There is no missing leg.
You are slightly confused because the schematic doesn't show the bounds of the transistor itself.
The connection "Out" in your diagram doesn't come out of the transistor. It is connected to the wire between the top resistor and the transistor.
Imagine the housing of the transistor around the schematic representation (like in the diagram below where the dotted line represents the housing.)
simulate this circuit – Schematic created using CircuitLab
The transistor has only three legs. The output comes from the junction between R1 and the transistor.
After seeing your comments, you are still wondering about two circuits.
The "circuits" you have in mind are as follows:
- Base of the transistor (from the left) to the emitter (bottom)
- Collector of the transistor (top) to the emitter (bottom)
I've labeled the diagram and added arrows to show the two current flows.
When a voltage on the base causes current to flow through the base to the emitter (1.), the transistor allows current to flow from the collector to the emitter (2.).
The current flow through (1) can be very small. Transistors have what is called current gain, whereby a small current through (1) causes a larger current through (2.)
If no current flows through (1) then no current flows through (2.)
So, for the two "circuits" you are thinking of, both must use the emitter. This is called a common emitter circuit. The wikipedia link includes a lot of info on the common emitter circuit, as well as links to the common collector and common base circuits that can also be built with BJT transistors.