No. 478] ODONTOPHORAL APPARATUS IN SYCOTYPUS 731 



cartilage on its ventral side in a shallow groove. It is held in place 

 by a sheet of connective tissue that binds it against the ramus, but, 

 at the same time, allows it to slide freely back and forth along the 

 face of the ramus. Each muscle of the pair extends to very near 

 the tip of its ramus, and is there inserted laterally. 



(3) The last pair — much smaller than the second but larger 

 than the first pair — arise close to, and laterally from, the second 

 and pass parallel to the second along the outer half of the ramus 

 on its ventral surface to be inserted, a centimeter or so anteriorly 

 to the end of the ramus, into its outer edge (Figs. 10, 11, prr., c). 

 The muscles of this pair are, like those of the second pair, contained 

 within a connective-tissue sheath (Fig. 16). 



The anterior parts of all these protractors are covered by the 

 cross fibers that pass between the two triangular cartilage ])ro- 

 tractors (Fig. 11, c/.). These three remarkably loiiu- iniiMlcs 

 (they would make fine material for physiological e.xixriinnit- 

 upon molluscan muscle because of their length and itgularity i 

 serve to pull the membranous poneli toward the base of the j)ro- 

 boscis, and consequently the lingual ribbon, wliich is adherent 

 to the inner surface of the dorsal wall of ihc j)ou(h. out over the 

 head of the odontophoral cartilage. Thtir mass is extremely 

 small when compared with that of the great retractor, atid this 

 is what one wonl.l natnrallv expect, sin.v the rasping take> place 



of the lingn; 

 of the ribbo 

 the surface t 

 13). 



Sycotypus are \er; 

 (electrical) twenty- 

 taken from the ale 



