\centerline{\structure{ \atom{C}\epin{H$_3$}\nnwsingle\atom{C}\wpin{H$_2$} \nnesingle\atom{C}\epin{H$_2$}\nnwsingle\atom{C}\wpin{H$_2$} \nnesingle\atom{C}\epin{H$_2$}\nnwsingle\atom{C}\wpin{H$_2$} \nnesingle\atom{C}\epin{H$_2$}\nnwsingle\atom{C}\wpin{H$_2$} \nnesingle\atom{C}\epin{H$_2$}\nnwsingle\atom{C}\wpin{H$_2$} \nnesingle\atom{C}\epin{H$_2$}\nnwsingle\atom{C}\wpin{H$_2$} \nnesingle\atom{C}\epin{H$_2$}\nnwsingle\atom{C}\wpin{H$_2$} \nnesingle\atom{C}\epin{H$_2$}\nnwsingle\atom{C} \side{\wdouble\atom{O}} \nnesingle\atom{O}\nesingle\atom{C}\epin{H$_2$} \nnesingle\firstbicycloatom{C}\side{\wsingle\atom{H}} \nnwsingle\atom{C}\wpin{H$_2$}\nnesingle\atom{O} \side{\nsingle\atom{P}\side{\esingle\atom{O$^\ominus$}} \side{\ndouble\atom{O}} \side{\wsingle\atom{O}\swsingle\atom{CH$_2$}\nwsingle \atom{~~H$_3$C---N$^\oplus$---CH$_2$} \side{\nsingle\atom{C}\epin{H$_3$}} \side{\ssingle\atom{C}\epin{H$_3$}}}} \ephantom\phantatom{OOO}\ephantom\ssephantom\phantatom{O} \sswphantom\secondbicycloatom{O}\sesingle\atom{C} \side{\nedouble\atom{O}} \ssesingle\atom{C}\epin{H$_2$}\sswsingle\atom{C}\wpin{H$_2$} \ssesingle\atom{C}\epin{H$_2$}\sswsingle\atom{C}\wpin{H$_2$} \ssesingle\atom{C}\epin{H$_2$}\sswsingle\atom{C}\wpin{H$_2$} \ssesingle\atom{C}\epin{H$_2$}\sswsingle\atom{C} \side{\wsingle\atom{H}}\ssedouble\atom{C} \side{\swsingle\atom{H}} \sesingle\atom{C}\epin{H$_2$}\ssesingle\atom{C}\wpin{H$_2$} \sesingle\atom{C}\epin{H$_2$}\ssesingle\atom{C}\wpin{H$_2$} \sesingle\atom{C}\epin{H$_2$}\ssesingle\atom{C}\wpin{H$_2$} \sesingle\atom{C}\epin{H$_2$}\ssesingle\atom{C}\epin{H$_3$}}} \medskip \centerline{\bf Figure~12. \rm 1-Palmitoyl-2-oleoyl-3-{\it sn\/}-glycerophosphocholin.}