Figure 5. Anatomy of the squid escape system. See also Figures 4b and b’. The escape system coordinates muscles of the fin and mantle on both sides of the body to facilitate fast jet-propulsion swimming (dotted line indicates the midline; for clarity, only one side of circuitry is detailed). First-order neurons arise in the ventral magnocellular lobe of the central brain (pink). The axons of these neurons cross and fuse at the midline. In the palliovisceral lobe, first-order neurons form connections with 7 second-order neurons (green). Six of these pairs innervate the retractor muscles of the head and funnel. The fibers of the remaining pair enter the stellate ganglion, where they innervate the processes of third-order cells (blue). The second- and third-order fibers form the giant synapse. The cell bodies of the 12–13 third-order neurons (only one schematized here) are located in the giant fiber lobe of the stellate ganglion. The fibers of each third-order cell leave the stellate ganglion and innervate the circular muscles of the mantle. Axons with greater diameters extend farther along the mantle.