Lord (Κυριε). In the LXX, not in the Hebrew. Quotation (the sixth) from Psalm 102:26-28 through verses Hebrews 1:10-12. Note emphatic position of συ here at the beginning as in verses Hebrews 1:11-12 (συ δε). This Messianic Psalm pictures the Son in his Creative work and in his final triumph.

Hast laid the foundation (εθεμελιωσας). First aorist active of θεμελιοω, old verb from θεμελιος (foundation) for which see Colossians 1:23.