There were four classes of priests in ancient Hinduism, though the classification varied over time. The four classes of priests are hotri, adhvaryu, udgatri and brahmana or purohita.
The hotri is the chief priest. Hotris are accomplished in the Rig Veda. The adhvaryu is the assistant priest. Adhvaryus are accomplished in the Yajur Veda. The udgatri is the assistant priest and more associated with chanting. Udgatris are identified with the Sama Veda. The Brahmana or purohita performed the duties that were not awarded to the other three groups.
The four classes of priests are mentioned in the Ramayana and the Mahabharata. They are also mentioned in the Puranas.
Hotri is associated with eastern direction, adhvaryu with western direction, brahmana with southern direction and udagtri with the northern direction.
Dakshina to each priest is performed facing the direction associated with the priest.