Internal bialgebroids, entwining structures and corings

The internal bialgebroid – in a symmetric monoidal category with coequalizers – is defined. The axioms are formulated in terms of internal entwining structures and alternatively, in terms of internal corings. The Galois property of the coring in question is related to the ${\times }_R$-Hopf algebra property. The language of entwining structures is used to discuss duality.