SNa motoneurons often inappropriately innervate a neighbouring non-target muscle, muscle 12. This is not accompanied by a denervation of muscles normally innervated by SNa suggesting the ectopic branching is likely to be formed by collateral sprouting of SNa axons. Ectopic innervation of muscle 12 is only rarely observed in a Con^Fvex238 genetic background, innervation of the native SNa target muscles is normal. Mutants also exhibit an increase in muscle adhesion in certain pairs of ventral muscle fibres. Concomitant with the increase in muscle adhesion there are abnormalities in muscle innervation. Muscles are normally innervated by the SNb motoneurons on their internal surface, mutants often exhibit muscles innervated on their external surface and only rarely on the internal surface. Innervation defect is due to a specific effect of Con, not an indirect influence of increased muscle adhesion.