RESPIRATION 



149 



complete separation between the air and food passages, the question 

 remains why such a strict separation was needed in the first place. The 

 great eighteenth-century Dutch anatomist, Petrus Camper, who devoted 

 a great deal of attention to the structure of Cetaceans, pointed out that it 

 enabled the animals to breathe and swallow simultaneously. His explana- 

 tion has ever since been repeated by a host of authors and would sound 

 feasible, were it not that Boenninghaus (1903) and other authors have 

 pointed out that there is really no need for such a mechanism in animals 

 which breathe exclusively above the surface and swallow their food 

 exclusively below. An alternative explanation might be that by sealing 

 off the trachea while food is ingested, air is prevented from escaping 

 through the mouth, or from going down the oesophagus. But this explana- 

 tion, too, will have to be rejected, for we know that man can swallow 

 fluids and solids underwater without any adverse effects. And aquatic 

 mammals (Mysticetes with their 'normal' throat and larynx included) 



Figure 86. Longitudinal section through the head of (a) a horse and (b) a porpoise, to show 

 the position oj the larynx and the structure of the throat and nasal passage. N = nasal passage ; 

 H = hard palate ; S = soft palate; A = annular muscle, which surrounds the beak of the 

 epiglottis of the porpoise ; T = tongue; E = epiglottis; A = arytenoid cartilage ; Tr = 

 trachea; = oesophagus; B = brain {and also - in the porpoise - upper jaw). {Partly after 



Rawitz, 1900.) 



