title: Fetal development and variations in the cartilages surrounding the human external acoustic meatus.
abstract: In contrast to the osseus part that develops from the tympanic ring of the squamous part of the temporal bone after birth, there is little information on fetal development of the cartilages surrounding the human external acoustic meatus. Using routine histology and immunohistochemistry, we examine sections of 22 fetuses (CRL 100-270mm) to study the development of these cartilages. Early external ear cartilages are composed of three groups: (1) a ring-like cartilage at the putative tragus on the anterior side of the meatus, (2) two or three bar-like cartilages along the inferior wall of the meatus, and (3) a plate-like cartilage in a skin fold for the putative helix on the posterior side. In contrast to the first and second pharyngeal arch cartilages, all the external ear cartilages express glial fibrillary acidic protein. Notably, the bar-like cartilages along the meatus are connected with a fascia-like structure to the second pharyngeal arch cartilage. Later, with considerable individual variation, new cartilage bars extend from the inferior cartilages to the superior side of the meatus. Thus, via an intermediate stage showing a chain of triangular elastic cartilages, a chain of bar-like cartilages on the inferior side appears to change into a complex of H-shaped cartilages. Numerous ceruminous glands are seen in the thick subcutaneous tissue overlying the cartilaginous part of the meatus. However, they do not insert into the cartilage. The external ear cartilages develop much earlier than, and independently of, the osseus part.
authors.affiliation: Department of Anatomy, Tokyo Dental College, 1-2-2 Masago, Mihama, Chiba 261-8502, Japan. yasuikari@nifty.com
authors.forename: Yasutoyo
authors.initials: Y
authors.lastname: Ikari
authors.forename: Yukio
authors.initials: Y
authors.lastname: Katori
authors.forename: Aiji
authors.initials: A
authors.lastname: Ohtsuka
authors.forename: Jose Francisco
authors.initials: JF
authors.lastname: Rodríguez-Vázquez
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Abe
authors.forename: Tetsuaki
authors.initials: T
authors.lastname: Kawase
authors.forename: Gen
authors.initials: G
authors.lastname: Murakami
authors.forename: Shin-ichi
authors.initials: S
authors.lastname: Abe
mesh_terms: D004424:Ear Canal / Q000166:cytology* / Q000196:embryology* / Q000254:growth & development; D004425:Ear Cartilage / Q000166:cytology* / Q000196:embryology* / Q000254:growth & development; D005260:Female; D006801:Humans; D008297:Male