The size of venous foramina and skull capacity in man and selected vertebrate species.

In many experiments it was proved that brain cooling systems in mammals and birds depend on the flow of the cool venous blood into the cranial cavity through a well-developed system of foramina. In order to investigate the anatomical basis of this mechanism a morphological study was undertaken. On 10 species of mammals and birds, a correlation between the skull capacity and the size of its main venous foramina was determined. A computer system of image analysis was used. In man the skull that was the largest, however consisted venous foramina of the smallest size. Moreover, the asymmetry of the foramina and the concentration of the outflow in one dominant foramen was the greatest. Probably the dominance of only one venous foramen on each side of the human skull provides the reduction of flow resistance and creates more advantageous conditions for blood outflow from the skull, and therefore, better conditions for brain cooling.