274 MR. W. P. PTCEAET ON THE MORPHOLOGY AND 



C. Sternum (fig. 4, p. 217) and Pectoral Arciii. 



The sternal plate is keelless ; the coracoid anchyloses with the scapula, and lacks the acro- 

 coracoid, the coraco-seapular angle is very wide ; fuvcula vestigial or absent. 



A. Coracoid grooves not widely separated. 



n. Metasternum pointed, no posterior lateral processes ; pro-coracoid not 



forming a distinct bar. 



a'. Coracoid grooves and bases of coracoids overlapping ; anterior lateral 



process long, directed upwards and backwards ; a pair of short recurved 



processes lying on the anterior sternal border between the anterior 



lateral processes ; with vestigial clavicles ; sternal plate nearly as broad 



as long ; coracoid longer than broad Dromceus. 



b'. Coracoid grooves not overlapping ; anterior lateral processes of sternum 

 short or olxsolete ; no clavicles ; sternal plate much longer than broad; 



coracoid as broad as long Casuarius. 



b. Metasternum more or less pointed, with large posterior lateral processes ; 

 pro-coracoid of great size, forming a distinct bar of bone ; body of the 

 sternum with a conspicuous ventral prominence ; no clavicles ; articular 

 surfaces for ribs of great width Struthio. 



B. Coracoid grooves widely separated. 



a. Corpus sterni basin-shaped with a marked ventral prominence ; posterior 



lateral processes absent ; anterior lateral processes conspicuous, each with 

 a large pneumatic aperture at the base ; articular surfaces for ribs 

 crowded together immediately behind the anterior lateral processes; 

 coracoid grooves at the base of the anterior lateral processes and separated 

 one from another by the wide emarginate body of the anterior border of 

 the sternum ; coracoids long and slender ; pre-coracoid relatively small . Rhea. 



b. Sternal plate flat, slightly or not at all pneumatic ; metastcrnal and posterior 



lateral processes always present ; facets for ribs not separated by deep 



pneumatic pits. 



a'. Articular facets for ribs widely spaced, and lying entirely behind the 



anterior lateral processes, and not separated by deep pneumatic pits ; 



coracoid neaily as broad as long ; pre-coracoid not conspicuous . . . Apteryx. 



b'. Facets for ribs crowded, few in number, and partly underlying the base 



of the anterior lateral processes ; coracoid extremely reduced . . . Dinornithidce. 



C. Sternal plate flat, pneumatic ; metasternal clement wanting ; facets for ribs 



separated by deep pits ; sternal plate exceedingly narrow from before 



backwards jEpyornis. 



' The sternum and pectoral arch of the Cri/iiftiri will be found described on pp. 221 & 263. 



