  The Pierre Auger Observatory allows the measurement of both longitudinal
profiles and lateral particle distributions of high-energy showers. The former
trace the overall shower development, mainly of the electromagnetic component
close to the core where the latter reflect the particle densities in the tail
of the shower far away from the core and are sensitive to both the muonic and
electromagnetic components. Combining the two complementary measurements,
predictions of air shower simulations are tested. In particular the muon
component of the tank signals, which is sensitive to hadronic interactions at
high energy, is studied with several independent methods. Implications for the
simulation of hadronic interactions at ultra-high energy are discussed.
