Why we have not discussed the cerebral veins
Infarction or hemorrhage caused by problems in the venous rather than the arterial system is fairly rare. Often the cause of venous thrombosis is one of the hypercoagulability states or blood volume depletion, and it is usually large veins and sinuses that are most affected.

To put it simply, what happens is that blockage of a large vein can 'back up' the circulation in a region, causing decreased arterial flow which in turn produces ischemia and infarction.  Clinical findings in these patients usually do not reflect the typical arterial territory syndromes that you have been learning about. One of the reasons for this may be that there are far more functional anastomoses in the venous than in the arterial system. For all these reasons, problems secondary to occlusion of cerebral veins are not particularly helpful in learning about the territories supplied by the cerebral arteries.