2o8 



WHALES 



Figure io8. Wax plug of a Blue 

 Whale and its position with respect 

 to the finger-shaped projection of 

 the eardrum attached to the ^ear- 

 bone\ {Lillie, igio.) 



We have already seen that Cetaceans have no obvious pinna, though 

 the fact that very young embryos have a rudimentary external ear points 

 to their distant terrestrial ancestors having had such an organ. All that 

 has remained of it in present-day Cetaceans, however, is the small slit 

 in the skin some distance behind the eye. However, an external auditory 

 meatus running through the blubber from the slit to the middle ear at the 

 base of the skull is found in all Cetaceans. The meatus is S-shaped and 

 not straight as it is in most mammals (Fig. 113), probably to prevent 

 excessive strain during the annual increase of the amount of blubber, 

 which is particularly marked in Rorquals. From the top of the S-bend, 

 a muscle runs to the upper skull, no doubt in order to keep the canal taut 

 when the blubber is too thin. Near the skull, the canal is surrounded by 

 cartilage from which a number of small muscles run to the skull - appar- 

 ently another remnant from the days when whales still had a movable 

 pinna. 



Although the external auditory meatus has so small a diameter ( i -5 mm.) 

 that it looks like a piece of string, it is - at least in Odontocetes - an open 

 tube, filled with seawater and discarded epithelium cells over its entire 

 length. The wall of the canal consists of dark epithelium, connective 

 tissue, and some striated muscle. In Mysticetes, the tube is open externally, 

 closed over a generally short central section consisting entirely of con- 

 nective tissue, and open again over the internal section which can be up 

 to three feet long and perceptibly increases in diameter towards the skull, 

 so that it looks like a funnel. However, the actual channel in this part of the 

 tube is very narrow, since the tube is almost completely filled by the conical 

 'wax plug' (Fig. 108). Actually, 'wax plug' is a very misleading term since 

 the wax (cerumen) formed by special glands in human ears is an entirely 

 different substance. The wax plug consists of concentric strips of horny 



