338 THE VERTEBRATE SKELETON. 



it is extremely small also in Apteryx. Clavicles are generally 

 well developed in the Carinatae, and small ones are found 

 also in Hesperornis, and in Emeus and Cassowaries. In the 

 other living Ratitae and in Stringops they are absent. In 

 some Parrots, Owls and Toucans they do not meet one another 

 ventrally. Clavicles are especially stout in some of the birds 

 of prey. They do not generally touch the sternum, but some- 

 times, as in the Pelican (fig. 63, C), Adjutant and Frigate bird, 

 they are fused with it. 



In all Ratitae the scapula and coracoid lie almost in the 

 same straight line with one another, in the Carinatae they are 

 nearly at right angles to one another. 



ANTERIOR LIMB. 



In the wing of nearly all birds the ulna is thicker than the 

 radius, but in Arcliaeopteryx the two bones are equal in size. 

 In the wing of Archaeopteryx there are three long digits with 

 distinct metacarpals. In all other birds the digits are modi- 

 fied, the metacarpals being commonly fused and the phalanges 

 reduced in number. In Palamedea and some other birds the 

 metacarpus bears a bony outgrowth, which when sheathed in 

 horn forms a spur. 



In most of the Ratitae and in the extinct Dodo (Didus) 

 and Solitaire (Pezophaps} the wing is very small, but the 

 .usual parts are recognisable. In Hesperornis apparently only 

 the humerus is present ; in some Moas, in which the wing is 

 imperfectly known, the presence of the humerus is indicated 

 by traces of a glenoid cavity. In most Moas the wing is 

 apparently completely absent. As compared with those in other 

 Ratitae, the wings of the Ostrich and Rhea are well developed. 

 In the Ostrich (fig. 64, B) and Rhea, as in nearly all Carinatae, 

 the manus has three digits, but in Apteryx there is only a single 

 digit, the second. The Penguins (fig. 64, A) too among Cari- 

 natae have only two digits, but in their case it is the pollex 

 which is missing. In the Ostrich the third digit has two 

 phalanges, in all other living birds it has only one phalanx. 



