Chullin 134 - The Owner of the Cow Converted
If someone converted to Judaism and he owned a cow, then if the cow was slaughtered before he converted, he is exempt from giving kohen's gifts from that cow, and if the cow was slaughtered after his conversion, he is obligated to give them. If it is uncertain which came first, he is exempt - because the burden of proof of ownership falls on the kohen who cannot prove it with certainty.
What exactly constitutes the foreleg given to a kohen? - From the carpus (knee) to the shoulder blade. The foreleg of a nazir's offering, coming from a ram, which is cooked and waved, is defined the same way. So is that portion of the hind leg which is given to a kohen from each peace offering. Rabbi Yehudah says that only the middle part of the thigh is given to a kohen.
What is a jaw? The portion that extends from the joint of the jaw to the opening of the trachea, and the tongue is included with it. Actually both jaws are meant. The kohanim merited the gifts because of Pinchas, who threw the spear with his right arm, and prayed with his jaws.
Art: Max Liebermann - Farmer and Cow