  We evaluate a one-loop, two-point, massless Feynman integral $I_{D,m}(p,q)$
relevant for perturbative field theoretic calculations in strongly anisotropic
$d=D+m$ dimensional spaces given by the direct sum $\mathbb R^D\oplus\mathbb
R^m$. Our results are valid in the whole convergence region of the integral for
generic (non-integer) co-dimensions $D$ and $m$. We obtain series expansions of
$I_{D,m}(p,q)$ in terms of powers of the variable $X:=4p^2/q^4$, where $p=|\bm
p|$, $q=|\bm q|$, $\bm p\in\mathbb R^D$, $\bm q\in\mathbb R^m$, and in terms of
generalised hypergeometric functions $_3F_2(-X)$, when $X<1$. These are
subsequently analytically continued to the complementary region $X\ge 1$. The
asymptotic expansion in inverse powers of $X^{1/2}$ is derived. The correctness
of the results is supported by agreement with previously known special cases
and extensive numerical calculations.
