SEARCH Articles Figures Tables A cross section through a Hz phase that illustrates that the interstitial areas are in the center. A few lipids are shown in the leftmost cylinder for orientation. Lipid hydrocarbon chains fill the interstitial as well as the annular regions. Deviations from the mean hydrocarbon chain-segment density or in the mean extended length of the chains correspond to an entropically expensive set of chain configurations. [Publishers Imprint]