File:HansonAnsonBast1959 fig01.jpg

From Embryology

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Fig. 1. The embryo of 4.5 weeks (7 mm)

In the embryo of 4.5 weeks (7 mm) the precursor tissue for the auditory ossicles is a common blastemal mass which is distinguishable from the surrounding mesenchyma only because of the greater concentration of its constituent cells (compare fig. 2).

A lobe-like portion of this mass is localed at the cmnial end of the second visceral bar (precursor of Reichert's cartilage), where it is grooved by the facial nerve. Part of this mass is the primordium of the stapes. However, it is still separate from the aggregation of which will become the otic capsule (the latter not included in the reconstruction). The stapedial artery extends from the source-vessel to encroach upon the interiomedial aspect of the blastema (fig. la); the chorda tympani branches from the facial nerve to pass medial to thefirst visceral bar, the forerunner of Meckel's cartilage (fig. 1b).

A mesenchymal bridge of cells between the first and second visceral bar extends from the proximal end of the mandibular bar (at I in fig. 1c) to a point on the hyoid bar (at II) just distal to the blastemal lobe of the stapes (fig. 1c). The primordia of the malleus and incus are not yet distinct structures within this condensation of cells which will soon give rise to them.


Hanson JR. Anson BJ. and Bast TH. The early embryology of the auditory ossicles in man. (1959) Q Bull Northwest Univ Med Sch. 33: 358-379. PMID: 14399619

Cite this page: Hill, M.A. (2024, February 24) Embryology HansonAnsonBast1959 fig01.jpg. Retrieved from

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G

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