38 WALTER K. FISHER, 



"inner lips", which as pointed out in another connection are so 

 abundantly supplied with nerves that they almost certainly subserve 

 the function of taste, or something allied thereto. The presence of 

 a strong retractor is a necessity to Avithdraw such highly sensitive 

 structures. Muscle la (Figs. 9 and 10) is small. It probably retracts 

 the forward portion of the pharynx. Its origin is on the radula tube, 

 and insertion along with muscle 5. Muscle 15 is a stout bundle which 

 passes from the dorso-lateral wing of the jaw (inner surface) and 

 lateral knob of the buccal cartilage of each side, underneath the 

 cartilage, where a portion may be said to have its origin. But a 

 goodly part of the muscle appears to simply continue from the in- 

 sertion on the jaw and knob of one side, under the cartilages, to^a 

 similar insertion on the other. As will be seen by Fig. 13, the "la- 

 teral knobs" of the radula supports are in reality separate pieces of 

 cartilage which are anchored to the main radula support by muscles 

 {23). Consequently X5, which is probably a mixed muscle, acts as an 

 anchor for these cartilages and a depressor of the jaw (?). It also 

 acts as a strengthener of the whole cartilage, which would tend (from 

 a longitudinal line of weakness along the middle) to fold together. 

 15 acts in exact opposition to any such strain. Muscle 16 (Figs. 5, 

 9 and 10) is inserted on the jaw and originates on the posterior knob 

 of the cartilage. Its contraction would tend to draw the jaw inward 

 and downward. Muscle 25 is similarly situated, though it is outside 

 of all of the buccal muscles, and is attached to the upper and outer 

 edge of the jaw. The sheet of muscle 17 is thin and passes from 

 side to side connecting the two lateral knobs of cartilage, and the 

 major portion ends in an aponeurosis of connective tissue fibres in 

 connection with muscles IG and 8, and the sheet lies between the 

 two, above 8 and below 16. A thin sheet of muscle (19 Fig. 3) ex- 

 tends over the dorsal half of each side of the buccal mass, covering 

 the retractor major of the radula. Its origin is on the posterior 

 knobs of the cartilage. It is inserted partly on the jaw (upper edge) 

 and extends partly as muscle 22, to the outer lip, or proboscis. The 

 contraction of this muscle would tend to lift the jaw and fore part of 

 proboscis. Small muscles {20) pass from the jaw to the head wall, 

 while others {21) anchor the pharynx and pharyngeal pockets to the 

 wall. Muscle 22 is partially a continuation of X9, but the greater 

 part of the thin sheet attaches along the upper edge of the jaw. 

 Bands in connection with this pass through muscles 20 like basket- 

 work. Muscle 18 (Figs. 3 and 10) properly not belonging to the 



