<p>Adjacent transverse sections through embryos at two developmental stages, hybridized to detect <i>Efnb2</i> (A,D), <i>Pou3f4</i> (B, E), or Sox9 (C, F). <i>c</i>, cartilaginous cochlear capsule; <i>cd</i>, cochlear duct; <i>eam</i>, external auditory canal; <i>eu</i>, nascent eustacian tube; <i>i</i>, incus; <i>m</i>, malleus; <i>ph</i>, pharynx, <i>spg</i>, spiral ganglion, <i>s</i>, stapes. Asterisk highlights the facial nerve. Double arrowheads in (A–C) highlight overlapping <i>Efnb2</i> and <i>Pou3f4</i> signals and relatively weak <i>Sox9</i> signal dorsal to the stapes. Single arrowhead in (F) highlights a lack of Sox9 signal in the corresponding region at E16.5. White arrowheads in (D, E) highlight overlapping <i>Efnb2</i> and <i>Pou3f4</i> signals at the forming S–V joint. Scale bar represents 200 microns in (A–C) and 250 microns in (D–F).</p
