Fig. 1.

Ganglion-specific expansion of large-diameter neurons in duck TG. (A, Left) Schematic diagram showing innervation of the duck bill with afferents from trigeminal ganglion. Mechanoreceptor densities in the skin of the dorsal face of the upper bill are based on earlier data (4). (Right) An evolutionary tree depicting tactile foragers and “nonspecialist” birds used in this study. PrV, principal nucleus of the trigeminal nerve; TG, trigeminal ganglion. (B–D) Size distribution histograms of somatosensory neurons from histological sections of TG and DRG from the indicated birds. For each sample, data are shown as mean ± SEM from ≥1,400 cells from ≥8 independent tissue sections.