Two examples of the BF-109 'G model, one airworthy, one residing in the Smithsonian in DC. They made a bunch of these and they constitute a lot of surviving examples.
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The 'greenhouse' framed cockpit was a good example of the Nazi regime's limited ability to produce complex perspex shapes at this stage. Everyone was using bubble canopies by this point of WW2.
If you look at most German aircraft of the era, they feature extensive framing on the perspex cockpit pieces. Making large perspex bits with good optical quality is hard. It is a challenge for restorations nowadays because all the moulds and tooling are gone.