AQUATIC MAMMALS 



the air pressure from the lungs the more securely it should clasp the 

 larynx. Thus in these sperm whales at least, the air under pressure 

 may be forced from the lungs through the larynx and into the naso- 

 pharynx, thus pressing backward against the palatopharyngeus, closing 

 it the more tightly the greater the pressure, its suggested primary func- 

 tion then being to prevent the escape of air from the nasopharynx into 

 the mouth. Some such procedure may be necessary in these animals 

 in connection with the remarkable specialization of the right nasal 

 passage. 



H. C. Raven's preparations of Monodon, however, suggest that in this 

 animal conditions are different, for the palatopharyngeus is very heavy 

 and different from what Kernan and Schulte showed for Kogia, which 

 may be due to the fundamentally different narial equipment of these 

 two genera. It has usually been assumed that odontocetes at least may 

 breath while at the surface at the same time that they swallow, and that 

 when submerged they could not expel air through the mouth even if 

 they so wished. But in the Monodon and Physeter which H. C. Raven 

 (MS) dissected the larynx had been withdrawn and the epiglottis was in 

 the oropharynx. Accordingly this authority is of the opinion that the 

 larynx is thrust upward only temporarily for breathing or other pur- 

 pose. If this actually be the case then it is certain that the small sphincter 

 valves of the lungs act alone in preventing the escape of air, for the 

 formation of the epiglottis is such that it could offer but little hindrance 

 to the involuntary escape of air from the trachea into the mouth. 



It may be mentioned that an elongated larynx for thrusting the epi- 

 glottis into the nasopharynx is not in itself an aquatic adaptation, for it 

 is a character that is developed to a considerable extent in some mar- 

 supials and ungulates. The odontocete ancestry may have had this pro- 

 vision in moderate form to begin with, or else have evolved it completely 

 for their particular needs. 



The Mysticeti do not have this tubular type of larynx. Benham 

 (1901) and others have described it but from these and existing sketches 

 I am unable to envision the conditions with satisfactory clarity and I 

 neglected to investigate the matter myself when I had the opportunity. 

 Apparently the arytenoid body closes the epiglottis from above, the latter 

 is triangular rather than tubular, and of very moderate length. 



In a consideration of the precerebral portion of the nasal apparatus 

 of the Cetacea it must be remembered that in most mammals the muscles 

 of the face proper have a variety of functions to perform, such as in- 

 volved twitching of the nose, snarling of the lips, and a host of others 

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