32 



the other fibres are wound and around which the lower jaw moves. Other 

 fibres (2) which arise from the dorsal end of the same lamella pass outward and 

 forward to the inner surface of the ala of the lower jaw. Fibres (4) which arise 

 h'om the forward part of the inner lamella of the upper jaw pass outward and 

 doAvnward over the edge of the inner lamella of the lower jaw and are inserted 

 upon its outer surface. The contraction of these muscles, causing the jaw to 

 rotate around the axis (Ax) , draws the lower jaw like a visor over the upper 

 jaw. A pair of superficial muscles (1) which arise fi'om the back end of the 

 upper jaw, pass forward and slightly downward to the middle of the outer 

 lamella of the lower jaw and open the mouth by drawing the lower jaw back- 

 ward and downward. The jaws are sufficiently powerful to cut and break the 

 bones of small fish or the pen of a quite large squid. 



The mouth contains the two palatine lobes and the odontophore. Each 

 palatine lobe is a muscular curtain which is attached to the hind and lower 

 edge of the inner lamella of the upper jaw and lies upon the inner surface of 

 the same lamella. The upper edges of the palatine folds are thickened (especially 

 near the distal end) and project into the mouth , meeting in the median line. 

 The outer surface of each fold is covered by a columnar mucous-secreting epithe- 

 lium and the inner surface by a columnar epithelium that seci-etes a thin sheet of 

 chitin which is covered with small backwardly directed teeth. The odontophore is 

 attached to the lower part of the hinder end of the upper jaw and projects 

 forward into the mouth cavity , lying below and partially between the palatine 

 lobes. The lower part of the odontophore is quite distinct from the rest and 

 is called (by Livon) the tongue : the upper part consists of the radula and its 

 appendages. The tongue has a muscular frame work , formed by an upper and 

 a lower pair of longitudinal bands which arise fi-oni the posterior edge of the 

 upper jaw and which are bound together by connective tissue and transverse 

 muscle fibres. The upper surface and the tip of the tongue are covered by a 

 thin sheet of chitin , but the sides and lower surface are covered by a palisadal 

 mucous epithelium which forms a large number of sparingly branched tubular 

 glands that occupy the spaces between and around the muscles of the tongue. 



The radula is secreted by a deep cylindrical sac which extends backward 

 from the middle of the ]jharynx to its dorsal end , describing a slight curve , 

 convex beneath. The sac is lined by a chitin-secreting , cubical or palisadal 

 epithelium which , upon all sides except the upper , is raised into small papillae 

 upon which the teeth are secreted. The epithelium of the upper surface of the 

 sac forms irregular folds covered by a thin sheet of chitin which project into 

 the lumen and occupy the spaces between the teeth. The teeth and this sheet 



