  We study the size dependence of the dynamical symmetry breaking in the
four-dimensional Nambu-Jona-Lasinio model. We show that the presence of
boundaries reduces the chiral breaking region, and this effect is strengthened
for a larger number of compactified dimensions. A critical value for the length
of the compactified dimensions exists, below which the dynamical symmetry
breaking is not possible. Considering finite temperature and chemical
potential, the chiral phase structure for the system with compactified
dimensions is obtained. A gradual decreasing of the chiral breaking region with
increasing of chemical potential is found. Also, at fixed chemical potential,
the decreasing of the size of the system changes the order of the chiral phase
transition.
