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The main blood supply to the circle is via the paired internal carotid arteries and the basilar artery. The basilar artery receives blood from the ventral spinal artery and the vertebral artery (the vertebral artery is a branch of the subclavian artery running through the vertebral foramina of C1 - C6). The internal carotid artery receives blood supply from the external carotid artery, the common carotid artery and in some species also from the vertebral artery via the occipital artery. The external carotid artery itself can also receive blood from the maxillary artery. In some species the maxillary artery is also directly able to supply the internal carotid artery, bypassing the external carotid artery via an anastomising ramus linking the internal carotid and maxillary arteries. This maxillary anastomising ramus allows blood to flow through the maxillary rete mirabile which is a network of vessels located within the cavernous sinus, facilitating the cooling of blood temperature and reducing fluctuations from pulsatile blood flows (see rete mirabile section below for further details on function). As mentioned above, the vertebral artery can also supply the internal carotid artery via the occipital artery but this too can be bypassed so that the vertebral artery can directly supply the internal carotid artery via a ramus to the internal carotid directly from the vertebral artery.

The main blood supply to the circle is via the paired internal carotid arteries and the basilar artery. The basilar artery receives blood from the ventral spinal artery and the vertebral artery (the vertebral artery is a branch of the subclavian artery running through the vertebral foramina of C1 - C6). The internal carotid artery receives blood supply from the external carotid artery, the common carotid artery and in some species also from the vertebral artery via the occipital artery. The external carotid artery itself can also receive blood from the maxillary artery. In some species the maxillary artery is also directly able to supply the internal carotid artery, bypassing the external carotid artery via an anastomising ramus linking the internal carotid and maxillary arteries. This maxillary anastomising ramus allows blood to flow through the maxillary rete mirabile which is a network of vessels located within the cavernous sinus, facilitating the cooling of blood temperature and reducing fluctuations from pulsatile blood flows (see rete mirabile section below for further details on function). As mentioned above, the vertebral artery can also supply the internal carotid artery via the occipital artery but this too can be bypassed so that the vertebral artery can directly supply the internal carotid artery via a ramus to the internal carotid directly from the vertebral artery.

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