Cephalins occur along with lecithin in all plant and animal cells. They are similar structure as that of lecithin but differ from lecithin in that the base attached to phosphoric acid is not choline. It may be one of the three bases, namely ethanolamine, serine, and inositol. Therefore, the three cephalins are known as follows:

1. Ethanolamine cephalin (phosphatidylethanolamine)
2. Serine cephalin (phosphatidyl serine)
3. Inositol cephalin (phosphatidylinositol)