Vascular ontogeny of the septal region in rats.

The development of the arterial and venous systems of the septum was studied in rat brains injected daily with India ink, from the 11th embryonic (E) until the first postnatal day. Arterial blood is supplied to the septum by the unpaired hemispheric artery, the stem and septal branches of which are to be recognized on the 14th and 15th embryonic days respectively. At earlier stages, e.g. on E12, a capillary network, the hemispheric plexus, can be seen between the two hemispheres contributing to the blood supply of the septum during the early phase (E14 to E18) of development. From E18 onwards, the arterial supply of the septum is derived only from direct branches of the hemispheric artery; one group of them being dorsal (infracallosal) and the other ventral (subcallosal). The venous drainage of the septum is bidirectional: 1) Veins of the ventral group leading to the interperioptic sinus are seen on E14. At first they collect blood only from a small rostral portion of the septum, but later their territory expands to include the anteroventral two-thirds of the septum. 2) The dorsal septal veins drain into the great cerebral vein (of Galen), or into the superior sagittal sinus directly. Initially, twigs run directly into the great cerebral vein. These later become the tributaries of the internal cerebral vein, which appears on E17 or E18. Until E18 this dorsally-directed drainage predominates, whereas at birth it becomes restricted to one third of the septum as a result of a gradual regression. The development of both arterial and venous circulations of the septum is complete at birth.