Adontosternarchus 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 : 56

Adontosternarchus Ellis, 1912

Adductor mandibulae. The malaris is composed of a single mass of fibers, originating from the mid-dorsal portion of the hyomandibula, with its anterodorsal fibers differentiate into an elongated endomaxillary ligament, equal to the fibrous portion of the malaris, inserting on the posteromedial margin of the maxilla; and the its anteroventral fibers inserted to the posterior margin of the anguloarticular and dentary. The malaris is positioned dorsolaterally to the dorsal portion of the rictalis and lateroventrally to the stegalis ( Fig. 23 ).

The rictalis originates in the metapterygoid, preopercle and hyomandibula, with its lateralmost fibers restricted to the anterior margin of the preopercular fossa. The mesialmost fibers of the rictalis converge into the intersegmental aponeurosis, with its lateralmost fibers inserting into the lateral margin of the anguloarticular. The stegalis arises from the hyomandibula, sphenotic, pterosphenoid, parasphenoid, and metapterygoid. Towards its anterior portion, the stegalis converges into the meckelian tendon which, in turn, inserts on the coronomeckelian bone; and with anterodorsal fibers converging to the mandibular tendon.

The segmentum mandibularis is located dorsally to Meckel’s cartilage, extending about 60% of the dorsal portion of this cartilage. The course of the ramus mandibularis trigeminus nerve is lateral to the rictalis and stegalis; 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, pterosphenoid, and sphenotic and inserting onto the hyomandibula. The origin of the levator arcus palatini is narrower than its insertion, approximately a half of its insertion. At the insertion, the anterolateral and posterolateral fiber bundles of the levator arcus palatini are lateral to the malaris, while its anteromesial and posteromesial bundles are medial to the malaris. 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 23 | Lateral view of dorsolateral musculature of Adontosternarchus clarkae (Apteronotidae), MZUSP 30072, 79.3 mm LEA. Green indicates the path of the recurrent ramus of anteroventral part of anterior lateral line nerve. Anatomical abbreviations in Tab. 1. Scale bar = 2 mm.