There are several forms of confessional prayers in early Irish, Anglo-Saxon, and continental manuscripts in which the sinner uses the parts of the body to confess. You can find such prayers quoted in Frantzen's Literature of Penance (consult the index; the book is on reserve).
Here is one, partially translated:
"I confess to you the thoughts of my heart, the words of my mouth, and the wrongs of my flesh, for my skin, my kidneys, my mouth, my tongue, my lips . . . ." The list includes hair, hands, and feet, everything wet or dry, inside or out.
Such a prayer has obvious affinities with charms (which are discussed in both the Medicine and Magic modules) as ways of seeking protection. A famous Irish form, the lorica or "breastplate" poem, invokes protection by naming parts of the body and asking that they be blessed. In this case the anatomical motif (so it can be called) is adapted for another use--not to seek protection but to catalogue imagined offenses of parts of the body.
The prayer is an intersection for medical knowledge, religious belief, and something else--the catalogue as a literary form. One kind of catalogue device that readily was adopted by the Church was the litany.
There are other prayers that are quite ambitious lists of sins. These had a more obviously legitimate function as complete or "universal" confessions, sometimes called a "general confession." Here's an example, translated from Old English, from the manuscript in the British Library, London, known as "Cotton Tiberius A.iii":
I confess, Lord Almighty God, and to Mary, the holy mother, and to all the holy ones, and to you bishop, all my sins, that I committed from my youth to the present time, which I became committed to God's foundation: in gluttony and in drunkenness and in wrong marriages and in fornication, in sadness and in laziness and in anger and in evil desire, in malice and in evilness, in hatred and quarrelsomeness, in common oaths and in deceitfulness, in lying and in vainglory, in arrogance, in vision and in vice, in hearing and in treachery, in smell and in touching, in false witness, in avarice, and in murder and in eating too soon and in gluttony and in all perverse acts. . . . .
Some comments: note that the prayer addresses the bishop, not the priest: this suggests a formal ceremony or public penance (see the NEC on this ritual); it appears that the person might be joining a group (note the reference to "God's foundation": what might this be?).
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