40 A BOOK OF WHALES 



looking like two ribs melted together, and that one 

 part of this double rib is attached to the last cervical 

 vertebra. This looks like a commencing dropping 

 out of the last cervical vertebra from its own proper 

 series ; it has been partly, at any rate, transferred 

 to the ensuing dorsal row. Another Sirenian feature 

 in the cervical vertebrae of the whales is the slender- 

 ness of the cervical series. This is seen not in the 

 Manatee, but in the recently extinct Rhytina of 

 Behring's Straits ; in that animal, however, the 

 vertebrae are not in the least decree fused. 



o 



In all mammals, with the exception of the whales, 

 the atlas is peculiar in that its centrum has broken 

 loose, and has attached itself to the following vertebrae, 

 the axis or epistopheus, from whose centrum it pro- 

 jects as the "odontoid process." In whales, as a rule, 

 this process is entirely wanting, but it is a significant 

 fact that the most considerable rudiments of it exist 

 in Platanista, and among the Platanistidae, upon 

 whose probably basal position among the Cetacea 

 we have already commented. The dorsal vertebrae 

 among these animals are of course those which bear 

 ribs, and their number varies much from species to 

 species, or from genus to genus. Nine to sixteen 

 are the limits of variation. The curious divergences 

 in the mode of articulation of the ribs serve to divide 

 the Cetacea; and under the description of the Sperm 

 whale, the Inia, and some other types, the differences 

 are dealt with. It has been pointed out that the 

 Cetacea differ from the Sirenia by the fact that the 

 latter have but few lumbar vertebrae, while in the 



