336 DB. ST. GEOBG£ MIVABT ON THE SKELELON OF [Apr. 2, 



Fig. 22. 



ca 



Lateral aspect of sternum of Psittacus eriikacus. 



CO. Costal angle. 



do. Defect of ossification. 



h. Muscular impression. 



i. Intermuscular ridge. 



k. Keel. 

 m. Manubrium. 

 pn. Pleurosteon. 



The Stebnum. 



The sternum (figs. 20, 21, & 22) has, in both species, the simple 

 form so common in the Parrots. The only differences I have 

 remarked are that in L. Jiavopalliatus the keel(i-) projects preaxiad 

 decidedly in front of the manubrium (m) ; the intermuscular ridge 

 {i) on the side of the ventral surface of the sternum is shghtly 

 nearer to the pleurosteou; the lateral margin behind the attachment 

 of the fifth sternal rib exceeds the length of the pleurosteon 

 measured from that point to the posterior margin of the attachment 

 of the first sternal rib. The surface of the sternum is also more 

 entire, the costal angle {ca) extends less dorsad relatively, while its 

 summit is antero-posteriorly broadened and the manubrium is 

 differently shaped. In P. erithacus it appears (m) rather pointed 

 towards its apex when viewed laterally. The anterior surface 

 presents a long vertical groove gradually tapering ventrad ; above 

 this, a hardly noticeable tendency to bifurcation may be detected. 

 Posteriorly it is transversely convex and not at all grooved longi- 

 tudinally. Its aaterior margin, below the anterior groove, is 

 concave preaxiad, whUe its posterior margin is concave postaxiad. 



The internal surface of the sternum presents at its preaxial end 

 two strongly marked transverse prominences just behind and 



^ii kU- 



