Platyurosternarchus Mago-Leccia, 1994

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 : 62-63

Platyurosternarchus Mago-Leccia, 1994

Adductor mandibulae. The adductor mandibulae, segmentum facialis lacks any subdivisions, however, at its origin, the segment is partially sectioned posterodorsally by the levator arcus palatini, becoming continuous at their mid-portion and partially differentiated towards their insertion sites. The segmentum facialis originates from the hyomandibula, quadrate, simpletic, pterosphenoid, parasphenoid, sphenotic, metapterygoid, and preopercle. The lateralmost fibers converge anteriorly to the buccopalatal membrane, where the anterodorsal portion differentiates into an endomaxilar ligament, equal to the fibrous portion of this portion of the segmentum facialis, 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; and, based on positional correspondence, this muscle portion presumably corresponds to the malaris.

The rictalis and stegalis differentiates towards their insertion sites, with the lateroventral fibers homologous, at least in part, with the rictalis, inserting into the coronoid process; and the medialmost set of fibers of the segmentum facialis, presumably homologous with the stegalis, converging to the meckelian tendon that, in turn, inserts on the coronomeckelian ( Fig. 22 ). The ramus mandibularis trigeminus nerve trespasses the presumed rictalis and stegalis, and lies lateral to both sections and mesial to the 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 presumed rictalis and dorsolaterally to malaris; while its anteromesial and posteromesial bundles are medial to the presumed rictalis. This muscle has a mesial arrangement where the anterior margin of the dilatator operculi reaching the anterodorsal margin of the levator arcus palatini.

Figures

FIGURE 22 | Platyurosternarchus macrostomus (Apteronotidae), MZUSP 57686, 189.5 mm LEA. A. Lateral view of dorsolateral musculature; B. Mesial view of the adductor mandibulae. Anatomical abbreviations in Tab. 1. Scale bars = 10 mm; 5 mm.