210 PHILOSOPHY OF ZOOLOGY. 



No teeth in the mouth. 



124. MONODON. Narwal. Although there are no teeth 

 within the mouth, there is a straight tusk, projecting an- 

 teriorly from the left upper lip, spirally twisted, sinis- 

 trally solid at the free extremity, and tubular where it is 

 inserted in the skull. Within the skull, on the other side, 

 appears the rudiments of a second tooth. 



This second tooth, on the right side, a figure of which, 

 belonging to a male, we have given in Plate I. fig. 6., is 

 solid throughout, spirally twisted dextrally in a very slight 

 manner, blunt, and somewhat puckered at the apex, bent 

 a little towards the base, the face of which is oblique, 

 smooth in the centre, and uneven towards the margin, and 

 bordered by a ring of tubercular eminences. The cavity 

 containing this kind of tusk, is, in some cases, closed with 

 bone in front, Sir E. HOME denominates this body a 

 milk tusk (Phil. Trans. 1813, p. 128.), and more re- 

 cently (Phil. Trans. 1820, p. 147.), has concluded, that 

 " as the permanent tusk in the narwhal begins to form 

 in a direct line immediately behind the origin of the 

 milk tusk, the great purpose of the milk tusk is evi- 

 dently to open the road for, and to direct the course of 

 the permanent tusk, till it is completely pushed out by it." 

 This opinion appears to us to be untenable. The blunt 

 point, the curved base, and its tuberculated margin, are ill 

 suited to its character as pioneer. There is, besides, no 

 evidence that these milk-tusks are ever shed, that perma- 

 nent ones are formed behind them, or that the sinistral 

 protruded tusk was ever preceded by any other. The cir- 

 cumstances of the case rather render it probable, that this 

 body is a nucleus or support to the pulpy substance which 

 secretes the tooth, that it is absorbed at an early period 

 when a tusk is formed, but remains in its place when no 

 tusk has been developed. An examination of the denti- 



