Craniocervical Junction

Abstract

The posterior cranial fossa, preformed in cartilage, is normally ossified from six centers. A single basi-occipital center is formed anteriorly. Laterally, two ex-occipital or lateral occipital centers follow on each side immediately adjacent to the hypoglossal canals, around which bone will eventually grow downwards. The condylar parts of the occipital bone ossify from the basi-occipital and lateral occipital centers. A pair of supra-occipital ossific centers develops in the posterior margin of the foramen magnum, which is thus bordered by areas formed from four cartilage bones. The dorsal part of the foramen magnum, always relatively wide, is ossified from the supra-occipital centers. The basi-occipital center of ossification can be identified in 51 mm embryos, the supra- occipital in 30 mm embryos and the lateral occipital in 37 mm embryos. The basilar and lateral parts are at first connected by wide bridges of cartilage, the anterior intraoccipital synchondroses. The squamous part of the occipital bone is connected to the lateral parts by the posterior intraoccipital synchondroses.