The hyoid bone is a small U-shaped bone (Fig. 8.9A) oriented in the horizontal plane just superior to the larynx, where it can be palpated and moved from side to side.
The body of the hyoid bone is anterior and forms the base of the U.
The two arms of the U (greater horns) project posteriorly from the lateral ends of the body.
The hyoid bone does not articulate directly with any other skeletal elements in the head and neck.
The hyoid bone is a highly movable and strong bony anchor for a number of muscles and soft tissue structures in the head and neck. Significantly, it is at the interface between three dynamic compartments:
Superiorly, it is attached to the floor of the oral cavity.
Inferiorly, it is attached to the larynx.
Posteriorly, it is attached to the pharynx (Fig. 8.9B).
The soft palate is a soft tissue flap-like structure “hinged” to the back of the hard palate (Fig. 8.10A) with a free posterior margin. It can be elevated and depressed by muscles (Fig. 8.10B).
The soft palate and associated structures can be clearly seen through an open mouth.
The skeletal muscles of the head and neck can be grouped on the basis of function, innervation, and embryological derivation.
In the head
The muscle groups in the head include: the extra-ocular muscles (move the eyeball and open the upper eyelid), muscles of the middle ear (adjust the movement of the middle ear bones), muscles of facial expression (move the face), muscles of mastication (move the jaw—temporo- mandibular joint), muscles of the soft palate (elevate and depress the palate), and muscles of the tongue (move and change the contour of the tongue).
In the neck
In the neck, major muscle groups include: muscles of the pharynx (constrict and elevate the pharynx), muscles of the larynx (adjust the dimensions of the air pathway), strap muscles (position the larynx and hyoid bone in the neck), muscles of the outer cervical collar (move the head and upper limb), and postural muscles in the muscular compartment of the neck (position the neck and head).
The superior thoracic aperture (thoracic inlet) opens directly into the base of the neck (Fig. 8.11). Structures passing between the head and thorax pass up and down through the superior thoracic aperture and the visceral compartment of the neck. At the base of the neck, the trachea is immediately anterior to the esophagus, which is directly anterior to the vertebral column. There are major veins, arteries, and nerves anterior and lateral to the trachea.
There is an axillary inlet (gateway to the upper limb) on each side of the superior thoracic aperture at the base of the neck (Fig. 8.11):
Structures such as blood vessels pass over rib I when passing between the axillary inlet and thorax.
Cervical components of the brachial plexus pass directly from the neck through the axillary inlets to enter the upper limb.
In the neck, the two important vertebral levels (Fig.
8.12) are: between CIII and CIV, at approximately the superior border of the thyroid cartilage of the larynx (which can be palpated) and where the major artery on each side of the neck (the common carotid artery) bifurcates into internal and external carotid arteries; and between CV and CVI, which marks the lower limit of the pharynx and larynx, and the superior limit of the trachea and esophagus—the indentation between the cricoid cartilage of the larynx and the first tracheal ring can be palpated.
The internal carotid artery has no branches in the neck and ascends into the skull to supply much of the brain. It also supplies the eye and orbit. Other regions of the head and neck are supplied by branches of the external carotid artery.
Airway in the neck