  The spin-dependent structure functions $g_1(x)$, $g_2(x)$, ${g}_2^{WW}(x)$
and ${\bar g}_2(x)$ and their moments are studied in the CM bag model. The
results show that (i) $\int_0^1g_2(x)dx=0$, i.e. the Burkhardt-Cottingham sum
rule holds, hence $g_2(x)$ must have at least one non-trivial zero besides
$x=0$ and $x=1$. (ii) $\int_0^1x^2g_2(x)dx$ is negative for the proton, neutron
and deuteron. (iii) $\int_0^1x^2g_2(x)dx$ is about one order of magnitude
smaller than $\int_0^1x^2g_1(x)dx$, hence the twist-3 matrix element is
approximately equal to the twist-2 matrix element. The results are compared
with most recent data and predictions from the MIT bag model, lattice QCD and
QCD sum rules.
