Bechorot 43 - Blemished that Disqualify a Kohen
All blemishes that disqualify a firstborn animal from being a sacrifice also disqualify a Kohen from serving in the Temple. Moreover, there are blemishes for animals that are not listed for Kohanim, and vice versa, but in truth all blemishes listed for one apply to the other. This is learned from the use of an extra word "wart" that is found in both laws and that connects them. Without this connection, we could argue that an animal's law should be stricter, since it itself is brought on the Altar, or alternatively that the Kohen's law is stricter, since he can perform many Temple services.
Unique to Kohanim is a requirement to be a typical descendant of Aharon. Thus it becomes a blemish to have a deformed head, and a hunchback, although Rabbi Yehudah declares a hunchback fit for Temple service. A bald-headed man is unfit. What is defined as bald? Whoever has no ring of hair circling from ear to ear.
A disqualified Kohen may still eat of the Kohanim's portions, and he has a claim to an equal share, together with all the members of his family, when the family gets its turn to serve in the Temple.
Art: John Constable - Portrait of a Balding Man