(Devarim 14;6) "And every beast that has split hooves, entirely cloven in two, and which chews the cud in beast, it shall you eat": Unless it has these three signs, it may not be eaten.
Abba Channan says in the name of R. Eliezer: The shesuah is a beast in itself; it has two backs and two spines.
R. Yashiah said: Wherever "tzippor" is written, a clean bird is intended.
R. Yitzchak said: A clean bird is called either "of" or "tzippor"; an unclean bird is called only "of."