The cranial venous system in the rat: anatomical pattern and ontogenetic development. II. Dorsal drainage.

The precise anatomical pattern and the developmental sequences of the dorsal cranial sinuses are described with special reference to the petrosquamosal sinus. The pattern of the dorsal cranial venous system of the rat is quite similar to that of man, although there are certain important differences. In rats, the transverse sinus bifurcates into the small dorsally directed sigmoid sinus and the large laterally directed petrosquamosal sinus. The latter emerges through the wide petrosquamosal fissure and joins the maxillary and posterior facial veins, sending two roots to each. The superior sagittal sinus anastomoses ventrally with the interperioptic sinus. This pattern is already established at an early developmental stage and is obvious by gestational day E 19. The anlages of the transverse and the sigmoid sinuses are formed from anastomoses between the three dural stems which drain the blood from the brain vesicles via the primary head vein into the anterior cardinal veins. The middle dural stem is connected by a rich capillary network to both the developing maxillary vein and the external jugular venous system before day E 16, thus establishing the anlage of the petrosquamosal sinus. Its definitive pattern is already discernible on day E 18. The external jugular vein becomes the main cranial venous outflow in the postnatal rat.