Orthosternarchus Ellis, 1912

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 : 60

Orthosternarchus Ellis, 1912

Adductor mandibulae. The malaris is composed of a single mass of fibers, originating from the mid-dorsal portion of the hyomandibula, converging anteriorly to the buccopalatal membrane, where the anterodorsal portion differentiates into an endomaxilar ligament, equal to three times of the fibrous portion of the malaris, to a insertion at the posteromesial margin of the premaxilla; and the anteroventral fibers converges into an ectomaxillary ligament poorly differentiated that inserts at the posterolateral face of the maxilla.

The ricto-stegalis originates in the quadrate, pterosphenoid, parasphenoid, hyomandibula, sphenotic, and metapterygoid. At its origin, the ricto-stegalis is a single mass of fibers, and partially differentiated towards their insertion sites. The fibers corresponding to the presumed rictalis inserts mainly into the coronoid process throught a ligament equal to the fibrous portion of the ricto-stegalis; and the presumed stegalis converges into the meckelian tendon to an insertion to the coronomeckelian bone.

The pattern consists of a fibrous composition of adductor mandibulae, segmentum facialis, however, some more mesial tendons ossify, resulting in the occurrence of intermuscular bones. The ramus mandibularis trigeminus nerve lies mesial to the segmentum facialis.

Levator arcus palatini. The levator arcus palatini has a trapezoidal shape, originating from the ventral margin of the frontal and sphenotic and inserting onto the hyomandibula. The origin of the levator arcus palatini corresponds to the 2/3 of its insertion. At the insertion of the levator arcus palatini, all fibers are located laterally to the malaris; and with only the posterodorsal fibers being mesial to the dilatator operculi, where the anterior margin of the dilator operculi does not exceeds the medial portion of the levator arcus palatini.