Thou shalt take all the fat, etc. Among all nations who have offered sacrifices, it has been very usual to select certain parts of the victim only for burning upon the altar, and to dispose otherwise of the remainder.
The Greeks commonly burnt on the altar the thighs and the fat only. The Romans burnt certain parts of the intestines only, and called them prosecta, prosiciae, or ablegmina. In Egypt, according to Herodotus, the greater part of the body was burnt; but the head, the neck, the shoulders, and the lower part of the legs, as well as the paunch, were reserved and not burnt (Herod.
2.40). The fat was generally regarded as the best part of the offering, and most acceptable to the gods. This was probably on account of its burning with a bright flame and helping to consume the rest of the offering.
The caul that is above the liver. Probably the membrane which covers the upper part of the liver, sometimes called "the small omentum." (reticulum jecoris, Vulg.