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Trabecula cranii: viscerocranial element of the new vertebrate head
Horáčková, Agáta ; Černý, Robert (advisor) ; Minařík, Martin (referee)
4 Abstract Trabeculae cranii comprise major paired elements that constitute cartilaginous basis of the rostral embryonic skull. Trabeculae were initially recognized as remnants of the pre-mandibular visceral arch. This assumption is originally based on the segmentation theory, that the vertebrate head is segmented in the same metameric pattern as the trunk. This theory is not considered valid anymore. Contemporary authors also reject the possibility, that the trabecula is a part of viscerocranium, even though it shares some developmental patterns with pharyngeal arch elements. The key character of a viscerocranial element should be it's developmental relationship with the endoderm. If the trabecula represents a pharyngeal cartilage, it will develop in a topographical relationship with the pre- oral gut endoderm. Basal actinopterygian fishes (African bichirs, European sturgeons, and Tropical gars) offer unique opportunity to examine this hypothesis because of recent description of the pharyngeal pouch-like component in the pre- mandibular head segment, which most likely represents an ancestral vertebrate character. In these fishes, the topographical relationship of trabeculae and endoderm was found using histological analyses, antibody stainings, and fate- mapping experiments. This work shows that trabeculae...
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The trabecular cartilage as a key structure for development and evolution of the anterior vertebrate cranium
Horáčková, Agáta ; Černý, Robert (advisor) ; Němec, Pavel (referee)
Anterior part of the skull is in embryos composed of two rod-like cartilages called trabeculae cranii. The final shape of the skull of jawed vertebrates is affected by the manner of composition of trabeculae. There are two types of arrangement of vertebrate skull: the platybasic, which is probably the original one, and the tropibasic, which has developed independently in birds, bony fishes and mammals. Jawless vertebrates (lampreys and hagfishes) also have cartilaginous elements called trabeculae, but there are doubts about homology of these structures between groups of jawed and jawless vertebrates. The trabeculae initially became interesting elements because of their possible position in premandibular segment as a former premandibular branchial arch. The two theories of origin of jaws, which do not assume there ever were any branchial arches before the mandibular, strictly disagree in the question of the nature of the trabeculae cranii.
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