1974 GR

someone posted this on a thread on NLM a bit ago:

"The Graduale Romanum (1974) identifies seven ad libitum antiphons for communion:
- Ego sum vitis
- Gustate et videte
- Hoc corpus
- Manducaverunt
- Panem de caelo
- Panis quem
- Qui manducat"

I do not have a 1974 GR, and if I did, I certainly don't have enough Latin skills to decipher it.* Nor do I even know what "ad libitum" means. Could anyone explain this, or give a citation in the GR for where I can find this? (If I were to have a schola, and not learn a different communion antiphon every week, would it be preferable to use the "ad libitum" antiphons, or to use some from the Graduale Simplex?)


*yes. I need to learn Latin. I took one semester of college latin, and will never forget my parents for forcing me to take spanish in high school instead of latin, even after I begged them...
but, there is SO often I pick up a book and it has many latin phrases scattered throughout, that a more educated person would understand, or even entire books that I ought to be able to understand, like the GR! (or am I really dumb and is there an English version of that? Isn't that what the Gregorian Missal is? just incomplete?) so anyhow, I just need to get motivated and sit down and force myself to learn this dead language...