164 AN ATTEilPT TO DESCRIBE THE ANIMALS THAT MADE 



Other means of distinguishing bipedal from quadrupedal tracks. 

 For in the latter the axis of the feet usually lies more oblique to 

 the line of direction, and they are more distant from it, than in the 

 former. In some of the tortoise tribe, for instance, the feet point 

 almost at right angles to the line of direction, and are very wide 

 apart. In this case, however, we have double rows of tracks, which 

 at once remove all doubt. 



Conclusion. — Such are the characters on which I rely to 

 discriminate and describe the animals that made the fossil foot- 

 marks. They depend for their value upon the principles of com- 

 parative anatomy and zoology. They assume that such relations 

 exist between the feet and general structure of animals, that, know- 

 ing the one, we can usually determine the other. I acknowledge 

 these relations to be sometimes too obscure to conduct us to an 

 infallible result. But the same is true in respect to most of the 

 parts of animals from which the comparative anatomist draws his 

 conclusions. We cannot, indeed, depend upon any one of the 

 characters derived from the feet to conduct us to certain results. 

 But when several conspire to the same end, we feel stronger con- 

 fidence in the conclusion. If applied to living animals, it seems to 

 me they would enable us to decide with a good degree of confi- 

 dence upon the following points : — 



1. Whether the animal is a biped or a quadruped. 



2. Whether vertebral or invertebral. 



3. To what class it belongs. 



4. To what order or family. Here, however, I think we 

 should often fail. 



5. To what genus. Here, also, I think we should not unfre- 

 quently confound different genera ; for the feet of many genera 

 are too nearly alike to be distinguished by their tracks. As ap- 



