Pat Flannery wrote in
:

http://www.freepressinternational.com/marshorn.html

That picture shows a Rover arm, with the normal attached instruments. There
is nothing extra or missing in it. Every single knob, line and doodad in
the picture is accounted for in the rover inventory.

http://marsrovers.jpl.nasa.gov/mission/spacecraft_rover_arm.html shows
schematics of what to expect on the arm.