Basisphenoid
The basisphenoid is a bone in the skull of vertebrates. It is an unpaired midline element that forms part of the posterior and ventral margin of the braincase; it is typically located anterior to the basioccipital and posterior to the parasphenoid. It ossifies endochondrally and makes up a part of the chondrocranium.[1] The parasphenoid contains the sella turcica, which houses the pituitary gland.[2]
Evolution
[edit]The basisphenoid originates as a part of the chondrocranium[1]; among placoderms, chondrichthyans, and early acanthodians it is present as a region of the cartilaginous braincase.[3]
In non-tetrapod osteichthyans, the basisphenoid contains grooves for the spiracle.[3] It is typically absent in teleosts.[4]
In many osteichthyans, including early stegocephalians and amniotes, the basisphenoid fuses to the parasphenoid (of dermal origin) very early in ontogeny; it may also fuse to the sphenethmoid.[5] In such cases, the two bones cannot be distinguished, and fused element is referred to as the parabasisphenoid.[6] Fusion of the two elements is thought to have occurred convergently in tetrapods and in actinopterygians.[5]
In non-mammalian synapsids, the basisphenoid is often covered ventrally by the parasphenoid, to which it may fuse; among cynodonts, it articulates with the prootic to form a portion of the bony labyrinth. The portion of the basisphenoid which forms part of the bony labyrinth is known as the basisphenoid wing.[7]
In mammals, the basisphenoid is much smaller and does not contribute to the bony labyrinth, due to an enlargement of the petrosal to form the promontorium.[7] It is typically fused to the presphenoid, orbitosphenoid, and the alisphenoid (of the splanchnocranium) to form the sphenoid.[1] It makes up the posterior part of the sphenoid base.[8]
References
[edit]- 1 2 3 Kardong, Kenneth (2015). Vertebrates: Comparative Anatomy, Function (7th ed.). McGraw-Hill.
- ↑ Jipa, Andrei; Jain, Vikas (2021). "Imaging of the sellar and parasellar regions". Clinical Imaging. 77: 254–275. doi:10.1016/j.clinimag.2021.05.022. ISSN 0899-7071.
- 1 2 Brazeau, Martin D. (2009). "The braincase and jaws of a Devonian 'acanthodian' and modern gnathostome origins". Nature. 457 (7227): 305–308. doi:10.1038/nature07436. ISSN 1476-4687.
- ↑ Jollie, Malcolm (1986). "A primer of bone names for the understanding of the actinopterygian head and pectoral girdle skeletons". Canadian Journal of Zoology. 64 (2): 365–379. doi:10.1139/z86-058. ISSN 0008-4301.
- 1 2 CLACK, J. A. (1998-01-01). "The neurocranium of Acanthostega gunnari Jarvik and the evolution of the otic region in tetrapods". Zoological Journal of the Linnean Society. 122 (1–2): 61–97. doi:10.1111/j.1096-3642.1998.tb02525.x. ISSN 0024-4082.
- ↑ Sterli, Juliana; Müller, Johannes; Anquetin, Jérémy; Hilger, André (2010). "The parabasisphenoid complex in Mesozoic turtles and the evolution of the testudinate basicranium". Canadian Journal of Earth Sciences. 47 (10): 1337–1346. doi:10.1139/E10-061. ISSN 0008-4077.
- 1 2 Luo, Zhexi; Crompton, Alfred W.; Lucas, Spencer G. (1995-03-14). "Evolutionary Origins of The Mammalian Promontorium and Cochlea". Journal of Vertebrate Paleontology. 15 (1): 113–121. doi:10.1080/02724634.1995.10011211. ISSN 0272-4634.
- ↑ Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 220–244. ISBN 0-03-910284-X.