Nantonos:
Which the OP saw, but was confused because the schematic is in several parts that do not seem to be connected at first glance.
Each signal has a name - the name is unique to that signal and defines the connections even if they are not drawn in.
For a simple circuit like this there isn't a good reason not to draw them, but in large circuits it gets horribly confusing to draw all the connections between different parts, so in general its good practice.