THE ANIMAL KINGDOM 



453 



The caudal vertebrae are fused to form a pygostyle. Birds are 

 oviparous. The egg is large and is incubated by the parents. 

 The left oviduct and left ovary only are functional. 



That birds are undoubtedly descended from reptilian ancestors 

 is indicated by embryogeny and by the anatomy of extinct and 

 modern birds as well. Archaeopteryx (Fig. 271), a prehistoric 



Fig. 271. — Archaeopteryx macura, restored. The fossil remains of this link 

 between reptiles and birds was found in the Jurassic of Bavaria. The jaws do 

 not have a beak but are provided with teeth. The tail consists of about twenty 

 separate vertebrae to which feathers are attached on either side. Each wing 

 has three clawed fingers. Feathers are well developed on the wings and tail but 

 the head and other parts of the body are naked. The bones are without air 

 sacs. (After Romanes, Darwin and after Darwinism, Open Court Publishing 

 Company.) 



bird, had toothed jaws, a vertebrated tail (instead of a pygo- 

 style), and three clawed fingers on the wing, all of which are 

 reptilian rather than avian in character. In modern birds the 

 fingers are so reduced and modified as to be practically non- 

 existent, yet in the young of the hoactzin, a South American 

 bird, the forelimbs are provided with fingerlike claws which, 

 with the feet, are used in climbing about the branches of trees in 

 a lizardlike fashion before the bird learns to fly. 



