118 THE THEORY OF EVOLUTION 



animals with very long and slender legs, evidently 

 swift runners. The other series, the so-called "gi- 

 raffe-camels," terminated in the upper Miocene; 

 these were browsers and display an increasing stat- 

 ure, especially in the length of the neck and fore 

 limbs. They adapted themselves to the growing 

 aridity of the western plains. 



Finally, may be mentioned an example from the 

 reptiles. The pre-eminently Mesozoic group of 

 reptiles known as the Dinosaurs has been made 

 quite familiar to the public by our great museums, 

 notably the American Museum in New York, the 

 National Museum in Washington, and the Carnegie 

 Museum in Pittsburgh. In the latter part of the 

 Cretaceous period, North America had a remarkable 

 family of Dinosaurs, harmless, plant-eating and 

 quadrupedal monsters. Though inoffensive, they 

 were well provided for defence, having three long 

 and sharp horns, one on the nose, like that of a rhi- 

 noceros, and one over each eye. The neck was pro- 

 tected by an enormous frill of solid bone, growing 

 out from the skull and reaching back to the 

 shoulders. The family may be traced far back 

 through the Cretaceous, the animals becoming 

 smaller and the horns shorter as we go back in 

 time, and the neck-shield becoming a mere outline 

 framework. When sufficient well-preserved material, 

 leading through long periods of time, can be ob- 

 tained, the result is always suggestive of a gradual 

 development. 



