Chapter 49: The submandibular region
The region between the mandible and the hyoid bone contains the submandibular and sublingual glands, suprahyoid muscles, submandibular ganglion, and lingual artery. The lingual and hypoglossal nerves and the facial artery are discussed elsewhere.
Submandibular gland (fig. 49-1)
The large, paired salivary glands are the parotid, submandibular, and sublingual glands. The submandibular gland is usually just palpable. It has a larger superficial part (body) and a smaller deep process (fig. 49-1). The two parts are continuous with each other, forming a "U" shape around the posterior border of the mylohyoid muscle. The body of the gland is in and inferior to the digastric triangle and also partly under cover of the mandible. It has three surfaces: inferior (covered by skin and platysma), lateral (related to the medial surface of the mandible), and medial (related to the mylohyoid, hyoglossus, and digastric muscles). The deep process lies between the mylohyoid and hyoglossus muscles the submandibular duct, which is crossed by the llingual nerve, runs anterior from this process (fig. 49-1). The submandibular duct opens by one to three orifices into the oral cavity on the sublingual papilla, at the side of the frenulum linguae. The branches of the duct can be examined radiographically after injection of a radio-opaque medium (sialography). The submandibular gland is supplied by postganglionic parasympathetic, secretomotor fibers derived from the submandibular ganglion (see fig. 49-3). The preganglionic fibers leave the skull with the chorda tympani (a branch of the facial nerve) and then join the lingual nerve on their way to the submandibular ganglion.
Sublingual gland (fig. 49-1)
The sublingual gland (fig. 49-1) is inferior to the mucosa of the floor of the mouth and is anterior to the deep process of the submandibular gland. Most of the 10 to 30 sublingual ducts open separately into the floor of the oral cavity (fig. 49-1). The innervation of the gland from the submandibular ganglion is similar to that of the submandibular gland.
Suprahyoid muscles (table 49-1).
The suprahyoid muscles (see fig. 50-6), which connect the hyoid bone to the skull, are the digastric, stylohyoid, mylohyoid, and geniohyoid muscles. The genioglossus and hyoglossus are described with the tongue.
The digastric muscle (see fig. 50-2C and D) consists of two bellies united by an intervening tendon. The anterior belly, from the mandible, and the posterior belly, from the medial aspect of the mastoid process, develop from pharyngeal arches 1 and 2, respectively, and hence are innervated by cranial nerves V and VII. The tendon that connects the anterior and posterior bellies of the muscle is anchored to the hyoid bone, commonly passing through the stylohyoid muscle. The posterior belly of the digastric muscle and the stylohyoid muscle are crossed superficially by the facial vein, the great auricular nerve, and the cervical branch of the facial nerve. Deep to the muscles lie the external and internal carotid arteries, the internal jugular vein, cranial nerves X-XII, and the sympathetic trunk.
The stylohyoid muscle (see fig. 50-6) lies along the upper border of the posterior belly of the digastric muscle and is innervated by cranial nerve VII.
The mylohyoid muscle (fig. 49-2) lies superior to the anterior belly of the digastric muscle and is innervated by cranial nerve V. The right and left mylohyoid muscles extend from the mandible to join each other in a median raphe and form a muscular floor (diaphragma oris) for the anterior mouth. This muscular sling supports the tongue and is important in propelling both solids and liquids from the oropharynx into the laryngopharynx.
Submandibular ganglion (fig. 49-3).
The submandibular ganglion lies on the lateral surface of the hyoglossus muscle, medial to the mylohyoid muscle, superior to the submandibular duct and hypoglossal nerve, and inferior to the lingual nerve, from which it is suspended by several branches. Preganglionic parasympathetic fibers derived from the chorda tympani travel in the lingual nerve and synapse in the submandibular ganglion. Some of the postganglionic secretory fibers enter the submandibular gland; others, by entering the lingual nerve, reach the sublingual gland. Postganglionic sympathetic fibers (from the superior cervical ganglion) pass through the submandibular ganglion and are distributed with the parasympathetic fibers.
Lingual artery (fig. 49-4).
The lingual artery arises from the external carotid artery near the level of the hyoid bone. It passes successively (1) posterior, (2) deep, and (3) anterior to the hyoglossus muscle. The first part of the artery lies mainly in the carotid triangle. It forms a loop on the middle constrictor and is crossed by the hypoglossal nerve. The second part runs deep to the hypoglossus muscle superior to the hyoid bone and gives branches to the dorsum of the tongue. The third part (arteria profunda linguae) ascends between the muscles of the tongue and anastomoses with the artery of the opposite side.
49-1 Around which muscle is the submandibular gland wrapped?
49-2 What is the significance of the innervation of the digastric muscle?
49-3 How are the mylohyoid muscles inserted?
49-4 From what is the submandibular ganglion suspended?
49-5 Which muscle is immediately lateral to the middle (second) part of the lingual artery?
Figure 49-1 The submandibular and sublingual glands, right lateral aspect, after resection of a portion of the mandible.
Figure 49-2 Relations of the mylohyoid and hyoglossus muscles. The lingual nerve, the deep process of the submandibular gland and the submandibular duct, and the hypoglossal nerve pass deep to the posterior border of the mylohyoid. The glossopharyngeal nerve, the stylohyoid ligament, and the lingual artery pass deep to the posterior border of the hyoglossus. The submandibular ganglion is shown suspended from the lingual nerve.
Figure 49-3 The submandibular ganglion and its connections, lateral aspect. The dotted lines represent parasympathetic fibers. Sympathetic fibers are shown by continuous lines.
Figure 49-4 The lingual artery. The interrupted lines indicate the borders of the resected hyoglossus muscle.