Models incorporating merging between dayside magnetosheath and magnetosphere field lines predict the location of the magnetotail boundary layer and bending of magnetotail field lines in the direction of the IMF. We review previous observations supporting these models and reexamine a case of dense magnetotail boundary layer plasma and strongly bent field lines observed by ISEE 3. We discuss observations of boundary layer plasma within a tangential discontinuity magnetopause. Our model to explain this phenomenon requires that interconnected magnetotail and magnetosheath field lines leave the magnetotail via a narrow ''window.'' Field lines in the dense boundary layer plasma veer away from the aberrated x axis more than those in the void magnetotail lobes in order to pass through the windows. Magnetosheath plasma must enter the magnetotail lobes through the windows at all downstream distances in order to supply the observed tailward flux of the lobe plasma.