Figure 6

Collagen1 is a marker of replacement cartilage and collagen muscle fibers. Transverse 10-12 μm sections, COL1 immunostaining at E10, 13, and 14. (A) High magnification image of the tympanic membrane and external auditory meatus. Collagen fibers (cf) underlie the medial tympanic endoderm (e), forming part of Platner's ligament (pl). The more lateral ectodermal layer of the tympanic membrane is thicker than the simple squamous epithelium of the endoderm (bars). The insertion site of the extracolumella process is indicated by a dotted line (bottom left). (B-E) Lateral is to the top and ventral to the right. (B) At E13, COL1 in the bony collar of the shaft, the periosteum (p), but not the perichondrium of the footplate (fp). Collagen fibers underlie the tympanic endoderm, extending around the extracolumella (exc). Large numbers of collagen fibers are detected in the external ophthalmic arterial (a) wall. (C) At E14, COL1 labels the periosteum of both footplate and shaft. Note the joint region in the shaft (arrowed), and a band of fibers in the annular ligament (al). (C, D) Labeled collagen fibers underlying the endoderm at E14. (C, E) The two tendons of Platner's ligament insert onto the base of the supracolumella/extracolumella arms (pl, arrowed). Abbreviations: a-external ophthalmic artery, c-columella, eam-external auditory meatus, ec-ectoderm, i-insertion point, jr-joint region.