So, is the constant current provided by the voltage source in the top right?
No,
the current source is a circuit by itself which is only feed by Vs.
In an IC it will be composed of transistors.
There are many ways to create a current source(google it).
These IC diagrams are merely conceptual, as you can see the other one is represented by the symbol alone.
Actually you have one shown "with details" in the specific IC,look at the red in the pic.