. The elasmobranch fishes. Chondrichthyes. THE ELASMOBRANCII FISHES 91 The second dorsal constrictor () is a very broad l)and lying between the spiracle and the first branchial cleft. It arises also along the fascia of the dorsal bundle, its anterior margin in Heptanchus maculatns being continu- ous with the first dorsal constrictor. In Heptanchus cinereus it is overlapped by the first constrictor. From its place of origin it extends downward and its anterior and more superficial fibers are inserted on the quadrate; the fibers lying underneath the superficial fibers join the upper segment
. The elasmobranch fishes. Chondrichthyes. THE ELASMOBRANCII FISHES 91 The second dorsal constrictor () is a very broad l)and lying between the spiracle and the first branchial cleft. It arises also along the fascia of the dorsal bundle, its anterior margin in Heptanchus maculatns being continu- ous with the first dorsal constrictor. In Heptanchus cinereus it is overlapped by the first constrictor. From its place of origin it extends downward and its anterior and more superficial fibers are inserted on the quadrate; the fibers lying underneath the superficial fibers join the upper segment of the hyoid; while those fibers lying back of them pass over to join the fibers of the ventral constrictor. In Heptanchus maculatns, where the dorsal constrictor meets the ventral there is superficially a heavy connective tissue 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 Elasmobran
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