BLOOMER : ANATOMY OF CERATISOLEN AND SOLECURTUS. 35 



as the free portions (Fig. 4, Ex. S\ & In. S\). The interior muscles of the 

 siphon are chiefly longitudinal and the outer ones circular, the latter thus 

 forming internal and external coverings. 



Externally, the free portions of the siphon are ribbed laterally. Inter- 

 nally, they are also ribbed laterally, but not so deeply ; whilst longitudinally 

 there are a number of rounded ribbings, with finer ones between. The 

 chambers gradually taper towards their distal ends. 



The anterior adductor muscle (Fig. 4, A. A.) is a comparatively narrow 

 plate of muscles. It spreads out on either side from the median line, and 

 obtains its maximum width where it is connected with the valves of the 

 shell. Dorsally, it is joined with the dorsal integument and the mantle 

 1 obes. Posteriorly, it is connected with the ventral integument. 



The posterior adductor muscle (Fig. 4, P. A.) is also a narrow plate 

 of muscles joined anteriorly by connective tissue with the retractor pedis 

 posterior muscle, and posteriorly with the dorsal integument, the siphon- 

 and the mantle lobes. 



ii. The Pedal Muscles. — The foot (Fig. 4, F.) is very large, deep and mus- 

 cular. The muscles are of three kinds, viz., longitudinal, ti*ansverse, and 

 circular. In the proximal portion, where the greater part of the viscera 

 is situated, the walls are thin and the muscles lie close together. Inside 

 the muscular integument are two layers of longitudinal muscles, between 

 which is a circular layer which passes around the foot at a right angle to 

 its axis. There are numerous bundles of transverse muscles which cross 

 the foot between the other muscles to the pedal integument. They are 

 also plentiful in the proximal part, where they pass either between or 

 through the viscera. Towards the distal half the muscles begin to fray 

 out more, intermingle with each other, and gradually increasing in number 

 soon become a network of powerful muscles, thus maldng the distal portion 

 an exceedingly muscular mass. 



The anterior retractor pedis muscles (Fig. 4, P. R. A.) are short and 

 thick, passing at the side of the liver to the valves. When they reach the 

 foot the muscle fibres spread out, passing both ventrally and anteriorly 

 over the inner longitudinal muscles, and bury themselves in the pedal 

 integument. There are no bifurcations of the free portions of the muscles. 



The posterior retractor pedis muscle (Fig. 4, P. R. P.) is comparatively 

 short, and bifurcates at its posterior end, the bifurcated parts being attached 

 by their dorsal surfaces to the valves of the shell. They are joined by 

 connective tissue with the posterior adductor muscle. On reaching the 

 pedal cavity the muscle spreads out ; and the fibres, passing in an anterior 

 direction as a portion of the longitudinal muscles of the foot, eventually 

 merge themselves in the pedal integument. 



The elevator pedis muscles (Fig. 4, E. P.) are situated at the posterio 

 dorsal point of the foot, and are connected with the valves at their most 

 dorsal parts. 



