Thank you for letting me see that. That... is Zinsco's implementation of a "Rule of Six" panel.
The obsolete "Rule of Six" is that you could have up to six main breakers to shut off your house. That's because houses were getting bigger and bigger electrical service, yet breakers larger than 60A were still very expensive. So a traditional main breaker like modern panels was not cheap enough for builders.
The "Rule of Six" allowed them to use cheap <=60A breakers for up to five large appliances, then the 6th breaker served a "built-in subpanel" that had the rest of your branch circuit loads (in the vernacular of the age, they called them "lighting" loads but it meant virtually all 120V loads).
Zinsco's approach was to only provide bus-bars in the "Rule of Six" area. And then the lower "lighting area" breakers didn't use busbars (except as something to physically clip onto), and fed the power from the left to the right, as you see. Zinsco was always into creative busing.
I see where this panel is being used for less and less. It's probably good to hasten that along. I count only 8 1-pole branch circuits that you are even using, so now would be a fantastic time to have the power company "pull the meter" (virtually, no doubt) and swap that panel for something modern. Like a Pushmatic :) No seriously, I would go CH or QO because they are compact, and a 42-space panel will fit there. If those joists are 14.5” apart, a new panel will drop right in.
One last thing, you see Zinsco's clever way of handle-tying breakers. Some of them have been flipped around so they no longer tie. You should flip them back so they are tied. That way it takes 6 throws instead of 8 (the person frantically turning off the power doesn't know some of them are dead).