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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]
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 lower jaw. The quadrate bone forms the lower jaw articulation in all classes except mammals.
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 ...
In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. [2] The bone forms an ancestral component of the dermal roof and is typically thin compared to other skull bones. [3] The squamosal bone lies ventral to the temporal series and otic notch, and is bordered anteriorly by the postorbital.
The jugal bone is located on either side of the skull in the circumorbital region. It is the origin of several masticatory muscles in the skull. [1] The jugal and lacrimal bones are the only two remaining from the ancestral circumorbital series: the prefrontal, postfrontal, postorbital, jugal, and lacrimal bones.
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 ...
The tuatara and some extinct rhynchocephalians have a more rigid skull with a complete lower temporal bar closing the lower temporal fenestra formed by the fusion of the jugal and quadrate/quadratojugal bones, similar to the condition found in primitive diapsids. However early rhynchocephalians and lepidosauromorphs had an open lower temporal ...
Turtles, though not diapsids in a purely anatomical sense, qualify as members of the clade Diapsida due to their likely diapsid ancestry. Some diapsids, particularly modern lizards, have an infratemporal fenestra which is open from below due to a lack of contact between the jugal and quadratojugal bones.