136 



WHALES 



Figure jj. Dorsal view of the 

 end of the trachea and bronchi of 

 a False Killer, ^ote the 

 eparterial bronchus. 



Figure 78. The left lung of a 

 cow, a Bottlenose Dolphin, and 

 a Fin Whale. The dotted area 

 indicates the particularly thin 

 section of the lung of the 

 Bottlenose Dolphin. 



themselves and at the thoracic cavity. As the neck in Cetaceans is 

 very short, they naturally have a very short trachea. In some dolphins 

 this wind-pipe is hardly 2 inches long, but in big whales its diameter 

 can be more than a foot, so that a small child could easily crawl through 

 it. Still, in view of the whale's size, this is by no means surprising. 

 It might be thought that a short trachea is a great advantage, since 

 the more air there is in the trachea, the greater is the dead space in 

 the pump system. Now, in porpoises the trachea does in fact represent no 

 more than 4 per cent of the lung capacity, but in Rorquals, with their 

 small lungs, the dead space represents 8 per cent, just as it does in 

 terrestrial mammals. 



In Cetaceans, the cartilage rings which support the trachea either 

 surround it completely or else have breaks here and there. Moreover, the 

 rings are sometimes fused with one another, so that the whole structure 

 looks more like a pitted cylinder than an annular cartilage system. At the 

 entrance of the thoracic cavity, the trachea branches into two bronchi, 

 supplying the left and the right lungs respectively -just as in all other 

 mammals. In Cetaceans, however, the trachea also divides into a third, 



