ECOLOGY AND BIOLOGY OF THE PACIFIC WALRUS 



171 



N 



Fig. 106. General structure of the mouth of the Pacific walrus: left, anterior view with 

 teeth fully occluded and lips slighth' open; all flesh has been removed from the left side of 

 the skull and mandible; right, same head in medial sagittal section, with mouth slightly 

 open. N, external nares; Pm. premaxillar\- bone; Tg, tongue; M, mandible; and Tk, 

 tusk. The incisive surfaces of the mandible and premaxilla do not meet when the mouth 

 is closed to its maximum; only the ample lips can seal the oral entrance. (Adapted from 

 photos by F. H. Fay) 



The extraordinary "vacuum pump" of the walrus, by means of which this 

 suction is accomplished, is powered by very large lingual retractors and 

 depressors (m. styloglossus, hyoglossus, and genioglossus) , complemented by the 

 highly vaulted palate, the long, firmly ankylosed mandibular symphysis, and the 

 unusually powerful m. tensor veli palatini and m. huccinatorius, which provide 

 rigidity to the walls of the "cylinder." The tongue is the "piston." The small, rigid 

 oral aperture, complemented by ample, muscular lips, insure that the full effect 

 of the vacuum is exerted only on objects held in the incisive area at the front of 

 the mouth (Fig. 106). 



In his exploration of the sea floor in an area where walruses had been feeding, 

 S. W. Stoker (personal communication) observed that visibility was obscured not 

 only by low light intensity but by high turbidity near the bottom. Stoker and I 

 speculated that the turbidity^ was due to the activity of the walruses, stirring up 

 the sediments in the course of their search for food. The importance of tactile 

 organs for locating and identifying prey in such a dark, murky habitat was 

 incontrovertable. Also, the need for a swift, efficient method to remove 40 kg per 

 day of siphons and feet from the small mollusks that resided there was 



