Pavlíková H., K. Witter, I. Mí‰ek: The Primordium of the Upper Vestibulum oris in the Domestic Sheep. Acta Vet. Brno 1999, 68:175-178.The oral vestibule is assumed to originate from the vestibular lamina, an invagination of the oral epithelium into the jaw. In mice, the oral vestibule originates from the vestibular lamina only in the incisor and diastema regions, while the buccal vestibule originates from a lateral excavation of the oral cavity. Detailed data on the development of the oral vestibule in other mammalian species are not available. The aim of this study was to explain the ontogenetic relationship between the vestibular lamina and the primordium of the vestibulum oris in the upper jaw of the domestic sheep. Heads of 19 staged embryos and fetuses were decalcified and embedded in paraffin. Serial transverse sections were stained and examined by light microscopy. The upper vestibular lamina is composed of large epithelial cells with lightly staining cytoplasm. In the incisor region, the lamina is extensively invaginated into the jaw mesenchyme and represents the primordium of the vestibulum oris. In the diastema region, the vestibular lamina shifts becoming more superficial extention from the oral epithelium. A deep lingual and superficial labial part of the vestibular lamina became apparent. The oral vestibule is derived only from the deep part. In the buccal region, tissue of the vestibular lamina remains superficial on the jaw arches and does not form a primordium of the oral vestibule. The buccal vestibule instead develops from a lateral excavation of the stomodeal cavity. The oral vestibule is not derivative of a single primordium.
Formation of the oral vestibule is ignored in most studies on tooth development, although dental and vestibular lamina are closely related to each other. Knowledge about morphogenetic processes shaping the oral vestibule is missing almost completely. The aim of this study was to assess the developmental relationship between dental and vestibular lamina as well as formation of the oral vestibule in the upper jaw of the field vole (Microtus agrestis), a small rodent representing an attractive model species for comparative dental studies. Three-dimensional reconstruction revealed that the upper vestibular lamina of the vole joins the antemolar part of the diastemal dental lamina, similar to mouse. Later, this lamina complex regresses and the vestibular lamina is separated from the molar epithelium. Participation of the vestibular lamina in dental lamina formation, as hypothesized for mouse, therefore remains unclear. Except for increased apoptosis in the regressing diastemal dental lamina, spatial segregation of mitoses or apoptoses could be detected neither in the jaw arch epithelium nor in the adjacent mesenchyme. Therefore, in contrast to tooth primordia, apoptosis and mitosis seem to play a minor role in shaping of the upper oral vestibule. The buccal vestibule develops secondarily, probably in consequence of general growth of the head and localized differentiation of cells.
Summary A striated muscle of the hard palate has been previously described in some rodents and rabbits. It is not termed in the official veterinary anatomical nomenclature. The aim of this work was to verify the existence of this muscle. Heads of the golden hamster (Mesocricetus auratus), the guinea pig (Cavia aperea f. porcellus), the laboratory rat (Rattus norvegicus var. alba), the field vole (Microtus agrestis) and the domestic rabbit (Oryctolagus cuniculus f. domesticus) have been dissected. Moreover, histological sections have been prepared from heads of the field vole. In all species under study, we could detect a striated muscle of the hard palate composed of an anterior and a posterior muscle. The anterior muscle originated on the os incisivum and diverged in anterior, lateral and posterior directions. The posterior muscle originated on the processus palatinus maxillae and verged into the m. buccinator. Inter-species differences could be detected in shape and position of the muscle. The palatal muscle was innervated by the ramus buccalis of the facial nerve. Whether this muscle should be classified as an individual facial muscle or as a part of the m. buccinator remains to be discussed.
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