Commentary for Berakhot 68:3

BOWING UPON ONE'S FACE. The Braiso presents this information about the various types of bowing as if this is an ordinary derivation. We understand that it is evident from this verse that קידה means to bow, so that one’s face touches the floor. The same should be true of the definition of השתחואה it means that one prostrated himself on the floor with outstretched arms and legs. Tosfos is convinced that this is not true. There are other verses that indicate otherwise.¹Tosfos in Shovuos 16b, quotes three verses that indicate that the meaning of השתחואה is that the face is touching the floor, which seems to contradict what the Braiso is teaching us that קידה means face to the floor. Those verses are:
ויוצא יוסף אתם מעם ברכיו וישתחו לאפיו ארצה
ויקד וישתחו לאפיו
אפים ארץ ישתחוו לך
In each of these three verses we see the word אפים and לאפיו used together with השתחואה. Tosfos sees that as a contradiction to our Braiso. See Tosfos HoRosh who offers a solution to Tosfos’ problem. See also Maharsho who quotes a verse in Sh’mos 34, 8, ויקד ארצה וישתחו In this verse we find קידה together with ארצה.. The Braiso tells us the definition of these terms based on a traditional teaching available to the author of the Braiso. The use of the verses is for us to remember the definitions and by linking them mentally to these verses. Tosfos here in Maseches B’rachos does not elaborate about his sources. We must explore other Tosfos in Maseches M’giloh and in Maseches Shovuos for greater clarity in this matter. And the Braiso cites a verse to prove its point, that קידה means that one bows with his face to the earth and השתחואה means that one prostrates himself.
Tosfos makes us aware that this conclusion based on the verses is problematic. Even though we also find other verses that indicate otherwise,¹Tosfos in Shovuos 16b, quotes three verses that indicate that the meaning of השתחואה is that the face is touching the floor, which seems to contradict what the Braiso is teaching us that קידה means face to the floor. Those verses are:
ויוצא יוסף אתם מעם ברכיו וישתחו לאפיו ארצה
ויקד וישתחו לאפיו
אפים ארץ ישתחוו לך
In each of these three verses we see the word אפים and לאפיו used together with השתחואה. Tosfos sees that as a contradiction to our Braiso. See Tosfos HoRosh who offers a solution to Tosfos’ problem. See also Maharsho who quotes a verse in Sh’mos 34, 8, ויקד ארצה וישתחו In this verse we find קידה together with ארצה.. if so, how can we conclude that these definitions are correct, perhaps we should follow the other verses?
We can answer: That it was known to the Tano from tradition that קידה means to bow to the extent that one’s face touches the ground. The verse is not the source of this information. It is the tradition that the Tano received from his teachers that the meaning of the word קידה is that the face touches the ground. And he cites the verse that proves his point. This verse does in fact speak of קידה as bowing with the face touching the ground. Even though it is not the source of the information it can certainly be used to show that the word does in fact mean that.

Later authorities forbade kneeling in prayer, because it was characteristic of Christian worship. Prostration has also fallen into disuse; but it was practised in the French Synagogues as late as the 13th cent. Abrahams, p. Ixxvii.