THYROID, ILLUSTRATION. THYROID, ILLUSTRATION Thyroid gland and arterial vascularization of the neck. The arteries of the neck are mainly composed of carotids, anteriorly, and vertebral arteries not visible here, posteriorly. They irrigate the structures of the neck, the head and the brain. The carotid arteries are issue from the aortic arch. The common carotid arteries, right and left, divide at thyroid_level into internal and external carotids. The external carotids give numerous collateral art