Squamosal bone

The squamosal ( squamosal, Os squamosum from Latin squama, " scale " ) is a large deck paired bones of the cranial vault of Osteognathostomata ( bony fish, including terrestrial vertebrates), which is always in close spatial relationship to the otic capsule. In anatomical drawings, it is usually marked with the symbol or sq. Sq.

The squamosal is phylogenetically the first time safely in the home group of land vertebrates ( Tetrapoda ) detected. These only known fossil, fish-like stem tetrapods (or basal Tetrapodomorphen ), it forms part of the side panel of the skull between the eye socket (orbit ) and Präoperculare. The Strahlenflossern is missing or are sometimes referred to as the " squamosal " or " Squamosoid " in the literature covering bones with representatives of this group is not homologous to the shed leg of Tetrapodomorpha. With today lungfish it is also not present.

In terrestrial vertebrates ( Tetrapoda ) it is due to the complete reduction of the Opercularserie ( bones of the operculum ) and a general shortening of postorbital skull now a part of the posterior cranial side wall. For more basal extinct tetrapods ( " labyrinthodonts " ), the squamosal is often involved in the front and in some cases also at the bottom of the so-called otic slot, an indentation in the rear edge of the side of the skull wall.

In the basic blueprint of Amniotenschädels it is with the parietal ( parietal ) in contact. In the basic blueprint of the skull diapsider reptiles shed the leg along with the postorbital at the top Temporalbogen, the bone bridge between the lower and upper temporal window involved.

In the basal synapsids it is involved with the Jugale at the bottom Temporalbogen (corresponds to the zygomatic arch of mammals). In mammals, the squamosal during ontogenesis melts relatively early with the otic bones ( Prooticum and Opisthoticum, which together form the petrous, and tympanic ). The corresponding compound bone is called the human temporal bone ( Temporal ) and whose greatest portion is substantially homologous to the squamosal, is as squamous ( scale part ) called (strictly speaking, the term squamosal even draws of the name pars squamosa from ). Is the concave articular surface of the (secondary) TMJ of mammals on the lower side of the shed Jochbogenanteils leg or the shed portion of the temporal bone.

Swell

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  • Anatomy of Mammals
  • Anatomy of Reptiles
  • Anatomy of the fish
Eusthenopteron Ossification Petrous part of the temporal bone Temporomandibular joint
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