Blood Supply to the Head and Neck

• Most arteries in the anterior cervical triangle arise from the common carotid artery or one of the branches of the external carotid artery.
• Most veins in the anterior cervical triangle are tributaries of the large internal jugular vein.

The Common Carotid Arteries

• The right common carotid artery begins at the bifurcation of the brachiocephalic trunk, posterior to the right sternoclavicular joint.
• The left common carotid artery begins arises from the arch of the aorta and ascends into the neck, posterior to the left sternoclavicular joint.

• Each common carotid artery ascends into the neck within the carotid sheath to the level of the superior border of the thyroid cartilage.
• Here it terminates by dividing into the internal and external carotid arteries. 

The Internal Carotid Artery

• This is the direct continuation of the common carotid artery and it has no branches in the neck.
• It supplies structures inside the skull.
• The internal carotid arteries are two of the four main arteries that supply blood to the brain.

• Each artery arises from the common carotid at the level of the superior border of the thyroid cartilage.
• It then passes superiorly, almost in a vertical plane, to enter the carotid canal in the petrous part of the temporal bone.

• A plexus of sympathetic fibres accompany it.

• During its course through the neck, the internal carotid artery lies on the longus capitis muscle and the sympathetic trunk.
• The vagus nerve (CN X) lies posterolateral to it.

• The internal carotid artery enters the middle cranial fossa beside the dorsum sellae of the sphenoid bone.
• Within the cranial cavity, the internal carotid artery and its branches supply the hypophysis cerebri (pituitary gland), the orbit, and most of the supratentorial part of the brain. 

The External Carotid Arteries 

• This vessel begins at the bifurcation of the common carotid, at the level of the superior border of the thyroid cartilage.
• It supplies structures external to the skull.

• The external carotid artery runs posterosuperiorly to the region between the neck of the mandible and the lobule of the auricle.
• It terminates by dividing into two branches, the maxillary and superficial temporal arteries.
• The stems of most of the six branches of the external carotid artery are in the carotid triangle. 

The Superior Thyroid Artery

• This is the most inferior of the 3 anterior branches of the external carotid.
• It arises close to the origin of the vessel, just inferior to the greater horn of the hyoid.
• The superior thyroid artery runs anteroinferiorly, deep to the infrahyoid muscles and gives off the superior laryngeal artery. This artery pierces the thyrohyoid membrane in company with the internal laryngeal nerve and supplies the larynx.

The Lingual Artery

• This arises from the external carotid artery as it lies on the middle constrictor muscle of the pharynx.
• It arches superoanteriorly, about 5 mm superior to the tip of the greater horn of the hyoid bone, and then passes deep to the hypoglossal nerve, the stylohyoid muscle, and the posterior belly of digastric muscle.

• It disappears deep to the hyoglossus muscle.
• At the anterior border of this muscle, it turns superiorly and ends by becoming the deep lingual artery.

The Facial Artery

• This arises from the carotid artery either, in common with the lingual artery, or immediately superior to it.
• In the neck the facial artery gives off its important tonsillar branch and branches to the palate and submandibular gland.
• The facial artery then passes superiorly under the cover of the digastric and stylohyoid muscles and the angle of the mandible.

• It loops anteriorly and enters a deep groove in the submandibular gland.

• The facial artery hooks around the inferior border of the mandible and enters the face. Here the pulsation of this artery can be felt (anterior to the masseter muscle).

The Ascending Pharyngeal Artery

• This is the 1^st or 2^nd branch of the external carotid artery.
• This small vessel ascends on the pharynx, deep to the internal carotid artery.
• It sends branches to the pharynx, prevertebral muscles, middle ear and meninges.

The Occipital Artery

• This arises from the posterior surface of the external carotid near the level of the facial artery.
• It passes posteriorly along the inferior border of the posterior belly of digastric.
• It ends in the posterior part of the scalp.
• During its course, it is superficial to the internal carotid artery and three cranial nerves (CN IX, CN X and CN XI).

The Posterior Auricular Artery

• This is a small posterior branch of the external carotid artery.
• It arises from it at the superior border of the posterior belly of the digastric muscle.
• It ascends posteriorly to the external acoustic meatus and supplies adjacent muscles, the parotid gland, the facial nerve, structures in the temporal bone, the auricle, and the scalp. 

The Internal Jugular Vein

• This is usually the largest vein in the neck.
• The internal jugular vein drains blood from the brain and superficial parts of the face and neck.
• Its course corresponds to a line drawn from a point immediately inferior to the external acoustic meatus to the medial end of the clavicle.

• This large vein commences at the jugular foramen in the posterior cranial fossa, as the direct continuation of the sigmoid sinus.

• The dilation at its origin is called the superior bulb of the internal jugular vein.
• From here it runs inferiorly through the neck in the carotid sheath.

• The internal jugular vein leaves the anterior triangle of the neck by passing deep to the SCM muscle.
• Posterior to the sternal end of the clavicle, it unites with the subclavian vein to form the brachiocephalic vein.
• Near its termination is the inferior bulb of the jugular vein contains a bicuspid valve similar to that of the subclavian vein.

• The deep cervical lymph nodes lie along the course of the internal jugular vein, mostly lateral and posterior.

Tributaries of the Internal Jugular Vein

• This large vein is joined at its origin by the: inferior petrosal sinus, the facial, lingual, pharyngeal, superior and middle thyroid veins, and often the occipital vein.

•  Provides a rigid support system
• Protects delicate structures (e. g., the protection provided by the bones of the vertebral column to the spinal cord)
• Bones supply calcium to the blood; are involved In the formation of blood cells (hemopoiesis)
• Bones serve as the basis of attachment of muscles; form levers in the joint areas, aIlowing movement

Innervation of the Skin

• Innervation of the skin is mainly through the three branches of the trigeminal nerve (CN V).
• Some skin over the angle of the mandible and anterior and posterior of the auricle is supplied by the great auricular nerve from the cervical plexus.
• Some cutaneous branches of the auricular branch of the facial nerve also supplies skin on both sides of the auricle.

• The trigeminal nerve is the general sensory nerve to the head, particularly the face, and is the motor nerve to the muscles of mastication.

The Ophthalmic Nerve

• This is the superior division of the trigeminal nerve, the smallest of the three branches and is wholly sensory.
• The ophthalmic nerve divides into three branches: the nasociliary, frontal and lacrimal just before entering the orbit through the superior orbital fissure.

• The nasociliary nerve supplies the tip of the nose through the external nasal branch of the anterior ethmoidal nerve.

• The frontal nerve is the direct continuation of CN V¹ and divides into two branches, the supraorbital and supratrochlear.
• The supratrochlear nerve supplies the middle part of the forehead.
• The supraorbital nerve supplies the lateral part and the front of the scalp.

• The lacrimal nerve, the smallest of the main ophthalmic branches, emerges over the superolateral orbital margin to supply the lacrimal gland and the lateral part of the upper eyelid.

The Maxillary Nerve

• This is the intermediate division of the trigeminal nerve.
• It has three cutaneous branches.

• The infraorbital nerve is the largest terminal branch of the maxillary nerve.
• It passes through the infraorbital foramen and breaks up into branches that supplies the skin on the lateral aspect of the nose, upper lip and lower eyelid.

• The zygomaticofacial nerve, a small branch of the maxillary, emerges from the zygomatic bone from a foramen with the same name.
• It supplies the skin over the zygomatic bone.

• The zygomaticotemporal nerve emerges from the zygomatic bone from foramen of the same name.
• It supplies the skin over the temporal region.

The Mandibular Nerve

• This is the inferior division of the trigeminal nerve.
• Of the three division of the trigeminal nerve, CN V³ is the only one that carries motor fibres (to the muscles of mastication).
• The main sensory branches of the mandibular nerve are the buccal, auriculotemporal, inferior alveolar and lingual nerves.

• The buccal nerve is a small branch of the mandibular that emerges from deep to the ramus of the mandible.
• It supplies the skin of the cheek over the buccinator muscle, the mucous membrane lining the cheek, and the buccal surface of the gingiva.

• The auriculotemporal nerve passes medially to the neck of the mandible and then turns superiorly, posterior to its head and anterior to the auricle. It then crosses over the root of the zygomatic process of the temporal bone, deep to the superficial temporal artery.

• It supplies the auricle, external acoustic meatus, tympanic membrane, and the skin in the temporal region.

• The inferior alveolar nerve is the large terminal branch of the posterior division of the mandibular nerve (the lingual nerve is the other terminal branch).
• It enters the mandible through the mandibular foramen to the mandibular canal. In the canal, it gives branches to the mandibular teeth.
• Opposite the mental foramen, this nerve divides into the mental nerve and the incisive nerve.
• The incisive nerve supplies the incisor teeth, the adjacent gingiva and the mucosa of the lower lip.
• The mental nerve emerges from the mental foramen and supplies the skin of the chin and the skin and mucous membrane of the lower lip and gingiva.

• The lingual nerve is the smaller terminal branch of the mandibular nerve.
• It supplies the general sensory fibres to the anterior two-thirds of the tongue, the floor of the mouth and the gingivae of the mandibular teeth.

The Muscles of Facial Expression

• These lie in the subcutaneous tissue and are attached to the skin of the face.
• They enable us to move our skin and change our facial expression. They produce their effects by pulling on the skin but do not move the facial skeleton.
• These muscles surround the facial orifices and act as sphincters and dilators.
• All facial muscles receive their innervation from the branches of the facial nerve (CN VII)-temporal, zygomatic, buccal, marginal mandibular, cervical.

Nerves of the Palate

• The sensory nerves of the palate, which are branches of the pterygopalatine ganglion, are the greater and lesser palatine nerves.
• They accompany the arteries through the greater and lesser palatine foramina, respectively.

• The greater palatine nerve supplies the gingivae, mucous membrane, and glands of the hard palate.

• The lesser palatine nerve supplies the soft palate.

• Another branch of the pterygopalatine ganglion, the nasopalatine nerve, emerges from the incisive foramen and supplies the mucous membrane of the anterior part of the hard palate.