LOCOMOTION AND LOCOMOTORY ORGANS 



107 



Figure 64. Right view of the seven cervical vertebrae of a Blue and a Pilot Whale. In the 

 Blue Whale, the vertebrae are f airly short and independent ; in the Pilot Whale only the yth 

 cervical vertebra is free {it is shown separately in the figure) . ( Van Beneden and Gervais, 1880.) 



depress the tail. Large blood vessels, to which we shall return in Chapter 55 

 are found in the chevron canal, surrounded by chevron bones. The 

 vertebrae of the flukes have neither chevrons nor other processes. In con- 

 formity with the overall shape of the flukes, they are small bones flattened 

 vertically as well as laterally. 



We have seen that the neck, thorax, and abdomen of most Cetaceans 

 are fairly rigid. All this, too, must naturally be reflected in the structure 

 of the vertebral column, and moreover, in such a way that the mutual 

 mobility of any two successive vertebrae is restricted. And, in fact, inter- 

 vertebral joints and articulating processes (zygapophyses) are lacking in 

 the greater part of the vertebral column of many Cetaceans. In most 

 Baleen whales, in Sperm Whales and in Ziphiids they are only present 

 in the second to fourth thoracic vertebrae, and in Common Dolphins and 

 Porpoises they extend no farther back than the fifth to tenth vertebra. The 

 mutual mobility of the vertebrae, already greatly reduced by flattening 

 the ends of the vertebral bodies, is restricted further by the fact that the 

 metapophyses of the posterior thoracic, and of all, or certainly the 

 anterior, lumbar vertebrae, are so long that they embrace the spinous 

 process of the preceding vertebra (see Fig. 65) . Moreover, beneath the 

 centre runs a strongly developed ligament, the longitudinal ventral 

 ligament, whose main function it is to prevent the vertebral column 

 from sagging. In the caudal vertebrae, however, these restrictions are 

 absent, and hence they can be moved far more freely. 



