124 THE SNAIL 



B. The Odontophore. 



Make a median longitudinal section through the buccal mass so as to expose 

 the odontophore. The posterior part of the floor of the pharynx is produced 

 backwards into a hollow diverticulum, the radula sac. A chitinous band, the 

 radulp, or rasping ribbon, armed on its upper surface with a number of minute 

 rasp-like teeth arranged in transverse rows, is secreted by the epithelial cells 

 lining the ventral wall of the diverticulum. In front of the radula sac lies a 

 cushion projecting into the cavity of the buccal mass or pharynx. The radula 

 passes over this cushion. The odontophoral cartilage, .which can be moved by 

 the intrinsic muscles, is firmly attached to the cushion. The radula works 

 against the horny jaw situated in the mouth. The radula, the cushion and the 

 muscles together constitute the odontophore. 



Make a drawing showing the above parts. 



Odontophoral cartilage 



Radula 



•Horny jaw 



Mouth 



Opening of 

 Pedal gland 

 Ra<lula''sac Intrinsic muscles 



Fio, 39. — Inner view of the left half of the head region of the Snail (Helix), 

 showing the odontophore and associated parts, x 2. 



