The cranial venous system in the rat: anatomical pattern and ontogenetic development. I. Basal drainage.

The anatomical pattern and development of the venous system of the cranial base in the rat is described. The anatomy of the venous system was determined from observations of vascular casts in adult rats; the development of the vascular system was established by examination of ink-injected embryos. A transverse sinus system was found to be present in the basal venous system. The sinus connects the posterior facial veins; its middle section transverses the cranial base through the basisphenoid canal, and it receives the venae ophthalmicae within the basisphenoid bone. The venae ophthalmicae in turn are connected to the perioptic veins and to the sinus interperiopticus intracranially. Dorsally, the venae ophthalmicae anastomose with the paired sinus cavernosus. The term sinus transversus basalis is proposed for the venous connection between the posterior facial veins within the basisphenoid bone of the rat. The anlage of the sinus transversus basalis is established by vascular networks during the final prenatal period, its formation, however, is only completed postnatally. The anlages of the venae periopticae, the venae ophthalmicae, the sinus cavernosus and the rami intercavernosi are already established at early developmental stages. The characteristic pattern is formed before birth.