THE SOUTHERN BOTTLENOSED WHALE 



33 



STERNUM (Fig. 9) 



The sternum consists of three elements, the largest of which is the manubrium. The manubrium 

 is roughly rectangular in outline. The anterior emargination is semicircular and not so pronounced 

 as in the South Australian specimen. There is a small posterior notch, and the bone extends tailwards 

 on the right side of this to a greater extent than on the left. Asymmetry is also displayed on the 

 lateral margins. The facets for the first pair of sternal ribs are equally prominent, but whereas the 



Fig. 9. Sternum. ( x |.) 



Fig. 8. Ribs. ( x i.) 



right side bears a facet a little way posteriorly to the first there is no corresponding one on the left. 

 The external surface of the bone is convex and the internal concave. 



Anteriorly, the second sternal element has a median notch, on the right side of which the anterior 

 margin is a little way behind that on the left side. This asymmetry is repeated on the posterior margin, 

 in which, however, the notch is wanting. The lateral margins are shallowly concave, and at the 

 antero- and postero-lateral corners are facets for the appropriate sternal ribs. 



