In the very lengthy sequence which accompanies this Mass in Sarum, there is one stanza in which there are textual problems. Here is the 'common' version, viz that in most of the printed editions.
Tensis ligno bracchiis manus conclavantur
cruci caro cruribus clavis tractabantur
nervi, venae, simili modo laniantur
pedes plantae etiam ferro concavantur.
There are no problems in the first line. Nor in the third line. In the forth line, two (of the very many) editions, 55p and 34, read pedum plantae, more elegantly. It could be original or it could be a deft improvement. Two 97 and 98, read conclavantur, a repetition of the ending of the first line, and therefore improbable. But this reading surely witnesses to concavantur. 55p and 34 have terebrantur; perhaps somebody had conclavantur in front of him, realised it could not be right, and (elegantly) guessed at terebrantur.
The second line is the problem. We need a plural subject or a plurality of subjects. 97, 98, 55p, and 34 achieve a plural subject by correcting the strange caro to membra.
55p and 34 read trucibus for cruribus. This seems to me a brilliant emendation (if is not original). c and t are nearly indistinguishable in medieval orthography.
97 and 98 substitute corporis for cruci, but thereby secure a line which is a syllable too long.
55p and 34 achieve sense by writing
cruci membra trucibus chordis alligantur
nice, but I can't see how the common version's tractabantur arose from alligantur. And I always think the best accounts of a crux are those which account for the corruption.