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A reappraisal and revision of the numbering of the pharyngeal arches

Research output: Contribution to journalReview article

Original languageEnglish
Pages (from-to)1019-1023
Number of pages5
JournalJournal of Anatomy
Issue number6
Early online date11 Aug 2019
Accepted/In press1 Jul 2019
E-pub ahead of print11 Aug 2019
Published1 Dec 2019

King's Authors


The pharyngeal arches are a prominent and significant feature of vertebrate embryos. These are visible as a series of bulges on the lateral surface of the embryonic head. In humans, and other amniotes, there are five pharyngeal arches numbered 1, 2, 3, 4 and 6; note the missing ‘5’. This is the standard scheme for the numbering of these structures, and it is a feature of modern anatomy textbooks. In this article, we discuss the rationale behind this odd numbering, and consider its origins. One reason given is that there is a transient 5th arch that is never fully realized, while another is that this numbering reflects considerations from comparative anatomy. We show here, however, that neither of these reasons has substance. There is no evidence from embryology for a ‘5th’ arch, and the comparative argument does not hold as it does not apply across the vertebrates. We conclude that there is no justification for this strange numbering. We suggest that the pharyngeal arches should simply be numbered 1, 2, 3, 4 and 5 as this would be in keeping with the embryology and with the general numbering of the pharyngeal arches across the vertebrates.

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