Digastric and Styloid Muscles
The digastric muscle (Fig. 7.35) consists of anterior and posterior bellies united by an intermediate tendon. The posterior belly attaches to the medial surface of the mastoid process and inclines forwards and downwards, becoming continuous with the intermediate tendon close to the hyoid bone. This tendon pierces stylohyoid and is anchored by a fascial sling to the hyoid bone. The anterior belly continues forwards from the intermediate tendon to attach to the inferior border of the mandible near the midline. Digastric elevates the hyoid bone during swallowing and assists mylohyoid and the lateral pterygoid in depressing the mandible when opening the mouth. The posterior belly is innervated by the facial (VII) nerve (p. 340). The anterior belly receives its motor supply from the mandibular (V3) division of the trigeminal nerve via the mylohyoid branch of the inferior alveolar nerve (p. 345).
Three muscles, stylohyoid, stylopharyngeus and styloglossus, attach to the styloid process but diverge to reach the hyoid bone, the pharynx and the tongue, respectively. Stylohyoid (Fig. 7.35) inclines down wards and forwards from the posterior surface of the styloid process to attach to the body of the hyoid bone alongside the lesser horn. The muscle or its tendon is pierced by the intermediate tendon of digastric near the hyoid bone. Stylohyoid elevates the hyoid and is innervated by the facial (VII) nerve.
Stylopharyngeus (Fig. 7.36) is attached to the medial side of the root of the styloid process and passes inferomedially on the lateral surface of the superior pharyngeal constrictor. It enters the wall of the pharynx between the superior and middle constrictors and blends with the other longitudinal muscles of the pharynx. The muscle elevates the pharynx and larynx during swallowing and is the only muscle innervated by the glossopharyngeal (IX) nerve.
Styloglossus (Fig. 7.36) inclines anteromedially from the tip of the styloid process and upper end of the stylohyoid ligament and passes between the superior and middle constrictors of the pharynx to enter the tongue. It elevates and retracts the tongue and, in common with other muscles of the tongue, is supplied by the hypoglossal (XII) nerve.