Ventral extension of ALi. Transversal section cut at the level of the commissural fibers (dotted line in Figure 10a). Two prominent ventral extensions are observed. A medial extension is adjacent to (and crosses) the posterior tuberculum (PT), a thalamic derivative. A more lateral extension arborizes in the M2 area. This region will form the preglomerular nuclei, the major diencephalic target of third-order lateral line projection in the adult. The outline of the major nuclei (dotted line) is based on autofluorescence, which reveals fibrous material (neuropils) as opposed to cell bodies (nuclei).