Some geometric properties of normal and tangent submanifolds

In this paper we study some special ruled surfaces in a 3-dimensional Riemannian manifold $\overline{M}$. Given an immersed surface M into $\overline{M}$, we consider the ruled surfaces that are normal or tangent to M and give some geometric relations between them, generalizing some recent results obtained in [3], [5]. We also give some general properties on normal and tangent submanifolds of arbitrary dimension.