A caudate sonnet is a form of a sonnet in which the normal pattern of fourteen lines is modified by one or more codas or ‘tails’ (Latin cauda meaning “tail”, from which the name is derived). The practice is believed to originate from Francesco Berni, the 16th c. Italian poet.
The form is rare in English verse, though it has been used for satirical purposes: for instance, Milton’s poem On the New Forces of Conscience Under the Long Parliament.
Gerard Manley Hopkins used the form in a less satirical mood in his “That Nature is a Heraclitean Fire”. However, unlike the curtail sonnet, his caudate sonnet is a full sonnet unmodified but with an extra six lines. Hopkins heightens the effect of the extension with an enjambment from the 14th line to the 15th.