וְשָׁחַ֨ט אֹת֜וֹ עַ֣ל יֶ֧רֶךְ הַמִּזְבֵּ֛חַ צָפֹ֖נָה לִפְנֵ֣י יְהוָ֑ה וְזָרְק֡וּ בְּנֵי֩ אַהֲרֹ֨ן הַכֹּהֲנִ֧ים אֶת־דָּמ֛וֹ עַל־הַמִּזְבֵּ֖חַ סָבִֽיב׃
Rashi on Leviticus
על ירך המזבח means ON THE SIDE OF THE ALTAR (cf. Rashi on Exodus 40:22).
Rabbeinu Bahya
Siftei Chakhamim
On the side. The side is called “thigh” because the thigh is on the side; similarly (Shemos 26:22): “ולירכתי המשכן (For the end of the mishkon),” (Ibid. 27): “לירכתים ימה (of the western [back] wall)” — [means] the side.