Just a fruendly reminder. The priest,while he has the missal on the altar, he reads the changeable propers, besides the Ordinary of the Mass which prayers can be lengthy. Over time, some have them memorized or nearly so, but the missale is meant to be thereper rubrics.
The priest indeed memorises the Prayers at the Foot of the Altar, his own, AS WELL as the Servers.
There are times when he has no server or anyone who can adequately give the response, so he has to give the responses himself.
Not to mention the occasions that he has to "step in" when the server present gets tongue-tied or stumbles.