io8 



WHALES 



We have already seen that the Cetacean skeleton, unlike that of terres- 

 trial mammals, does not so much have to carry the entire weight of the 

 body, as to anchor the musculature. This function is very important, for 

 the muscles of a Blue Whale weigh roughly 40 tons, i.e. 40 per cent of the 

 animal's total weight, while the skeleton accounts for only 17 per cent. In 

 Fin and Sei Whales these proportions are respectively 45 per cent and 

 16 per cent, and 54 per cent and 13 per cent. Dolphins and porpoises, too, 

 have proportions of about this order, and it seems clear that muscles play 

 a predominant part in these animals. Sperm Whales, whose muscles make 

 up I o per cent of the body weight, are the only exceptions ; their special 

 position in the list is probably due to their large heads. 



The great mass of muscle which moves the tail and the flukes is thus 

 situated in the lumbar region. For here a whole system of long and 

 powerful tendons gradually fans out to become attached to each of the 

 various caudal vertebrae, which can therefore be moved separately. 

 Moreover, whole sections, such as the flukes, can be moved with respect 

 to the other sections, so that the fact that, during motion, the flukes make 

 an angle with the rest of the tail (see above) is not due to their passive 

 reaction to the pressure of the water as it is in the fish, but to an active 

 muscular exertion. Though the tendons are attached to the vertebrae of 

 the flukes, they are also joined to the complicated system of tough fibres 

 and lamellae of which the peculiar white connective tissue of the flukes is 

 built up. As early as 1883 the great German anatomist Roux made a 

 study of Cetacean flukes, and showed how complicated and how ingenious 

 the structure of these organs really is. It appears that whenever the tendons 

 exert a pull on the vertebrae of the flukes, the entire tissue system is 

 tensed, giving the flukes their characteristic shape and rigidity. 



A close examination of Figs. 66 and 67 will show that there are great 

 diflferences between Cetaceans, particularly in respect of the form of their 

 lumbar and anterior caudal vertebrae. In some species, e.g. Sperm Whales 

 and Ziphiids, the transverse processes of these vertebrae are short, the 

 spinous processes are long, and the metapophyses placed low. In dolphins 



Figure 65. Front view of thoracic vertebra of 

 a Little Piked Whale. 



-< SPINOUS PROCESS 



METAPOPHYSIS 

 NEURAL ARCH 



TRANSVERSE PROCESS 

 "CENTRUM 



