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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.
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 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 jugal bone has expanded into the region the lower temporal opening would normally occupy. Paired squamosal bones extend beyond the skull's back margin to form small horn-like projections. The skull of Doswellia lacks several bones found in other archosauriforms, including the postfrontals , tabulars , and postparietals .
The lower edge of each orbit was formed by a long forward branch of the jugal bone, which overlies an equally elongated rear branch of the tooth-bearing maxillary bone. The skull was somewhat broader than that of most other "younginiforms", as indicated by the width and curvature of the frontal and prefrontal bones.
Also basal is the fact that the hip joint is overhung by a hood-shaped extension of the antitrochanter; the front of this hood reaches further to below and to the outer side. There is no clear brevis shelf. The pubic bones and the ischia resemble each other in having a "foot" and being per pair connected via bony skirts, pierced by a foramen. [8]
The back of the skull ended in a hook-like shape, which was offset to the quadrate bone. The orbit (eye opening) was large and circular, and a large spur-like bone, the palpebral, protruded backwards into the upper part of the opening. Below the eye socket, the jugal bone gave rise to a
In contrast, the jugal (cheek bone) is robustly built and oriented laterally. The jugals are the widest point of the skull and triangular in cross-section. The splanchnocranium's (back part of cranium) lateral wall, jugal, and quadratojugal (cheekbone) form a transversely broad structure.