Menachos Chapter 11, Mishnah 4. The opening of the Mishnah sums up the topic discussed in the previous Mishnah - when and where the menachos may be prepared, since according to several opinions they may be prepared even outside the Azarah. The wording of the Mishnah is difficult to translate, but its meaning is clear: any service that may be performed outside the Azarah may be done in any vessel at all - on a cutting board or in a plastic container - and there is no need for a sanctified service vessel of the Beis HaMikdash. On the other hand, any service that must be performed in the Azarah must be done specifically in a service vessel.
The words of the Mishnah:
"Kol hamenachos yesh bahen ma'aseh kli bifnim" - any minchah whose preparation is done inside, within the Azarah, must be done through the act of a vessel, meaning a service vessel.
"V'ein bahen ma'aseh kli bachutz" - a service that may be performed outside the Azarah, such as the kneading according to certain opinions, does not require a service vessel at all, and may be done even on a simple wooden board or in any other container.
The shape of the Shtei HaLechem:
From here the Mishnah returns to the central topic of the chapter - the Shtei HaLechem and the Lechem HaPanim. First the Mishnah asks: "Keitzad shtei halechem?" - what did the two leavened wheat loaves that were waved on Shavuos look like, and what was their shape:
"Arkan shivah" - seven tefachim long.
"V'rachban arba" - four tefachim wide.
"V'karnoseihen arba etzba'os" - four protrusions, similar to the Mizbeach in the Beis HaMikdash, which had corners protruding upward. Except that the corners of the Mizbeach were a full amah, whereas here they are four fingerbreadths. A fingerbreadth is the width of the thumb, and four fingerbreadths are about a tefach, the width of the palm - roughly three or four inches.
It emerges that the Mishnah does not give a height for the loaf. In practice this was a flat bread, rolled out from the required amount of flour: the recipe called for an isaron, which is about a gallon - roughly three and a half liters, approximately 3.6 liters - of flour. The flour was kneaded into dough, and the dough was made seven by four, and whatever thickness it came out to is its thickness. Onto the four corners additional pieces of dough were attached vertically, so that the shape looked like an upside down table. An unusual shape, but it is based on a halachah l'Moshe miSinai - this is the tradition we have as to how it was made.
From the wording of the Rambam in the Yad it sounds as though he understands that the "corners" refer to the thickness of the loaf, and according to this it was a block of bread one tefach high and seven by four in length and width. The commentators raise a difficulty on this, aside from the fact that the term "karnos" does not indicate thickness, that there is not enough flour in an isaron to make something so large. This is a difficulty on the Rambam, and this would be the halachah for one who holds that the halachah follows the Rambam.
The shape of the Lechem HaPanim:
The Mishnah continues: "Lechem hapanim arko asarah v'rachbo chamishah v'karnosav sheva etzba'os". Each one was made from two esronim of flour - about two gallons, roughly seven liters. It too was made as dough laid out to a measure of ten tefachim long by five tefachim wide, a significant size: ten tefachim approach nearly a meter, and the width about eighteen inches - roughly a hundred by fifty centimeters. Except that this bread did not remain flat: the two ends of the rectangle were folded upward, until a U shape was formed, like a very simple table or like a box without a lid and without two of its walls - a cardboard box.
The Lechem HaPanim also had protrusions, and they came out of the corners of the folded walls - the faces, the sides - and they were in fact parallel to the base. The shape looks like an upside down writing desk, whose four corners point inward and run parallel to the floor. This is a boxlike item, highly unusual, and it is worth seeing a picture of it - that picture is worth a thousand words.
Rabbi Yehudah's mnemonic:
"Rabbi Yehudah omer: shelo tit'eh - zad"d yah"z" - Rabbi Yehudah says: so that you should not err. In order that no mistake be made in the measurements, Rabbi Yehudah gave a siman, a memory device:
Zad"d - zayin, dalet, dalet, which in gematria are seven, four and four: the shtei halechem were seven tefachim long, four tefachim wide, and their horns were four fingerbreadths.
Yah"z - yud, hei, zayin, which are ten, five and seven: the lechem hapanim was ten tefachim long, five tefachim wide before the folding, and its horns were seven fingerbreadths - seven thumb-breadths, which is a tefach and three quarters of a tefach, turning inward.
The derashah of Ben Zoma:
Ben Zoma brings a derashah that supports the unusual shape of the lechem hapanim. The verse says: "venasata al hashulchan lechem panim lefanai tamid" - and you shall place on the table showbread before Me always. Why is it called lechem panim, bread of faces? So that it should have faces - the two sides of the bread must face one another. That is, one takes the flat loaf and folds up its two sides, and the two sides, as it were, look at and face each other, and these are the faces.
According to the version of the text that Rashi had, which the Bartenura also brings, there is an additional meaning here: not "panim" but "pinim", from the word pinah, a corner or an angle - that it should have corners. According to this version we have a source not only for its having faces, the side walls that face one another, but also for the protrusions, which are like small pointed corners that point inward.
In summary: in this Mishnah we learned the rule that any service performed inside requires a kli shareis, a sacred vessel, while one performed outside requires no vessel at all. We then examined the shape of the shtei halechem - seven by four with horns of four fingerbreadths, and the shape of the lechem hapanim - ten by five with horns of seven fingerbreadths, its walls folded upward. We further learned Rabbi Yehudah's siman, zad"d yah"z, and Ben Zoma's derashah from the verse "lechem panim" - that its faces should turn toward one another, and according to the version of Rashi and the Bartenura, "pinim", from the word corners.
In any case, in order to grasp these shapes properly, it is worth taking the trouble to look at a picture of the shtei halechem and the lechem hapanim, for anyone who has not seen this before.