The most common and most likely answer to this crossword clue is the 8 plus 4 letter word PARIETAL LOBE
I've seen this crossword clue in The Guardian
P
A
R
I
E
T
A
L
L
O
B
E
Buddy explains!
The straight part
We know that "Part of the 10" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case part of the 10 = parietal lobe.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.