Presphenoid
The presphenoid is an unpaired midline bone present in the skull of many vertebrates. It occurs in the sphenoid region, anterior to the basisphenoid and posterior to the ethmoid region.[1][2] When present, it may make up some or all of the bony nasal septum.[1] In humans, it fuses with the orbitosphenoids, the alisphenoids, the basisphenoid, and the pterygoids (including the ectopterygoids[3]) to form the sphenoid bone.[4][5]
Anatomy
[edit]The presphenoid contains the optic canals[5] and forms the floor of the anterior cranial fossa.[6] In some animals, such as recumbirostrans, the presphenoid makes up the interorbital septum.[2] In certain mammals, it forms a thin vertical sheet of bone that makes up the bony nasal septum; this is similar to the role played by the mesethmoid in other mammal groups. This has led to a long history of confusion between the two elements.[1][7]
The presphenoid articulates anteriorly with the ethmoid region - particularly the mesethmoid, if present; the wings of the presphenoid also articulate with the cribriform plate, when present. Posteriorly it articulates with the basisphenoid, and laterally with the orbitosphenoids.[2][8][7]
In different taxa, the presphenoid may develop from one or two ossification centers, or may not ossify.[1]
Evolution
[edit]The presphenoid is a part of the chondrocranium, and is derived from the ancestral cartilaginous skull of early fishes.[9]
The presphenoid undergoes ossification sporadically in different clades. It is, for instance, ossified in some, but not all, recumbrirostrans.[2] It is thought to be absent in reptiles (including birds).[10]
The presphenoid is believed to be ancestrally present in mammals; it has been lost in xenarthrans, pangolins, horses, and some eulipotyphlans, but is present in most other modern mammals.[1] The presphenoid was historically thought to be absent in humans, but a 2026 developmental study demonstrated its presence.[4]
References
[edit]- 1 2 3 4 5 Sánchez-Sánchez, Guadalupe R.; Galliari, Fernando C.; Carlini, Alfredo A. (2024). "The skull base in Cingulata (Xenarthra, Mammalia): early ossification, homologies, and comparisons across mammals". Journal of Mammalian Evolution. 31 (4): 37. doi:10.1007/s10914-024-09734-3. hdl:11336/247250. ISSN 1064-7554.
- 1 2 3 4 Pardo, Jason D.; Szostakiwskyj, Matt; Anderson, Jason S. (2015-06-24). "Cranial Morphology of the Brachystelechid 'Microsaur' Quasicaecilia texana Carroll Provides New Insights into the Diversity and Evolution of Braincase Morphology in Recumbirostran 'Microsaurs'". PLOS ONE. 10 (6) e0130359. Public Library of Science. Bibcode:2015PLoSO..1030359P. doi:10.1371/journal.pone.0130359. ISSN 1932-6203. PMC 4479878. PMID 26107260.
- ↑ Presley, R.; Steel, F. L. D. (1978-01-01). "The pterygoid and ectopterygoid in mammals". Anatomy and Embryology. 154 (1): 95–110. doi:10.1007/BF00317957. ISSN 1432-0568. PMID 677485.
- 1 2 Hirano-Kawamoto, Ai; Yamamoto, Masahito; Honkura, Yohei; Murakami, Gen; Hayashi, Shogo; Katori, Yukio (2026-06-30). "Distinct delayed development of the basisphenoid–ethmoid interface in human fetuses: a histological study using human fetuses". Anatomy & Cell Biology. 59 (2). Korean Association of Anatomists: 318–328. doi:10.5115/acb.25.299. PMC 13291705. PMID 42056064.
- 1 2 Mead, James G.; Fordyce, R. Ewan (2009). "The therian skull : a lexicon with emphasis on the odontocetes". Smithsonian Contributions to Zoology (627). Smithsonian Institution Scholarly Press: 1–249. doi:10.5479/si.00810282.627.
- ↑ Triantafyllou, George; Piagkou, Maria (2025-08-20). "The Developing Human Sphenoid Bone: Linking Embryological Development to Adult Morphology". Biology. 14 (8): 1090. doi:10.3390/biology14081090. ISSN 2079-7737. PMC 12384024. PMID 40906422.
- 1 2 Ichishima, Hiroto (2016). "The ethmoid and presphenoid of cetaceans". Journal of Morphology. 277 (12): 1661–1674. Bibcode:2016JMorp.277.1661I. doi:10.1002/jmor.20615. ISSN 1097-4687. PMID 27645469.
- ↑ Pardo, Jason D.; Anderson, Jason S. (2016-08-26). "Cranial Morphology of the Carboniferous-Permian Tetrapod Brachydectes newberryi (Lepospondyli, Lysorophia): New Data from µCT". PLOS ONE. 11 (8) e0161823. Public Library of Science. Bibcode:2016PLoSO..1161823P. doi:10.1371/journal.pone.0161823. ISSN 1932-6203. PMC 5001628. PMID 27563722.
- ↑ Kardong, Kenneth (2015). Vertebrates: Comparative Anatomy, Function (7th ed.). McGraw-Hill.
- ↑ Jollie, Malcolm T. (1960-01-01). "The head Skeleton of the Lizard". Acta Zoologica. 41 (1–2): 1–64. Bibcode:1960AcZoo..41....1J. doi:10.1111/j.1463-6395.1960.tb00474.x. ISSN 0001-7272.