In this paper an expository account on singularities of reversible
vector fields on manifolds and boundary singularities is
presented. Also we present the bifurcation diagram of a boundary
cusp of codimension three, i.e, a Bogdanov-Takens singular point
in the boundary of the semi plane $\{(x,y)\in {\R}^2:\; x\geq 0\}$
whose topological unfolding is given by the quadratic three
parameter family
$y\frac{\partial}{\partial x}+(x^2+ax+c+ \alpha y(x+b))\frac{\partial}{%
\partial y}, \;\; \alpha =\pm 1$.
This study can be applied to the
analysis of the behavior of singularity of the germ of vector field $%
X_{0}(x,y)=(y,2x(x^4+x^2y))$ in the class of reversible vector
fields.