The extension to Lechmere opened in 1912, but saw major
changes in the first decade of this present century, when a stretch of
elevated running near North Station was replaced with an underground
route. The transition point appears in this image. The old
elevated and part of the Science Park station (which was added in the
mid-1950s) are to the left. The much newer infrastructure to the
right takes the line toward the nearby subway portal.