S8 THE PHYSICAL KINSHIP 



bird whose remains have yet been found, was 

 about the size of a crow. It had thirty-two teeth 

 and twenty caudal vertebrae. Two specimens 

 of it have been found in the Jurassic slates oi 

 Bavaria. One of these fossils is in the British 

 Museum, and the other in the Museum of Berlin. 

 Other toothed birds have been found fossil by 

 Dr. Mudge in the cretaceous chalk of North 

 America. These last had short, fan tails like 

 existing birds. 



From the toothed birds developed the beaked 

 birds the keel-breasted birds (the group to which 

 most existing birds belong) and the birds with 

 unkeeled breasts, i.e., the ostrich-like birds. The 

 ostrich-like birds are runners. They have rudi- 

 mentary wings, and the keel of the breast-bone, 

 which in the keel-breasted birds acts as a stay 

 for the attachment of the wing muscles, is lacking. 

 The ostrich-like birds are probably degenerate 

 flyers, the flying apparatus having become obsolete 

 through disuse. The feathers of birds are gene- 

 rally supposed to be the modified scales of 

 reptiles. 



The most .brilliant offspring of the reptiles were 

 the mammals, animals capable of a wider distribu- 

 tion over the face of the earth than the cold- 

 blooded reptiles, on account of their hair and their 

 warm blood. Cold-blooded animals of great size 

 are able to inhabit but a small zone of the existing 

 earth's surface the torrid belt. They cannot 

 house themselves during the seasons of cold, as 

 men can ; nor escape to the tropics on the wings 



