Your two carotid arteries start in different places but mirror each other
The right common carotid artery branches off in the neck, while the left springs from the aortic arch inside the chest. Yet both climb the neck on matching paths and split in two near the fourth cervical vertebra, one branch heading into the skull for the brain, the other fanning out over face and neck.
The common carotids carry oxygen-rich blood to the head and neck. The right one arises from the brachiocephalic trunk and has only a short stretch in the chest; the left comes straight off the aortic arch and rises through the upper chest before entering the neck. Average diameters are about 6.5 millimetres in adult men and 6.1 in women. At the top edge of the thyroid cartilage each divides: the internal carotid runs deep into the skull to feed the brain, while the external carotid stays nearer the surface and sends branches to the face and neck.
In the neck each artery travels inside the carotid sheath, a tube of connective tissue that also holds the internal jugular vein and the vagus nerve, each wrapped separately. Low down the artery is buried beneath several muscle layers; higher up it lies closer to the skin, within a space surgeons call the carotid triangle. Tucked behind the fork is the carotid body, a small reddish-brown oval.
Anatomy varies more than textbooks imply. In about 12 percent of people the right carotid rises above the usual level, and the fork is often higher than normal, sometimes opposite or above the hyoid bone. One reported artery was just 4 centimetres long. A dissection study of 81 donors found 159 bifurcations whose height varied between and even within individuals, and higher forks sat closer to the hypoglossal nerve, which matters for surgery on the artery.
Doctors examine the carotids with Doppler ultrasound or angiography. In one study, men in their twenties averaged a peak blood speed of 115 centimetres per second, against 88 in men over 80. Because it is large and close to the surface, the carotid is used to find a pulse when wrist pulses fade; a detectable carotid pulse has been estimated to mean systolic pressure above 40 mmHg.
Source: Common carotid artery
