  Using data from the Southern Galactic Plane Survey we present a possible
distant spiral arm in the fourth quadrant of the Milky Way. The very distinct
and cohesive feature can be traced for over 70 deg as the most extreme positive
velocity feature in the longitude-velocity diagram. The feature is at a
Galactic radius between 18 and 24 kpc and appears to be the last major
structure before the end of the HI disk. We compare the feature with a Galactic
spiral model and show that it is well reproduced by a spiral arm of pitch
angle, i ~ 9 deg. The arm is quite well confined to the Galactic plane,
dropping at most 1 kpc below the Galactic equator. Over most of its length the
arm is 1 - 2 kpc thick.
