Commentary for Middot 3:5
וְטַבָּעוֹת הָיוּ לִצְפוֹנוֹ שֶׁל מִזְבֵּחַ, שִׁשָּׁה סְדָרִים שֶׁל אַרְבַּע אַרְבַּע, וְיֵשׁ אוֹמְרִים, אַרְבָּעָה שֶׁל שֵׁשׁ שֵׁשׁ, שֶׁעֲלֵיהֶן שׁוֹחֲטִין אֶת הַקֳּדָשִׁים. בֵּית הַמִּטְבָּחַיִם הָיָה לִצְפוֹנוֹ שֶׁל מִזְבֵּחַ, וְעָלָיו שְׁמֹנָה עַמּוּדִים נַנָּסִין, וּרְבִיעִין שֶׁל אֶרֶז עַל גַּבֵּיהֶן, וְאֻנְקְלָיוֹת שֶׁל בַּרְזֶל הָיוּ קְבוּעִין בָּהֶם, וּשְׁלֹשָׁה סְדָרִים הָיוּ לְכָל אֶחָד וְאֶחָד, שֶׁבָּהֶם תּוֹלִין. וּמַפְשִׁיטִין עַל שֻׁלְחָנוֹת שֶׁל שַׁיִשׁ שֶׁבֵּין הָעַמּוּדִים:
There were rings [in the floor] to the north of the altar. [They were set] six rows with four rings [in each], while some say [there were] four rows with six rings [in each], through which they would slaughter the holy [sacrifices]. The slaughtering area was north of the altar. There were eight low stone pillars there, and squares of cedar wood were placed on top of them. Hooks of iron were attached to them and [each block] had three rows of hooks from where they hung and skinned the animals, [then placing the meat] on tables of marble [that were] between the pillars.
Bartenura on Mishnah Middot
English Explanation of Mishnah Middot
The slaughter house was to the north of the altar, and on it were eight small pillars on top of which were blocks of cedar wood, in which were fixed hooks of iron, three rows in each, upon which they would hang [the sacrifice] and they would strip its hide on tables of marble that stood between the pillars. Section one: There were twenty-four rings on the north side of the altar, either in six rows of four, or four rows of six. They would put the animal’s head in the ring to slaughter it. Section two: The mishnah describes the slaughterhouse, especially the hooks on which they would hang the meat after the sacrifice was slaughtered. It is also describes the tables upon which the meat would be washed.
This mishnah describes the set-up used to slaughter the sacrifices. Some of this mishnah was also found in Tamid 3:5 (coincidental, I think, that the number of the mishnah is the same).