וַיְהִ֤י הַגּוֹרָל֙ לְמַטֵּ֣ה מְנַשֶּׁ֔ה כִּי־ה֖וּא בְּכ֣וֹר יוֹסֵ֑ף לְמָכִיר֩ בְּכ֨וֹר מְנַשֶּׁ֜ה אֲבִ֣י הַגִּלְעָ֗ד כִּ֣י ה֤וּא הָיָה֙ אִ֣ישׁ מִלְחָמָ֔ה וַֽיְהִי־ל֖וֹ הַגִּלְעָ֥ד וְהַבָּשָֽׁן׃
Rashi on Joshua
To Mochir, the firstborn of Menashe. Since he was the firstborn, he was the first to take a portion in the days of Moshe, on the other side of the Jordan, and thus Gilod and Boshon were his portion.