Cartilages of the Larynx

The laryngeal cartilages (cartilagines laryngis) () are the epiglottic, thyroid, cricoid, arytenoid, sesamoid, and interarytenoid cartilages. Only the arytenoid cartilage is paired.

The epiglottic cartilage (cartilago epiglottica) forms the basis of the epiglottis. In outline, the rostral margin of the cartilage forms a thin, dorsally concave triangle with its apex pointing cranially. The epiglottis resembles a sharp-pointed spade. Its laryngeal surface (facies laryngea) formerly aboral surface, is concave and faces dorsocaudally. The opposite lingual surface (facies lingualis), formerly the oral surface, is convex and faces the oral pharynx. The lingual surface is attached to the middle of the body of the hyoid bone by the short, stout hyoepiglottic muscle. On either side of the median mucous fold that covers the muscle is a deep pocket of mucosa, called the vallecula (vallecula epiglottica), which may attain a depth of 1.5 cm. Each vallecula is limited laterally by a small fold of stratifed squamous epithelium running from the lingual surface of the epiglottis near its caudolateral angle to the lateral wall of the laryngeal part of the pharynx. The stalk of the epiglottis (petiolus epiglottidis) is in the form of a thickened handle of fibrous tissue that unites the midcaudal portion of the epiglottis and the dorsal cranial surface of the thyroid cartilage. The normal position of the epiglottis allows the apex to rest dorsal to the soft palate.

The thyroid cartilage (cartilago thyroidea) () is the largest cartilage of the larynx. It forms the middle portion of the laryngeal skeleton and is open dorsally. It consists of right and left laminae (lamina dextra et sinistra), which are united ventrally to form a short but deep trough. An inconspicuous oblique line (linea obliqua) on the lateral surface serves primarily for the insertion of the sternothyroid muscle. Each lamina is expanded dorsally to form transversely thin processes, the rostral and caudal cornua (cornu rostralis et caudalis).

The rostral cornu has a hyoid articular surface (facies articularis hyoidea) on its medial side for articulation with the thyrohyoid bone. Similarly, on the medial side of the caudal cornu is a cricoid articular surface (facies articularis cricoidea) for articulation with the caudolateral aspect of the lamina of the cricoid cartilage. Separating the rostral cornu from the thyroid lamina is the thyroid fissure (fssura thyroidea). The cranial laryngeal nerve and the cranial laryngeal artery pass through this fissure. Where the two laminae fuse ventrally, a slight ventral laryngeal prominence (prominentia laryngea) is formed. The laryngeal prominence, known as the Adam’s apple in humans, is not visible externally in the dog, but it can be palpated.

The ventral caudal border of the thyroid cartilage possesses the median deep caudal thyroid notch (incisura thyroidea caudalis), whereas the cranial border is slightly convex from side to side. The caudal border of the thyroid cartilage is united to the ventral arch of the cricoid cartilage by the cricothyroid ligament (ligamentum cricothyroideum). The cranial border is joined to the basihyoid and thyrohyoid bones by the thyrohyoid membrane (membrana thyrohyoidea).

The cricoid cartilage (cartilago cricoidea) () is the only cartilage of the larynx that forms a complete ring. The dorsal portion is approximately five times wider than the ventral portion. The expanded dorsal part is the lamina of the cricoid cartilage (lamina cartilaginis cricoideae). It possesses a median crest (crista mediana) for muscle attachment. Occasionally a pair of vascular foramina is located in the lamina, one on each side of the cranial portion of the crest. The arch of the cricoid cartilage (arcus cartilaginis cricoideae) extends ventrally from the lamina and completes the enclosure of the caudal part of the cavity of the larynx. It is bilaterally concave in a transverse direction. The cricoid cartilage possesses two pairs of articular surfaces. An indistinct pair of thyroid articular surfaces (facies articularis thyroidea) for articulation with the apices of the caudal cornua of the thyroid cartilage, are located at the junction of the lamina and the arch about 1 mm from the caudal border. A more prominent pair of arytenoid articular surfaces (facies articularis arytendoiea), for articulating with the arytenoid cartilages, are located on the rostral border of the lamina lateral to the median crest. Both pairs of articular surfaces are enclosed in articular capsules and form synovial joints with the cartilages with which they articulate. The sides of the ventral arch of the cricoid cartilage are gradually reduced in width ventrally. Midventrally, in a medium-sized dog, the narrowest part of the arch is only 5 mm long; in such a dog the middorsal lamina would be approximately 2 cm long.

The arytenoid cartilage (cartilago arytenoidea) () is an irregular cartilage, one on either side, that articulates with the craniodorsal border of the cricoid cartilage. When the laryngeal cartilages are viewed laterally, the arytenoid is largely hidden from view by the thyroid lamina.

The morphologic characteristics of the arytenoid cartilage vary greatly in diferent species of mammals, so that what may appear as a process of the arytenoid in one species may be a separate cartilage in another. In the dog, the arytenoid cartilage embodies the corniculate cartilage and the cuneiform cartilage of other mammals. As a result, this compound cartilage may be described as possessing a corniculate process, a muscular process, a vocal process, and a cuneiform process.

The articular surface (facies articularis) is a slightly oval, concave surface on the caudal border of the arytenoid, which faces caudomedially and joins the arytenoid articular surface of the cricoid cartilage, to form the cricoarytenoid articulation (articulatio cricoarytenoidea). The muscular process (process muscularis) is a relatively thick, rounded process that is located directly lateral to the articular surface. The m. cricoarytenoideus dorsalis inserts on this process. The corniculate process (processus corniculatus) is the longer and more caudal of the two dorsal processes that form the dorsal margin of the laryngeal inlet. The vocal process (processus vocalis) is a caudal ventral projection of the arytenoid cartilage. It is approximately 3 mm thick and 5 mm long at its base. The vocal ligament and the m. vocalis, from the thyroid cartilage, attach to the vocal process ().

The cuneiform process (processus cuneiformis) is the most rostral portion of the arytenoid cartilage. It is connected by a narrow neck () to the main portion of the arytenoid cartilage and is considered by some authors to be a separate cartilage. In the dog, the cuneiform process is roughly triangular in shape. The ventral portion lies in the vestibular fold, and the dorsal portion serves as the medial attachment of the aryepiglottic fold and aids in forming the laryngeal inlet. Attached to the cuneiform process are the ventricular ligament and the m. ventricularis (). Duckworth (1912) suggested that the cuneiform cartilage arose in mammals from the lateral margin of the epiglottis.

The sesamoid cartilage (cartilago sesamoidea) () is an oval or dumbbell-shaped nodule located cranial to the cricoid lamina and between the arytenoid cartilages. It is occasionally paired, in which case an intersesamoid ligament or fibrous union joins the two. Primarily, the sesamoid cartilage appears to be intercalated in the transverse arytenoid muscle. There is frequently a small contact surface with the dorsal portion of each arytenoid cartilage.

The interarytenoid cartilage (cartilago interarytenoidea) is small, fat, and easily overlooked. It lies cranial to the cricoid lamina and caudodorsal to the transverse arytenoid muscle and sesamoid cartilage. In this superfcial position the interarytenoid cartilage is embedded in connective tissue that attaches the arytenoid cartilages and the cricoesophageal tendon to the cricoid lamina.