Fig. 4. Hypothesized models for the organization of the covalently bound sphingolipids in the SC in house sparrows from mesic and desert environments. (A) Water shell model. The hexose group of cerebrosides would sequester water molecules. Desert sparrows, with more cerebrosides, could hold a higher amount of water, therefore reducing rates of CWL. (B) Hexose link model. Hexose molecules from cerebrosides would establish molecular interactions with the sphingosine heads of the ceramides that form the outer layer of the intercellular lamellae. In both models, covalently bound ceramides connect adjacent corneocytes.