  Canards are special solutions of slow/fast systems which are ubiquitous in
neuroscience and electrical engineering. Two distinct classes of canard
solutions have been identified and carefully studied: folded singularity
canards and torus canards. Recently, an explicit and analytic relationship
between these seemingly unrelated families of solutions was established in the
classical forced van der Pol equation (Burke et al., J. Nonlinear Sci.
26:405--451, 2015). In this article, we generalize the results of Burke et al.
(2015) to the broader class of time-periodically forced planar slow/fast
systems, which includes the forced van der Pol and the forced FitzHugh-Nagumo
equations. We analytically determine the parameter values in this class of
systems for which the two types of canard solutions exist, and show that the
branches of primary canards of folded singularities continue into those of the
torus canards as the forcing frequency is increased. We illustrate our results
in the paradigm problem of the forced FitzHugh-Nagumo system.
