Has anyone got an old picture of the City branch Euston platforms
facing EAST, from before about the 1920s?

Its just that there should be some unique weird bridge thing in the
middle of the platform back then, and I haven't found any pictures of
it.

Basically what it boils down to is that the two "vents" in this
picture http://www.abandonedstations.org.uk/...6_Euston41.jpg

are really corridoors to the original platform exit. Here's the inside
of one of them, complete with old posters -
http://www.subbrit.org.uk/sb-sites/s...n/euston11.jpg

The platforms there were originally islands, so the only way to get to
the platform from those corridoors would be by (highly visible)
bridge, crossing the (now filled in) northbound tracks.

That would be fairly unique - the vents are in the middle of the
platform, and there are two of them, so unlike all other bridges over
the tracks on island platforms on deep tubes, the bridge structure
must actually have been visible from the platforms.

So there must somewhere be a picture of that?