98 THE MAIN CURRENTS OF ZOOLOGY 



mulated enabled Professor Henry F. Osborn, and 

 others, to separate the equus line from the other fossil 

 horses and to indicate the direct line of descent. 



From the zoological standpoint especial interest 

 has centered about the fossil remains of man and of 

 pre-humans that are throwing light on the question 

 of human lineage. 



The story of prehistoric man is imperfectly known, 

 although sporadic explorations have already accu- 

 mulated an interesting series of evidences bearing on 

 the subject, such as primitive stone implements of 

 human manufacture, crude sketches of extinct 

 animals by prehistoric artists, and fossil remains of 

 primeval man showing gradations in the shape and 

 the capacity of skulls. All these correlated sources 

 afford most convincing proofs of man's great antiq- 

 uity. He has left traces of his occupancy of the 

 earth, especially in central and southwestern Europe 

 and in England, long before the dawn of the historical 

 period. 



The prehistoric stone implements are found asso- 

 ciated with the bones of extinct animals in caves, and 

 imbedded in the strata of soil and gravel that have 

 remained undisturbed for many centuries. The stone 

 implements are of three grades: Neoliths, the more 



