The incudopetrosal joint of the human middle ear: a transient morphology in fetuses. Issue 1 (11th March 2020)

• Record Type: Journal Article
• Authors: Rodríguez‐Vázquez, José Francisco; Yamamoto, Masahito; Kim, Ji Hyun; Jin, Zhe‐Wu; Katori, Yukio; Murakami, Gen
• Is Part Of: Journal of anatomy. Volume 237:Issue 1(2020)
• Page Start: 176
• Page End: 187
• Publication Date: 2020-03-11
• Subjects: human fetus -- incudopetrosal joint -- incus -- middle ear -- otic capsule; Anatomy -- Periodicals; 571.3
• DOI: 10.1111/joa.13181
• Languages: English
• ISSNs: 0021-8782

Abstract

Abstract: In spite of the amount of research on fetal development of the human middle ear and ear ossicles, there has been no report showing a joint between the short limb of incus and the otic capsule or petrous part of the temporal bone. According to observations of serial histological sections from 65 embryos and fetuses at 7–17 weeks of development, the incudopetrosal joint exhibited a developmental sequence similar to the other joints of ossicles, with an appearance of an interzone followed by a trilaminar configuration at 7–12 weeks, a joint cavitation at 13–15 weeks and development of intraarticular and capsular ligaments at 16–17 weeks. These processes occurred at the same time or slightly later than any other joint. Thus, the joint development might coordinate with vibrating ossicles in utero . The growing short limb of incus appeared to accelerate an expansion of the epitympanic recess of the tympanic cavity. Additional observations of five late‐stage fetuses demonstrated the incudopetrosal joint located in the fossa incudis joint changing to syndesmosis. Consequently, a real joint with a cavity existed transiently between the human neurocranium and the first pharyngeal arch derivative (i.e. incus) in contrast to the tympanostapedial joint or syndesmosis between the neurocranium and the second arch derivative. The newly described joint might have an effect on the widely accepted primary jaw concept: the mammalian jaw should thus have been created within the first pharyngeal arch, although the connection with neurocranium by the stapes is of a different origin. Abstract : Union of the incus‐otic capsule is distinguishable between the short limb of the incus and the lateral protrusion of the otic capsule. The initial perichondrium and precartilaginous cells are continuous in the incus‐otic capsule union.