Fig. 12. Structural characteristics of muscle-nerve relations at stages 20 through 22 (chick). A. Section of stage-22 LR-P/Q anlage stained with antineurofilament antibodies to reveal two separate nerves entering the muscle. B and C. Sections from a stage-20 Bodian-stained embryo showing the spatial relations between the LR-P/Q anlage and sixth nerve axons. The sixth nerve bifurcates as it reaches the muscle rudiment. One bundle (red arrows in B, C) continues rostrally, then curves laterally to contact the less dense rostral portion of the muscle condensation, which will form the P and Q muscles. The other axonal bundle (black arrow on left in B) directly enters the LR primordium. The inset in B illustrates the onset of accessory abducens motor neuron migration in rhombomere 5 of an age-matched, DiI-labeled specimen. The arrow points to a migrating perikaryon. (Wahl C, Noden D, Baker R: Developmental relations between sixth nerve motor neurons and their targets in the chick embryo. Dev Dyn 201:198, 1994)