Fig. 3.

Development of periosteal innervation in the thoracic region. Axons from thoracic sympathetic neurons are closely associated with rib periosteum as they grow to the sternum.a, Bundles of TH-IR sympathetic axons were observed leaving the ganglion (g) and extending along a rib (asterisk) on E17. The axons are indicated byarrows. b, TH-IR sympathetic axons (arrows) were observed in contact with the periosteum of the rib (asterisk) on E17. c, A bundle of TH-IR axons bifurcates, and some course along associated with the periosteum of the rib (asterisk). a andb are the same magnification. Scale bars:a, b, 10 μm; c, 20 μm.