The anterior or outer wall of the cavity is formed by the mantle; the posterior, inner, or visceral wall by a delicate membrane.
"Journal of the Proceedings of the Linnean Society - Vol. 3" by Various
The pleuro-peritoneal cavity is first distinctly formed at a time when only two visceral clefts are present.
"The Works of Francis Maitland Balfour, Volume 1" by Francis Maitland Balfour