500 



ZOOLOGY 



SECT. 



The sternum varies in shape. 

 Sometimes it consists of a pre- 

 sternum and a series of several 

 sternebrae without xiphisternum ; 

 sometimes (Fig. 1080) it is a con- 



FIG. 1080. Sternum of Roqual (Balcenoptera 

 musculus). (After Flower.) 



tinuous plate of bone, occasion- 

 ally with median notches or 

 fontanelles. 



In the skull (Fig. 1081) the 

 brain-case is rounded, the jaws 

 greatly elongated, often unsym- 

 metrical. The parietals (Pa.) do 

 not meet in the middle line 

 above, being separated by the 

 supra-occipital (SO.) with an 

 inter-parietal (IP.) ; there is thus 

 no sagittal suture. A large supra- 

 orbital plate is developed from 

 the frontal. There are large and 

 stout zygomatic processes of the 

 squamosal, but the jugals are ex- 

 tremely small. In all the recent 

 forms the maxilla (Mx.) is very 

 large and extends backwards to 

 overlap a good deal of the frontal, 

 and forwards nearly to the ex- 

 tremity of the snout : while the 

 premaxillse (P. MX.), which are 

 long narrow bones, bound but a 

 very small part of the oral border 

 of the upper jaw. The nasals 

 (Na.) are very small. The tym- 



