"LANTERN OF AKISTOTLE." 197 



(512.) The five curious jaws described above are fixed together by a 

 set of muscles (fig. 96, Ic &), consisting of short fibres passing between 

 the external edges of the contiguous segments of the lantern, and 

 evidently capable of powerfully approximating the grinding surfaces 

 and rubbing them upon each other. The jaws, moreover, are provided 

 with five other osseous pieces (d d), arranged in a radiating manner 

 between the bases of the different segments, with which they are con- 

 nected by ligaments, and likewise by the pentagonal muscle (i i) that 

 runs from one to the other. 



(513.) The above-described parts complete the apparatus required for 

 connecting the different portions of this remarkable mouth; but the 

 movements of the whole are effected by a very complicated set of levers 

 and muscles, which must next be noticed. 



(514.) The levers attached to the jaws are five long and slender pro- 

 cesses (fig. 97, 1, d d), each arising from the central extremity of one 

 of the radiating osseous pieces (c c), and arching outwards considerably 

 beyond the base of the lantern, to terminate by a forked extremity. 

 But there are likewise other processes projecting from the inner surface 

 of the shell ; these, two of which are seen in fig. 96, 66, are also five 

 in number, and are placed around the orifice of the mouth : they are 

 generally perforated in the centre, so as to resemble so many bony 

 arches ; and from them, as well as from the spaces which separate them, 

 numerous muscles derive their origin. Of these muscles, ten (//) arise 

 from the spaces between the arches, two being inserted into the outer 

 edge of the base of each jaw; so that the effect produced by their con- 

 traction, when they all act in concert, will be to approximate the whole 

 mass of the mouth to the oral aperture of the shell, and of course cause 

 the points of the incisor teeth to protrude externally ; or, if they act 

 separately, they can draw the base of the lantern in any direction, or 

 cause the grinding surfaces of the jaws to work against each other. 



(515.) The antagonists to the muscles last mentioned are ten others 

 (.9 #)> Arising from the extremities of the arches themselves, and run- 

 ning in a radiating manner towards the apex of the lantern, so that the 

 point of each piece or jaw receives a muscle from two of those pro- 

 cesses. These fasciculi, from the manner in which the arches project 

 into the cavity of the shell, will draw inwards the entire mass ; or, 

 if they act separately upon the jaws whereunto they are individually 

 fixed, they will produce movements precisely opposite to those caused 

 by the contractions of the muscles derived from the spaces between the 

 bony processes ; or, if both sets should act in concert, they become the 

 antagonists of the muscles (i i, Tc Tc) that connect the jaws to each other, 

 and by causing the separation of the different pieces they necessarily 

 enlarge not only the opening of the month, but all the passage leading 

 to the oesophagus through the axis of the lantern. 



(516.) Yet even these are not all the muscles that act upon the 



