Fig. 8

Chondrification of the dorsal (pq) and ventral (m) cartilages within a single precartilage condensation in the mandibular segment. Left side views of Alcian blue-labeled whole-mounted embryos, photographed with Nomarski optics (from Schilling and Kimmel, 1997). (A) 53 h. The eye is at the top of the field and the rudiment of the adductor mandibular muscle (am, mediating movement between pq and m) is visible. Other abbreviations are as in Fig. 1. The dorsal cartilage, the palatoquadrate (pq), has begun to chondrify (become Alcian-positive) within the same mandibular condensation that will also form Meckel’s cartilage (m). An unlabeled bridge of condensed mesenchyme, present just beneath the muscle rudiment, connects these two labeled regions and shows there is but a single condensation. See also Fig. 10, for the appearance of the condendensation in a live embryo. This bridging region will eventually develop as the joint between pq and m. (B) Another embryo at about the same stage in which m is also lightly labeled, and the joint-forming bridge remains unlabled. The arrowhead indicates the hyomandibular pouch, separating the mandibular and hyoid arches. (C) 60 h. Both cartilages, but not the joint region between them, are strongly labeled. Scale bar, 50 μm.