Complete closure of the secondary palate must progress through two consecutive events: the converging movement of the palatal shelves and their subsequent fusion at the line of contact. Each step is indispensable in normal palatal development since, theoretically, a palatal cleft might be the consequence of a failure of either.
Until recently, the mechanisms of shelf movement received most attention (Peter, 1924; Lazarro, 1940; Walker & Fraser, 1956; Larsson, 1960). However, recent investigations have focused on the subsequent step, properly referred to as fusion. These studies, based on organ culture methods (Pourtois, 1966) and electron microscopy (Mato, Aikawa & Katahira, 1966; Farbman, 1967; Smiley & Dixon, 1967), have emphasized the complexity of the fusion process. This process may be viewed as a sequence of four interdependent events: (1) differentiation of the cell layers at the edge of the shelves resulting in the formation of a ‘zone of stickiness’ (Pourtois, 1968); (2) fusion of these differentiated epithelial cells leading to the formation of a laminated wall of epithelium between the shelves; (3) rupture of that partition permitting contact between the elements of the mesenchyme from either side; and (4) finally, degeneration of the epithelial remains of the seam marking the completion of the fusion process.
Differences in Complement-Dependent Chemotactic Activity Generated by Bullous Pemphigoid and Epidermolysis Bullosa Acquisita Immune Complexes: Demonstration by Leukocytic Attachment and Organ Culture Methods
