Normally you'll see "a" or "b". This denotes that only a portion of the verse is being quoted, "a" designation the former portion, and "b" the latter. I suppose that beginning, middle, and end might be designated "a" "b" and "c" respectively, however, the usages I'm aware of are only former and latter portion, thus "a" and "b". Thus John 6.37a: "All that the Father giveth me shall come to me". John 6.37b: "...him that cometh to me I will in no wise cast out".