Giant Sunfish

Mola mola Linnaeus

MUSCLES OF THE CHEEK

ADDUCTOR MANDIBULAE (Figures 178, 179: A 1α A 1β, A 2α, A 2β, A 3).—A 1α is fairly small, arising from the fascia over A 2 beneath the orbit, and inserting on the posteroventral face of the maxilla. A 1β originates from the posterolateral face of the palatine and the lateral parasphenoid. It passes anteroventrally to insert on the posterodorsal face of the maxilla. A 2α originates from the dorsolateral preopercle, the anterior and dorsal hyomandibular and by a small slip from the ventromedial face of the pterotic. It passes anteriorly, lateral to ramus mandibularis V, to insert with A 2β and A 3 in the Meckelian fossa. A 2β originates from the lateral parasphenoid (some fibers arising as far back as the posterolateral margin of the bone beneath the basioccipital), the anteroventral and ventral prootic, and the dorsomedial faces of the hyomandibular and metapterygoid. It lies medial to ramus mandibularis V, and inserts together with A 2α and A 3 in the Meckelian fossa. A 3 arises from the lateral quadrate, symplectic, mesopterygoid, and hyomandibular and passes forward to join the insertion tendon of the A 2 complex.

LEVATOR ARCUS PALATINI (Figure 178: L.A.P.).—This is a small muscle, originating from the ventral face of the sphenotic at the rear of the orbit and passing down to insert on the dorsal face of the hyomandibular medial to the posterior extension of A 2α.

DILATATOR OPERCULI (Figure 178: D.O.).—Origin is from the ventral face of the lateral process of the sphenotic. The fibers insert aponeurotically on the dorsal margin of the opercle.

LEVATOR OPERCULI (Figure 178: L.O.).—This is a well-developed muscle, originating from the ventrolateral face of the pterotic and inserting on the posterodorsal face of the opercle.

ADDUCTOR ARCUS PALATINI (Figure 179: A.A.P.).—The muscle is well developed, and passes ventrolaterally from its origin on the lateral face of the parasphenoid to insert on the dorsomedial faces of the palatine, mesopterygoid, metapterygoid, and hyomandibular. Posteriorly, the origin is aponeurotic. Anteriorly, a very small bundle of fibers passes anterolaterally from the parasphenoid to the palatine. It possesses a ventral aponeurosis, and R. maxillaris V passes through it. It bears a striking resemblance to the retractor arcus palatini of the balistoids and ostracioids.

ADDUCTOR OPERCULI (Figure 180: AD.OP.).—The fibers arise from the ventral face of the pterotic and insert on the posterodorsomedial face of the opercle.

MUSCLES OF THE HYOID REGION

VALVULUS.—Origin is from the ventromedial face of the angular, the fibers sweeping anterodorsomedially to fade into the tissues of the mandibular buccal valve.

PROTRACTOR HVOIDEI (Figure 178: PR.HY.).—The fibers arise from the posteroventral face of the dentary and attach to the lateral faces of the anterohyal and posterohyal. The more posteroventral fibers pass medially to a midventral raphe.

HYOHYOIDEI ABDUCTORES (Figure 178: H.AB.).—There are three of these muscles. The dorsalmost passes from the anterodorsomedial face of ray 2 to the posteroventromedial face of ray 3, the second has the same sites of attachment, but involving rays 1 and 2, while the third muscle connects the ventromedial face of ray 1 with the ventromedial regions of the anterohyal and ventrohyal. The muscles are well developed.

HYOHYOIDEI ADDUCTORES (Figures 178, 180: H.AD.).—The muscle is well developed in the lateral wall of the opercular cavity, where it attaches to the medial faces of branchiostegal rays 2-θ. A small anterior slip passes ventrally to attach to the dorsal face of ray 1. Some of the dorsal fibers arise from the medial face of the preopercle and the anterodorsal face of the cleithrum. Ventrally, the fibers attach to the anteromedial face of the cleithrum and the aponeurotic fascia covering the pharyngoclaviculares. Posterodorsally, fibers of the muscle arise from the medial face of the hyomandibular, ventral pterotic, and the fascia covering the wall of the opercular cavity, which, in molids, extends dorsally to the region of the sixth to seventh vertebrae (medial to the posterior part of the pterotic and the supracleithrum). These fibers form the dorsal and medial walls of the cavity between the pterotic and the fifth vertebra, ultimately fading out in the aponeurotic sheet which attaches to the dorsomedial margin of the cleithrum.

HYOHYOIDEUS INFERIORIS (Figure 178: HY.IN.).—This muscle is well developed, passing dorsolaterally from the midline to the lateral face of the anterohyal and the base of the first branchiostegal ray.

STERNOHYOIDEUS (Figures 178, 180: STH.).—Origin is from the anteroventral face of the cleithrum. The ventral fibers pass medial to the rectus communis to the posterior face of the ventrohyal, while the dorsolateral fibers lie lateral to this muscle, also attaching to the ventrohyal.

VENTRAL BRANCHIAL MUSCLES

PHARYNCOCLAVICULARIS EXTERNUS (Figures 178, 180, 181: PHC.E.).—The muscle is well developed near its origin from the ventromedial face of the cleithrum, but fades into an aponeurotic sheet on the inner wall of the opercular cavity, just lateral to the heart. A small ventral bundle continues anterodorsally to insert on the anteroventral face of ceratobranchial 5.

PHARYNGOCLAVICULARIS INTERNUS (Figures 180, 181: PHC.I.).—A large bundle of the muscle inserts on the posteroventral margin of ceratobranchial 5. Most of the fibers grade into the fascia formed by the pharyngoclavicularis externus and the hyohyoidei adductores. A small dorsal bundle continues posteriorly to attach to the medial face of the cleithrum.

OBLIQUI VENTRALES I-III (Figure 181: OBL.V.).—The muscles span the articulations between the ventral faces of the ceratobranchials and the respective hypobranchials of the first three arches.

TRANSVERSI VENTRALES IV, V (Figure 181: TR.V.).—The anterior muscle crosses the midline between the anteroventromedial faces of the fourth ceratobranchials. Transversus V spans the midline between the anteroventromedial faces of the fifth ceratobranchials, and is somewhat larger.

RECTUS VENTRALIS I (Figures 180, 181: RECT.V.).—The muscle connects the anterolateral faces of the first ceratobranchial and hypobranchial to the posterodorsal face of the dorsohyal.

RECTUS COMMUNIS (Figures 180, 181: R.COMM.).—The fibers arise aponeurotically from the posteroventromedial face of the ventrohyal. They grade into a thin, aponeurotic sheet which inserts on the anteroventral face of ceratobranchial 5.

DORSAL BRANCHIAL MUSCLES

LEVATORES EXTERNI I, III, IV (Figure 180: L.EXT.).—Origin is from the dorsomedial face of the hyomandibular, and the muscles are small. Levator I inserts on the dorsolateral face of epibranchial 1 and the ligament between the first and second ceratobranchials. Levator III inserts on the dorsolateral faces of epibranchials 2 and 3, with the bulk of the fibers serving the latter bone. Levator IV is best developed, and inserts along the dorsomedial face of epibranchial 4.

LEVATORES INTERNI II, III (Figure 180: L.INT.).—Both muscles originate from the posteroventral face of the prootic and pass anteroventrally. Levator II inserts on the lateral face of infrapharyngobranchial 2, while levator III inserts on the dorsolateral faces of infrapharyngobranchials 2 and 3.

OBLIQUUS DORSALIS III (Figure 182: OBL.D.).—The muscle connects the posterodorsal face of epibranchial 3 with the posterodorsal faces of infrapharyngobranchials 2 and 3.

TRANSVERSI DORSALES II, IV (Figures 180, 182: TR.D.).—Transversus II arises from the midline beneath and including the ventrolateral surface of the parasphenoid. The more anterior fibers have migrated forward along the parasphenoid, so that this part of the muscle passes posterolaterally from its origin. Insertion is on the dorsomedial face of infrapharyngobranchial 2. Transversus IV passes across the midline between the medial faces of the fourth epibranchials.

RETRACTOR DORSALIS (Figure 182: D.RETR.).—Origin is from the posterodorsolateral faces of the exoccipital and basioccipital, and the neural spine of the first vertebra. The muscle inserts on the posterodorsomedial faces of infrapharyngobranchials 2–4.

ADDUCTORES IV, V (Figures 180, 182: AD.).—Adductor IV is well developed and connects the medial and posteromedial faces of epibranchial 4 and ceratobranchial 4. Adductor V is small, passing from the anterodorsal tip of ceratobranchial 5 to the posterolateral face of epibranchial 4.

SPHINCTER OESOPHAGI (Figures 180, 181, 182: S.O.).—The muscle surrounds the esophagus, attaching primarily to the posterior faces of epibranchial 4 and ceratobranchial 5. Dorsally, some fibers become longitudinally oriented, lying both lateral and medial to the retractor dorsalis. They attach to the posteromedial faces of epibranchial 4 and infrapharyngobranchial 3. Ventrally, some fibers also take on a longitudinal orientation, lying dorsal to transversus ventralis V and attaching to the anteromedial face of ceratobranchial 5.

MUSCLES OF THE PECTORAL REGION

ABDUCTOR SUPERFICIALIS (Figure 178: ABD.S.).—The fibers arise from the anterolateral face of the cleithrum and insert on the dorsolateral faces of the principal fin rays.

ABDUCTOR PROFUNDUS (Figure 178: ABD.P.).—Origin is from the lateral faces of the cleithrum and coracoid, the muscle inserting on the posterolateral faces of the principal rays and the lateral base of the vestigial ray.

ARRECTOR VENTRALIS (Figure 178: ARR.V.).—The muscle arises from the lateral cleithrum dorsal to the abductor superficialis, and inserts on the anterodorsal face of the medial half of the vestigial fin ray.

ADDUCTOR SUPERFICIALIS (Figure 183: ADD.S.).—The fibers arise from the anterodorsomedial face of the cleithrum, and insert on the anteromedial faces of the principal rays some distance distal to their bases.

ADDUCTOR PROFUNDUS (Figure 183: ADD.P.).—Origin is from the medial faces of the cleithrum and coracoid and the posterolateral face of the latter bone. The muscle inserts on the posteromedial faces of the principal rays a little distal to their bases.

ARRECTOR DORSALIS (Figure 183: ARR.D.).—This is a small muscle, originating from the medial face of the cleithrum and inserting on the medial face of the medial half of the vestigial fin ray.

PROTRACTOR PECTORALIS (Figures 178, 180: P.P.).—The muscle originates from the posterodorsal tip of the hyomandibular and the pterotic behind it. It attaches to the anterodorsal face of the cleithrum. The medial fibers intermingle somewhat with the lateral fibers of the levator pectoralis. The muscle lies lateral to the adductor operculi but medial to the levator operculi.

LEVATOR PECTORALIS (Figure 180: TR.).—The fibers of this muscle pass medial to the adductor operculi, and arise from the fascia of the opercular cavity beneath the posterior extension of the hyomandibular. The fibers insert on the anterodorsomedial face of the cleithrum.

MUSCLES OF THE DORSAL FIN

ERECTORES AND DEPRESSORES DORSALES (Figures 178, 184: EREC. + DEPR.).—Only the erectors and depressors of the first two fin rays have separate tendons. In the next fourteen rays, the erectors and depressors have fused, and insert by a single tendon along the lateral face of each ray a little distal to the base. Origin is from the lateral faces of the vertebral centra and neural spines, the posterodorsal surface of the skull, and the septum in the midline dividing the dorsal and anal fin musculature. The ventral fibers are continuous with the surrounding fibers, particularly anteriorly. The muscles to the more anterior rays tend to lie nearer the midline, those to middle rays being best developed. The lateral fibers of the more anterior muscles also take origin from the medial face of the thick, subdermal fascia (represented as cut surface in Figure 178, but not in Figure 184).

SUPRACARINALIS ANTERIOR.—This is a small muscle which arises from the posterodorsal face of the supraoccipital. The fibers soon grade into a long, thin tendon which attaches to the anterodorsal face of the first dorsal pterygiophore.

MUSCLES OF THE ANAL FIN

ERECTORES AND DEPRESSORES ANALES. (Figure 184: EREC. + DEPR.).—The first two fin rays have separate erector and depressor tendons, the tendons to the other fourteen fin rays being compound, owing to the fusion of the erector and depressor muscles. Insertion of these tendons is on the lateral faces of the rays a little distal to their bases. The fibers originate from the lateral septum, the centra and haemal spines of the seventh to sixteenth vertebrae, and the basal pterygiophores of the anal fin. The fibers do not encroach on the abdominal cavity, and intermingle in the dorsal region.

LATERAL BODY MUSCLES

EPAXIALIS (Figures 178, 184: EPAX.).—The muscle is much reduced. Anteriorly, it arises from the posterodorsal tip of the epiotic. It passes posteriorly as a very thin sheet, just below the skin, and gradually becomes broader. It is separated from the erector-depressor complex by a tough fascia, from the medial surface of which the lateral fibers of this latter complex arise. Vague myomeres are recognizable, there being some fifteen of them before the fibers become continuous with the section serving the dorsal eight caudal fin rays. This main posterior section arises from the lateral faces of the caudal fin supporting elements and the centra and neural spines of the fourteenth to sixteenth vertebrae. Insertion is tendinous on the anterolateral bases of the eight dorsal caudal fin rays.

OBLIQUUS SUPERIORIS (Figure 184: OBL.S.).—Posteriorly, vague fibers in the subdermal tissue are continuous with the amerodorsolateral surface of the muscle mass serving the ventral caudal fin rays. The mass of this musculature arises from the lateral faces of the ventral caudal fin supporting elements and the centra and haemal spines of the fifteenth and sixteenth vertebrae. Insertion is tendinous on the anterolateral bases of the eight ventral caudal fin rays.

OBLIQUUS INFERIORIS (Figure 178: OBL.I.).—The muscle is reduced to two small fiber bundles. The anteroventral one arises from the posteromedial face of the coracoid, and soon fades out in the fascia overlying the abdominal cavity. The other section arises from the posteroventral tip of the postcleithrum and passes posteroventrally into the subdermal tissue, fading out just above the first pterygiophore of the anal fin. It is just possible that this section represents the residual first in· clinator analis, but it seems more likely that it is part of the obliquus inferioris.