LOCOMOTION AND LOCOMOTORY ORGANS 



103 



Figure 60. Stass's experiment for recording the motions of the flukes in a swimming dolphin. 



{Stass, 1936.) 



Figure 61. Experiments with a 3 feet 6 inch porpoise to determine the vertical mobility of 

 various parts of the body. {Slijper, 1936.) 



consists of two rounded prominences, enables the whale to 'nod' but not 

 to shake its head, i.e. to turn the head about its own axis. Even so, the 

 head can be inclined sideways, for the joint acts as a kind of neck, though 

 not sufficiently to enable the whale to look back. 



The reason why whales and dolphins cannot shake their heads is the 

 a])sence of a joint between the atlas and the axis (the second cervical 

 vertebi'a), and the great compression of the other cervical vertebrae. 

 The extent of the compression (and the consequent short neck) is best 



