ANATOMY

The brain is supplied in blood by four arteries.

These arteries are divided into anterior and posterior axes.

Anterior axes are :

-Left and right common carotid arteries, which divide in the neck to form the internal and external carotid arteries.

-The internal carotid has only one major branch : the ophthalmic artery.

-The external carotid has many branches.

In humans, each common carotid divides in two in the neck, on each side, about an inch higher than Adam’s apple.

Posterior axes are : left and right vertebral arteries which merge to form the midline basilar artery.

There are many anastomoses between the anterior and posterior axes and between the right and left sides around Willis Polygon (or Willis’ circle)