No. 3-] THE MUSCULATURE OF CHITON. 619 



Middendorff describes the muscles as running parallel to one 

 another till they reach the sides of the animal, and as then 

 separating into groups, leaving spaces filled with a spongy sub- 

 stance (anterior and posterior groups of pedal muscles with 

 nephridia between). Three parts of the " Bauchmuskel " under 

 each shell partially bound these spaces, and appear to corre- 

 spond (i) to what I have called the inner fibres of the anterior 

 group, at the attachment to the shell (Poll's pyramidal muscle); 



(2) perhaps, to the inner fibres of the posterior group, and 



(3) to the oblique dorsal-shell muscle ; he adds that a longi- 

 tudinal muscle runs along either side of the dorsal artery, being, 

 therefore, the median dorsal-shell muscle, 



Haller marks on one of his figures what he refers to as a 

 longitudinal muscle in the narrow part of the foot, but which 

 I interpret as the fibres of the oblique muscles. 



Lang briefly mentions: (i) longitudinal muscles over the 

 foot on either side (the oblique muscles apparently cut trans- 

 versely in cross-section, as Haller also figures them); (2) mus- 

 cles in the dorso-ventral direction from the sides of the shell 

 into the foot (latero- and medio-pedal) ; and (3) the muscles 

 passing in various directions in the foot. The dorso-ventral 

 muscles he regards as the representatives of the shell muscle 

 of Fissurellidae, etc., and of the spindle muscle of the other 

 Gastropods ; he further describes the crossing of the medio- 

 pedal muscles of opposite sides. 



The buccal muscles of Cryptochiton were described in detail 

 by Middendorff (1847), ^^d Schiff in 1858 gave a short account 

 of the muscles of the radula in Chiton piceus ; Schiff refers to 

 Middendorf's paper, but leaves his reader to compare the 

 muscles described in the two accounts. Both authors have 

 described the position of the cartilages and radula, the trans- 

 verse muscles between the cartilages, muscles surrounding the 

 cartilages, and other muscles attached to the radulk sheath, to 

 the cartilages, and to the shells and body-wall. Middendorff's 

 figures are not altogether clear, and neither of the authors has 

 studied the muscles in section, so that it is sometimes difficult 

 to understand the exact position of the muscle attachments; 

 in some cases, I have found a different attachment from that 



