Histological cross sections showing the differentiation of the jaw joint of Sorex araneus. A In the newborn (d1 6-4-3) the skeletal elements of the joint are in great proximity, but their histogenesis is not much advanced. B At day 5 (d5 31-6-3) the processus glenoideus inferior is represented by a blastema at the lower end of the squamosum. C At day 10 (d10 57-2-1) the dorsal chamber of the mandibular joint has grown ventrally and meets the processus glenoideus inferior of the squamosal, which consists entirely of secondary cartilage. D At day 15 (d15 47-2-2), the processus glenoideus inferior is almost completely ossified endochondrally from its ventromedial side. A discus articularis is separated off in the upper compartment only. Abbreviations: see Fig. 14, alt – ala temporalis, alo – ala orbitalis, cam – caput mandibulae, cop – commissura orbitoparietalis, dar – discus articularis, den – dentary, eth – ethmoid.