The sections of the initial combinatorial ontologies that require expanding to describe formation of the primitive heart tube. (A) This shows that we are dealing with the anatomical concepts of heart, cardiogenic plate, and primitive heart tube. (B) This shows that we need to describe the events that occur during the development of an epithelial sheet. (C) This illustrates that we need to include the processes involved in cell differentiation. The colored portion of the graph corresponds to the similarly colored diagram in the schematic shown in Figure 6.