Subway Line Connection To Commuter Rail

I was thinking earlier today about this and I'm sure some people also have. Are all subway lines connected to the commuter rail? I know the green line is connected at Riverside and the red line is connected at Cabot. I also believe the orange line is connected at Wellington but I'm not sure. Anybody know about the blue line? This also brings up the question about if the subway lines are all connected or are they all independent of each other?

There was a short-lived connection to the Blue Line near Airport that I think was used to deliver the #3 cars. Another connection point was at Central Avenue on the Mattapan Line with the Old Colony's Milton Branch.

With the exception of the connection between the Mattapan Line and the Red Line at Codman Yard, there are no longer any connections between the different subway lines, though at one time all of them had at least one connection to the trolley network.

Checking out the recent work done on the Medford Junction just north of Wellington, you can see a connecting track on the western side of the Orange Line that looks like it was restored.

Somewhere I read a description of a really complicated route that a hypothetical car could have taken to run the length of all the four lines, involving a ramp at Sullivan Square, a connection between the Cambridge-Dorchester subway and the trolley system near Eliot Shops (near Harvard Sq), the street track over the Longfellow Bridge, and a lot of street track in general. Maybe it was in this thread https://www.railroad.net/viewtopic.php? ... bway+lines or in one of the similar threads linked from the second page of that one.

Historic connections between the subway lines and surface routes:

Red Line-Mattapan Line @ Codman Yard (still intact)

Red Line to surface lines @ Codman Yard (a short spur track that came down Gallivan Blvd from the Dorchester Ave line and went up the driveway to the yard. I believe it was only used during construction of the Red Line. A short piece of track is still visible in the driveway.)

Main Line El to surface lines @ Arborway (a short-lived ramp from the elevated down into the north end of the Arborway yard complex. A few pieces of girder angling away from the elevated tracks remained until the elevated was torn down in 1987)

Blue Line to Red Line via Longfellow Bridge (A short remnant of the surface car line that once ran from Cambridge to East Boston via the East Boston Tunnel. Remained in use until Orient Heights opened in 1952)

Red Line to surface lines near Harvard Sq (a connecting track from the Red Line's Eliot Shops to the adjacent Bennett St Carhouse)

Main Line El to surface lines @ Sullivan Sq (connecting tracks from the elevated shops down to the surface car facilities)