  We investigate the three dimensional substructure of hadronic showers in the
CALICE scintillator-steel hadronic calorimeter. The high granularity of the
detector is used to find track segments of minimum ionising particles within
hadronic showers, providing sensitivity to the spatial structure and the
details of secondary particle production in hadronic cascades. The
multiplicity, length and angular distribution of identified track segments are
compared to GEANT4 simulations with several different shower models. Track
segments also provide the possibility for in-situ calibration of highly
granular calorimeters.
