Hyomandibular


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Hy`o`man`dib´u`lar


a.1.(Anat.) Pertaining both to the hyoidean arch and the mandible or lower jaw; as, the hyomandibular bone or cartilage, a segment of the hyoid arch which connects the lower jaw with the skull in fishes.
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The orbital fissure can be observed ahead of the otic capsules, in dorsal position, and the hyomandibular branch of the facial nerve in ventral position.
The triangular-shaped opercle ossified completely and articulated with the hyomandibular at this stage.
Tricas and New (1998) found similar results when recording the neural discharge from the hyomandibular nerve in the round stingray, Urolophus hallen.
Fourth, fifth and sixth infraorbitals short and wide, covering posterior margin of hyomandibular.
Identification: D II-VI (9-13), A II-IV 9-15, dorsal fin high and pointed, adipose fin present, pelvic fins with well developed axillary process, vertebrae 65-68, manubrium absent, with hook-shaped processes on the capitulum, anterior edge of hyomandibular round, only 19 to 26 gill rakers present on lower limb of first gill arch.
Many structures have been used to estimate the age of fishes, including scales, otoliths, vertebrae, fin rays and spines, opercular bones, cleithra, urohyal bone, and hyomandibular bone.
More than 30 different elements including articulated combinations were identified such as commonly used paired cranial bones (dentary, articular, quadrate, maxilla and premaxilla), and other useful, but not as often used, paired elements including, for example, cleithrum, opercular, post-temporal, hyomandibular and palatine.
Approximately 460 million years ago, the anterior gill arches of some aquatic vertebrates evolved into jaws and their supporting structures, including the hyomandibular bone.
A small sensory structure that develops in association with the hyomandibular cleft in vertebrate embryos (von Bartheld, 1990) is retained beyond early embryological development in only a few vertebrates (Simonetta, 1953).
Level two: Lateral view, right side of mandibular arch: 9, posterior limit of hyomandibular articular condyle; 10, dorsal tip of hyomandibular dorsal process; 11, anterior limit of hyomandibular opercular condyle; 12, anterodorsal limit of hyomandibular symplectic synchondrosis; 13, anterior limit of preopercular-quadrate suture; 14, posterodorsal limit of quadrate (in tricomycterids, this is represented by a slender dorsal process, while in other loricarioids, the process is absent and the landmark is identified as the posterodorsal extremal limit of the quadrate); 15, anterior tip of quadrate mandibular condyle.