John Lightfoot on Matthew 26:7

[Poured it upon his head, as he sat at meat.] Therefore, it was not the same supper with that in John 12:1; for then our Saviour's feet were anointed, now his head. I admire that any one should be able to confound these two stories. Oil, perfumed with spices, was very usual in feasts, especially sacred; and it was wont to be poured upon the head of some one present.

"The school of Shammai saith, He holds sweet oil in his right hand, and a cup of wine in his left. He says grace first over the oil, and then over the wine. The school of Hillel saith, Oil in his right hand, and wine in his left. He blesseth the sweet oil, and anoints the head of him that serves: but if the waiter be a disciple of the wise, he anoints the wall; for it is a shame for a disciple of the wise to smell of perfumes." Here the waiter anoints the head of him that sits down.