Was Devir inside Yehudah's portion?
Malbim: Yes (verse 49). This is why it is not mentioned regarding Binyamin's border (18:19).
Why does it say "Poneh El ha'Gilgal"?
Rashi: The border widens and goes to the north towards Gilgal, opposite Ma'ale Adumim. The border is south of the Nachal; the Nachal is outside of Yehudah's border.
Here it says that that Gilgal is opposite Ma'ale Adumim. Below (18:7), it says that Gelilos are opposite Ma'ale Adumim!
Radak: There was a reason why it was called Gilgal, and also Gelilos.
Malbim: There were many Gelilos opposite Ma'ale Adumim. Only Gilgal was south of the border, in Yehudah. The others were in Binyamin's border.
What is the meaning of "Ma'ale Adumim"?
Radak citing Targum Yonasan: It is the ascent of Adumim.
What was the Nachal?
Rashi: It was a valley and slope without water.
What is the meaning of "v'Hayu Totz'osav El Ein Rogel"?
Malbim: Ein Rogel is the extremity of how far the border juts out. After this it returns to be straight, in line with the border between Devir and Even Bohan.
What is the meaning of "Ein Rogel"?