32 



posteriorly to tlie ventral part of the posterior eartilag'es 

 and spreading out towards their anterior origin behind 

 and at the base of the inner lips. 



(h) Dorso-lateral protractor muscles attached at the 

 front end around the expansions of the dorsal palatal 

 plate, and, behind, to the sides of the posterior cartilage. 



(c) Antero-lateral retractor muscles going from the 

 sides of the anterior cartilages to the floor of the neck 

 cavity. These may be divaricators of the cartilages. 



(d) Xumerous fibres, more or less irregularly arranged, 

 and including some posterior ventral retractors going 

 from the odontophore to the floor of th© neck cavity. 

 The protractor muscles seem to be by far the most 

 important, and probably, therefore, the act of retraction 

 is mainly a natural relapse to normal conditions from a 

 state of strain. 



The chief Intrinsic Muscles (fig. l-3?>) are: — 



(«) Two transverse layer-like bands connecting the 



ventral sides of the anterior and lateral cartilages together. 



These are separated by (b). 



(b) A pair of muscle bands going forwards from the 

 posterior cartilages to the epithelium beneath the front 

 end of the radula. 



(c) Muscle bands connecting the anterior and antero- 

 lateral cartilages dorsally, and 



(d) Muscle bands connecting these cartilages ventrally. 

 Besides the above muscles, various l)ands of connective 



tissue bind the antero-lateral and the posterior cartilages 

 to the anterior, and some further minute details are shown 

 in the figures (figs. l-3<7, h, c). 



The Radidar Sac (figs. 0, 12) is a long cylindroidal 

 diverticulum of the post-palatal section of the buccal 

 cavity. Arising at the upper limit of the back of the 

 cushion, it first runs doAvnwards close to this, and then, 



