. The elasmobranch fishes. Chondrichthyes. THE ELASMOBRANCII P^TSHES 93 Tliere are in Heptanclius inaculatus two levator labiales muscles. One of these {lls.^, fig. 92) arises from the median side of the antorbital process, passes backward over the angle of the jaw, and as a fibrous band divides the adductor mandibulae into dorsal and ventral parts. The other labialis (Us.) arises from the cranium in front of the antorbital process and nearer the mid- ventral line as a wide and loose band of connective tissue; it passes under the orbit, and over the adductor mandibulae to be inserted at the an
. The elasmobranch fishes. Chondrichthyes. THE ELASMOBRANCII P^TSHES 93 Tliere are in Heptanclius inaculatus two levator labiales muscles. One of these {lls.^, fig. 92) arises from the median side of the antorbital process, passes backward over the angle of the jaw, and as a fibrous band divides the adductor mandibulae into dorsal and ventral parts. The other labialis (Us.) arises from the cranium in front of the antorbital process and nearer the mid- ventral line as a wide and loose band of connective tissue; it passes under the orbit, and over the adductor mandibulae to be inserted at the angle of the jaw. ADDUCTORS The adductor mandibulae (, fig. 92) is an immense and complex muscle which closes the jaws. Superficially it is divided into a dorsal and a ventral part by the insertion of the first labialis muscle. The fibers of the adductor mandibulae arise from the quadrate and are inserted in two groups: first, a smaller deep posterior group is in- serted directly on the man- dible; second, a major group joins the tendon of the la- bialis, and fibers are then continued from the lal)ialis tendon ventrally to insert on the mandible. The insertion in general is somewhat ob- scured bj- a fibrous capsule over the ventral part of the muscle. An adductor is absent from the hyoid, but adductors similar to the deep posterior part of the adduc- tor mandibulae are present on all the branchial arches. These muscles have their origin in a groove on the inner side of the epibranchial (see p. 149, fig. 143, ad.) and join the ceratobranchial cartilage. They act in closing the bran- chial arch and hence in spreading the cartilaginous branchial rays to enlarge the gill pocket. Ventral Longitudinal Muscles. Fig. 94. Interareuales muscles, Heptanchii-'i maculatus. (From Davidson.) eh}''', first to seventh epibrancliial cartilages; }'^, first to fifth dorsal interareuales; }''^, first to sixth lateral interareuales; ph}~^, first to sixth pharyngo- branchial cartilages; s.
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