The evolution of the novel mammalian jaw articulation has resulted in an increased complexity of the dentary bone, reflecting the multiple roles it now fulfils as the primary bone of the mandible. Signalling through the Tgf-β type II receptor is important in the development and patterning of the proximal dentary processes, especially the angular process, and secondary cartilages. We show that expression of Tgf-β2 is associated with the developing angular process, and that the connective tissue marker Scleraxis is co-expressed with Tgf-β2. Scleraxis expression is lost around the angular process of Tgfbr2 conditional knockouts and Tgf-β signalling can induce Scleraxis expression in explant culture. Induction of secondary cartilages in explant culture can be prevented by inhibition of Tgf-β signalling. This study suggests that the proper development of the processes and their secondary cartilages relies on both Tgf-β signalling and mechanical forces working in concert. Developmental Dynamics 237:1604–1613, 2008. © 2008 Wiley-Liss, Inc.