||Philip W. Wertz, The nature of the epidermal barrier: biochemical aspects, Volume 18, Issue 3, 8 February 1996, Pages 283–294, doi:10.1016/0169-409X(95)00077-K p.291 left column bottom paragraph
||Wertz P.W. and Downing, D.T. (1983) Ceramides of pig epidermis: structure determination, J. Lipid Res. 24, 759-765 & Long, S.A.. Wertz, P.W., Strauss, J.S. and Downing, D.T. (1985) Human stratum corneum polar lipids and desquamation. Arch. Dermatol. Res. 277, 284-287.PubMed ID6886564, 4004327
||p.286 left column top paragraph:"The largest group of stratum corneum lipids, the ceramides, comprise 50% of the total lipid and are structurally heterogenous [primary sources]. Six chromatographically distinct fractions of ceramides have been isolated and characterized by a combination of chemical, chromatographic and spectroscopic techniques, and representative structures are shown in Fig. 3."