The Gwawdodyn is a traditional welsh poetic form consisting of quatrain stanzas. the first two and the final line are all nine syllables, while the third line is ten syllables. the first second and fourth line all rhyme, while the third line rhymes only internally, with itself, sometimes this internal rhyme shifts to the end of line three and the beginning of line four.[1][2][3][4]
^Turco, Lewis; Turco, Lewis (1986). The new book of forms: a handbook of poetics. Hanover: University Press of New England. ISBN978-0-87451-380-6.