The most common and most likely answer to this crossword clue is the 6 letter word SEPTUM
I've seen this crossword clue in Independent
S
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More clues leading to the result SEPTUM
Buddy explains!

The straight part
We know that "(anatomical) wall" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case (anatomical) wall = septum.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SEPTUM mean?
SEPTUM noun- A wall separating two cavities; a partition
- A partition that separates the cells of a fruit.
- A partition that separates the cells of a (septated) fungus.
- One of the radial calcareous plates of a coral.
- One of the transverse partitions dividing the shell of a mollusk, or of a rhizopod, into several chambers.
- One of the transverse partitions dividing the body cavity of an annelid.
- A nose piercing that goes through the nasal septum.