Joint pole heading oxen (4)
I believe the answer is:
seam
'joint' is the definition.
(seam is a kind of joint)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for seam that I've seen before include "Line of sewing - stratum of coal" , "Sewing join" , "Join - stratum of ore" , "Join round cricket ball" , "The line where two edges are stitched together" .)