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 : 57-58

“ Apteronotus ” gr. bonapartii (Castelnau, 1855)

Adductor mandibulae. The malaris is sectioned into a dorsal subsection promalaris and a ventral subsection retromalaris, which are well-differentiated, except for some set of fibers associated with the ricto-stegalis. The promalaris is positioned dorsolaterally to the dorsal portion of the ricto-stegalis, and arises from the mid-dorsal portion of the hyomandibula. This subsection converges to the buccopalatal membrane, with its anterodorsal fibers differentiate into a moderate endomaxillary ligament, equal to 2/3 of its fibrous portion, to an insertion at the connective tissue between the anterior margin of the premaxilla and upper lip. The retromalaris is positioned lateroventrally to the ricto-stegalis, arising from the anteroventral portion of the preopercle and hyomandibula, with its fibers converging into an elongated ectomaxillary ligament, equal to one and a half of its fibrous portion, that inserts at the posterolateral face of the maxilla ( Fig. 25 ).

The ricto-stegalis originates in the pterosphenoid, parasphenoid, hyomandibula, sphenotic, and metapterygoid. 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, 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.

The segmentum mandibularis is located dorsally to Meckel’s cartilage, extending about

30% 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 promalaris and ricto-stegalis, while its anteromesial and posteromesial bundles are medial to the promalaris and ricto-stegalis (specifically to the presumed 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 25 | Lateral view of dorsolateral musculature of Apteronotus bonapartii (Apteronotidae), MPEG 3038, 217.5 mm LEA. Anatomical abbreviations in Tab. 1. Scale bar = 5 mm.