VERTEBRATA 



161 



(the external or " little " toe is always wanting) ; many 

 have three, the hallux, or "big " toe, being absent ; while 

 the ostrich has but two, answering to the third and 

 fourth. The normal number of phalanges, reckoning 

 from the hallux, is 2, 3, 4, 5. The toes always end in 

 claws. 



Birds have neither lips nor teeth, epiglottis nor dia- 

 phragm. The teeth are wanting, because a heavy mas- 

 ticating apparatus in 

 the head would be 

 unsuitable for flight. 

 The beak, crop, and 

 gizzard vary with the 

 food. It is a pecul- 

 iarity of all birds, 

 though not confined 

 to them, that the gen- 

 erative products and 

 the refuse of digestion 

 are all discharged 

 through one common 

 outlet. 



The sole organs of 

 prehension are the 

 beak and feet. The 

 circulation is double, 

 as in mammals, start- 

 ing from a four- 

 chambered heart (Fig. 273). Respiration is more com- 

 plete than in other vertebrates. The lungs are fixed, and 

 communicate with air sacs in various parts of the body, as 

 along the vertebral column, and also with the interior of 

 many bones, as the humerus and femur, which are usually 

 hollow and marrowless. 41 Both brain and cord are much 

 larger relatively than in reptiles (Fig. 338); the cranium 

 DODGE'S GEN. ZOOL. ,11 



deb 



FIG. 139. Principal parts of a bird: a, primaries; 

 6, secondaries; c, spurious wing; d, wing coverts; 

 e, tertiaries; _/, throat, or jugulum; g, chin; k, bill; 

 the meeting line between the two mandibles is the 

 commissure; the ridge on the upper mandible is 

 called culmen; that of the lower, gonys; the space 

 between the base of the upper mandible and the 

 eye is the lore; /*, forehead; k, crown; /, scapular 

 feathers; m, back; n, metatarsus, often called tarsus 

 or tarsometatarsus; o, abdomen; p, rump; q, upper 

 tail coverts; r, lower tail coverts. 



