Stubbs preserved large bone from horse's leg (4)
I believe the answer is:
ulna
'bone from horse's leg' is the definition.
'ulna' can be an answer for 'bone' (ulna is a kind of bone). I'm not sure about the 'from horse's leg' bit.
'stubbs preserved large' is the wordplay.
'stubbs' becomes 'una' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'preserved' is an insertion indicator.
'large' becomes 'l'.
'una' going around 'l' is 'ULNA'.
Can you help me to learn more?
(Other definitions for ulna that I've seen before include "Bone from the human elbow" , "a section of framework" , "Part of body" , "Part of bone-structure" , "part of anatomy" .)