640 DR. C. F. SONNTAG ON THE COMPARATIVE ANATOMY 



The tongues of the Oclontoceti diflfer greatly from those of the 

 Mystacoceti, and both differ considerably from those of the other 

 mammalian orders. Some are so simple that they resemble the 

 tongues of fishes. 



Size : — In many Cetacea the tongue fills the space between 

 the halves of the mandible, but it does not do so in the ISTarwhal 

 {Monodon monoceros), Balcenoptera borealis (29), and Delphina- 

 pterus leucas. Barclay (2) showed that the food must pass far back 

 to reach the tongue, if it is an organ of taste in the latter. In 

 Balmnoptera hoop)s (10) it forms a large mass, projecting upwards 

 between the baleen plates like an intermolar eminence. The 

 bulk may be so increased by gaseous decomposition after death 

 that the tongue protrudes from the mouth. This protrusion, 

 howevei", does not take place in the Odontocete tongue. 



Consistence : — In the Odontoceti the tongue is firm, hard and 

 muscular, and the upper surface feels like parchment. In the 

 Mystacoceti, on the other hand, it is soft, from the presence of a 

 large amount of oil or fat which, according to Owen (27), sepa- 

 rates the mucous membrane from the muscles. Schulte (29) has 

 also shown that masses of fat sej)arate the musculi genioglossi in 

 Balcenoptera horealis. The oil will exude from the cut surface 

 of the tongue for a long period in preserved specimens. Some 

 have, in fact, likened the tongue to a sac of blubber, Rawitz (28) 

 and Eschricht (13) described the fat in adult animals, and 

 Kiikenthal (21) saw it in a 11 7*5 cm. foetus of Balcenoptera 

 musculus. 



Mobility : — John Hunter (20) showed that the tongues of the 

 Odontoceti are more muscular and mobile than those of the 

 Mystacoceti, and attributed the difference to the methods of 

 feeding. In the former they are organs of prehension, but they 

 are passive in the latter, for the food flows into the open mouth. 

 Scoresby (31) described the mode of feeding in Balcena mysticetus 

 as follows : — "When the whale feeds, it swims with considerable 

 velocity under water, with its mouth wide open ; the water enters 

 by the fore part, but is poured out again at the sides, and the 

 food is entangled and sifted, as it were, by the whalebone, which 

 does not allow anything to escape." 



In the Odontoceti the mobility varies. In Orcella hrevirostris 

 (1) it is great, for the free part extends back as far as the fourth 

 interdental space. In Platanista gangetica the apex is bound to 

 the mandibular symphysis by a fold of mucosa, but the edges ai-e 

 free and mobile. The animal is blind and burrows in the mud 

 at the bottom of rivers for small fishes and Crustacea, which con- 

 stitute its diet. So the sensitive edges of the tongue may be 

 organs of exploration. In Mesoplodon hidens, according to 

 Turner (34), the tip is mobile from side to side. 



In both suborders the tongue is more mobile in the new-born 

 animal than in the adult. 



Shape : — The tongue is large and shapeless in the adult 

 Balcenoptera hoops (10), but it is broad and squat in the foetal 



