1 76 A BOOK OF WHALES 



It will be seen from what immediately follows that 

 in some respects the Platanistidae are the most 

 primitive of existing Odontocetes. 



The mode of attachment of the ribs to the dorsal 

 vertebrae has been used in the classification of the 

 Odontocetes. As a matter of fact there is an 

 interesting series of modifications in these attach- 

 ments which does away with any hard and fast lines 

 of classification, though to some extent the groups 

 can be defined from the facts. 



What we may consider in the meantime to be the 

 typical arrangement occurs in Dolphins ; in Orca 

 gladiator, for example, the first rib has both capitulum 

 and tuberculum ; the former is attached to the centrum 

 of the last cervical, the latter to the transverse process 

 of the first dorsal vertebra. The next six ribs are 

 similarly attached by two heads to the transverse 

 process of each vertebra and to the centrum of the 

 vertebra behind. The last five have but one head, 

 the tubercular, which is of course attached to the 

 transverse process of its vertebra. 



Kogia, though a Sperm whale, has many delphinoid 

 characters, upon which we shall comment later. The 

 first eight ribs have a double attachment, the capitulum 

 is inserted on to centrum of each vertebra, and the 

 tuberculum to transverse process of vertebra behind. 

 The next five are attached to processes of centrum 

 only, each to a longish process of the centrum. But 

 there is no real difference from what we find in 

 dolphins, for the process to which the last ribs are 

 attached gradually moves down the transverse process 



