  The main change with respect to the previous version is a change of
terminology : we call "ordinary" the webs previously called "regular". A
holomorphic $d$-web of codimension one in dimension $n$ is "ordinary", if it
satisfies to some condition of genericity. In dimension at least 3, any such
web has a rank bounded from above by a number $\pi'(n,d)$ strictly smaller than
the bound $\pi(n,d)$ of castelnuovo. This bound $\pi'(n,d)$ is optimal.
Moreover, for some $d$'s, the abelian relations are sections with vanishing
covariant derivative of some bundle with a connection, the curvature of which
generalizes the Blaschke curvature. In dimension 2, we recover results of
H\'enaut and Pantazi
