The cricoid cartilage is a ring of hyaline cartilage, which in youth is situated at the inferior part of the larynx and is the only complete ring of cartilage of the airways. It may be considered the structural unit of the larynx. It is smaller, but thicker and stronger, than the thyroid, and it forms the lower and posterior parts of the wall of the larynx. It consists of two parts: a posterior quadrate lamina, and a narrow anterior arch, one-fourth or one-fifth of the depth of the lamina [2].

In youth, the thyroid cartilage consists of hyaline cartilage, is located above the cricoid, and is the largest cartilage of the larynx. It consists of two halves fused anteriorly in the middle line of the neck and creating an acute angle. The angle is more acute in men than in women.

The epiglottis is a thin sheet of elastic cartilage, at every age, covered by mucous membrane; it has the shape of a leaf and its lower part represents the “petiole,” also called the “epiglottis petiole.” The petiole continues with the thyro-epiglottic ligament, which represents the epiglottis anchor to the dihedral angle of the thyroid cartilage.

The arytenoid cartilages form the part of the larynx to which the vocal ligaments and vocal folds are attached. Their “body” consists of hyaline cartilage and their “vocal process,” elastic cartilage. The arytenoids are situated at the upper border of the lamina of the cricoid cartilage, at the back of the larynx. They have a pyramidal form, three surfaces, a base, and an apex.

The posterior surface is triangular and concave, and is attached to the arytenoid muscle and transverse muscle [2]. The anterolateral surface is convex and presents two depressions for attachment to the false vocal cord (vestibular ligament) and the vocal muscle. The medial surface is narrow and smooth, and it presents a mucosal lining that forms the lateral aspect of the respiratory part of the glottis.

The base of each cartilage is broad with a concave smooth surface, for articulation with the cricoid cartilage. Its lateral angle is short, rounded, and prominent, it projects backward and laterally, and is termed the muscular process. It gives insertion to the posterior cricoarytenoid muscle behind and the lateral cricoarytenoid muscle in front. Its anterior angle, also prominent, but more pointed, projects horizontally forward; it gives attachment to the vocal ligament, and is called the vocal process. The apex of the cartilages is pointed, curved backward, and surmounted by a small conical, cartilaginous nodule, the corniculate cartilage [2].

The corniculate cartilages are two small conical nodules situated in the posterior parts of the aryepiglottic folds of the mucous membrane; they are sometimes fused with the arytenoid cartilages. They articulate with the apices of the arytenoid cartilages, serving to extend them posteriorly and medially.

The two small cuneiform cartilages rest one on either side, in the aryepiglottic fold. They form small, whitish elevations on the surface of the mucous membrane just anterior of the arytenoid cartilages [3].

In the larynx, there are ligaments that connect the thyroid cartilage and epiglottis with the hyoid bone and the cricoid cartilage with the trachea (extrinsic ligaments) and others that connect the numerous cartilages of the larynx to each other (intrinsic ligaments). Extrinsic ligaments are the thyrohyoid membrane, the lateral hyothyroid ligament, the hyo-epiglottic ligament, and the cricotracheal ligament, and intrinsic ligaments are the conus elasticus and the quadrangular membrane.

The muscles of the larynx are extrinsic, passing between the larynx and parts around it, and intrinsic, confined entirely to the larynx.

The infrahyoid strap muscles (the sternothyroid, the sternohyoid, and the thyrohyoid), the mylohyoid, digastric, geniohyoid, and stylopharyngeus muscles all act in concert to provide laryngeal stabilization and allow the vertical displacement of the larynx, by changing the length of the vocal tract.

The intrinsic muscles (Fig. 2.3) of the larynx are responsible for altering the length, tension, shape, and spatial position of the vocal folds, by changing the orientation of the muscular and vocal processes of the arytenoids with the fixed anterior commissure [4]. The muscles are usually categorized as follows: three major vocal fold adductors, one abductor, and one tensor muscle.

The vagus nerve descends into the carotid sheath, giving off three major branches: the pharyngeal branch, the superior laryngeal nerve (SLN), and the recurrent laryngeal nerve (RLN) [4]. The SLN arises from the inferior ganglia of the vagus nerve and divides into internal and external branches. The internal laryngeal branch is almost entirely sensory, but some motor filaments are said to be carried by it to the arytenoideus. The external laryngeal branch supplies the cricothyroid muscle. The RLN supplies all the muscles of the larynx except the cricothyroid muscle and perhaps a part of the arytenoideus muscle. It also supplies the glottic and subglottic mucosa and the myotatic receptors of the laryngeal musculature [4].

The laryngeal cavity extends from the laryngeal entrance to the lower border of the cricoid cartilage, where it is continuous with the lumen of the trachea (Fig. 2.4).

It is divided into two parts by the projection of the vocal folds, between which there is the “rima glottidis.” The portion of the cavity of the larynx above the vocal folds is called the vestibule; it contains the ventricular folds and, between these and the vocal folds, there are the ventricles of the larynx. The portion below the vocal folds is, at first, of an elliptical form, but lower down it widens out, assumes a circular form, and is continuous with the tracheal lumen.

The entrance of the larynx is a triangular opening, bounded in front by the epiglottis; behind by the apices of the arytenoid cartilages, the corniculate cartilages, and the inter-arytenoid notch; and on either side, by a fold of mucous membrane enclosing ligamentous and muscular fibers, stretched between the side of the epiglottis and the apex of the arytenoid cartilage. This is the aryepiglottic fold. On the posterior part of the margin where the cuneiform cartilage forms a more or less distinct whitish prominence lies the cuneiform tubercle.

The ventricular folds (“plicae ventriculares”) are two thick folds of mucous membrane, each enclosing a narrow band of fibrous tissue, the ventricular ligament, which is attached in front to the angle of the thyroid cartilage, immediately below the attachment of the epiglottis, and behind to the antero-lateral surface of the arytenoid cartilage. The lower border of this ligament constitutes the upper boundary of the ventricle of the larynx [2].

The vocal folds (true vocal cords) are concerned with the production of sound, and enclose two strong bands, named the vocal ligaments (“ligamenta vocales”; inferior thyro-arytenoid).

Each ligament consists of a band of yellow elastic tissue, attached in front to the angle of the thyroid cartilage and behind to the vocal process of the arytenoid. Its lower border is continuous with the thin lateral part of the conus elasticus. Its upper border forms the lower boundary of the ventricle of the larynx ((Fig. 2.5).