THE ORIGIN OF MAN 65 



saurus is perhaps its extremely small brain, the 

 estimated weight of which is but two and a half 

 ounces. They were very stupid, depending for 

 defense upon the automatic control of the muscles 

 after the feeble glimmer of thought had given 

 the initial impulse. The final group of plant 

 feeders, the Ceratopsia or horned dinosaurs mark 

 the culmination of medieval time. These forms 

 had a huge head upon which were horns two, 

 three or five in number, borne upon the nose or 

 above the eyes. The neck was protected by a 

 wide spreading flange of massive bone with ser- 

 rate edges and invested in a close fitting covering 

 of a horny substance. The animals fought as a 

 rhinoceros might by charging and impaling its 

 enemy with a sweeping upward thrust of its head. 

 It is thought that the bird-footed dinosaurs and 

 the birds were derived from the same reptilian 

 stock, as the structure of the shoulders and hip 

 bones and the ankle joints are extraordinarily 

 like those of the birds, and that in the birds the 



