Peculiarities of morphogenesis of the bones of skull base at an early period of human ontogenesis

Abstract

The aim is to find out the chronological sequence of appearance of germs and peculiarities of development of bones of the skull base at an early period of human ontogenesis.Material and methods. 17 series of consecutive histological sections of specimens of embryos and prefetuses aged from 4 till 12 weeks of intrauterine development (IUD) using a complex methods of morphological examination (anthropometry, morphometry, histological sections, three-dimensional computer reconstruction) were studied.Results. Chondrification of the ectomeningeal capsule begins in the 7 th week of IUD (prefetuses 14.0-16.0 mm of parieto-coccygeal length (PCL)) and there are 3 pairs of cartilaginous sources of the bones of the skull base: parachordal cartilage (behind the pituitary gland); pituitary cartilage (on both sides of the pituitary gland); prechordal cartilage (in front of the pituitary gland) are defined. The bones of the skull base are formed as a result of endochondral osteogenesis, while most skull bones are characterized by membranous osteogenesis. At the 8th week of IUD chondrocranium is defined as a holistic structure, continuous with the anlage of the skull, so the morphogenesis of some skull bones is both cartilaginous and membranous. The first of the cartilaginous anlages of the skull base was found parachordal cartilage behind the pituitary gland. Pituitary cartilages are formed around the rudiment of the pituitary gland. Laterally, the centers of chondrification occur in the anlage of orbitosphenoidal cartilages, which are the sources of the development of small alars of the sphenoid bone. The alar-sphenoidal cartilages are the sources of the large alars of the sphenoid bone. The anterolateral process of the orbitosphenoidal cartilage occurs near the orbital part of the anlage of the frontal bone. At the 7 th weeks of IUD, the skull base contains separate foci of chondrogenesis, and at the end of the 8th week of IUD they merge into a single perforated main cartilaginous plate with primitive vascular-nerve openings.Conclusions. 1. In the development of the base and calvaria of the human skull 3 consecutive stages can be distinguished: 1) the emergence of the mesenchymal source (ectomeningeal capsule); 2) the formation of cartilaginous anlages through the development and fusion of numerous individual foci of chondrogenesis in the mesenchyme; 3) ossification of the cartilaginous anlages of more than 100 foci of osteogenesis. 2. The processes of chondrification of the anlages of the skull base are observed at the beginning of the prefetal period of ontogenesis (the 7 th week of the IUD), and at the end of the 8 th week of the IUD as a whole the cartilaginous base of the human skull is formed.