  We discuss the wormholes associated with the four-dimensional Schwarzschild
(S4), Schwarzschild anti De Sitter (SaDS4), and Reissner-N\"ordstrom (RN4)
black holes, in Schwarzschild, isotropic and Kruskal-Szekeres cordinates. The
first two coordinate systems are valid outside the horizons, while the third
one is used for the interiors. In Schwarzschild coordinates, embedding for
SaDS4 exists only for a finite interval of the radial coordinate r, and similar
restrictions exist for RN4. The use of the K-S coordinates allows us to give an
explicit proof of the pinching-off of the bridges, making them non-traversable.
The case of the extreme Reissner-N\"ordstrom (ERN4) is also discussed.
