It looks like a variable resistor, ...
Agreed. The convention is that when the wiper arrow lies across the resistor that it is a preset potentiometer or"trim-pot" used to adjust or calibrate the equipment. These usually feature a screwdriver adjustment rather than a knob. (The regular potentiometer symbol arrowhead usually just touches the resistor at the midpoint.)
The lower variable resistor seems to set a minimum resistance value for the combination.
Figure 1. A selection of preset potentiometers. Source:Robot Room.
... but the rest of the circuit is attached to the tail of the arrow. I feel as though this circuit is trying to describe a voltage divider. Is this true?
That sounds right. It's difficult to know without knowing what the circuit is for and what U and M are.