  In the first part of this work the classical and statistical aspects of the
dynamics of an inextensible chain in three dimensions are investigated. In the
second part the special case of a chain admitting only fixed angles with
respect to the $z-$axis is studied using a path integral approach. It is shown
that it is possible to reduce this problem to a two-dimensional case, in a way
which is similar to the reduction of the statistical mechanics of a directed
polymer to the random walk of a two-dimensional particle.
