Figure 2. (A) Tracheal cartilage rings fused with each other to form a sleeve of tracheal cartilage. The middle region of hyoid bone is absent (blue dashed line, anterior view of the tracheal cartilage sleeve [TCS]). (B) No tracheal ligaments are present (vertical section of bronchus: red dashed line in a; hematoxylin and eosin staining (H&E), scale bar=5 mm). (C) The posterior membranous septum is narrow (red arrowheads) (posterior view of the TCS). (D) Narrowing of the posterior membranous septum is also identified in the cross-section of the tracheal cartilage. Red arrowheads indicate the posterior membranous septum (cross-section of bronchus: blue dashed line in C; H&E, scale bar=5 mm). (E) Chronic inflammation and hyperplasia of bronchial glands are seen (H&E, ×40: blue dashed line in D).