Figure 5. Schematic drawing illustrating a hypothetical model of the contribution of the Hertwig’s epithelial root sheath (HERS) to the periodontal ligament cell populations. After its fragmentation, HERS gives rise to the epithelial rests of Malassez, but may also be the source of cementoblasts and other mesenchymal cells that populate the periodontal ligament. The illustration shows an early stage of root formation that is associated with the formation of acellular extrinsic fiber cementum.