726 THE AMERICAN NATURALIST [Vol. XL 



All these muscles pull the cartilage forward in the proboscis, 

 and it is by means of them that the dentate ribbon, which passes 

 over the rim of the head of the cartilage, is brought forw^ard into 

 position for rasping. 



Their nervous supply comes through one of the nerves of the 

 cerebral ganglion. The nerve on each side runs along beneath 

 the protractors near their origin, sending branches to each, and 

 ends forward in the triangular protractor (Fig. 10, 1). 



Radula (LixGi-AL OR Dfatatf. Ribbox) 



The radula is a dentate ribb,,., which i> a-lhcivnt to the mem- 

 brane — radular membrane {snhrad iihir iiicitihr(inr) — that lines 



