The anatomy of the common squid, Loligo pealii, Lesueur . dunite, thus forming a conical tube, the siphon, whichleads from the mantle cavity to the exterior. This musculartube is attached dorsally by a pair of large muscles, thesiphonal retractors. Each siphonal retractor is a strongrounded muscle which, arising from the side of the ventralend of the vane of the pen, passes obliciuely downwardand forward in a depression between the liver above and in front, and thestomach, caecum, and nephridia below and behind. and terminates in one sideof the siphon. View^ed from below. the two siphonal retr
The anatomy of the common squid, Loligo pealii, Lesueur . dunite, thus forming a conical tube, the siphon, whichleads from the mantle cavity to the exterior. This musculartube is attached dorsally by a pair of large muscles, thesiphonal retractors. Each siphonal retractor is a strongrounded muscle which, arising from the side of the ventralend of the vane of the pen, passes obliciuely downwardand forward in a depression between the liver above and in front, and thestomach, caecum, and nephridia below and behind. and terminates in one sideof the siphon. View^ed from below. the two siphonal retractors appear asparallel bands which are separated at the back by theanterior vena cava andwhich disap]>ear between the nephridia and the gills. The arrangement of the intrinsic muscles of the sii)hon is very similar sothat of the mantle fibres except . that theie are longitudinal fibres which areapparently continuous with those of the retractor. The majority of these fibresform two pairs of bundles: an upper jmir which lies near the median line, and. Fig. 10. 24 a lower pair which passes (ihlii|utly duwinvanl tu the middle i»f the lowersurface. At the sitle of the sijihon. l»nt facing downward is the sijihdnaJcartilage, a grooved i)late to which many niusele libres are attached and whichtits over the corresponding pallial cartilage. The siphon is attached to the headand liver case by the two siphonal valves and the bridle. The latter is formedby two pairs of muscles, the siphonal protracters, which arise from the pedalprocess of the skull and pass outward and backward to their insertion upon theupper surface of the mantle. Each siphonal valve is a rectangular sheet which is attached by its upper edge to the nuchal cartilage, by its frontedge to the liver case and by its lower edge to the siphonal cartilage. Thefree edge of this valve projects backward and prevents w^ater which has enteredthe mantle chamber between the valve and the collar from escaping againthro
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