No. 3.] THE MUSCULA TURK OF CHITON. 607 



region of the attachment of the latero-pedal, another buccal 

 muscle (" lateral protractor ") passes across from the mantle to 

 the buccal mass (Fig. 3, Ipra, Figs. 9, 11, Ipr). The anterior 

 limit of the attachment to the shell of the medio-pedal fibres is 

 relatively posterior to that of the latero-pedal fibres (Fig. 13, II), 

 for the oblique radula muscle, approaching the anterior group 

 from the lateral edge of the shell, cuts off the attachments of 

 the outer muscles of the group obliquely, and, with the lateral 

 protractor muscles, passes anterior to the latero-pedal fibres to 

 reach the buccal mass (Fig. 9, or). Under the posterior part of 

 II (or most anterior edge of the apophysis of III), medio-pedal 

 fibres that bound the body cavity are interrupted, on a line 

 with the narrowest part of the foot, by a thick mus.cle to the 

 buccal mass ("posterior lateral" Figs. 10, 12, //). 



In front of the region of the anterior group, the buccal 

 musculature occupies the large space over the posteriorly 

 slanting fibres (Fig. 9, 6) of an oblique muscle from I and II. 

 The anterior group of fibres (here including the latero- and 

 medio-pedal with the postero-oblique, but not the usual antero- 

 oblique) occupies under II a relatively posterior position {cf. 

 Fig- 3), i-e., it lies much nearer to the posterior group, and 

 farther from the anterior edge of the apophysis than under the 

 other shells. The foot proper ends, and the "head-fold" takes 

 its place in front of the region of the anterior group, so that 

 this group is in a position to supply the foot itself. 



The head-fold is joined to the body of the animal in the 

 same way as the foot, spreading out under the mantle chamber ; 

 anteriorly it is parallel with the edge of the mantle, and the 

 portion spread under the mantle chamber is continued pos- 

 teriorly as a lobe on either side, dorsal to the foot ; the 

 projecting edge of the foot is rounded anteriorly, ventral to the 

 head-fold {cf. Fig. 9, where the head-fold and the underlying 

 anterior edge of the foot are met in cross-section), and in the 

 center of the head-fold lies the mouth, bordered by a thick 

 circular lip. The muscles, therefore, under the anterior half 

 of II and under I have to do with the head-fold and lips, and 

 not with the foot proper ; one exception to this, however, is to 

 be noticed. 



