AVES 



263 



tilian habit of shedding theirs in great flakes, with feathers 

 attached."^ 



General Structure.— The skull (Fig. 2U) is thin; the bill or 

 horny beak varies much according to its use; and there is, as in 

 reptiles, only one occipital condyle. The neck is long and flex- 

 ible. In different kinds of birds, the number of neck vertebrae 

 varies from eight to twenty-four. 



The wings are adapted for flight in our birds. While the 

 ostrich cannot fly, its rudimentary wings are compensated for 

 by its very strong legs, which are adapted for rapid running. 

 No other animal has wings of the same structure as a bird's. 

 The characteristic structure of the wing-bones is the hand. It 

 is comparable with the human hand. 



Fig. 214. — Skull of parrot: 22, Premaxillary bone ensheathed in horn; 

 15, nasal bones; v, mandible, the end sheathed with horn; I, malosquamosal 

 zygomatic style or maxillojugal bar; g, postfrontal bone; o, lacrimal 

 bone; n, nostril, showing also the articulation of the nasopremaxillary 

 bone; e, quadrate bone; m, orbit; 1, occipital bone. (After Owen.) 



The legs and feet (Fig. 215) of birds are adapted for running, 

 scratching, swimming, or perching. Note the position of the 

 thigh (femur) on the side of a bird. Do you see any advantage 

 of such a position? Distally the femur or thigh is joined to the 

 tibiotarsus and the fibula, which is found partially united with the 

 tibiotarsus. The proximal row of tarsal bones unites with the 

 distal end of the tibia, hence the name tibiotarsus or ''drum- 

 stick" in the chicken. The distal row of tarsal bones unites with 

 the metatarsal bones to form the tarsometatarsus or simply the 

 tarsus, which bears the usually four-clawed toes. One toe is 

 generally directed backward and three forward. 



Where is the knee in the bird? The ankle? Do you see any 



1 Baskett, " Story of the Birds," p. 33. 



