Wow Redrobes! That is a very impressive cross section and I await the level maps that you come up with for it. Great job.

I do agree with Arcana to some extent. If the skull is the site of an Archmage's lair (or former Archmage's lair), it would stand to reason that there would be some extradimensional space or rooms. Let the first few levels conform to the shape of the skull, but as the party descends lower into the dungeon, the levels need not necessarily conform to the outlines of the body. There might be unusual archways (permanently opened two way gates) that serve as the ingress and egress to the extradimensional spaces. To some extent my thinking is influenced by the maps of some of the structures in Ptolus by Monte Cook--the Tower of Shade and the stronghold of the good outsiders have levels that do not conform to the shape of the building they are located in.

Regardless, looks good so far, keep it up.