Fig. 6. Model of events needed for proper sympathetic ganglion formation. Schematic model showing important events in a spatiotemporal pattern for discrete sympathetic ganglion formation adjacent to the ventral edge of a rostral somite. 1. Neural crest cells migrate from the neural tube through the rostral somites. 2. Neural crest cells disperse adjacent to the dorsal aorta. ephrinB1 expression is established in inter-ganglionic regions between developing ganglia. 3. N-cadherin adhesion and inhibitory ephrinB1 expression induce formation of discrete ganglia. A, anterior; c, caudal somite; da, dorsal aorta; nc, notochord; nt, neural tube; P, posterior; r, rostral somite.