  We analyze the resolved neutral hydrogen emission properties of a sample of
eleven of the nearest spiral galaxies. Between 60 and 90% of the total HI line
flux within the optical disk is due to a high brightness network (HBN) of
emission features which are marginally resolved in their narrow dimension at
about 150 pc and have a face-on covering factor of about 15%. Averaged line
profiles of this component are systematically non-Gaussian with a narrow core
(less than about 6 km/s FWHM) superposed on broad Lorentzian wings (30 km/s
FWHM). An upper limit to the gas temperature of 300 K follows directly from the
narrow line profiles, while simple modeling suggests kinetic temperatures equal
to the peak emission brightness temperature (80-200 K) in all cases but the
outer disks of low mass galaxies, where the HBN becomes optically thin to the
21 cm line. Positive radial gradients in the derived kinetic temperature are
found in all spiral galaxies. The distributions of brightness temperature with
radius in our sample form a nested system with galaxies of earlier
morphological type systematically displaced to lower temperature at all radii.
The fractional line flux due to the HBN plummets abruptly near the edge of the
optical disk where a diffuse outer gas disk takes over. We identify the HBN
with the Cool Neutral Medium.
