An inkling of this is to be found in the author of the Micrologus…the author writes that it is almost a general custom that the deacon reading the Gospel turn toward the north. But he takes exception to this, not only because the north side is the side for the women, and it is therefore unbecoming that the deacon turn that way, but also because it is plainly contra Romanum ordinem, according to which the deacon stands on the ambo turned to the south, that is, the side of the men. He explains the variant practice, which had already become fixed and rooted, as a conscious imitation of the movement and position of the priest who, when saying Mass without a deacon, does really have to say the Gospel at the north side of the altar in order to leave the other side free for the sacrificial activity, and who thus could give the appearance of actually turning towards the north.
Why should the priest not face the people when he is reading the Gospel? Interestingly, that is what a plain reading of the Ritus Servandus would enjoin, except that it is only explained by a defunct Roman custom.The spot from which the deacon at a solemn function could read the Gospel most conveniently and fittingly had to be chosen in such a way that on the one hand the reader had the people before him, and on the other he did not turn his back on the bishop and the clergy surrounding him. In the basilicas of the dying ancient period, where the cathedra of the bishop stood in the apse, he would therefore have to stand to the side, in the forward part of the choir, to the right of the presiding bishop (for all the ranks of honor were reckoned with the cathedral of the bishop as the point of departure). He would thus face either north or south depending on the position of the apse and the cathedra, whether to the west, as they were in the older Roman structures, or to the east, as later became customary.