Head And Neck Anatomy_james L. Hiatt, Leslie P. Gartner (dragged).pdf

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Chapter 15 Submandibular Region and Floor of Mouth

CONTENTS AND BOUNDARIES

hyoglossus muscles permits the passage of neurovascular and lymphatic elements into and out of the floor of the oral cavity.

Summary Bite. The submandibular region and floor of the mouth are contained mostly within the submandibular triangle and the space spanning across the midline between them. Contained within this region are the suprahyoid muscles as well as the muscles of the tongue. Two of the major salivary glands are also contained in this region.

Muscles contained within the submandibular region and the floor of the mouth and/or forming its boundaries include the anterior and posterior bellies of the digastric, stylohyoid, mylohyoid, and geniohyoid muscles. Both intrinsic and extrinsic tongue musculatures, namely, the styloglossus, genioglossus, and hyoglossus muscles, also occupy the region. Strictly described, the middle pharyngeal constrictor muscle also may be included because it originates from the hyoid bone. The platysma, a muscle immediately deep to the skin, overlies this region. Cutaneous sensation to the area is provided by branches of the cervical plexus. Additionally, branches of several cranial nerves, including the trigeminal (cranial nerve V), facial (cranial nerve VII), and hypoglossal (cranial nerve XII) nerves, provide sensory, special sensory, motor, and secretomotor innervation to the structures within this region. The major vascular supply to the region is provided by branches of the lingual artery but branches of the facial and maxillary arteries also contribute to its vascularization. Venous drainage is accomplished by like-named veins and the anterior jugular vein. Two of the three major salivary glands, the submandibular and sublingual glands, occupy the submandibular and sublingual regions, respectively. These two glands receive postganglionic parasympathetic innervation from the submandibular ganglion located in the vicinity of the submandibular gland. The submandibular region is bounded superiorly by the inferior rim of the mandible and inferiorly by the anterior and posterior bellies of the digastric muscle, as these two bellies converge onto the hyoid bone to form the submandibular triangle. The mylohyoid muscle, spanning between the two sides of the mandible, is attached inferiorly to the anterior aspect of the hyoid bone. Its superior surface underlies the tongue, thus forming the floor of the mouth, whereas its inferior surface forms the floor of the submandibular triangle. Attached to much of the posterior aspect of the hyoid bone is the hyoglossus muscle ascending into the tongue. The interval between the mylohyoid and

MUSCLES AND FASCIA Summary Bite. Muscles contained within the submandibular region include the suprahyoid muscles and those attaching either to the mandible or to the hyoid bone. The tongue muscles are also included in this region, with the exception of the palatoglossal muscle, which originates from the palate and is innervated by the trigeminal instead of the hypoglossal nerve. The mylohyoid muscle forms the floor of this region.

Muscles constituting the submandibular region and the floor of the oral cavity include the suprahyoid muscles of the anterior triangle of the neck and those attaching either to the mandible or hyoid bone forming the floor of the mouth and/or the tongue. Both intrinsic and extrinsic muscles of the tongue are generally described with this region, the exception being the palatoglossus muscle, which originates from the palate and is thus more appropriately described with muscles of that region. The suprahyoid structures are enclosed in the investing fascia of the neck. This fascia is attached to the hyoid bone and extends superiorly, attaching to the inferior border of the mandible. Enclosing the anterior belly of the digastric muscle, the investing fascia continues posteriorly and laterally to encase the submandibular gland. The deeper layers of this fascia envelop the muscles of the submandibular region, including those of the tongue. Fusing with the deep fascia of the posterior digastric muscle, the investing fascia assists in forming the stylomandibular ligament. The fascial compartment containing these structures reaches the floor of the mouth, the sublingual gland, and the tongue. Clefts between the fascial layers posteriorly, at the border of the mylohyoid muscle, into the lateral pharyngeal cleft and into the cleft around the submandibular gland.

Suprahyoid Muscles Digastric Muscle Summary Bite. The digastric muscle consists of two heads that originate from different locations; however, both insert onto the hyoid bone via an intermediate tendon. These two heads, along with the inferior border of the mandible, form the boundary of the submandibular triangle.

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Table 15-1 Suprahyoid Muscles and Extrinsic Muscles of the Tongue Muscle

Origin

Insertion

Innervation

Action

Posterior belly of digastric

Mastoid notch of temporal bone

Intermediate tendon

Facial nerve

Posterior belly: draws hyoid bone posteriorly

Anterior belly of digastric

Digastric fossa of mandible

Intermediate tendon

Mandibular division of trigeminal

Anterior belly: draws hyoid bone anteriorly Both bellies: elevates hyoid bone and open mandible when hyoid bone is fixed

Stylohyoid

Styloid process (posterior and lateral surfaces)

Body of hyoid bone

Facial nerve

Draws the hyoid bone superiorly and posteriorly; also assists in fixing the hyoid bone

Mylohyoid

Mylohyoid line of the mandible

Median raphe (anterior fibers) and the body of the hyoid bone (posterior fibers)

Mylohyoid nerve (mandibular division of trigeminal nerve)

Depresses mandible (when hyoid bone is fixed); elevates the hyoid bone (when the mandible is fixed)

Geniohyoid

Inferior mental spine of the mandible

Body of the hyoid bone

Cl (transported by the hypoglossal nerve)

Draws hyoid bone anteriorly

Genioglossus

Superior mental spine of the mandible

From the tip to the back of the tongue (also body of the hyoid bone)

Hypoglossal nerve

Protrudes the tongue and depresses the tip of the tongue

Hyoglossus

Body and greater cornu of the hyoid bone

Body of the tongue

Hypoglossal nerve

Depresses the tongue

Styloglossus

Styloid process (anterior surface) and stylomandibular ligament

Body of the tongue to the tip of the tongue

Hypoglossal nerve

Retracts the tongue and elevates its tip

Palatoglossus

Fascia and lateral aspect of soft palate

Side of the tongue

Pharyngcal plexus

Elevates root of the tongue and constricts the fauces

The digastric muscle consists of two portions: a posterior belly, which arises from the mastoid notch of the temporal bone, and an anterior belly, arising from the digastric fossa of the anterior lower border of the mandible. Both of these muscle bellies descend to the hyoid bone to be inserted by an intermediate tendon (Table 15-1). A fibrous loop surrounds the tendon as well as the body and the greater cornu of the hyoid bone. At the loop, the tendon perforates the stylohyoid muscle at its attachment on the hyoid bone. The combined function of the two bellies of the digastric is to elevate the hyoid bone and also to assist in opening the mouth when the hyoid bone is fixed by the infrahyoid muscles. Acting independently, the anterior belly draws the hyoid anteriorly, whereas the posterior belly draws it posteriorly. Embryologically, the digastric muscle is really two separate muscles, each derived from different pharyngeal arches. The anterior belly originates from

the mandibular arch (pharyngeal arch I) and is innervated by a branch of the mylohyoid nerve from the mandibular division of the trigeminal nerve. The posterior belly develops in the hyoid arch (pharyngeal arch II) and is innervated by a branch of the facial nerve that enters its deep surface at midbelly. The posterior belly of the digastric muscle is vascularized by the posterior auricular artery, with contributions from the suprahyoid branch of the lingual artery and muscular branches of the occipital artery. The anterior belly is vascularized by the submental branch of the facial artery. Stylohyoid Muscle Summary Bite. The stylohyoid muscle originates from the styloid process of the temporal bone and descends to the hyoid bone in association with the posterior belly of the digastric muscle, which perforates it close to the insertion.

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Chapter 15 Submandibular Region and Floor of Mouth

The stylohyoid muscle arises from the posterior and lateral surfaces of the styloid process of the temporal bone (Fig. 15-1 and Table 15-1). As this muscle descends to insert on the body of the hyoid bone, it is in close association with the posterior belly of the digastric muscle, which perforates it close to its insertion. The stylohyoid muscle functions to draw the hyoid bone superiorly and posteriorly, in addition to assisting in fixing it. Motor innervation to this muscle is provided by a branch of the facial nerve that enters its midbelly. Vascular supply is provided by posterior auricular and occipital branches of the external carotid artery. Additional vascular elements may reach the muscle via the suprahyoid branch of the lingual artery and from muscular branches of the facial artery.

The mylohyoid muscle assists in depressing the mandible when the hyoid bone is fixed. When the mandible is fixed, the muscle elevates the hyoid bone, and consequently the tongue, for swallowing. The mylohyoid nerve from the inferior alveolar branch of the mandibular division of the trigeminal nerve innervates this muscle as the nerve approaches its inferolateral border. Vascular supply is provided by the anastomoses from the submental branch of the facial artery and the sublingual branch of the lingual artery. Geniohyoid Muscle Summary Bite. The geniohyoid muscle originates superior to the mylohyoid muscle from the inferior mental spine of the mandible and inserts upon the hyoid bone.

Mylohyoid Muscle Summary Bite. The mylohyoid muscle originates from the mylohyoid line on each half of the mandible and inserts upon itself in the median raphe to form the floor of the oral cavity.

The mylohyoid muscle forms the floor of the mouth as it unites in the midline with its counterpart from the opposite side of the mandible. This muscle arises from the entire length of the mylohyoid line of the mandible, from the symphysis menti to the region opposite the last molar tooth (Fig. 15-2 and Table 15-1). Anteriorly, the fibers of each side insert into a median raphe, whereas the more posteriorly oriented fibers insert into the body of the hyoid bone.

Figure 15-1. Suprahyoid region.

Immediately superior to the mylohyoid muscle is the geniohyoid muscle, originating from the inferior mental spine (genial tubercle) of the mandible before descending to the anterior surface of the body of the hyoid bone (Figs. 15-1 and 15-2, and Table 15-1). At its insertion, the geniohyoid is in contact with its counterpart from the opposite side of the mandible. The geniohyoid muscle functions to draw the hyoid bone anteriorly and, in so doing, draws the tongue as well because some of the extrinsic muscles of the tongue are attached to the hyoid bone. The geniohyoid muscle is innervated by fibers of the first cervical nerve, which are transported to it via the hypoglossal nerve. Vascularization is provided by the sublingual branch of the lingual artery.

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Figure 15-2. Submandibular and sublingual glands.

Group Actions

The suprahyoid muscles, all of which attach to the hyoid bone and another structure superior to it, function as a group to assist in swallowing by lifting the hyoid bone, the floor of the mouth, and the tongue. As food passes down the esophagus, the stylohyoid and posterior digastric muscles retract the hyoid bone to prevent regurgitation. This muscle group may also assist in fixing the hyoid bone and in retracting the mandible when the hyoid bone is fixed by the infrahyoid muscles.

The tongue muscles are composed of two groups: intrinsic tongue muscles and extrinsic tongue muscles (Figs. 15-1, 15-3, 15-4, and Table 15-1). The intrinsic muscles of the tongue are confined within the tongue itself and are described as longitudinal, transverse, and vertical muscles. The longitudinal muscle group is subdivided into a superior and an inferior group. The intrinsic muscles function generally to alter the shape of the tongue as necessary in mastication, deglutition, and phonation. The varying shapes of the tongue can be predicted by relating the fiber orientations of the intrinsic muscles as named. The four extrinsic muscles of the tongue originate outside it: the genioglossus, hyoglossus, styloglossus, and palatoglossus muscles. The palatoglossus muscle, as was stated at the beginning of the chapter, is described in Chapter 16 rather than here because it originates from the palatal region.

Tongue Muscles

Genioglossus Muscle

Summary Bite. Intrinsic muscles of the tongue are confined within the tongue, whereas the extrinsic muscles originate from various places and insert into the tongue.

Summary Bite. The genioglossus muscle originates from the superior mental spine and inserts into the internal aspect of the inferior surface of the tongue.

Summary Bite. The suprahyoid muscles all originate from various areas superior to the hyoid bone, but all insert upon the hyoid bone, hence their names end in “hyoid.” As a group, these muscles assist in fixing the hyoid bone for swallowing and for retracting the mandible. They function in concert with the infrahyoid muscles of the neck.

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Chapter 15 Submandibular Region and Floor of Mouth Palatopharyngeal arch

Fungiform papilla

Lingual tonsil

Foramen cecum

Palatine tonsil

Epiglottis

Sulcus terminalis

Median sulcus

Palatoglossal arch

Circumvallate papilla

Foliate papilla

Figure 15-3. Dorsum of the tongue.

Superior longitudinal Styloid process Stylohyoid ligament Styloglossus Hyoglossus

Apex or tip of the tongue Genioglossus Mental spine of mandible Geniohyoid Mylohyoid

Hyoid bone Extrinsic muscles

A

Lateral view

Genioglossus

Digastric Hyoid bone

B

Medial view of right half of bisected tongue

Figure 15-4. Muscles of the tongue. (A) Lateral view. (B) Medial view of the right half of bisected tongue.

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The genioglossus muscle arises from the superior mental spine (genial tubercle) of the mandible directly above the geniohyoid muscle (Figs. 15-1, 15-4A and B, and Table 15-1). From here, the muscle fans out to enter the entire length of the inferior surface of the tongue. The most anterior fibers curve upward to insert into the tip of the tongue. The posterior fibers pass to the base of the tongue, whereas some of the most inferior fibers are attached to the body of the hyoid bone. The genioglossus muscle acts to protrude the tongue, whereas the most anterior fibers depress the tongue tip.

The styloglossus muscle arises from the anterior surface of the styloid process of the temporal bone and the stylomandibular ligament (Figs. 15-1 and 15-4A, and Table 15-1). It then descends anteriorly and medially to enter the tongue from the lateral aspect, as it turns horizontally. Most fibers of the styloglossus muscle continue on to the tip of the tongue. Some of the posterior fibers decussate with those of the hyoglossus muscle. This muscle functions to retract the tongue, whereas the more anterior fibers elevate the tip.

Hyoglossus Muscle

Summary Bite. All of the muscles (extrinsic as well as intrinsic) of the tongue, with the exception of one, are innervated by the hypoglossal nerve (cranial nerve XII). The palatoglossal muscle, which originates from the palate, is innervated by the pharyngeal plexus. Vascular supply is provided by branches of the lingual artery, again except for the palatoglossal muscle, which is vascularized by arteries of the palate.

Summary Bite. The hyoglossus muscle originates from the hyoid bone and passes vertically to insert into the tongue.

The hyoglossus muscle originates from the side of the body and greater cornu of the hyoid bone, passing vertically to enter the tongue, where the fibers intermingle with those of the styloglossus muscle (Figs. 15-1, 15-4A and B, and Table 15-1). A separate slip of muscle, referred to by some as the chondroglossus muscle because it is separated from the hyoglossus by a small interval, is considered a part of the hyoglossus in this text. The hyoglossus functions as the major depressor of the tongue. Styloglossus Muscle Summary Bite. The styloglossus muscle originates from the styloid process of the temporal bone and inserts into the tongue on its lateral surface to intermingle with fibers of the hyoglossus muscle.

Innervation and Vascularization

All of the tongue musculature is innervated by the hypoglossal nerve, with the exception of the palatoglossus, which is innervated by the pharyngeal plexus (Figs. 15-5 and 15-6). The vascular supply to the muscles of the tongue is provided primarily by the deep lingual artery, the terminal branch of the lingual artery (Figs. 15-7 and 15-8). The exception, again, is the palatoglossus, which is served by the arteries of the palate.

Group Actions Summary Bite. The intrinsic tongue muscles generally function to alter the shape of the tongue, whereas

Clinical Considerations Lingual Cancer Cancer of the tongue is the most common cancer of the oral cavity (36.2%). About 95% of the cancers located on the tongue and floor of the mouth are squamous cell carcinomas that are correlated with a history of high use of alcohol and tobacco. Two thirds of the tongue cancers occur on the lateral surfaces of the middle third of the tongue, whereas one third are located on the ventrolateral or the anterior undersurface of the tongue. Malignancies in the posterior portion of the tongue

metastasize to deep cervical lymph nodes early on, whereas those on the anterior part of the tongue do not metastasize to the deep cervical lymph nodes until later in the disease. Thus, because the deep cervical lymph nodes drain into the internal jugular vein, it is extremely important that the disease be identified and treated as early as possible to prevent metastases into structures within the neck.

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Chapter 15 Submandibular Region and Floor of Mouth

Lingual glands Deep lingual artery

Frenulum of the tongue

Deep lingual veins Lingual nerve

Opening of submandibular duct

Sublingual duct Sublingual gland Sublingual caruncle

Sublingual fold

Figure 15-5. Inferior surface of the tongue and floor of the mouth. Mucosa has been removed from the left side.

the extrinsic tongue muscles generally function to direct the movement of the tongue (e.g., retract, protrude). All tongue movements are the result of coordinated contractions of several intrinsic and extrinsic muscles.

Complex movements of the tongue are accomplished by intricate and coordinated contractions of both intrinsic and extrinsic muscles of the tongue. Generally,

“movements” other than those that basically alter the shape of the tongue are the result of contractions of the extrinsic muscles, although one group seldom functions alone. The overlapping, intermingling, and decussating nature of the intrinsic and extrinsic muscle groups permit the fine coordinated effort so necessary in speech.

Styloglossus Intrinsic muscles of tongue

Hypoglossal nerve (CN XII) C1 Nerve roots of cervical C2 plexus C3

Genioglossus Hypoglossal nerve (CN XII) Internal carotid artery Ansa Inferior root cervicalis Superior root

Geniohyoid Hyoglossus Nerve to thyrohyoid Thyrohyoid Omohyoid Sternohyoid Sternothyroid

Figure 15-6. Hypoglossal nerve. Notice its association with the ansa cervicalis.