1 78 A BOOK OF WHALES 



dorsal vertebra approach near together, and in the 

 next become completely fused. Hereafter the ribs 

 are attached by but one head, which is really, be it 

 observed, produced by a fusion between the capitulum 

 and tuberculum, not by a disappearance of one or the 

 other. 



Now in Physeter we have a trace of this arrange- 

 ment in the case of the tenth rib, for there the 

 transverse process is still present and fuses with the 

 central facet, though it takes no actual share in the 

 formation of the surface for the articulation of the rib. 

 In Kogia the facet on the centrum of vertebra 7, and 

 still more on vertebra 8, is a little raised, so that 

 here is left a trace of the arrangement obtaining in 

 Inia. In the dolphins it has totally vanished, so that 

 the fact that in the posterior ribs of the dolphins the 

 tubercular head alone, and in Kogia the capitular head 

 alone, remains is really not a fundamental difference, 

 but only one of degree. They are the two extremes 

 united by such intermediate forms as Physeter, and 

 the Ziphioids, both springing from some such original 

 form as is exemplified by Inia. We arrive therefore 

 at the conclusion that the transverse processes of the 

 lumbar vertebrae of these whales are compound 

 structures partly belonging to the neural arch and 

 partly to the centrum, but that as a rule one of these 

 elements preponderates, or is even the only one which 

 enters into their formation. 



This series of facts obviously leads to the inference 

 that in Inia we have a primitive form of Odontocete. 

 At any rate, the different disposition of the ribs in 



