Arterial

Common Carotid Artery

Arises on Left side from Arch of Aorta
- Lies anterior to Subclavian Artery up to the Sternoclavicular Joint
On Right side, Brachiocephalic Trunk bifurcates behind the Sternoclavicular Joint into Common Carotid and Subclavian Arteries
Gives off no branches proximal to its bifurcation
Lies within medial part of Carotid Sheath
- Internal Jugular Vein lateral to it and Vagus nerve deeply placed between
- Sympathetic trunk behind the artery and outside sheath
Bifurcates at level of upper lamina of Thyroid Cartilage (upper border of C4)
Terminal portion of artery often shows a slight dilatation (Carotid Sinus) – includes the commencement of the Internal Carotid Artery
Common Carotid Relations
- Posterior (outside sheath) = sympathetic trunk, pharyngeal veins and superior laryngeal branch of vagus.
- Medial = ascending pharyngeal artery
- Lateral = IJV, and vagus nerve deep b/n artery and vein
- Superficial, near origin, it is crossed by: lingual vein, facial vein, XII, and superior root of ansa cervicalis (embedded in the sheath).
- Overlapped higher by SCM, and posterior border of digastric, stylohyoid and posterior auricular artery

At its commencement, lies against side wall of Pharynx anteromedial to Internal Carotid Artery
Ascends in front of Internal Carotid deep to the Posterior Belly of Digastric and Stylohyoid
Pierces the Parotid Fascia to enter the Parotid Gland
Divides within the gland behind the neck of the Mandible into Maxillary and Superficial Temporal Arteries
As it lies within the Parotid Gland, it is separated from the Internal Carotid by the deep part of the Gland, its fascia, Styloid Process and it’s continuation the Stylohyoid Ligament, Styloglossus and the ‘Pharyngeal Structures’
- Stylopharyngeus muscle
- Glossopharyngeal Nerve
- Pharyngeal Branch of the Vagus Nerve
Facial Vein crosses artery with Hypoglossal Nerve lying between
Lies mostly in the anterior border of SCM

Branches of External Carotid Artery

Before dividing into 2 terminal branches (Superficial Temporal Artery and Maxillary Artery), it gives off 6 branches – 3 from in front, 2 from behind, and one from its deep (medial) aspect
Three from in Front:
Two from Behind:
- Occipital Artery
- Posterior Auricular Artery
One from deep:
- Ascending Pharyngeal Artery
Some Anatomists Like Freaking Out Poor Medical Students

Arises at Bifurcation of Common Carotid
Continues upwards within Carotid Sheath
At its commencement, Carotid Sinus – arterial wall is thin and contains Baroreceptors
- Supplied by the Glossopharyngeal Nerve and Vagus Nerves
Carotid Body – small structure lying behind the bifurcation – receives 2 or 3 small glomic arteries
- Chemoreceptors supplied by Glossopharyngeal and Vagus Nerves
Lateral to External Carotid at its origin but soon passes posteriorly to a medial and deeper level
Has no branches and passes to the Carotid Canal in base of the skull

Relations

Posterior:
- Sympathetic Trunk (Outside Carotid Sheath)
- Pharyngeal Veins
- Superior Laryngeal Branch of the Vagus Nerve
Medial:
- Ascending Pharyngeal Artery
Lateral:
- Internal Jugular Vein
Deep:
- Vagus Nerve between Artery and IJV
Anterior:
- Crossed by Lingual Vein
- Facial Vein
- Occipital Artery
- Hypoglossal Nerve
At a higher level, crossed by Posterior Belly of Digastric and Stylohyoid and Posterior Auricular Artery and the structures that separate it from the External Carotid

Incision along anterior border of SCM
Muscle retracted backwards
Facial and Lingual Veins divided
Carotid Sheath incised
Hypoglossal Nerve must be safeguarded and this may require division of the lower SCM branch of the Occipital Artery
Emergence of branches from the External Carotid ensures its differentiation from the Internal Carotid

Emerges from the Jugular Bulb at the posterior compartment of the Jugular Foramen
Continuation of the Sigmoid Sinus
At first behind the Internal Carotid Artery
Lies on transverse process of Atlas
- Crossed by the Accessory Nerve
Receives Inferior Petrosal Sinus as its first tributary just below base of skull
Sinus passes back lateral or medial to the Glossopharyngeal, Vagus and Accessory Nerves
Vein passes down to gain the lateral side of first the Internal Carotid and then the Common Carotid, within the loose lateral part of Carotid Sheath
- Vagus Nerve placed deeply between the vein and arteries
Overlapped in its lower aspect by SCM
Joins the Subclavian Vein to form the Brachiocephalic Vein behind the Sternal end of the Clavicle

Deep Cervical Lymph Nodes within the Carotid Sheath are closely adjacent to IJV throughout
Posterior:
- Cervical Plexus lying on Levator Scapulae and Scalenus Medius
- Phrenic Nerve on Scalenus Anterior
- Thoracic Duct – crosses behind the Left IJV at the level of C7
Anterior:
- Union of Inferior and Superior Roots of the Ansa Cervicalis
- Low down, the tendon of Omohyoid – useful guide
Lateral:
- Inferior Root of Ansa Cervicalis