Whilst Father is quite correct that only cloistered monks and nuns now, at least as a general rule, chant (or recite) Matins in the middle of the night, he doesn't point out the difference between Matins and the 'Office of Readings' in McOffice.
Matins, as chanted or recited by Priests and Religious of the Traditional Orders and Institutes who use the Rubrics of His Holiness Pope John XXIII (the majority of them), contains nine Psalms every day. On ordinary days it has three readings. On Sundays and major Feasts, it has nine. There are 'independent' groups who use older Rubrics, wherein virtually every day has nine readings. The McOffice version, on the other hand, has three Psalms and two readings, invariably.