  We examined dynamic heterogeneity in a model tetrahedral network
glass-forming liquid. We used four-point correlation functions to extract
dynamic correlation lengths xi_4^a(t) and susceptibilities chi_4^a(t)
corresponding to structural relaxation on two length scales a. One length scale
corresponds to structural relaxation at nearest neighbor distances and the
other corresponds to relaxation of the tetrahedral structure. We find that the
dynamic correlation length xi_4^{a} grows much slower with increasing
relaxation time than for model fragile glass formers. We also find that chi_4^a
~ (xi_4^a)^z for a range of temperatures, but z < 3 at the lowest temperatures
examined in this study. However, we do find evidence that the temperature where
Stokes-Einstein violation begins marks a temperature where there is a change in
the character of dynamically heterogeneous regions. Throughout the paper, we
contrast the structure and dynamics of a strong glass former with that of a
representative fragile glass former.
