446 



CEPHALOPODA. 



as in the former there is no bony support to the horny jaws, and 

 consequently some other means of sustaining them must be had 

 recourse to. We accordingly find the place of the jaw-bones sup- 

 plied by a fibro-cartilaginous substance (fig. 209, c) that fills the 

 interior of each mandible, and thus gives it sufficient solidity for 

 all required purposes. Externally, the jaws are imbedded to a 

 considerable depth in a strong mass Fig. 208. 



of muscle (fig. 08, &), composed 

 of several layers of fibres variously 

 disposed, so as to open or close the 

 jaws with a degree of force propor- 

 tioned to their large size. Here, 

 therefore, is an apparatus fully ade- 

 quate to co-operate with the elabo- 

 rately constructed prehensile arms 

 whereby these predatory animals 

 seize their prey ; and a victim once 

 involved in the tenacious grasp of 

 the tentacula, and dragged to this 

 powerful beak, can have but little 

 chance of resisting means of destruc- 

 tion so formidable as those granted 

 to the Cephalopoda. 



The mandibles of Nautilus Pom- 

 pilius, instead of being entirely 

 composed of horn, as is invariably 

 the case in these genera that, being 

 provided with tentacula armed with 

 suckers, are thus capable of seizing 

 active and slippery animals, would 

 seem to be rather calculated to break 

 to pieces the testaceous coverings of Mollusca or the armour of 

 the Crustacea. They possess indeed the shape of the jaws al- 

 ready described, but are blunt at their extremities (Jig. 10, w, o), 

 and thickened by a covering of a dense calcareous substance ; so 

 that they appear manifestly adapted to crush hard substances, 

 rather than to cut or lacerate the tender bodies of fishes.* The 

 jaws of the Nautilus, like those of the Octopus above described, 

 are embedded in a powerful mass of muscles (p) whereby they are 

 opened and shut with great force, and are also provided with a 



* Owen. Memoir on the Pearly Nautilus ; London, 1832, 4to. 



