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In tetrapods with a quadratojugal bone, it often forms a portion of the jaw joint. Developmentally, the quadratojugal bone is a dermal bone in the temporal series, forming the original braincase. The squamosal and quadratojugal bones together form the cheek region [4] and may provide muscular attachments for facial muscles. [5]
The quadrate bone is a skull bone in most tetrapods, including amphibians, sauropsids (reptiles, birds), and early synapsids. In most tetrapods, the quadrate bone connects to the quadratojugal and squamosal bones in the skull, and forms upper part of the jaw joint. The lower jaw articulates at the articular bone, located at the rear end of the ...
The posterior end of the lower jaw bones contains a quadrate bone, allowing jaw extension. The anterior tips of the lower jaw bones are joined by a flexible ligament allowing them to bow outwards, increasing the mouth gape. [74] [75] The Pacific tree frog and the Baja California chorus frog are some of the only frog species that make a "ribbit ...
These extended margins of thinned bone are called supratemporal fossae. Synapsids, including mammals, have one temporal fenestra, which is ventrally bordered by a zygomatic arch composed of the jugal and squamosal bones. This single temporal fenestra is homologous to the infratemporal fenestra, as displayed most clearly by early synapsids. [2]
Jugal bone labelled Ju, in pale green, at centre left. The jugal is a skull bone found in most reptiles, amphibians and birds. In mammals, the jugal is often called the malar or zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species.
A quadratojugal bone, which in modern birds is fused to the jugal, is preserved in Pterygornis. [30] The presence of these primitive features of the skull would have rendered the Enantiornithes capable of only limited cranial kinesis (the ability to move the jaw independent of the cranium). [31]
The squamosal and quadratojugal bones, which lie behind the jugal, are quite large and are embayed from behind to accommodate the internal ears. [4] [5] Parareptiles were traditionally considered to have an ‘anapsid’-type skull, with the jugal, squamosal, and quadratojugal firmly sutured together without any gaps or slits between them. This ...
This bone is roughly L-shaped in these taxa, with a tall dorsal process (vertical branch), a short anterior process (forward branch), and a tiny or absent posterior process (rear branch). The bones surrounding the quadratojugal also reconfigure to offset the changes to the quadratojugal.