"The Head That Once Was Crowned with Thorns"

"The Head That Once Was Crowned with Thorns" is sung to the tune "St. Magnus."  Here's the last phrase:

In the second verse, the text here, describing Jesus, is "And heav'n's eternal Light."  "Eternal" is sung with a melisma (D C B A), giving a sense of duration.

There's a similar feature in the last (sixth) verse, where the text here, now describing the cross, is "Their everlasting theme."  "Everlasting" is also sung with a melisma (D D C B A) for a sense of duration.