MOUTH AND NOSE 



the bronchioles with a diameter of less than 0.5 mm. are provided with 

 numerous muscular sphincter valves and that the terminal air sacs are 

 guarded by the same means, as discussed more fully in the last chapter. 

 Heretofore investigators have been obliged to consider the possible 

 means whereby the nasal, or laryngeal, equipment of the Cetacea was 

 enabled to prevent the escape of air from the lungs under the enormous 

 pressure to which the animal is subjected during deep dives. Wislocki's 

 discovery puts an entirely different aspect on the matter, however. 

 Although the individual sphincters of the bronchioles may be assumed 

 to be relatively feeble in action, the amount of air which each imprisons 

 is so minute, and the valves occur in such prodigious numbers, that 

 this equipment alone seems entirely adequate to prevent the escape of 

 air even into the esophagus against the wishes of the animal. Pre- 

 sumably these valves close at the end of inspiration and open at the 

 initiation of expiration, and it is reasonable to assume that their presence 

 is characteristic of all Cetacea. The simultaneous relaxation of these 

 small sphincter muscles at the same time that the nostrils are opened 

 would account for the way in which the air, imprisoned in the lungs 

 under the pressure applied by the relaxed thorax plus the pressure of 

 the surrounding water, rushes forth with a veritable pop. But there 

 is no reason for believing that bronchial sphincter valves must remain 

 closed between breaths, and the animals may at times inflate a part of 

 the nasopharynx before the nose is actually opened, as I have been led 

 to believe by watching the escape just preceding expiration of small 

 bubbles of air around the external slit of the blowhole. 



In the Odontoceti the larynx is prolonged in a tube-like manner, 

 projecting the epiglottis into the nasopharynx, and this may be closely, 

 clasped by the soft palatopharyngeus muscle. This is quite remarkably 

 developed in the Physeteridae and Kogidae especially, in which the naso- 

 pharynx branches from the oropharynx upon the side and the larynx 

 is correspondingly situated. Lillie (1910) stated that the latter was 

 situated upon the left side in two specimens of cachalot. Raven (MS) 

 makes the same statement, as well as Kernan and Schulte (1918) in 

 the case of Kogia; and the dissimilarity in size of the choanae is un- 

 doubtedly the precise reason for the laryngeal asymmetry. 



Kernan and Schulte have shown the pharyngeal region of Kogia 

 (fig. 12) to good advantage. They said that the conditions are such 

 as to prevent the entrance of water from the mouth into the nasal 

 passage, and this may be a superficial function also, but the construc- 

 tion of the arc of the palatopharyngeus is clearly such that the greater 



[91] 



