MOUTH OF THE CUTTLE-FISH. 



573 



Fig. 287. 



shell unoccupied. At intervals, as the Nautilus thus removes itself 

 further and further from the bottom of its abode, that portion of its 

 mantle which covers the general surface of its visceral sac (fig. 284, a) 

 secretes floors of shelly substance behind it ; and thus the septa (s s) 

 are formed, whereby the shell is separated into chambers, every chamber 

 having in turn been occupied by the body of the Nautilus. The gradual 

 prolongation of the fleshy siphon (h) is easily understood, because it 

 naturally increases in length with the growth of the animal : but how 

 the two muscles (fig. 284, </), that fix the body to the shell, progressively 

 advance their points of attachment as the shell enlarges, is not so readily 

 explained ; neither are we prepared to account satisfactorily for the 

 accomplishment of this part of the process. 



(1536.) It has been already stated 

 that in all Cephalopods the aperture 

 of the mouth is situated in the centre 

 of the disk formed by the union of 

 the origins of the feet (figs. 282, 289). 

 The oral orifice is generally surrounded 

 by a broad circular lip (fig. 287, A, a), 

 which being not unfrequently fringed 

 or papillose, there is little doubt of 

 its possessing sufficient sensibility to 

 render it of material assistance in 

 manducation. 



(1537.) The circular lip partially 

 conceals a pair of strong horny man- 

 dibles, not unlike the beak of a 

 parrot, but differing in this parti- 

 cular, that in the Cephalopod the 

 upper mandible is the shorter of the 

 two, and is overlapped by the lower 

 jaw. The mandibles detached from 

 the soft part are represented in fig. 

 287, B, a, 6). There is likewise an- 

 other important difference between 

 the structure of the beak of the 

 Cuttle-fish and that of the Bird, in- 

 asmuch 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 supplied by a fibro- 

 cartilaginous substance (fig. 288, c) that fills the interior of each man- 

 dible, and thus gives it sufficient solidity for all required purposes. 



Jaws of the Cuttle-fish. A : a, fleshy 

 orifice of the mouth ; b, muscular mass 

 of the mouth ; <?, mandibles ; d, oeso- 

 phagus. B, horny beak of the Cuttle- 

 fish, in outline. 



