head, skull
顱 centers on the head as a physical structure, especially the bony skull. It is a formal anatomical term rather than a common everyday word.
顱 combines 頁 (head) with 盧, which likely contributes the sound. The character is a phono-semantic compound specifically for the skull or cranium.
The left side 盧 looks like a complex container, and the right side 頁 is a head. Picture a sturdy container protecting the head: that container is the skull.
For ロ, imagine a low, bony dome covering the head: low -> ロ, like the low rounded shape of a skull.