TT #128 · Parshas Tazria · Aliyah 2 · Passuk 12
English: If the eruption spreads out in the skin, so that the eruption covers all the skin of the affected person from head to foot, as far as the priest can see,
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:12
Torah Temimah cites Sifra (Toras Kohanim) for excluding hidden body areas from the phrase “for every appearance”.
Sifra — Vayikra 13, Midrash Sefer
English: “For every appearance” excludes hidden areas of the body.
Textual derivation
The rule concerns appearances that can be seen; hidden areas are excluded from this inspection standard.