 \label{fig:Massivestruc} Internal structure of our $12 M_\odot$ stellar model, at the phases labeled in Figure \ref{fig:MassiveIGWhist}. At all stages shown, the star is a red supergiant with radius $R \sim 10^3 R_\odot$. The He-burn stage is core helium burning, while the C-burn, O-burn, and Si-burn stages are shell carbon, oxygen, and silicon burning phases, respectively. Vertical shaded bars are drawn near the base of the surface convection zone for the He-burn stage, and near the base of the convective shell burning region of the other stages. {\bf Top:} Density profiles $\rho$ of the inner regions of our models. The envelope density profile is similar for each model, but central densities vary by orders of magnitude. {\bf Middle:} Enclosed mass profiles. For C/O/Si-burning, the models are chosen such that the mass internal to the convective shell burning region is $M_c \sim 1.2 M_\odot$. {\bf Bottom:} The Brunt-V\"{a}is\"{a}l\"{a} frequency, $N$, of our models. We have also plotted horizontal dashed lines at the convective turnover frequencies $\omega_c$ below the relevant convective zone. IGW propagate in the regions where $\omega_c < N$, shown by the horizontal extent of the dashed lines. 