  Oriented ribbon graphs (dessins d'enfant) are graphs embedded in oriented
surfaces. The Bollob\'as-Riordan-Tutte polynomial is a three-variable
polynomial that extends the Tutte polynomial to oriented ribbon graphs. A
quasi-tree of a ribbon graph is a spanning subgraph with one face, which is
described by an ordered chord diagram. We generalize the spanning tree
expansion of the Tutte polynomial to a quasi-tree expansion of the
Bollob\'as-Riordan-Tutte polynomial.
