MOUTH AND NOSE 



the intermandibular space, but not always (Monodon). The esophagus 

 is not noticeably reduced in diameter in this group, and the muscles for 

 deglutition, although strong and compact, are not remarkable. 



In the baleen whales the oral condition is very different. In this group 

 the mouth is of enormous size to allow for the unique feeding habits, 

 but the details differ considerably. In all forms the lower jaw is very 

 much broadened and bowed out, but the actual size of the mouth varies 

 so as properly to accommodate the baleen equipment. The mouth is 

 apparently larger, relatively speaking, in the humpback (Megaptera) 

 than in any of the true balaenopterid whales, and of fairly prodigeous 

 size in balaenids, for in the latter group it may be more capacious than 

 the thoracic and abdominal cavities combined (Flower and Lydekker, 

 1891). The reason for such oral disparity is evidently correlated with 

 food habits, but it is difficult to observe precisely the finer points of such 

 actions below the surface of the water, even upon the rare occasions 

 when one can approach sufficiently close to a feeding whale. It is 

 usually claimed that the mysticetes feed by swimming slowly along, the 

 rostrum level with the surface and the mandible dependent, the mouth 

 being wide open. It is not logical that the mouth should be held in this 

 position for long or at speed. Except possibly in the balaenids, if these 

 animals maintained the mouth ivide open while feeding upon small 

 food, the mandible would fall below the ends of the baleen plates, 

 so that all food would pass out of the mouth with the free flow of 

 water. Even such an experienced observer as Andrews (1909) is 

 noncommital in regard to the precise action of the mouth during feed- 

 ing. He has stated, however, that when feeding on shrimp both Megap- 

 tera and Balae)wptera turn upon the side, a posture which he has illus- 

 trated by photographs, and that when the jaws are closed the water 

 rushes out in streams. Regardless of the position of the body the pro- 

 cedure of a balaenopterid when shrimp are being consumed is presum- 

 ably for the animal to swim slowly through a swarm of the crustaceans 

 with the mouth opened for but a foot or two. Then only will the ba- 

 leen operate efficiently as a strainer, for the oral cavity will then act as 

 a closed filter, the water flowing away laterally through the baleen 

 fibers and leaving the shrimp in the mouth. The form of the mouth and 

 length of baleen plates in the balaenids (see figure 9) allows the mouth 

 to be opened much farther for best efficiency, though no one can say 

 why this is the case. 



If balaenopterids cannot find shrimp, they will feed on anchovies, or 

 if these are unavailable, then on smelts, or small mackerel. In other 



[79] 



