When swallowing, the soft palate and parts of the larynx act as valves to ensure proper movement of food from the oral cavity into the esophagus (Fig. 8.16D).
The soft palate elevates to open the oropharyngeal isthmus while at the same time sealing off the nasal part of the pharynx from the oral part. This prevents food and fluid from moving upward into the nasopharynx and nasal cavities.
The epiglottis of the larynx closes the laryngeal inlet and much of the laryngeal cavity becomes occluded by opposition of the vocal folds and soft tissue folds superior to them. In addition, the larynx is pulled up and forward to facilitate the moving of food and fluid over and around the closed larynx and into the esophagus.
In newborns, the larynx is high in the neck and the epiglottis is above the level of the soft palate (Fig. 8.16E). Babies can therefore suckle and breathe at the same time. Liquid flows around the larynx without any danger of entering the airway. During the second year of life, the larynx descends into the low cervical position characteristic of adults.
Triangles of the neck
The two muscles (trapezius and sternocleidomastoid) that form part of the outer cervical collar divide the neck into anterior and posterior triangles on each side (Fig. 8.17).
The boundaries of each anterior triangle are: the median vertical line of the neck, the inferior margin of the mandible, and the anterior margin of the sternocleidomastoid muscle.
The posterior triangle is bounded by: the middle one-third of the clavicle, the anterior margin of the trapezius, and the posterior margin of the sternocleidomastoid.
Major structures that pass between the head and thorax can be accessed through the anterior triangle.
The posterior triangle in part lies over the axillary inlet, and is associated with structures (nerves and vessels) that pass into and out of the upper limb.
The skull has 22 bones, excluding the ossicles of the ear. Except for the mandible, which forms the lower jaw, the bones of the skull are attached to each other by sutures, are immobile, and form the cranium.
The cranium can be subdivided into: an upper domed part (the calvaria), which covers the cranial cavity containing the brain, a base that consists of the floor of the cranial cavity, and a lower anterior part—the facial skeleton (viscerocranium).
The bones forming the calvaria are mainly the paired temporal and parietal bones, and parts of the unpaired frontal, sphenoid, and occipital bones.
The bones forming the base of the cranium are mainly parts of the sphenoid, temporal, and occipital bones.
The bones forming the facial skeleton are the paired nasal bones, palatine bones, lacrimal bones, zygomatic bones, maxillae and inferior nasal conchae and the unpaired vomer.
The mandible is not part of the cranium nor part of the facial skeleton.
The anterior view of the skull includes the forehead superiorly, and, inferiorly, the orbits, the nasal region, the part of the face between the orbit and the upper jaw, the upper jaw, and the lower jaw (Fig. 8.18).
The forehead consists of the frontal bone, which also forms the superior part of the rim of each orbit (Fig. 8.18).
Just superior to the rim of the orbit on each side are the raised superciliary arches. These are more pronounced in men than in women. Between these arches is a small depression (the glabella).
Clearly visible in the medial part of the superior rim of each orbit is the supra-orbital foramen (supra-orbital notch; Table 8.1).
Medially, the frontal bone projects inferiorly forming a part of the medial rim of the orbit.