The Context

One of the twenty-four Priestly gifts enumerated in the Parshah is the firstborn ox, sheep, or goat, which is offered as a sacrifice and then given to the kohanim to consume. “Their flesh shall be yours; like the breast of the waving and the right thigh, it shall be yours.” (Bamidbar 18:18)

Rashi explains the comparison the Torah is making between this offering and the “breast... and right thigh.”