No. 3-] THE MUSCULATURE OF CHITON. 617 



The lateral protractor muscles from shell II are attached to 

 the outside of the cartilage, posterior to the attachment of the 

 longitudinal protractors from I (Fig. 11, Ipr). 



The oblique radula muscle from II, that crosses the pedal 

 muscles with the lateral protractor, is attached to the lateral 

 projection of the radula sheath (Figs. 9, 11, 01). 



A group of dorsal muscles (Figs. 10, 11, dr) on either side 

 passes obliquely forward from shell II (anterior to the opening 

 of the gland into the oesophagus), to be attached to the portion 

 of the radula sheath that is immediately posterior to the region 

 where the thread-like muscles of the sheath (ins^) are attached 

 to it. It is these muscles that have been described as com- 

 pressing the median dorsal shell muscle under II. 



Immediately ventral to the attachment to the shell of these 

 oblique muscles from II, are muscles from the floor of the body 

 cavity, in the median line, that pass posteriorly and laterally 

 (Figs. 10, 12, vpr), to be attached to the cartilage posterior to 

 the attachment of the thread-like muscles {mst) from the radula 

 sheath. 



The lateral portion of each cartilage is bound to the muscu- 

 lar head-fold by a large muscle on either side of the posterior 

 limit of the mouth (Figs. 9, 12, <^/). A similar muscle occurs 

 more posteriorly under the edge of the apophysis of III, run- 

 ning from the muscular mass that bounds the body cavity 

 laterally, to the lateral portion of the buccal muscles and car- 

 tilage (Figs. 10, \2, pi). 



The anterior portions of the cartilages of the opposite sides 

 are joined to one another ventrally by a thick transverse 

 muscle (Figs. 7, 9, 12, vtr). Finally, on the dorsal side of the 

 buccal mass is a Y-shaped muscle (Fig. 1 1, and in cross-section, 

 Figs. 7, 9, 10, y) attached to the radula sheath. 



Historical, 



The earliest account which I have found of the musculature 

 of Chiton is the description by Poli in his work on the "Mol- 

 lusca of the Sicilies," published in 1791. His first figure 

 represents the animal from the ventral side after the removal 



