Fig. 3. Comparison between Lbx1 and markers for the somitic dermomyotome, epaxial/hypaxial programmes and myogenic precursors at HH19/20. Lateral views of chick heads (A,C,E,G,I,K,M,O,Q) and cross sections at rhombomere 2 levels (B,D,F,H,J,L,N,P,R). To facilitate comparison, Lbx1 expression is shown in the centre of the figure (I,J). To provide anatomical landmarks, Isl1 was used to stain the cranial ganglia in red (except M,N). (A,B) Pax3, a master regulator of trunk myogenesis, is not expressed in the head mesoderm. (C,D) Pax7 and (E,F) Paraxis, co-expressed with Lbx1 during hypaxial muscle precursor migration in the trunk, coincide with Lbx1 in the pre-otic mesoderm (arrows). (G,H) The hypaxial programme marker Sim1 is expressed throughout the cranial mesenchyme (arrows). (H) Note that Sim1 expression is highest next to the neural tube, avoiding the territory beneath the Vth ganglion (arrow). (K,L) The epaxial programme marker Wnt11 is absent from the head mesoderm, instead labelling in the ectoderm around the eye (arrows). (M-R) Cranial expression patterns for the myogenic markers Dach2, Six1 and Pitx2. (M) Dach2, besides signals in the peri-optic mesenchyme (black arrows) appears to be expressed underneath the trigeminal ganglion (white arrow). Cross-sections show that staining resides at the interface between the trigeminal ganglion and the hindbrain (N, arrow). (O,P) Six1 shows widespread expression throughout the head mesenchyme (arrows). (Q,R) Pitx2, besides the peri-optic mesenchyme, shows prominent expression in the pre-otic mesoderm under the trigeminal (arrows). V, trigeminal ganglion. Scale bars: in A, 500 µm for A,C,E,G,I,K,M,O,Q; in B, 100 µm in B,D,F,H,J,L,N,P,R.