402 



ZOOLOGY 



SECT. XIII 



characters between Ratitse and Carinata?, but, as with the 

 sternum, the differences are adaptive and not of phylogenetic 

 significance. In most Carinatse both coracoid and scapula are 

 large and united with one another by ligament ; the coracoid 

 has an acrocoracoid and the scapula an acromian process ; the 

 coraco-scapular angle is acute ; and there is a furcula. In the 

 Ratitse the coracoid (Fig. 1006, cor.) and scapula (scp.) are much 



reduced in proportional size and 

 are ankylosed with one another : 

 the acrocoracoid (acr. cor.) and acro- 

 mion (acr.) processes are reduced or 

 absent; the coraco-scapular angle 

 approaches two right angles: and 

 there is no furcula, although separ- 

 ate vestiges of clavicles are present 

 in the Emu and Cassowary. In 

 some of the Moas (Pachyornis, &c.) 

 the shoulder-girdle is wholly ab- 

 sent. But, as in the case of the 

 sternum, the distinction is not 

 absolute. In Hesperornis, the Dodo, 

 the Solitaire, Aptornis, Notornis, 

 Ocydromus, and Cnemiornis the 

 bones of the shoulder-girdle are 

 proportionally small, the coraco- 

 scapular angle exceeds 90, and 

 in some cases, such as certain 

 Parrakeets and Owls, the furcula is 



feeble, or represented by paired vestiges, or absent. Curiously 

 enough, considering that increase in the coraco-scapular angle is 

 usually correlated with diminished powers of flight, it also 

 slightly exceeds 90 in the Albatross and some of its allies. 



In most adult Birds the procoracoid is reduced to a process on 

 the dorsal end of the coracoid, but in the Ostrich and in the 

 embryo of Apteryx it is well developed and separated by a 

 fenestra from the coracoid. A small bone, the accessory scapula, 

 is sometimes found on the outer side of the shoulder joint. 



The variations in the structure of the wing are mostly matters 

 of proportion, but a remarkable flattening of all the bones is very 

 characteristic of Penguins (Fig. 1002 bis), which are further dis- 

 tinguished by the presence of a sesamoid bone, the patella ulnaris, 

 taking the place of the olecranon process. In the Emu and Kiwi the 

 first and third digits of the normal wing have atrophied during de- 

 velopment, the middle one alone remaining. In the Moas (Fig. 1007) 

 no trace of a wing has been found, and in one species only is there 

 even a trace of the glenoid cavity. In the embryos of several 

 Birds an additional digit has been found on the ulnar or postaxial 



FIG. 1006. Apteryx mantelli. The 

 left shoulder-girdle. A, anterior ; B, 

 lateral (outer) surface, acr. acromion ; 

 acr. cor. acrocoracoid ; cor. coracoid ; 

 ffl. glenoid cavity : pr. cor. Ig. pro-cora- 

 coid reduced to a ligament ; scp. 

 scapula. (After T. J. Parker.) 



