94 A BOOK OP WHALES 



Sirenia, the resemblances which they exhibit to the 

 Cetacea by no means disappear. 



The bony framework of the head is perhaps the 

 part of the skeleton which shows most unlikeness 

 in the two groups. And this fact is not without 

 significance, for it is precisely in that region that 

 external influence would not play so strong a part 

 as it might well be supposed to do elsewhere. " The 

 skull," remarks Professor Zittel,* "shows not the 

 least resemblance to the Cetaceans." Nevertheless, 

 the .nasal bones are much shortened, though that is 

 a character found elsewhere. It is no use to give 

 any detailed analysis of the skull and comparison with 

 that of the whales. In the vertebral column the fusion 

 of the second and third vertebrse of the neck must 

 not be looked upon as being really a strong point 

 of likeness to whales, since in the Edentata the same 

 fusion occurs. More important, perhaps, as a likeness 

 is the thin character of the centra of those vertebrse 

 in Rhytina. The reduction in number of the ver- 

 tebrae of the lumbar region is paralleled in Inia, 

 which, as has been often remarked, would appear to 

 be an early type of whale. 



More striking as evidence of likeness between the 

 Sirenia and the Cetacea is the shortened sternum, and 

 the fewness of the ribs attached thereto. But here 

 again we may have to do with the need of powerful 

 respiratory movements in these diving animals. As 

 to the hind limb, it is instructive to notice that a pair 

 of hind limbs do not seem to be at all necessary to 

 swimming and diving creatures. 



* Handbitch der Palceontologic, Abth. I., Bd. iv. 



