BFCCINUM. 297 



proboscis to the posterior end of the pharynx. By 

 contraction of these muscles the pharynx can be moved 

 forward. 



The protractors of the Odontophore have already 

 been referred to. They are first a pair of muscles which 

 run from the walls of the proboscis to the sides of the 

 odontophore, really to the lateral " cartilages " of the 

 odontophore, and a pair which are situated ventrally and 

 anteriorly (figs. 18, 21, V. pr. m.). These are also 

 inserted in the odontophoral cartilages. In addition to 

 these might be included the miiscles of the buccal cavity 

 walls, which are attached to the radular sheath. The 

 action of all these muscles is to pull forward the radular 

 apparatus. 



The Retractor muscles are much more complicated, 

 and are at first somewhat difiicult to follow. There are 

 two series of these muscles, dorsal and ventral, lying 

 above and below the odontophoral cartilage respectively. 

 The dorsal retractors are much more numerous, and 

 larger than the ventral, and, as will be seen later, this is 

 to be correlated with the movements of the radula and 

 the arrangement of teeth on the same. 



The first retractor to be observed is the most dorsal 

 unpaired median baud (fig. 16, C.d.vi.), which is attached 

 to the end of the radular sac, and after running back 

 some distance is inserted into the walls of the proboscis. 



Before referring to the other dorsal retractors 

 attached to the radula, mention must be made of two 

 curious muscles which run from the end of the radular 

 sac, at the point of insertion of the central dorsal muscle, 

 to the two cartilages (fig. 16, c.c). They are thus fixed 

 to two apparently unstable points. The action of these 

 dorsal occlusor muscles and the median dorsal muscle is 

 interesting, for the contraction of the former will bring 



