Unlike a regular priest, a High Priest cannot marry a widow.
In Tractate Keritot, page 6b, the Gemara discusses the composition and the unique status of the Shemen HaMishchah (the sacred anointing oil) used by Moses. The discussion explores the prohibition of replicating this oil and the penalties for applying it to "strangers" (non-priests). keritot 6b page 78 jebhammoth 61 best
To understand the connection between Keritot 6b and Yevamot 61, one must look at the laws regarding the and the specific holiness required of a High Priest. The Sanctity of the Anointing Oil (Keritot 6b) Unlike a regular priest, a High Priest cannot marry a widow