Then one uses Arrowheads[]
In[180]:= Graphics[{Arrowheads[{-.1, 0}], Arrow[ParametricPlot[{Cos[t], Sin[t]}, {t, 0, -1}][[1, 1, 3, 2]]]}, Axes -> True]
or even better does a function headEnd[]
to generate {-.1, 0} or {0,.1} to place the heads to the right end with the right orientation.
There is a documentation for FullForm, one looks into it's output and finds out, where the interesting things do appear, just try it yourself. This method is unfortunately not version independent, but given that Mathematica is also modular (everything is an expression), it is often successful.