CEPHALOPODA. 447 



distinct muscular apparatus destined to protrude them when in use, 

 and again to retract the whole mass of the mouth deeply into the 

 body when unemployed. The mechanism provided for the pro- 

 trusion of the mandibles is a strong semicircular muscle (Jig- 210, 

 r, r), which firmly embraces the base of the oral apparatus, and 

 by its contraction pushes it outwards among the labial tentacula 

 (A, k) ; while, on the other hand, four retractor muscles, the upper 

 pair of which are represented in the figure referred to (<?, <?), arise 

 from the extremities of the cranial cartilage, and, running forwards 

 to be inserted into the oral mass, are the agents whereby the whole 

 is again withdrawn and thus concealed from view. 



(488.) The tongue of the CEPHALOPODA, as in the Mollusca 

 described in the two last chapters, is an exceedingly important in- 

 strument, and from its construction would here seem to be an 

 organ of taste, as well as a necessary assistant in deglutition. Tn 

 the annexed figure, representing a vertical section of the beak of a 

 very large Onychoteuthis, the shape and disposition of the differ- 

 ent parts of the tongue are well seen. The substance of the 



Fig. 209. 



a 



tongue itself is fleshy (fig. 209, e, i), and its movements are 

 principally performed by the action of its own intrinsic muscular 



