  We study the anomalous conductance plateau around $G = 0.7(2e^{2}/h)$ and the
zero-bias anomaly in ballistic hole quantum wires with respect to in-plane
magnetic fields applied parallel $B_{\parallel}$ and perpendicular $B_{\perp}$
to the quantum wire. As seen in electron quantum wires, the magnetic fields
shift the 0.7 structure down to $G = 0.5(2e^{2}/h)$ and simultaneously quench
the zero bias anomaly. However, these effects are strongly dependent on the
orientation of the magnetic field, owing to the highly anisotropic effective
Land\'{e} \emph{g}-factor $g^{*}$ in hole quantum wires. Our results highlight
the fundamental role that spin plays in both the 0.7 structure and zero bias
anomaly.
