THE SKULL 



the head is such that backward pressure of the water is appHed both to 

 the rostrum and the throat, so that when the animal is swimming the 

 upward and downward force of the water could easily be equalized by 

 slight adjustments in the posture of the head. And this position of 

 stability must be regarded as the normal one. In the balaenopterid type 

 the dorsum of the whole head is so flattened and so held horizontally 

 that any downward pressure by water resistance would be relatively 

 negligible. The gular region is more curved, however, off^ering more 

 resistance to the water when the mouth is closed and the throat expanded 

 slightly by force of the baleen plates. Hence in these whales the only 

 action of water resistance when the animal is swimming at speed with 



Figure 20. Left lateral view of the skull of the right whale, Eubalaena glacialis, 

 redrawn from Holder. 



the mouth closed is to push upward and backward against the throat, 

 forcing the head up and supporting it without the aid of muscular eff^ort. 

 If one subscribe to the belief, which I do not, that these whales ever 

 move to any extent while feeding with the mouth wide open, the chief 

 water force would be applied through the condyles of the mandible. 

 And water force applied to the baleen plates while the mouth is open 

 could be obviated by a slight tilting upward of the snout. In short, all 

 of the above mechanical forces save purely backward pressure at the 

 muzzle may be simply overcome by a slight tilting of the head in one 

 direction or another. The result is th^t the balaenopterid type of whale 

 is enabled consistently to hold its head in a more elevated position than 

 is practicable for the balaenid type. In fact it must do so. In the balaenid 



[135] 



