ZOOLOGY 



number articulate with both 

 transverse processes and bodies 

 by distinct tubercles and heads. 

 The sternum varies in shape. 

 Sometimes it consists of a pre- 

 sternum and a series of several 

 sternebrse without xiphister- 

 num; sometimes (Fig. 1149) it 



FIG. 1149. Sternum of Rorqual (Balanojitera 

 musculus). (After Flower.) 



is a continuous plate of bone, 

 occasionally with median notches 

 or fontanelles. 



In the skull (Fig. 1150), the 

 brain-case is rounded, the jaws 

 greatly elongated, often unsym- 

 metrical. The parietal s (Pa) do 

 not meet in the middle line 

 above in most Cetacea, being- 

 separated by the supraoccipital 

 (SO.) and an interparietal (IP.)', 

 there is thus no sagittal suture. 

 A large supra-orbital plate is 

 developed from the frontal. 

 There are large and stout zygo- 

 matic processes of the squamosal, 

 but the jugals are extremely 

 small. In all the recent forms 

 the maxilla (Mx.) is very large 

 and extends backwards to over- 

 lap a good deal of the frontal, 

 and forwards nearly to the ex- 

 tremity of the snout ; while the 

 prem axillae (P. Mx.\ which are 



