. The anatomy of the common squid : Loligo pealii, Lesueur. Loligo pealii; Mollusks -- Anatomy. 17 visceral mass and extend over the edge of the pen to the mantle. However, the chief connection is furnished by the pen . to whose upper surface the mantle is attached, whereas the large siphonal. nuchal and cephalic retractors are attached to its lower surface. The pallial cavity is very large and extends back nearly to the dorsal point of the mantle. By the expansion and contraction of the mantle a large quantitJ^ of water is drawn into and expelled from the pallial chambei'. The two triangular
. The anatomy of the common squid : Loligo pealii, Lesueur. Loligo pealii; Mollusks -- Anatomy. 17 visceral mass and extend over the edge of the pen to the mantle. However, the chief connection is furnished by the pen . to whose upper surface the mantle is attached, whereas the large siphonal. nuchal and cephalic retractors are attached to its lower surface. The pallial cavity is very large and extends back nearly to the dorsal point of the mantle. By the expansion and contraction of the mantle a large quantitJ^ of water is drawn into and expelled from the pallial chambei'. The two triangular fins are thin muscle-sheets and together, they form a flat rhomboidal plate which is attached to the upper ; surface of the mantle and extends from its dorsal point over •'/a of its length. The longest side, the base. of each fin is attached to the mantle and the two free edges are of nearly equal length. The dorsal angles of the two tins form together an acute angle which ends in a rounded tip. The lateral angle of each fin is obtuse and very much rounded. The ventral ends of the fins are some distance apart and each forms a small auricular lobe. The dorsal points of the cartilages of the fins are firmly united by strong masses of connective tissue, but at the middle the fins are not closely connected and overlap one another considerably. They are united by a thin subcutaneous sheet of muscle. which extends across their upper surfaces, as well as by the muscles which bind them to the mantle. The long attached base of the fin is underlaid and supported by a strip of cartilage — the fin cartilage — which is thin and broad except at its dorsal end ^vhere it becomes a strong bar that cui'ves downward and inward over the dorsal point of the mantle. The fin has very thin free edges, and increases in thickness gradually toward the base where it is attached to the cartilage at an angle of about 30° (text figuie (ii. The fins are attached to the mantle by the follow- ing three m
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