AQUATIC MAMMALS 



that of the blubber layer but, together with the fatty tissue within the 

 angle of the jaws, is of different consistency, and hence specialized, the 

 refined oil from these regions being the finest lubricant for precision 

 instruments so far known, and correspondingly valuable. The develop- 

 ment of this frontal fat body is variable in different sorts of toothed 

 whales. In long-snouted porpoises such as Tursiops and Delphinus its 

 development is but moderate, while in the adult Monodon it is large, 

 and is relatively so great in Globiocephala (fig. 10) as to cause the 

 forehead to bulge forward beyond the jaws. 



In the latter case the frontal bulk must act as a definite retardant 

 to speedy locomotion. If the adipose cushion, or "melon" as it is 

 called in the trade, had the function simply of a shock-absorber it would 

 hardly develop to such proportions, nor would it have its present con- 

 sistency, but should be more gristley and perhaps, as whales are prone 

 to fatness, have some deposit among the fibers of the same sort of fat 

 as constitutes the blubber layer; but hardly a particular grade of fine 

 fat of the same composition as that found within the angle of the jaws. 



In explanation of the above state of affairs it seems to be most likely 

 that originally the water pressure against the anterior braincase of the 

 toothed whales stimulated the formation of a simple fibrous thickening in 

 this area to act as a buffer. This development once having begun, the 

 region should then have been in a state plastic for further adaptations, 

 and I believe that its present condition indicates a specialized physio- 

 logical function of the adipose cushion to which that of a shock-absorber 

 is now of secondary importance. This is but a personal opinion, how- 

 ever, and entirely unproven. 



Sharply marked off from the other toothed whales in details of the 

 facial regions are the sperm whales (Kogidae and Physeteridae) . In 

 the cachalot the fatty tissue of the head is of two sharply differentiated 

 kinds. Occupying the entire bottom of the facial basining and project- 

 ing beyond the bony snout is a prodigious mass of fibrous tissue so 

 tough that it must be hewn with an axe. This holds fat as a sponge 

 holds water, and from it may be secured about 10 or 12 barrels of oil. 

 It is the adipose cushion, or "junk" of whalers and seems largely homolo- 

 gous with the adipose cushion of other toothed whales. The sperma- 

 ceti organ proper is a huge ovoid body occupying the upper half of the 

 rostral basin and separated from the junk by the expanded right narial 

 passage. After surrounding tissue has been removed it is said to be 

 composed of an envelope of extremely strong, fibrous tissue of tendinous 

 aspect. Within this is a zone of partly solid oil held by a spongy net- 



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