The Skull and Brain (Idra Rabba) — A"A's intrinsic government mode; The Three Heads (Idra Zuta) — A"A's mode in generating Zeir Anpin (Z"A).
A"A has two anatomical accounts. Skull and Brain (Idra Rabba) is A"A's intrinsic governmental mode. Three Heads (Idra Zuta) is A"A's mode in generating Z"A. Both are valid; they describe different operational stances.
Op. 95 closes the A"A unit (Op. 90–95) with the doctrinal-philosophical claim that one Partzuf can have two valid anatomies. The Skull and Brain anatomy is from Idra Rabba; the Three Heads anatomy is from Idra Zuta. They look like rival accounts; Klach says they are not.
The Op. 8 doctrine — Sefirot can support contradictory likenesses simultaneously — applies here at the Partzuf level. A"A intrinsically (in its standing mode of cosmic-governmental operation) has the anatomy of Skull and Brain — the operational interior in which A"A's mercy is held and radiated. A"A in its generating Z"A mode (when A"A is producing the operational descendant Z"A) has the anatomy of Three Heads (Keter, Avira, Mocha — three layers of upper-anatomical structure that together produce Z"A).
The two anatomies are not in conflict because they describe two different operational stances of the same Partzuf. Intrinsic and generating-the-branches are two different functional modes; the cosmic-anatomical features that operate in each mode are different.
This methodological move runs through the second half of the book. Op. 109's general rule of Partzuf-pair interrelation (chain of development + clothing) is the same logic generalised: every Partzuf-pair has two valid modes of relation, both real, both required for complete operational understanding.