1)
What is the "Mechaseh"?
1.
Rashi and Targum Onkelos: It is the Cheilev that covers the stomach.
2.
Ramban and Moshav Zekenim: It refers to all the Chalavim - the Cheilev that covers the stomach, the Cheilev on the stomach, the Cheilev on the kidneys and the Cheilev on the flanks, all of which cover.
QUESTIONS ON RASHI
2)
Rashi writes that "Mechasei" is the Cheilev that covers the stomach. But all the Chalavim cover?