  Fine-structure mid-infrared emission lines with critical densities in the
regime 10^4 to 10^6 cm^-3 can be employed to probe the outflow from Wolf-Rayet
stars at radii of \sim 10^15 cm. Narrow-band mid-infrared imaging and
spectroscopy of the nearest WR star to the sun, gamma Velorum is analysed for
spatially resolved forbidden line emission in the Wolf-Rayet outer wind. The [S
IV] 10.52 and [Ne II] 12.81 micron emission regions are found to be spatially
extended, compared to unresolved continuum and He and C recombination line
emission. The [S IV] and [{Ne II] emission line distributions have a high
degree of azimuthal symmetry, indicating a spherically symmetric outflow. A
model wind with a modest degree of clumping (clumping factor f \sim 10)
provides a better match to the observations than an unclumped model. The
overall line intensity distributions are consistent with a freely expanding,
spherically symmetric 1/$r^2$ outflow with constant ionization fraction and
modestly clumped density structure.
