Sternarchorhynchus Castelnau, 1855

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 : 67-68

Sternarchorhynchus Castelnau, 1855

Adductor mandibulae. The malaris arises from the mid-dorsal portion of the hyomandibula and preopercle, converging anteriorly to the buccopalatal membrane, where the anterodorsal portion differentiates into a poorly differentiated endomaxilar ligament, equal to three time of the fibrous portion of the malaris, to an insertion at the posterodorsal face of the maxilla; and the anteroventral fibers converges into an ectomaxillary ligament that inserts at the posterolateral face of the same bone ( Fig. 27 ). The malaris is positioned lateroventrally to the ricto-stegalis.

The ricto-stegalis originates in the quadrate, sympletic, endopterygoid, 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 presumably corresponding to the rictalis inserts mainly into the coronoid process throught a ligament equal to the fibrous portion of this section; and the presumed stegalis converges into the meckelian tendon which, in turn, inserts on the posterodorsal margin of the dentary. The segmentum mandibularis is absent ( Fig. 27B ). The ramus mandibularis trigeminus nerve lies mesial to the segmentum facialis.

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 equal to 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 anterodorsal margin of this muscle.

Figures

FIGURE 27 | Sternarchorhynchus goeldii (Apteronotidae), MPEG 1193, 1, 148.3 mm LEA. A. Lateral view of dorsolateral musculature; B. Mesial view of the adductor mandibulae. Anatomical abbreviations in Tab. 1. Scale bars = 5 mm.