The Arteries
The carotid arteries
The carotid arteries are the primary blood supply to the head, neck and brain. Inside the skull
they anastomose with branches from the vertebral arteries. In the neck they anastomose with
branches from the thyrocervical trunk and costocervical trunk.
The right and left common carotid arteries
The right common carotid artery
branches from the brachiocephalic trunk behind the right
sternoclavicular joint It passes to the right in front of the trachea to lie on its right side. The other
major limb of the brachiocephalic trunk is the right subclavian artery. Occasionally the
brachiocephalic trunk gives off a small artery to the thyroid gland, the thyroidea ima artery. The
left common carotid arises directly from the aortic arch, just before the origin of the left
subclavian artery. These two vessels may arise from a common left brachiocephalic trunk. Each
carotid artery ascends the neck in a connective tissue sheath which encloses the vagus nerve and
the internal jugular vein. The internal jugular vein lies lateral to the common carotid artery with
the vagus nerve in between. At the upper border of the thyroid cartilage the common carotid
arteries divide to form the internal and external carotid arteries.
The external carotid artery
The external carotid arteries supply the muscles of the neck, the pharynx, larynx, thyroid, ears,
mouth, nose, face and scalp. The named branches are:
The internal carotid artery
As the internal carotid artery from from the common carotid artery, the vessel dilates to form the
carotid sinus. The walls of the carotid sinus carry receptors for arterial pressure, innervated by
the glossopharyngeal nerve. Another sensory organ, the carotid body, lies behind the common
carotid bifurcation. The internal carotid artery ascends to the base of the skull which it enters
through the carotid canal. Entering the skull the artery passes anteriorly across the foramen
lacerum and through the cavernous sinus. Emerging from the cavernous sinus the artery
terminates by dividing into the anterior and middle cerebral arteries. There are no branches from
the cervical part of the internal carotid. The ophthalmic artery is the largest of its intracranial
branches leaving at the emergence from the cavernous sinus and entering the orbit by the optic
canal to supply all of the structures of the orbit. Smaller branches also arise fro the internal
carotid arery as it passes through the skull. These branches supply the meninges, the trigeminal
ganglion, the pituitary gland, and the tympanic cavity.
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