B 



CHAPTER 29 



Class Aves. Birds 



iRDS are considered the most interesting 

 of all animals. This is largely due to their 

 beautiful and varied colors, their pleasing 

 songs and call notes, their interesting be- 

 havior, their marvellous powers of flight, 

 their mysterious migrations, and their many 

 fascinating activities associated with their 

 nests, eggs, and young. Bird clubs, which 

 have arisen all over the country, and the 

 large numbers of birds sold in pet shops are 

 evidences of their popular appeal. 



Because birds have reptilian origin, some 

 have called them glorified reptiles. Birds 

 have reptilian scales on their legs; and the 

 earliest ones, which we know only from fos- 

 sils, had reptilian teeth, 



THE COMMON PIGEON 



The common pigeons have been derived 

 from the rock dove which ranges from 

 Europe through the Mediterranean coun- 

 tries to central Asia and China. The pigeon 

 is much used for studies of bird anatomy, 

 not only because of its convenient size and 

 availabihty, but also because it so well illus- 

 trates the many adaptations for life in the 

 air, such as feathers, wings, hollow bones, 

 and the rigid trunk skeleton. 



External features 



The body of the pigeon is spindle-shaped 

 and therefore adapted for rapid movement 

 through the air. Three regions may be rec- 

 ognized: head, neck, and trunk. The head 

 is prolonged in front into a pointed horny 

 bill, at the base of which is a patch of naked 

 swollen skin, the cere. Between the bill and 

 the cere are the two oblique, slitlike nostrils 

 (Fig. 306). On either side is an eye which 

 is provided with upper and lower lids, and 

 with a well-developed third eyelid or nictitat- 

 ing membrane (Fig. 434). The third eyelid 

 can be drawn across the eyeball from the 

 anterior corner. Below and behind each eye 

 is an external ear opening which leads to the 

 tympanic cavity. 



432 



