LOCOMOTION AND LOCOMOTORY ORGANS IO9 



and porpoises, the transverse processes are long and the metapophyses 

 placed high, particularly in the posterior lumbar and the anterior caudal 

 regions. In these regions, the spinous processes incline forward, while those 

 of the first group incline backwards just like all their other spinous 

 processes. The big whales share the last two characteristics with the first 

 group, and the long transverse processes with the second group. It is very 

 difficult to enter into a detailed explanation of this phenomenon, because 

 to do so would involve giving a full account of the structure of the muscles 

 (see Slijper, 1946). Moreover, it is far from clear in what way the differ- 

 ences are connected with the animals' respective methods of propulsion. 

 In any case the shifting upward of the mammillary processes of the posterior 

 lumbar and anterior caudal region in porpoises and dolphins gives a 

 longer lever arm to the muscles attached to these processes. Consequently, 

 in porpoises and dolphins these muscles can work with a higher degree 

 of efficiency than in the other Cetaceans (Slijper, i960). 



As we stand on the deck of the factory ship and watch the heavy bone- 

 saws chewing through vertebrae, jaws and other bone, we cannot help 

 being astonished by the lightness of the material. Now, a whale's bones 

 consist of only a very thin shell of compact bone, the rest being made up 

 of thin bony bars with large spaces between them. This gives the bone a 

 spongy structure. Spongy bone is found also in all terrestrial mammals, 

 but there it is surrounded by a inuch thicker shell of compact bone. 

 Consequently the bones are very much heavier. Now the bones of terres- 

 trial animals have to bear their owners' entire weight, while aquatic 

 animals are supported by the water - hence the difference. 



All bones have the cavities in their spongy part filled with bone marrow. 

 The skeletons of young animals contain red bone marrow, a vascular soft 

 tissue in which the red and white blood corpuscles are formed. In the 

 course of development, however, most of the red marrow is replaced by 

 yellow marrow. In the vertebral column this piocess starts simultaneously 

 from the cervical and the caudal vertebrae, until red marrow is restricted 

 to the thoracic vertebrae only and, here and there, to the ribs. Yellow bone 

 marrow consists entirely of fatty tissue, and fatty tissue is also found in 

 red bone marrow, though to a much smaller extent. For this reason, oil is 

 obtained not only from the blubber of a whale but from its bones as well. 

 The fat content of the skeleton is 51 per cent - 84 per cent in the head, 

 a maximum of 24 per cent in vertebrae containing red bone marrow, and 

 32-68 per cent in vertebrae containing yellow marrow, and in other parts 

 of the skeleton. The bones therefore contribute a third of a whale's total 

 oil yield. 



Because of this large proportion of fat in the skeleton and also because 

 of the presence of large quantities of blubber, the specific gravity of 



