In this paper, we study various topological properties of generic smooth maps between manifolds whose regular fibers are disjoint unions of homotopy spheres. In particular, we show that if a closed $4$ -manifold admits such a generic map into a surface,then it bounds a $5$ -manifold with nice properties. As a corollary, we show that each regular fiber of such a generic map of the $4$ -sphere into the plane is a homotopy ribbon $2$ -link and that any spun $2$ -knot of a classical knot can be realized as a component of a regular fiber of such a map.