330 THE VERTEBRATE SKELETON. 



strainers. In Parrots and Hawks, on the other hand, nearly 

 the whole of the beak is hard. 



The toes and tarso-metatarsus are usually featherless and 

 are covered either with granular structures or with well- 

 formed scales. The toes are nearly always provided with 

 claws, and these vary in correlation with the character of the 

 beak. Claws 1 also sometimes occur on the manus. Thus 

 Archaeopteryx and some Ostriches and Rheas have claws on 

 all three digits. Most Ostriches and Rheas, and many Anseres 

 and birds of prey, have them on the first two digits, while the 

 Secretary bird (Gypogeranus) and many fowls, ducks, and birds 

 of prey, especially kestrels, have a claw only on the pollex. 

 In the Cassowary, Emeu, Apteryx and some Ostriches and 

 Rheas only the second digit is clawed. 



Claws should not be confounded with spurs, which are 

 conical horny structures developed on bony outgrowths of 

 the radial side of the carpus, metacarpus, or metatarsus. 

 They occur in a number of birds, but are most commonly 

 developed in gallinaceous birds, by which they are used for 

 fighting. A single spur occurs on the metacarpus in Mega- 

 podius, in Palamedea, in Parra jacana and in ffoplopterus 

 spinosus, the Spur-winged plover. The Derbiaii Screamer, 

 Chauna derbiana, has two metacarpal spurs, borne on the 

 first and second metacarpals. The Spur-winged goose, Plec- 

 tropterus gambensis, has a carpal spur borne on the radial 

 carpal. Metatarsal spurs are quite common. 



The male Solitaire (Pezophaps) has large bony excrescences 

 on the wrist which may, like spurs, have been sheathed in 

 horn and used for fighting. 



Teeth do not occur in any living birds, but conical teeth 

 imbedded in separate sockets are present in Archaeopteryx 

 and Ichthyornis, while in Hesperornis similar teeth occur im- 

 planted in continuous grooves in the mandibles and maxillae, 

 the premaxillae being toothless. 



1 W. K. Parker, Phil. Trans, vol. 179, p. 385, 1888 ; and Ibis, 1888, p. 124. 



