. The elasmobranch fishes . CSV. CSV. Fig. 92. Lateral view of the constrictor muscles, Heptanchus (From Davidson.) , adductor mandibulae; , antorbital process; csd.^-^, first to eighth dorsal con- strictors; csv.^'^, second to eighth ventral constrictors; Us., medial levator labialis; lls.^, lateral levator labialis; , levator maxillae; md., mandible; , postorbital process; p-q., palatoquadrate (pterygoquadrate) ; sc, scapular cartilage; sp., spiracular cleft; tr., trapezius muscle. The third to the eighth {csd.^) dorsal constrictors are more slender and have
. The elasmobranch fishes . CSV. CSV. Fig. 92. Lateral view of the constrictor muscles, Heptanchus (From Davidson.) , adductor mandibulae; , antorbital process; csd.^-^, first to eighth dorsal con- strictors; csv.^'^, second to eighth ventral constrictors; Us., medial levator labialis; lls.^, lateral levator labialis; , levator maxillae; md., mandible; , postorbital process; p-q., palatoquadrate (pterygoquadrate) ; sc, scapular cartilage; sp., spiracular cleft; tr., trapezius muscle. The third to the eighth {csd.^) dorsal constrictors are more slender and have their origin largely from the dorsal fascia and by tendons through the tra- pezius muscle {tr.). Tlie superficial fibers pass over into those of the ventral constrictors, while deeper fibers, acting as interbranchial muscles (see p. 149, fig. 143, ), lie just anterior to the cartilaginous branchial rays. In a section cutting through the dorsal constrictor between two gill clefts, the dorsal con- strictors (csd.) are the thicker bundles lying over the margin of the septum; and the deeper fibers (), comparable to the interbranchial muscle of the more specialized Elasmobranehs, extend inward as thinner bands. VENTRAL CONSTEICTORS The ventral constrictors of Heptanchus cinereus are seen in figure 93. They have their origin from a seam of connective tissue in the midventral line. The superficial, posterior fibers pass over into the dorsal constrictors, but the deeper ones are inserted on the ceratobranchial segments of the visceral arches.
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