AQUATIC MAMMALS 



markable third sheet — Schulte's longitudinal muscle of the ventral 

 pouch — which may be either a superficial and extraordinary division of 

 the mylohyoid, or an equally astonishing platyspia. The action of 

 these three is undoubtedly assisted by what seems to be the digastric, 

 specialized for this purpose and continuing caudad onto the sternum. 

 It is interesting to note that the caudal limit of the long gular muscle 

 (either mylohyoid or platysma) coincides exactly with the extent of 

 the external plicae. 



The feeding actions, then, of those whales which have gular fur- 

 rows is apparently as follows. When the mouth is opened for the 

 purpose of securing food while the animal is slowly swimming, the 

 inrush of water distends the gular region (as noted by Lillie, 1910), 

 which is abundantly allowed for by the furrows and elasticity of the 

 musculature involved. Then, when the whale wishes to swallow what 

 it has captured, the weak tongue lies quiescent but the specialized gular 

 musculature, including the digastric, contracts in the powerful way for 

 which it is fitted, expelling the water from the mouth and restoring 

 the throat and its plicae to their normal, static state of tone. The con- 

 ditions occurring clearly indicate that this is fact — not theory. 



Of passing interest here is the presence upon the under side of the 

 rostrum, near its tip, in the mysticetes of a pair of shallow pits which, 

 in a specimen of Balaenoptera physalus, Lillie (1910) found led into 

 two narrow tubes which ended blindly about two inches from their 

 mouths. These have been termed naso-vomerine organs and are popu- 

 larly believed to be the vestiges of Jacobson's organs, now separated 

 from the nostrils by a distance as much as ten feet. 



The esophagus of the Odontoceti may be said to be of normal size, 

 but that of the Mysticeti is remarkable for its small diameter. That of 

 a finback of 70 feet was not larger than five inches at the most, and 

 down its length was a close-ranked procession, in single file, of foot 

 long mackeral, all headed to join the host of their fellows in the huge 

 stomach. The latter is complex, and even more so in odontocetes. 



The teeth in aquatic mammals as in other sorts have developed to 

 conform to the character of the food consumed and the manner of 

 obtaining it, and as most aquatic mammals feed chiefly upon fish, the 

 usual tendency is for the teeth to become simplified into sharp points 

 for the grasping of slippery prey. 



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