PERMANENT ELECTRIC POLARIZATION AND PYROELECTRIC BEHAVIOUR OF VERTEBRATE SKELETON .4. CRANIAL BONES OF MAN

Like the bones of the axial and the appendicular skeleton, the bones of the human skull are pyroelectric and hence piezoelectric, too. There are two directions of electric polarization, one at right angles to the other, which can be clearly distinguished by appropriate measurements. The first of these two directions of polarization in the cranial bones follows the longitudinal direction of the collagen fibres or the osteons which develop from them. This longitudinal polarization is particularly marked in the cranial bones of foetuses and children in their first years of life. Up to the 2nd or 3rd postnatal year the electrical axes inside the parietal bone and the frontal bone, for example, emanate like radii from a centre formed by the parietal tuber and the frontal tuber respectively, and extend right to the very periphery of the bone. The axes are aligned exactly parallel to the fibre striation of the bony tissue which is macroscopically visible at this age. After the 3rd year of life, this strictly radial orientation disappears and the electrical axes become adjusted to the partly new contours of the cranium. The second direction of polarization in the cranial bones persists through life. It goes from the external surface to the internal surface, i.e. it is at right angles to the lamellae and tissue layers of the bones. It is true that the sense of direction differs in lamina externa, diploë and lamina interna, but it never changes in the course of ontogenesis. Analogous electric polarization phenomena were found in the cranial bones which develop from connective tissue and those which are cartilaginous in origin; this was demonstrated in respect of the two types of bone forming the occipital bone. A comparative study of the dermatocranium and the various large scales of Acipenser sturio showed that the polarization pattern is similar to that found in our investigations of the human skull bones. Our findings in respect of the cranial bones are supplemented by a survey of the electric polarization pattern in the topographically adjacent structures, i.e. pericranium, galea aponeurotica and scalp and also the dura mater encephali. © 1969 Springer-Verlag.