ANATOMICAL FEATURES OF THE FLOOR STRUCTURES OF THE ORAL CAVITY IN HUMAN EMBRYONES AND PREFETI

Objective – to determine the chronological sequence of the appearance of the sources and the features of the development of the structures of the human oral cavity floor. Materials and methods. A series of consecutive histological sections of 24 human embryo and prefetus specimens aged 4 to 12 weeks of intrauterine development (4.0-75.5 mm parieto- coccygeal length) were studied using a complex of morphological research methods (anthropometry, morphometry, microscopy, 3D reconstruction, statistical analysis). Results. At the beginning of the 4th month of intrauterine development, the mandibular branchial arches form the maxillary and mandibular processes, the latter of which is the source of the rudiment of the mandible and elements of the floor of the oral cavity. At the 5th week of prenatal development, in the mesenchyme of the mandibular process of the first branchial arch, hardenings are observed – rudiments of the muscles of the oral cavity floor. During the 6th week of ontogenesis, intensive formation of Meckel’s cartilage is observed, which at this stage serves as the place of attachment of the muscles of the floor of the oral cavity. At the 7th week of intrauterine development, the rudiments of the digastric muscle are observed. Conclusions. 1. The source of the rudiments of the muscles of the oral cavity floor are two mesenchymal cell masses, which are determined at the 5th week of prenatal development: ventro- medial (rudiment of the geniohyoid and genioglossus) and dorso- lateral (rudiment of the hyoglossus, chondroglossus and stylohyoid). 2. At the 6th week of the prenatal period of ontogenesis, Meckel’s cartilage serves as the place of attachment of the muscles of the oral cavity floor – initially the mylohyoid, at the end of the 6th week – the geniohyoid, and at the 7th week – the digastric muscle. 3. The period of intrauterine development from the end of the 5th to the beginning of the 6th week should be considered critical due to the possible time of appearance of variants of the structure of the muscles of the floor of the mouth and the possible occurrence of congenital defects. 4. The place of attachment of the muscles of the floor of the mouth is the inner surface of Meckel’s cartilage, but during the 8th-11th week of intrauterine development, the attachment sites move to the bone edges of the rudiment of the body of the mandible, which cover Meckel’s cartilage from below. 5. In the pre-fetal period of development, only the geniohyoid and mylohyoid were found to attach to the hyoid bone.