OCR Text |
Show 336 DR. ST. GEORGE MIVART ON THE SKELETON OF [Apr. 2, Fig. 22. .ca Lateral aspect of sternum of Psittacus erithacus. ca. Costal angle. k. Keel. do. Defect of ossification. in. Manubrium. h. Muscular impression. pn. Pleurosteon. i. Intermuscular ridge. THE STERNUM. 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. fiavopalliatus the keel (k) projects preaxiad decidedly in front of the manubrium (m); the intermuscular ridge (i) on the side of the ventral surface of the sternum is slightly nearer to the pleurosteon; 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 tbe 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 (ni) 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 longitudinally. Its anterior margin, below the anterior groove, is concave preaxiad, while 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 |