Sefer Ha'mitzvos Ha'Katzar (The concise book of mitzvos)
By the Chofetz Chaim
This book lists the Torah mitzvos that can be observed today
First Section – the Positive Commandments
51. It is a positive commandment that all who bring a pure animal as a karbon (offering) is to give the foreleg, cheek, and maw to the Cohain (priest)
As it states in Devarim (Deuteronomy) 18:3, "And give to the Cohain the foreleg, cheeks, and maw." These are as follows. The foreleg: the right one from the shank being where the two parts join to each other. The cheeks: from the jawbone to the windpipe (large ring) with the tongue between them. They are not to be plucked nor skinned but given to the Cohain with the skin and wool. The maw: the fat inside of it and the outside of it. The custom is for the Cohain to leave the fat for the owner. All of these things are called the "Matanos" (gifts) in all places. The Cohain is allowed to sell the Matanos or feed them to dogs because there is no holiness in them. A Cohain may also give them to a non-Cohain friend who is in pressing circumstances.
In our times, following the opinion of Rabi Ilai (Talmud Chullin 136a), we do not give these to the Cohanim anymore [this is outside of Eretz Yisroel. In Eretz Yisroel the custom is still to give it to them] There are those that are stringent on themselves to still give. It is fitting and proper in order to fulfill this positive commandment.