This enters the hair follicle and involves the cuticle surrounding it, small crusts form which increase in diameter and thickness and then become elevated at their margin, forming a cup-shaped scab, the favus cup, which gives the disease its distinctive character.
"Special Report on Diseases of Cattle"
U.S. Department of Agriculture J.R. Mohler
There is favus or scall-head, called also "porrigo," which has its primary seat in the hair follicles.
"Fungi: Their Nature and Uses"
Mordecai Cubitt Cooke