31 



muscular mass enclosing it is known as the Buccal Mass 

 (fig. 17, B.M.). The buccal mass is surrounded, and 

 therefore concealed, by the muscular bases of the arms 

 (PL 111, fig. 1-1, B.M., arm). The pharynx is furnished 



with two powerful cliitinous jaws, whose shape curiously 

 resembles that of a pa riot's Leak, and which are placed 

 dorsally and ventral! v. Unlike the parrot, however, the 

 ventral jaw of Eledone, which bites outside the dorsal, is 

 the larger and wider (PI. IY, fig. 27, J 1 and ,/.). These 

 jaws bite vertically with great force, tearing up the food 

 captured and held by the suckers before it is passed on to 

 the rasping action of the radula. The anterior edge of 

 each jaw is thick, and dark brown in colour. The 

 trenchant border is sharp, and a raised ridge some 

 distance behind this gives attachment to the muscles 

 working the jaws (fig. 27, v.). This part of the jaw is 

 exposed by cutting away the lip (PI. IV, fig. 24). 

 Further in, they decrease in thickness, and their colour 

 lightens, and posteriorly they are thin, colourless, and 

 semi-transparent. On the floor of the pharynx, slightly 

 anterior to the middle point, is a muscular outgrowth — 

 the tongue (fig. 24, t.). This forms the anterior wall of 

 the Radula sac, at the base of which is the growing point 

 of the radula (fig. 24, rad.). The Radula is a broad 

 cliitinous ribbon which, issuing out of its sac, runs over 

 the upper and anterior surface of the tongue, which is 

 responsible for the rasping action of the radula, as it 

 works forwards, backwards and laterally. The tongue is 

 strengthened internally by two small cartilaginous strips, 

 which give it rigidity and also provide attachment for its 

 motor muscles. Here, then, the food cut up by the jaws 

 is further triturated. The teeth of the radula are large, 

 and each row consists of three on each side of a central 

 large tooth. The innermost of the three is the smallest, 



