File:HansonAnson1962 fig01.jpg

Fig. 1. Embryo 7 week 18 mm

The malleus, like the incus and stapes, develops from a mesenchymal blastema located within the first two branchial arches. In the earliest stages of differentiation (approximately 10 mm) the malleus is an indistinctly outlined component of this cellular blastema.

As the primordial tissue of the ossicles differentiates into precartilage, then cartilage, the malleus becomes histologically demarcated from the incus. In an embryo of seven weeks, the enlargement of mesenchymal cells within the ossicles indicates early pre-cartilaginous cellular development.

The chorda tumpani serves to separate the manubrium of the malleus from the long crus of the incus (as the nerve passes toward the first branchial arch). At this stage the malleus has already lost its primary connection to that portion of the second visceral bar which will become the styloid process. Secondary continuity of the ossicular chain is established as the long crus of the incus approximates the portion of the stapedial ring destined to become the head of the stapes.

At a higher level (not shown) Meckel’s cartilage is continuous with the head of the malleus, which, in turn, approximates the body of the incus. The precartilaginous tissue of the developing otic capsule (outline indicated by arrows) is differentiating around the membranous labyrinth.

Reference

Hanson JR. and Anson BJ. Development of the malleus of the human ear; Illustrated in atlas series. (1962) Q Bull Northwest Univ Med Sch. 36(2): 119–137. PMID: 13904457.

Cite this page: Hill, M.A. (2024, April 19) Embryology HansonAnson1962 fig01.jpg. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/File:HansonAnson1962_fig01.jpg

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