Meckel's cartilage
The (paired) Meckel's cartilage (Meckel's cartilage, the Cartilago Meckeli , named after its discoverer JF Meckel (1820)) is the embryonic forerunner of the lower jaw bone of the jaws . Traditionally, it is set to be serial homologous to a ceratobranchiale of the gill arch (which is not necessary). In ontogenesis , it is partly covered by cover bones (e.g. the tooth-bearing dentition ), e.g. Partly displaced by replacement bones (the largest is the articular ) (the front and rear ends ossify even in humans). In bony fish, the cartilage remains a functionally important element in the lower jaw, which provides elasticity.
In mammals , as soon as the dentate appears as the sole lower jaw, Meckel's cartilage forms the basis for the series of ossicles (the primary jaw joint between the palatoquadratum and Meckel's bone became the joint between the anvil and the hammer ). Only the dorsal part of the former primary temporomandibular joint, i.e. the hammer-anvil joint, articulatio incudomallearis, remains and later forms part of the sound conduction apparatus of the middle ear .
From the cartilage of the proximal end of the second branchial arch which is stirrup , stapes . The remaining distal part initially forms a long cartilage clasp, the Reichert's cartilage - named after Karl Bogislaus Reichert - which becomes the styloid process after its chondral ossification and unites with the temporal bone . The middle part becomes the ligamentum styloideum and the most distal part ossifies to the little hyoid horn , cornu minus ossis hyoidei .
The Meckel's cartilage is a cartilage clasp of the first branchial arch, it acts as embryonic and temporary lead structure for the installation of the lower jaw ( mandible ) extending lateral to the Meckel cartilage via a spare bone formation , chondral ossification forms for this purpose, the cartilage builds up completely and is bone replaced.
During the embryological development, Meckel's cartilage is gradually broken down up to the 24th week. At the two dorsal ends, part of the auditory ossicles , the ossicula auditus , more precisely the hammer , malleus as well as the anvil , incus and the sphenomandibular ligament develop .
literature
- W. Westheide, R. Rieger (Ed.): Special Zoology. Volume II: Vertebrates or Skull Animals. 2nd Edition. Springer, Berlin / Heidelberg 2010, ISBN 978-3-8274-2039-8 .
- Jochen Fanghänel among others: Waldeyer anatomy of humans . 18th edition. De Gruyter, Berlin 2009, ISBN 978-3-11-019353-4 .
Individual evidence
- ↑ Graphic on the development of the temporomandibular joints and their derivatives ( Memento of the original from February 25, 2014 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Jan Langmann: Medical Embryology. Normal human development and its malformations. Thieme , Stuttgart / New York 1980, ISBN 3-13-446606-6 , p. 150.
