39+ STRUCTURE AND CLASSIFICATION OF BIRDS 



tip ; the hypapophyses die away on the fourth dorsal 

 vertebra. 



With regard to the caudal vertebrae, the most remarkable 

 fact is that vs^hile there is no pygostyle there is no rudi- 

 mentary state of affairs observable ; for the last few vertebrse 

 have greatly expanded transverse processes, which would not 

 move independently. Maesh thinks that ' the end of the tail 

 would move mainly as a whole. This would give great 

 power, similar to that in the beaver's tail or the flexible blade 

 of an oar.' 



As to the shoulder girdle, the scapula is in the same 

 straight line, or nearly so, with the coracoid ; it belongs, in 

 fact, to what Fuebeinger has termed the ' platycoracoidal ' 

 type, seen also in the Struthiones. But, contrary to what we 

 find in those birds, there is not a fusion between the cora- 

 coids and scapula in Hesperornis, and there is, moreover, a 

 complete pair of clavicles. The coracoid has a strong pro- 

 coracoidal process, and also a supra-coracoidal foramen, as in 

 various Struthiones. 



The two coracoids are widely removed at their articula- 

 tion with the sternum. The clavicles, though complete, 

 appear to have joined each other ventrally by a joint ; they 

 arise from the procoracoid. The sternum, which has articu- 

 lar surfaces for five ribs, has no keel. It is notched in the 

 middle line posteriorly, and is wider in front than behind. 

 The elongated form of the sternum is compared by Maesh 

 to that of TJria. The ribs have uncinate processes. 



The/o?-e limh of Hesperornis appears to have consisted 

 only of the humerus, as no other bones were discovered, and 

 as there were no distal facets for articulation with a radius 

 and ulna. 



The pelvis of Hesperornis in its general form resembles 

 that of Podiceps. The constituent bones are, however, 

 entirely free distally. The acetabulum is closed by bone, a 

 state of affairs only seen in the emu and to some extent in 

 Tinamus. 



The ischium has no processes tending upwards to the 

 ilium and downwards to the pubis, as in Struthiones. 



