Fig. 2-32 Facial Muscles. Fig. 2-33 Trigeminal Nerve (CN V)

Fig. 2-32 Facial Muscles. Fig. 2-33 Trigeminal Nerve (CN V) leaving the Skull. 51 thetic agent at the infraorbital foramen or in the infraor- posterior to its head and anterior to the auricle. It then bital canal (e.g., for treatment of wounds of the upper crosses over the root of the zygomatic process of the lip and cheek or for repairing the maxillary incisor teeth). temporal bone, deep to the superficial temporal artery. The site of emergence of this nerve can easily be deter- As its name suggests, it supplies parts of the auricle, mined by exerting pressure on the maxilla in the region external acoustic meatus, tympanic membrane (ear- of the infraorbital foramen and nerve. Pressure on the drum), and skin in the temporal region. The inferior al- nerve causes considerable pain. Care is exercised when veolar nerve is the large terminal branch of the posterior performing an infraorbital nerve block because compan- division of CN V3; the lingual nerve is the other terminal ion infraorbital vessels leave the infraorbital foramen with branch. It enters the mandibular canal through the man- the nerve. Careful aspiration of the syringe during injec- dibular foramen. In the canal it gives off branches that tion prevents inadvertent injection of the anesthetic fluid supply the mandibular (lower) teeth. Opposite the mental into a blood vessel. The orbit is located just superior to foramen, the inferior alveolar nerve divides into its ter- the injection site. A careless injection could result in minal incisive and mental branches. The incisive nerve the passage of anesthetic fluid into the orbit, causing supplies the incisor teeth, the adjacent gingiva, and temporary paralysis of the extraocular muscles. the mucosa of the lower lip. The mental nerve emerges The Mandibular Nerve. This nerve (CN V3) is the from the mental foramen and divides into three branches, inferior division of the trigeminal. CN V3 has three sen- which supply the skin of the chin and the skin and sory branches that supply the area of skin derived from mucous membrane of the lower lip and gingiva (gum). the embryonic mandibular prominence. It also supplies motor fibers to the muscles of mastication. Of the three PAROTIDOMASSETER REGION divisions of the trigeminal, CN V3 is the only division of The boundaries are: superiorly – zygomatic arch; CN V that carries motor fibers. The main sensory bran- inferiorly – lower edge of mandible; medially – anterior ches of the mandibular nerve are the buccal, auricu- margin of masseter; laterally – ramus of mandible (Fig. lotemporal, inferior alveolar, and lingual nerves. The 2-34). buccal nerve is a small branch of CN V3 that emerges The layers are: the skin is thin, mobile; the hypo- from deep to the ramus of the mandible to supply the dermic fat is developed moderately, it consist of the skin of the cheek over the buccinator muscle. It also superficial vessels and nerves (branches of the facial, supplies the mucous membrane lining the cheek and mandibular nerves); the fascia proper (f. parotideo- the posterior part of the buccal surface of the gingiva masseterica, or investing layer of deep cervical fascia) (gum). The auriculotemporal nerve passes medial to is divided into two leafs around the parotid gland, which the neck of the mandible and then turns superiorly, formed the capsule for it. Fig. 2-34 Parotid gland and Facial nerve (CN VII) on the Face. 52 The Parotid Gland of the mandibular nerve (V3). This division of the trigemi- The parotid gland (see Fig. 2-34) lies beneath the nal nerve exits the skull through the foramen ovale. skin in front of and below the ear. It is contained within The auriculotemporal nerve also carries secreto- the investing layer of the deep fascia, called locally the motor fibers to the parotid gland. These postganglionic parotid fascia (f. parotideomasseterica) and the gland parasympathetic fibers have their origin in the otic gan- can be felt only under pathological conditions. glion associated with the mandibular nerve (V3) and The boundaries are: anterior – masseter muscle, are just inferior to the foramen ovale. ramus of mandible, and internal pterygoid muscle; pos- Preganglionic parasympathetic fibers to the otic terior – mastoid process and sternocleidomastoid ganglion come from the glossopharyngeal nerve (CN IX). muscle; superior – external auditory meatus and tem- Structures traversing the Parotid Gland poromandibular joint; inferior – sternocleidomastoid The main trunk of the facial nerve enters the pos- muscle and posterior belly of digastric muscle; lateral terior surface of the parotid gland about 1 cm from its – investing layer of deep cervical fascia, skin, and emergence from the skull through the stylomastoid fo- platysma muscle; medial – investing layer of deep cer- ramen about midway between the angle of the man- vical fascia, styloid process, internal jugular vein, inter- dible and the cartilaginous ear canal. At birth the child nal carotid artery, and pharyngeal wall. has no mastoid process and the stylomastoid foramen The parotid duct leaves the anterior edge of the is subcutaneous. parotid gland midway between the zygomatic arch and About 1 cm from its entrance into the gland, the the corner of the mouth. It crosses the face in a trans- facial nerve divides to form five branches (see Fig. 2-35): verse direction and, after crossing the medial border of temporal, zygomatic, buccal, mandibular, and cervical. the masseter muscle, turns deeply into the buccal fat In most individuals, an initial bifurcation forms an upper pad and pierces the buccinator muscle. It enters the temporofacial and a lower cervicofacial division, but six inside of the vestibule of mouth near the second upper major patterns of branching (from simple to complex) molar tooth. have been distinguished. The parotid gland receives its arterial supply from The external carotid artery enters the inferior sur- the numerous arteries that pass through its substance. face of the gland and divides into the maxillary and su- Sensory innervation of the parotid gland is pro- perficial temporal arteries. The latter gives rise to the vided by the auriculotemporal nerve, which is a branch transverse facial artery (Fig. 2-35). Each of these bran- Fig. 2-35 Vasculature of the Face. 53 ches emerges separately from the superior or anterior nerve. Injury to the auriculotemporal nerve produces surface of the parotid gland. Frey’s syndrome, in which the skin anterior to the ear The superficial temporal vein enters the superior sweats during eating (“gustatory sweating”). surface of the parotid gland and receives the middle The Parotid Bed temporal vein to become the posterior facial vein. Still Complete removal of the parotid gland reveals the within the gland, the posterior facial vein divides; the following structures (the acronym VANS may be help- posterior branch joins the posterior auricular vein to form ful in remembering them): one Vein: internal jugular; the external jugular vein, while the anterior branch two Arteries: external and internal carotid; four Nerves: emerges from the gland to enter the common facial glossopharyngeal (CN IX), vagus (CN X), spinal acces- vein. Remember, the nerve is superficial, the artery is sory (CN XI), and hypoglossal (CN XII); four anatomical deep, and the vein lies between them. entities starting with “S”: one styloid process and three The preauricular lymph nodes (see Fig. 2-10) in muscles: styloglossus, stylopharyngeus and stylohy- the superficial fascia drain the temporal area of the scalp, oid (Fig. 2-36). the upper face, and the anterior pinna. Parotid nodes within the gland drain the gland itself, as well as the PROFOUND FACIAL REGION nasopharynx, nose, palate, middle ear, and external auditory meatus. These nodes, in turn, send lymph to The position of this region is under the mandibu- the subparotid nodes and eventually to the nodes of lar ramus. Profound facial region consists of two inter- the internal jugular and spinal accessory chains. muscular spaces: interpterygoid and temporopterygoid. The great auricular nerve reaches the posterior The boundaries of the region are corresponding border of the sternocleidomastoid muscle and, on the with the infratemporal fossa. It is an irregular-shaped surface of the parotid gland, follows the course of the space lying behind the maxilla, deep to the ramus of external jugular vein. It is sacrificed at parotidectomy. the mandible and inferior to the temporal bone. Numbness in the preauricular region, the lower auricle, Bony boundaries of the infratemporal fossa: late- and the lobe of the ear results from injury to this nerve, ral wall – ramus of the mandible; medial wall – lateral but it disappears after 4 to 6 months. pterygoid plate and free border of this plate followed to The auriculotemporal nerve, a branch of the man- the foramen ovale; anterior wall – the infratemporal sur- dibular nerve (V3), traverses the upper part of the pa- face of the maxilla (limited superiorly by the inferior or- rotid gland and emerges with the superficial temporal bital fissure and medially by the pterygomaxillary fis- blood vessels from the superior surface of the gland. sure); posterior wall – the anterior surface of the condy- Within the gland, the auriculotemporal nerve communi- lar process (head and neck) of the mandible and the cates with the facial nerve. Usually, the order of the styloid process of the temporal bone; roof – inferior sur- structures from the tragus anteriorly is: auriculotempo- face of the greater wing of the sphenoid (separated

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