The Ritson MS (British Museum Add. MS 5665) preserves for us a choir repertory whose oldest layer is given over to 44 carols—Latin, English, and macaronic. Provisionally they may be dated from about the end of the second third of the fifteenth century. Together with other fifteenth century carol manuscripts they offer considerable support to Margit Sahlin's thesis (Etude sur la carole médiévale. Uppsala dissertation, 1940) that the carol became an ornament of the processional rites of the Catholic Church. As it is applied to England, her argument runs briefly as follows: The religious and didactic carol of the fourteenth and fifteenth centuries is a musical-literary species directly indebted to the liturgy in matters of both form and content. It had been adopted by the Church from popular usage in the fourteenth century, retaining the technique of the earlier dance-song which paralleled, in certain ways, that of responsorial chant.