  A graphs of rank n (homotopy equivalent to a wedge of n circles) without
``separating edges'' has a canonical n-dimensional compact C^1 manifold
thickening. This implies that the canonical homomorphism f:Out(F_n)-> GL(n,Z)
is trivial in rational cohomology in the stable range answering a question
raised by Hatcher and Vogtmann [6]. Another consequence of the construction is
the existence of higher Reidemeister torsion invariants for IOut(F_n)=ker f.
These facts were first proved by the first author in [8] using different
methods.
