SOME INTERNAL STRUCTURES 53 



Some other peculiarities of the skull bones of the 

 Cetacea are dealt with under the description of the 

 different families. 



THE SHOULDER GIRDLE 



The shoulder girdle of the whales consists of an 

 apparently single bone, which has a highly character- 

 istic form, liable to some range of variation. The 

 major part of this bone is formed of the scapula, 

 while a process directed forward is the coracoid, 

 more pronounced in the larger number of whales 

 than in any other among the higher mammalia. 

 The scapula is broad and flattened, but both the 

 breadth and the degree of flattening is not by any 

 means uniform. In the Sperm whale the bone is 

 gently concave. It is very much broader (i.e., longer 

 in an antero-posterior direction) in the Rorquals than 

 in the Right whales. Near to the anterior edge of 

 the blade-bone is a ridge, which ends in a particularly 

 long process the acromion. Only in the Megaptera 

 is this process, and also the coracoid process under- 

 lying it, markedly reduced. In Platanista there is 

 another abnormality of structure. The acromion co- 

 incides absolutely with the anterior margin of the 

 blade-bone, so that the ridge of the "spine" of the 

 scapula is quite absent as a distinct structure. It is 

 worthy of note that in Megaptera, which has the 

 longest flippers of all whales, the acromion and the 

 coracoid process should be reduced to a minimum or 

 even practically absent. 



