Bones a girl finally broke grabbing end of wall (5)
I believe the answer is:
ulnae
'bones' is the definition.
(ulna is a kind of bone)
'a girl finally broke grabbing end of wall' is the wordplay.
'a girl' becomes 'una' (**).
'finally' indicates one should take the final letters.
'grabbing' means one lot of letters goes inside another.
'end of' says to take the final letters.
The last letter of 'broke' is 'e'.
The final letter of 'wall' is 'l'.
'una'+'e'='unae'
'unae' going around 'l' is 'ULNAE'.
(Other definitions for ulnae that I've seen before include "Thin bones in upper arms" , "Army parts" , "parts of limb" .)