300 



THE VERTEBRATE ANIMALS 



two behind. Hawks and eagles are provided with strong talons 

 with which the prey is seized and killed. 



Adaptation for semiaquatic life is seen in plovers, herons, or 

 storks, where long legs and long toes enable the birds to seek their 

 food in soft mud among reeds or lily pads, or along sand flats. 

 True aquatic birds, on the other hand, are provided with webbed 

 toes. The foot of the common barnyard duck, for example, is 

 much like that of the alligator. In the ostrich and cassowary 

 the wings are not used for flight ; here the lower limbs have taken 

 up the function of rapid motion. 



Perching. The habit of perching is an interesting one. In 

 many perching birds the tendons of the leg and foot, which regulate 



the toes, are self-locking; while 

 asleep such birds hold themselves 

 perfectly. A certain part of the 

 ear, known as the semicircular ca- 

 nals, has to do with the function of 

 balancing. In the flamingoes and 

 other birds, which do not perch, 

 balancing appears to be automatic ; 

 thus the bird is able to sleep when 

 in an upright position. 



Tail. The tail is sometimes 

 used in balancing; its chief func- 

 tion, however, appears to be that 

 of a rudder during flight. Most 

 birds have under the skin of the 

 tail a large oil gland, whence comes 

 the supply of oil that is used in 

 waterproofing the feathers in preen- 

 ing. 



The Skeleton. The skeleton 

 combines lightness, flexibility, and 

 strength. Many bones are hollow 

 or have large spongy cavities. 

 The bones of the head and neck show many and varied adaptations 

 to the life that the bird leads. The vertebra which form the frame- 

 work of the neck are strong and flexible. They vary in shape and 



Skeleton of a fowl : C, clavicle ; CV, 

 cervical vertebrae ; K, keeled ster- 

 num ; PG, pelvic girdle ; PcG, bones 

 of pectoral girdle (except clavicle). 



