RESPIRATION 



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smaller, bronchus (Fig. 77) which supplies the apical part of the right 

 lung. A similar extra bronchus is also to be found in all Artiodactyles 

 (with the exception of the camel and the llama) ; thus cattle, sheep, deer, 

 and so on, are once again shown to be close relatives of the Cetaceans 

 (see Chapter 2). 



In most mammals, the lungs, viewed laterally, look like a triangle with 

 the apex at the under side. Dolphins have retained this triangular shape 

 to some extent, though the ventrally placed apex looks extraordinarily 

 thin and contains a minimum of lung tissue. Most of that tissue is found 

 on the dorsal side of the thoracic cavity, and this phenomenon is even 

 more marked in Bottlenose Whales, Sperm Whales and Rorquals (Fig. 

 78), whose lungs are long, fairly flat and even more dorsally placed 

 (Fig. 79). Similar lung characteristics are also found in sea-cows, and, 

 although to a lesser extent, in seals and sea-lions, and must clearly be 

 considered adaptations to aquatic stability. We have seen in Chapter 2 

 that the higher the light, air-filled lungs are placed, and the lower the heavy 

 heart and liver, the greater the animal's stability in the water. 



As a consequence, the thorax, too, shows characteristic differences from 

 that of terrestrial mammals. A great many authors, not only of elementary 

 but also of advanced textbooks, have made contradictory statements on 

 this subject, and while I do not wish to take issue with them in detail, 



Figure yg. Differences in the position and form 

 of the lungs and the angle of the diaphragm 

 between {a) a Fin Whale and (b) a horse. 



