Wing bone

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The wing bone ( Os pterygoideum ) in zoology usually called pterygoid , is a bone of the posterior palate region of the osteognathostomata . It is always in a more or less close anatomical relationship with the brain skull and in the amniotes it serves as a point of attachment for the jaw muscles.

Fishy osteognathostomas

The pterygoid is a pair of cover bones of the palate region and already appears in the basic structure of the osteognathostomata. In fish-like osteognathostomes, it is called entopterygoid and is distinguished from an ectopterygoid that is always closely associated with it . Both ento- and ectopterygoid are dentate, and their teeth, together with those on other dermal bones of the palate ( Dermopalatina ), form the so-called internal dental arcade . In addition, both meat fins (Sarcopterygii) and ray fins (Actinopterygii) have a bone element on the underside of the cranium , the metapterygoidis called. However, this is not a dermal bone, but an ossification of the palatoquadratum ( replacement bone ) and consequently has a different evolutionary origin than the ento- and ectopterygoid.

In modern bony fish (Teleostei), ectopterygoid, entopterygoid and metapterygoid are components of the jockstrap . All three can be dentate, i.e. This means that the metapterygoid must also contain parts of the cover bone.

Terrestrial vertebrates

Skull of an "Andean toad" in the palate view with pterygoid marked in red. In the open, clasp-like skull of the frog auger , the pterygoid is a relatively delicate element with no broad contact with the anterior palate. Note also that in modern amphibians the base phenoid is reduced so that the pterygoid articulates with the parasphenoid.

"Amphibians"

In the tetrapods , the homologue of the entopterygoid of the fish-like osteognathostome is traditionally referred to only as the pterygoid . In the basal terrestrial vertebrates there is a flat and often two-dimensional element of the rear palate roof and projects inwardly (mediad) to the lower part of the brain capsule, the Basicranium (especially the basisphenoid and / or the parasphenoid ) more or less closely associated. To the front (rostrad) it often has contact with various anterior palatal bones, mostly with the palatine, and outwards (laterad) usually with the ectopterygoid. Backwards (caudad) it is in fact always connected with the quadratum. In addition, like the other dermal palatal bones, it often has small teeth. In the modern amphibians are not. In these, the ectopterygoid is also completely reduced. In the caecum , the pterygoid is fused with the quadratum to form the pterygoquadratum .

Amniotes

A and B: Isolated right pterygoid of a fossil monitor in lateral (A) and ventral (B) views. Note that in "lizards" (as well as crocodiles and birds) the pterygoid, in contrast to the basal sauropsids and bridge lizards, does not have a long rostral process and therefore no part of the anterior palate. C: The anatomical position of the pterygoid (marked in red) in the vicinity of the quadratum and the brain capsule in the skull shown as a silhouette is exemplary for many other "lizards".

Also in the amniotes a general reduction of the palatal teeth takes place in the course of their evolution and so in almost all recent amniotes the pterygoid is edentulous. The snakes make an exception .

In the extinct basal sauropsids or eureptiles and synapsids (" pelycosaurs "), the pterygoid is still relatively similar to that of the basal tetrapods. It is a flat, three-rayed bone, which is divided into
• an elongated anterior (rostral) process that rests outwards (laterally) on the palatine (palatine bone) and in front (rostral) on the vomer ("ploughshare") and a large part of the inner one (medial) edge of the anterior roof of the palate (in the form of the central suture or the outer border of the interpterygoid space , also called interpterygoid gap ) forms,
• a rather flat, laterad oriented transverse process that protrudes into the subtemporal fossa,
• and an elongated posterior (caudal), often rod-like or strip-like process that is in contact with the square ("square leg").

Comparative anatomy of the right pterygoids of various early diapsids in ventral view (not to scale); note the dentition still present in all representatives (apr = anterior / rostral process, qpr = square process, tpr = transverse process).

The transverse process is considered to be one of the most important newly acquired traits in the evolution of the amniotes. It serves as an attachment point for the pterygoid muscle , the largest adductor of the lower jaw. Near the origin of the caudal process, the pterygoid of the basal amniotes has a dorsal socket into which a lateral outgrowth of the rostral part of the base phenoid engages. This flexible connection is called the basipterygoid joint . It ensures a certain mobility and flexibility of the skull (see →  skull kinetics ). A basipterygoid joint or its equivalent are also present in the "higher" diapsids , both in the recent "lacertilia" and bridge lizards as well as in the extinct non-avian dinosaurs . They are also under the term synovial Basalgelenk (ger .: synovial basal joint together). In many "lizards", the pterygoid is part of a "push rod system" through which the pterygoid is pressed against the posterior palate when the lower jaw is lowered over the square that swings forward, thus lifting the upper jaw slightly. Crocodiles (Crocodylia) have, like some dinosaurs, very strongly developed transverse processes (with the involvement of the ectopterygoid), but no basal joint. Their skull is largely akinetic. Independent of the skull kinetics, there is generally a reduction in the rostral process of the pterygoid in the sauropsid line. The snakes and the bridge lizards are an exception . In the latter in particular, the pterygoid is still very similar to that of the basal eureptiles.

The birds (Aves), in contrast to their recent sister group , the crocodiles, have a kinetic skull and also have a basipterygoid joint. In the hens and ducks (Galloanserae) this is designed as a so-called rostropterygoid joint . The name refers to the advanced position of the contact between the pterygoid and the basicranium, so that it does not take place on the base phenoid, but on the parasphenoid.

The palate of a cat's skull. The wing leg is marked in light blue

The akinetic skull of mammals (Mammalia), on the other hand, has no basal joint. However, a skull element homologous to the pterygoid of the other amniotes is present. However, it is significantly reduced in size and does not lie horizontally, but is a more or less vertical plate ( lamina ) in the bony border of the nasopharynx , without any significant portion of the palate. In addition, in many mammals it is no longer an independent bone, but is incorporated in the rostral part of the basic phenoid (in mammals also called the sphenoid , sphenoid or sphenoid bone ; the corresponding rostral process is called the pterygoid process ). This significant reconstruction was made possible by the changes in the area of ​​the temporomandibular joint and the modification of the quadratum to an auditory bone and in particular because the most important jaw adductors in mammals, the masseter and temporalis muscles, are located on the posterior lateral wall of the skull (tempora) and on the zygomatic arch (zygomatic arc ) sit instead of on the back of the palate. The pterygoid or pterygoid process also serve as a base for the pterygoid muscle in mammals. With the representatives of some groups, u. a. Primates and predators , the lower edge of the pterygoid has a small, caudadic, hook-shaped appendix, the hamulus pterygoideus .

literature

  • Robert Lynn Carroll: Vertebrate Paleontology and Evolution. WH Freeman and Co., New York 1988.
  • Milton Hildebrand, George E. Goslow: Comparative and functional anatomy of the vertebrates. Springer, 2004, ISBN 3-540-00757-1 .
  • Gerhard Mickoleit: Phylogenetic systematics of vertebrates. Publishing house Dr. Friedrich Pfeil, Munich 2004, ISBN 3-89937-044-9 .
  • Franz-Viktor Salomon: Bony skeleton . In: Franz-Viktor Salomon u. a. (Ed.): Anatomy for veterinary medicine. Enke-Verlag, Stuttgart 2004, pp. 37-110. ISBN 3-8304-1007-7

Individual evidence

  1. ^ Rainer R. Schoch: Amphibian Evolution - The Life of Early Land Vertebrates. Wiley-Blackwell, Chichester (West Sussex) 2014, ISBN 978-0-470-67178-8 , p. 22
  2. ^ Robert L. Carroll: The Origin of Reptiles. Pp. 331–353 in: Hans-Peter Schultze, Linda Trueb (eds.): Origins of the Higher Groups of Tetrapods: Controversy and Consensus. Cornell University Press, Ithaca NY 1991, ISBN 0-8014-2497-6 , p. 333.
  3. ↑ Casey M. Holliday, Lawrence M. Witmer: Cranial kinesis in dinosaurs: intracranial joints, protractor muscles, and their significance for cranial evolution in diapsids. Journal of Vertebrate Paleontology. Vol. 28, No. 4, 2008, 1073-1088, doi: 10.1671 / 0272-4634-28.4.1073 (alternative full text access on the author's website ( Memento from September 28, 2013 in the Internet Archive )).
  4. ^ Term coined in: E. Weber: On the evolution of basicranial joints in birds, especially in hens and ducks (Galloanseres). Journal for zoological systematics and evolutionary research. Vol. 31, No. 4, 1993, pp. 300-317, doi: 10.1111 / j.1439-0469.1993.tb00198.x .
  5. ^ R. Presley, FLD Steel: The pterygoid and ectopterygoid in mammals. Anatomy and Embryology. Vol. 154, No. 1, 1978, pp. 95-110, doi: 10.1007 / BF00317957 .
  6. ^ Michael Novacek: Patterns of Diversity in the Mammalian Skull. Pp. 438-546 in: James Hanken, Brian K. Hall (Eds.): The Skull. Volume 2: Patterns of Structural and Systematic Diversity. University of Chicago Press, Chicago · London 1993, ISBN 0-226-31570-3 , pp. 460 f.
  7. ^ Paragraph up to then largely based on Joy M. Richman, Marcela Buchtová, Julia C. Boughner: Comparative Ontogeny and Phylogeny of the Upper Jaw Skeleton in Amniotes. Developmental Dynamics. Vol. 235, No. 5 ( Craniofacial Development Special Issue ), 2006, pp. 1230-1243, doi: 10.1002 / dvdy.20716 (Open Access).