Apteronotus, Lacepede, 1800

Peixoto, Luiz Antônio Wanderley & de Pinna, Mário, 2022, Patterns of diversification and phylogenetic structure in the dorsolateral head musculature of Neotropical electric eels (Ostariophysi: Gymnotiformes), with a myological synonymy, Neotropical Ichthyology (e 210009) 20 (1), pp. 1-117 : 58-59

Apteronotus gr. leptorhynchus (Ellis, 1912)

Adductor mandibulae. The malaris is composed of a single mass of fibers, originating from the mid-dorsal portion of the hyomandibula and preopercle, converging anteriorly to the buccopalatal membrane, where the anterodorsal portion differentiates into an elongated endomaxilar ligament, twice to the fibrous portion of the malaris, to a insertion at the connective tissue between the anterior margin of the premaxilla and upper lip; and the anteroventral fibers converges into an ectomaxillary ligament that inserts at the posterolateral face of the maxilla. The malaris is positioned lateroventrally to the ricto-stegalis.

The ricto-stegalis originates in the preopercle, quadrate, pterosphenoid, hyomandibula, and sphenotic. At its origin, the lateralmost portion of the ricto-stegalis, presumably corresponding to the rictalis, is separated dorsally from the fibers of the presumed stegalis by the levator arcus palatini, becoming continuous at their mid-portion and partially differentiated towards their insertion sites. The fibers corresponding to the rictalis inserts mainly into the coronoid process; and the presumed stegalis converges into an intersegmental aponeurosis weakly differentiated, where its ventral portion differentiates into the meckelian tendon to an insertion to the coronomeckelian bone, and the anterodorsal fibers converges into the mandibular tendon ( Fig. 30 ).

The segmentum mandibularis extends posteriorly for a significant distance, with the major portion of the segment localized beyond the posterior limit of the lower jaw, and arising along the anterior part of the intersegmental aponeurosis and from the mandibular raphe that is shared with the anterior portion of the segmentum facialis. The segmentum mandibularis is located dorsally to Meckel’s cartilage, extending about 60% of the dorsal portion of this cartilage. The ramus mandibularis trigeminus nerve trespasses the ricto-stegalis, and lies lateral to the presumptive stegalis and mesial to the rictalis and malaris.

Levator arcus palatini. The levator arcus palatini has a roughly parallelogram shape, originating from the ventral margin of the frontal and sphenotic and inserting onto the hyomandibula. The origin of the levator arcus palatini is slightly wider than its insertion. At the insertion, the anterolateral and posterolateral fiber bundles of the levator arcus palatini are lateral to the presumptive rictalis, while its anteromesial and posteromesial bundles are medial to the rictalis. The levator arcus palatini has a mesial arrangement where the anterior margin of the dilator operculi exceeds the median portion of this muscle.

Figures

FIGURE 30 | Apteronotus rostratus (Apteronotidae), USNM 317229, 142.3 mm LEA. A. Lateral view of dorsolateral musculature; B. Mesial view of the adductor mandibulae. Green indicates the path of the recurrent ramus of anteroventral part of anterior lateral line nerve. Anatomical abbreviations in Tab. 1. Scale bars = 5 mm; 4 mm.