664 MAMMALIA. 



to explain the varieties of their structure and the mode of their 

 formation. 



The most remarkable form of teeth, one indeed that is unique, 

 is met with in the Whalebone Whale (Balana mysticetus). The 

 teeth in this Cetacean are -not, indeed, instruments of mastication ; 

 but form a very curious apparatus, adapted to strain the waves 

 of sea as through a sieve, and thus obtain from the ocean a suffi- 

 ciency of food for the sustenance of its monstrous body. 



The whalebone (as it is improperly called) is attached to the 

 gums of the upper jaw, being arranged in thin flat plates of some 

 breadth, and varying in length according to the size of the whale.* 

 These plates are placed in several rows, similar to teeth in other 

 animals; they stand parallel to each other, having one edge di- 

 rected towards the circumference of the mouth. The outer row 

 is composed of the longest plates, and these are in proportion to 

 the varying distances between the two jaws, some being fourteen 

 or fifteen feet long, and twelve or fifteen inches broad, but towards 

 the anterior and posterior part of the mouth they are very short. 



Tnferiorly each plate of whalebone is terminated by a broad 

 fringe of horny fibres resembling hair ; and, seeing that in some 

 whales there are above three hundred plates composing the outer 

 row on each side of the mouth, the reader may form some idea of 

 the extent of this enormous strainer, whereby the little Clio 

 Borealis, and other small Mollusca, that swarm so abundantly in 

 the Northern ocean, are caught by shoals preparatory to their being 

 swallowed. 



For what is known concerning the growth of whalebone, we are 

 indebted to John Hunter ; and, as it would be difficult to curtail 

 his clear and concise description of the process, it is here given in 

 his own words. -f- 



" The formation of whalebone is extremely curious, being in 

 one respect similar to that of hair, horns, spurs, &c. ; but it has 

 besides another mode of growth and decay, equally singular." 



" These plates form upon a thin vascular substance, not imme- 

 diately adhering to the jaw-bone, but having a more dense sub- 

 stance between, which is also vascular. This substance, which 

 may be called the nidus of the whalebone, sends out thin, broad 

 processes answering to each plate, on which the plate is formed, as 

 the cock^s spur or the bulPs horn on the bony core, or a tooth on 



* J. Hunter, on the Structure and (Economy of Whales. Philos. Trans. 1787. 

 t Vide supra. 



