AKBAMGEMENT OF WHALEBONE. 



67 



they become very short. There is, however, whalebone and 

 whalebone, and whereas in the Greenland whale the length 

 of the longest plates varies from some ten to twelve feet, 

 while the total number of plates in the series is about 380, 

 in the great rorquals or fin-whales the length is only a few 

 inches, while the number of plates is considerably less. 

 To accommodate the enormous whalebone plates of the 

 Greenland whale, the bones of the upper jaw are greatly 

 arched upwards, while the slender lower jaw is bowed out- 

 wards, thus leaving a large space both in the vertical and 

 horizontal directions, the transverse diameter of the space 

 being much wider below than above. When the mouth is 



Fig. 24. — Section througli tlie Skull of tlie G-reeulaud Wliale, with 

 the outline of the soft parts. The ai-ro^vs indicate the position of 

 the nasal passage and aperture. 



closed, the plates of whalebone are folded obliquely back- 

 wards, with the front ones lying beneath those behind 

 them ; but directly the jaws are opened, the elastic nature 

 of this wonderful substance causes it to spring at once into 

 a vertical position, and thus form a sieve-like wall on both 

 sides of the mouth, the thin ends of the plates being pre- 

 vented from pushing outwards by the stiff lower lip which 



