A traditional Vedic yagna was conducted by three main priests - a Hotar who would chant hymns from the Rig Veda Samhita, an Adhvaryu who would chant hymns from the Yajur Veda Samhita, and an Udgatri who would chant (or rather sing) hymns from the Sama Veda Samhita. (The Samhitas are the core par...