The Gallo-Roman physician Marcellus was born in Bordeaux. He may have served as magister officiorum under Theodosius I, or may have been royal physician. Sarton (Introduction to the history of science I, 391) considered his work "an extrordinary mixture of traditional knowledge, popular (Celtic) medicine, and rank superstition. Interesting also for the historian of botany because of the great number of plants mentioned."
For this edition "Cornarius worked from a manuscript written in the mid-9th century that was superior to the one used for the Teubner edition of 1889 but which was thought to have been lost; it was rediscovered in 1913 and used for the 1916 edition of Marcellus published in Teubner's Corpus Medicorum Latinorum series. Referred to as the Codex Parisinus, it contains Cornarius's corrections and marginal notes" (Wikipedia article on Janus Cornarius).
The writings by Galen in this edition are: De causis respirationis liber 1, De utilitate respirationis, liber 1, De difficultate respirations libri III, De uteri dissectione liber 1, De foetus formatione liber 1, De semine libri II.
Digital facsimile from Google Books at this link.