And what about those Short Readings?
156. The short readings or “chapters” (capitula) are referred to in no. 45, which describes their importance in the liturgy of the hours. They have been chosen to give clear and concise expression to a theme or an exhortation. Care has also been taken to ensure variety.
157. Accordingly, four weekly series of short readings have been composed for Ordinary Time. They are incorporated into the psalter in such a way that the reading changes during the four weeks. There are also weekly series for the seasons of Advent, Christmas, Lent, and Easter, In addition there are proper short readings for solemnities, feasts, and some memorials, as well as a one-week series for night prayer.
Remember, you do-it-yourself liturgists: no Gospel readings.
158. The following determined the choice of short readings:
in accordance with tradition, exclusion of the Gospels;
respect for the special character of Sunday, or even of Friday, and of the individual hours;
use only of the New Testament for the readings at evening prayer, following as they do a New Testament canticle.
This is an interesting bit of fussiness, given that during the Easter season at Mass, Old Testament psalms are sung in between New Testament proclamations, the first Eastertime reading being from Acts.