The nerves, muscles and blood vessels in this region are small and delicate. Be very careful not to destroy them. (Figure 6-1)

Identify the sphincter-like orbicularis oris muscle encircling the mouth . Running from the lateral borders of this muscle find the thin descending muscle fibers of the sheet like platysma . This muscle continues down into the upper reaches of the anterior thoracic wall. Ascending from the lateral borders of the orbicularis oris find the fibers of the zygomaticus . Actually, there is a zygomaticus major which is more lateral and a minor which is closer to the nose.

While you are following the course of these muscles can you trace their motor nerve supply? You should be able to see nerve fibers of cranial nerve VII , the facial nerve emanating from the parotid gland . If you're lucky you may see 4 or 5 of these branches as they go to the muscles of expression. Don't confuse these nerve branches with the larger parotid duct , which lies a fingers width below the zygomatic arch and in the middle of these nerve branches.

The masseter is directly deep and running perpendicular to the parotid duct and anterior to the parotid gland. If you follow the parotid duct anteriorly, you can see it turn medial at the anterior edge of the masseter and pierce the buccinator muscle as it heads to its termination in the oral cavity next to the second maxillary molar. Examine the extent of the buccinator muscle. This important muscle is really the lateral wall of our mouth or our cheek, and acts to keep food between the occlusal surfaces of the teeth instead of between our cheek and gums.

Now look for the facial artery and vein as they weave their way superiorly across the mandible, buccinator and under the zygomaticus, finally ending near the medial angle of the eye.

Interestingly, the facial vein drains into the internal jugular vein , while the veins of the scalp drain into the external jugular vein . See if you can find the external jugular vein as it crosses the sternocleidomastoid muscle.

Now identify the rest of the muscles of expression and the various branches of the trigeminal nerve. This is the primary sensory nerve of the face. Slightly lateral and inferior to the angle of the mouth, you should see the depressor anguli oris . Deep to this muscle, find the mental nerve , which is a sensory branch of V3, as it emerges from the mental foramen.

Superior to the mouth and medial to the zygomaticus, identify the levator labii superioris muscle. Deep to this muscle, find the infraorbital nerve , a sensory branch of the maxillary division of V2.

Now identify the circular fibers of the orbicularis oculi as it encircles the eye. See if you can distinguish both the orbital and palpebral parts of this muscle. Now examine the inferiorly reflected flap of the frontalis muscle hanging down over the orbit. Look for the supraorbital nerve , a sensory branch of V1 on the deep side of this muscle.

Shift your attention to the lateral side of the neck. If you look slightly anterior and deep to the sternocleidomastoid muscle you will see a neurovascular bundle, the carotid sheath which contains the internal jugular vein , the common carotid artery , and the vagus nerve or cranial nerve X.

Near the level of the thyroid cartilage of the larynx, or adams apple, the common carotid splits into a more posterior internal carotid artery , and an anterior external carotid artery . If you can see a dilated area at the superior end of the common carotid and the beginning of the internal carotid you have found the carotid sinus . The carotid sinus contains pressoreceptors that respond to changes in blood pressure. Signals from these receptors are sent to the central nervous system via cranial nerve IX.

Now identify the branches of the external carotid as they make their way to structures in the neck and face. The superior thyroid artery leaves the external carotid near the posterior aspect of the hyoid bone, and, as you might guess, it supplies a portion of the thyroid gland.

The lingual artery should be the next most superior branch of the external carotid. This artery should run anteriorly under the digastricus and mylohyoid muscles toward its destination - the tongue. The hypoglossal nerve can be seen lying on the lateral or superficial surface of this artery.

The facial artery arises just superior to the lingual. Many times the facial and lingual arteries have a common trunk. See if you can follow the facial artery as it runs anteriorly and deep to the angle of the mandible, and then emerges over the inferior and posterior edge of the body of the mandible. An individual's pulse can be taken at this point, as the artery can be pressed against the bony mandible and you can feel arterial pulsations.

In order to see the remaining branches of the external carotid and some of the deeper structures of the face, part of the zygomatic arch and a portion of the ramus of mandible have been cut away. This procedure has left the coronoid process of the mandible in place. See if you can find the temporalis muscle and its attachment to the now free coronoid process of the mandible.

Examine the opened temporal mandibular joint . Can you see the articular cartilage of this joint? We now should be able to see the two terminal branches of the external carotid, the superficial temporal and the maxillary arteries. The superficial temporal artery runs superiorly and superficial to the temporalis muscle, and anterior to the external ear. The more deeply placed maxillary artery runs anterior and horizontal.

Most of the time the maxillary artery runs superficial to the lateral pterygoid ,but in 33% of us the maxillary artery runs deep to the lateral pterygoid. When this is the case the lateral pterygoid has probably been removed.

Remember, the fibers of the lateral pterygoid run horizontal, attaching to the condyle of the mandible, while the fibers of the medial pterygoid run more vertical, attaching to the medial side of the angle of the mandible.

One of the first large branches of the maxillary artery is the middle meningeal artery . This artery runs in a superior direction, entering the cranial vault through the foramen spinosum. In this same region, look for two important sensory branches of the mandibular (V3) division of the trigeminal - the inferior alveolar nerve and the lingual nerve . These two nerves usually emerge from the interval between the two pterygoid muscles with the inferior alveolar being the more posterior of the two nerves. If you're lucky (and brilliant) you may be able to see the tiny chorda tympani , a sensory, taste branch of cranial nerve VII. It leaves the lingual nerve and courses posterior and superior.