Fig. 9. Circular propagation of E and F events at the margin. (A) In a quartered, splayed preparation a stimulating electrode (S) was placed on one radial strand while a recording electrode (R) was placed on another near its junction with the manubrium (m). A cut through the radial strand (RS) at site a blocked that pathway to the manubrium. The dotted lines represent tissues containing one or more radial and circular conduction pathways as described in the text. p, peduncle; v, velum. (B) Upper trace (B1) shows propagation of both E and F events to the manubrium via a route that includes a circular component at the margin. Lower trace (B2) shows blockage of E events by cutting the circular (ring) canal at site b. This cut also went through the inner nerve ring, showing that F impulses can propagate circularly in the outer nerve ring.