  Branched actin networks at the leading edge of a crawling cell evolve via
protein-regulated processes such as polymerization, depolymerization, capping,
branching, and severing. A formulation of these processes is presented and
analyzed to study steady-state network morphology. In bulk, we identify several
scaling regimes in severing and branching protein concentrations and find that
the coupling between severing and branching is optimally exploited for
conditions {\it in vivo}. Near the leading edge, we find qualitative agreement
with the {\it in vivo} morphology.
