

 is only by careful examination, upon a long row of tracks, that 

 the double impression can be recognized ; and moreover, some 

 animals of this sort bring their tracks so nearly into a single line, 

 that a biped origin is readily ascribed to them. The sketch on 

 Plate 19, fig. 2, is not an exaggeration of some cases of this sort, 

 which have fallen under my notice. Here it is only the fifth im- 



