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Trabecular cartilage

Trabecular cartilage
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Latin trabecula cranii
Anatomical terminology
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Trabecular cartilages (trabeculae cranii, sometimes simply trabeculae, prechordal cartilages) are paired, rod-shaped cartilages, which develop in the head of the vertebrate embryo. They are the primordia of the anterior part of the cranial base, and are derived from the cranial neural crest cells.

The trabecular cartilages generally appear as a paired, rod-shaped cartilages at the ventral side of the forebrain and lateral side of the adenohypophysis in the vertebrate embryo. During development, their anterior ends fuse and form the trabecula communis. Their posterior ends fuse with the caudal-most parachordal cartilages.

Most skeletons are of mesodermal origin in vertebrates. Especially axial skeletal elements, such as the vertebrae, are derived from the paraxial mesoderm (e.g., somites), which is regulated by molecular signals from the . Trabecular cartilages, however, originate from the neural crest, and since they are located anterior to the rostral tip of the notochord, they cannot receive signals from the notochord. Due to these specialisations, and their essential role in cranial development, many comparative morphologists and embryologists have argued their developmental or evolutionary origins. Today’s general theory is that the trabecular cartilage is derived from the neural crest mesenchyme which fills anterior to the mandibular arch (premandibular domain).

As clearly seen in the lamprey, Cyclostome also has a pair of cartilaginous rods in the embryonic head which is similar to the trabecular cartilages in jawed vertebrates. However, in 1916, Alexej Nikolajevich Sewertzoff pointed out that the cranial base of the lamprey is exclusively originated from the paraxial mesoderm. Then in 1948, reported the detail of the skeletogenesis of the lamprey, and showed that the “trabecular cartilages” in lamprey appear just beside the notochord, in a similar position to the parachordal cartilages in jawed vertebrates. Recent experimental studies also showed that the cartilages are derived from the head mesoderm. Today, the “trabecular cartilages” in the Cyclostome is no longer considered to be the homologue of the trabecular in the jawed vertebrates: the (true) trabecular cartilages were firstly acquired in the Gnathostome lineage.


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