  We have extended the work of Papers I and II of this series to determine at
higher spatial resolution the properties of the embedded Orion-S Molecular
Cloud that lies within the ionized cavity of the Orion Nebula and of the thin
ionized layer that lies between the Cloud and the observer. This was done using
existing and new [NII](658.3 nm) and [OIII] (500.7 nm) spectra that map the
central region of the Orion Nebula (the Huygens Region). However, it remains
unclear how the surface brightness of the ionized layer on the Orion-S
Molecular Cloud and that of a foreground Nearer Ionized Layer are linked, as
the observations show they must be. It is shown that the Cloud modifies the
outer parts of the Huygens Region in the direction of the extended hot X-ray
gas.
