Cranial and postcranial myology of adult Corydoras aeneus is described and results discussed in comparison to other ostariophysan, siluriform and/or loricarioid fishes. Further, a brief discussion on m. adductor mandibulae homologies is given providing arguments for the use of the terminology proposed by Diogo and Chardon (2000) in future studies dealing with the myology of Siluriformes. Doing this, we here identified an A1OST, A2, and A′3 section in C. aeneus and recognised the homology of the m. retractor tentaculi muscle with the A″3. Next to this, the opercular system is discussed, focussing on similarities in this system in both a callichthyid (C. aeneus) and loricariid (Ancistrus cf. triradiatus) representative. In both these families, the m. dilatator operculi is enlarged and the direction of the operculo-hyomandibular articulation has shifted. In addition, in both lineages, the m. hyohyoidei abductor has also shifted its orientation, acting as an adductor. These similarities seem to corroborate the 'decoupling hypothesis' by Schaefer and Lauder (1986) in which a decoupling of elements in primitive members of a lineage leads to a higher morphological diversity within that lineage combined with the possible acquisition of new functions.