I’m Australian, but some of the older switchboards in industrial installations are similar in appearance to the top image.
The middle would have a busbar (or three if it’s a three phase panel) that connects the circuit breakers to the main switch. The cables are connected to the far left and far right sides of the breakers.
It could be different in the US, though, if anyone with more relevant experience wants to chime in.
Edit: looking back at the top image, I’m reminded that the US uses split phase in some places, so that top panel likely has two busbars down the middle.
I’m Australian, but some of the older switchboards in industrial installations are similar in appearance to the top image.
The middle would have a busbar (or three if it’s a three phase panel) that connects the circuit breakers to the main switch. The cables are connected to the far left and far right sides of the breakers.
It could be different in the US, though, if anyone with more relevant experience wants to chime in.
Edit: looking back at the top image, I’m reminded that the US uses split phase in some places, so that top panel likely has two busbars down the middle.