  We study the properties of the straight segments forming in N-body
simulations of the galactic discs. The properties of these features are
consistent with the observational ones summarized by Chernin at al. (2001).
Unlike some previous suggestions to explain the straight segments as gas
dynamical instabilities, they form in our models in the stellar system. We
suggest that the straight segments are forming as a response of the rotating
disc to a gravity of the regions of enhanced density (overdensities) corotating
with the disc. The kinematics of stars near the prominent overdensities is
consistent with this hypothesis.
