# Thyroid Cartilage: Anatomy, Landmarks and Function The thyroid cartilage is the largest cartilage of the larynx. It is formed by two flat plates, called laminae, that fuse ventrally at the laryngeal prominence and carry a superior cornu and an inferior cornu on each side. Its job is structural: it shields the vocal folds, anchors the hyoid apparatus above and the cricoid cartilage below, and gives the intrinsic laryngeal muscles a rigid frame to pull against during breathing, swallowing, and sound production. This article is educational and is not a substitute for veterinary diagnosis or treatment. ## What the Thyroid Cartilage Is and Where It Sits The larynx is a cartilaginous box at the entrance to the trachea. In domestic mammals it sits between the hyoid apparatus and the first tracheal rings, deep to the hyothyroid musculature and the thyroid gland, and ventral to the pharynx and esophagus. The larynx has three unpaired cartilages (epiglottic, thyroid, and cricoid) and two paired cartilages (arytenoid and corniculate). The thyroid cartilage is the largest of the unpaired group and forms most of the ventral and lateral wall of the larynx. The word "thyroid" comes from the Greek for shield-shaped, and the name describes the shape rather than any relationship to the thyroid gland. The gland lies just caudal and ventral to the cartilage and is named after it, not the other way around. This is a common point of confusion. The thyroid gland is an endocrine organ that produces thyroxine and triiodothyronine. The thyroid cartilage is a structural component of the airway. They share a name and a neighborhood and nothing else. The cartilage is hyaline in type. Hyaline cartilage is a firm, smooth, translucent tissue built from type II collagen and proteoglycans, and it is the same tissue that lines joint surfaces in the limbs. In the larynx it provides stiffness without brittleness, which matters because the larynx must hold its shape against negative pressure during inspiration while still flexing during swallowing. ## The Two Laminae and the Laryngeal Prominence Each lamina is a roughly quadrilateral plate of cartilage. The two plates meet in the midline ventrally at an angle, and the ridge formed where they join is the laryngeal prominence. In people this ridge is the visible Adam's apple. The angle between the laminae is sharper in males, so the prominence projects further forward and is easier to see and feel. In females the angle is wider and the ridge is flatter. Comparative measurements in humans confirm a pronounced size difference between male and female larynges, while in sheep the laryngeal skeleton of males and females is very similar in size [1]. The sex difference in the human larynx is therefore a human trait, not a general mammalian one. The laryngeal prominence is a midline structure. It is the point where the two laminae fuse, and it is the thickest part of the ventral laryngeal wall. Behind it, on the inner surface, the anterior commissure of the vocal folds attaches. The anterior commissure is the point where the two vocal folds meet at the front of the glottis. Its position relative to the outer surface of the thyroid cartilage matters clinically because the tendon of the vocal folds attaches to the inner perichondrium at a fairly consistent level. In a study of 105 patients undergoing feminization laryngoplasty, the anterior commissure attached most commonly 8 mm above the inferior border of the thyroid cartilage (36% of cases), followed by 10 mm (25%) and 9 mm (22%) [2]. That range, roughly 6 to 10 mm above the inferior edge in adults, is the anatomical basis for safe limits during cartilage-reducing surgery. It is a human figure and should not be transferred to animals without species-specific data. ## The Superior and Inferior Cornua Each lamina sends out two projections, or horns, called cornua. The superior cornu is a slender, curved process that rises from the upper posterior corner of the lamina and points dorsally and slightly medially. The inferior cornu is shorter and thicker and projects caudally from the lower posterior corner. The superior cornu has a close relationship with the carotid arteries, which is relevant in people and likely in other species with a similar neck layout. In a study of 214 head and neck CT angiograms, the carotid bifurcation was above the level of the superior cornu of the thyroid cartilage in 89% of sides and below it in 11%. The common carotid artery lay lateral to the superior cornu in 73.4% of sides, and mean minimum distances increased from the common carotid (2.33 ± 1.82 mm) to the external carotid (4.38 ± 3.07 mm) and internal carotid (6.18 ± 3.67 mm) [3]. Those distances are small. They explain why the superior cornu is used as a surgical landmark and why an unusually close vessel can, in selected cases, cause symptoms of vascular compression. The inferior cornu is the working end of the cartilage. It carries the articular surface for the cricothyroid joint, which is described below. ## Landmarks of the Thyroid Cartilage The table below lists the main landmarks, what they are, and what they do. | Landmark | What it is | Function | |--|--|--| | Lamina (two) | Flat hyaline plates forming the lateral and ventral walls | Protect the vocal folds and give muscle attachment | | Laryngeal prominence | Midline ridge where the laminae fuse | Thickest ventral point, site of the anterior commissure internally | | Superior thyroid notch | V-shaped gap in the upper midline between the laminae | Allows the epiglottis to sit and move during swallowing | | Superior cornu | Slender dorsal process from the upper posterior corner | Anchors the thyrohyoid membrane and the lateral thyrohyoid ligament | | Inferior cornu | Short caudal process from the lower posterior corner | Forms the cricothyroid joint with the cricoid cartilage | | Oblique line | Raised ridge on the outer surface of each lamina | Attachment for the sternothyroid, thyrohyoid, and inferior constrictor muscles | | Thyrohyoid membrane | Fibroelastic sheet between the superior cornu and the hyoid | Suspends the larynx from the hyoid and allows it to rise during swallowing | | Cricothyroid joint | Synovial joint between the inferior cornu and cricoid | Allows the thyroid cartilage to tilt and change vocal fold tension | The superior thyroid notch is the V-shaped indentation at the top of the laryngeal prominence. It is a normal feature of the human and many mammalian larynges. In sheep the upper incisure of the thyroid cartilage is absent, which is one of the more conspicuous differences from the human larynx [1]. That single detail matters when a sheep larynx is used as a surgical or experimental model, because the shape of the upper opening changes how instruments and implants sit. The oblique line is a subtle ridge that runs diagonally across the outer surface of each lamina, from the superior cornu toward the lower front. It is the attachment point for three muscles: the sternothyroid, which pulls the larynx caudally, the thyrohyoid, which pulls the hyoid and larynx together, and the inferior constrictor of the pharynx, which helps drive the bolus downward during swallowing. Because the line is a raised ridge, it is also a useful orientation landmark when a larynx is dissected or imaged. ## Articulations: Hyoid Above, Cricoid Below The thyroid cartilage does not float. It is suspended from the hyoid apparatus above and articulated with the cricoid cartilage below. The connection to the hyoid is the thyrohyoid membrane, a sheet of fibroelastic tissue that runs from the superior cornu and the upper border of the lamina to the caudal border of the hyoid. The membrane is reinforced laterally by the lateral thyrohyoid ligament, which often contains a small nodule of cartilage. This entire suspension system lets the larynx move up and down. During swallowing, the larynx rises, the epiglottis folds back over the entrance, and the bolus passes on either side into the esophagus. Without that mobility, food and air would compete for the same opening. The connection to the cricoid is the cricothyroid joint, a synovial joint between the inferior cornu and the lateral surface of the cricoid cartilage. A synovial joint is a freely movable joint with a fluid-filled cavity. The cricothyroid joint allows the thyroid cartilage to rotate and tilt relative to the cricoid. That movement changes the distance between the thyroid prominence and the arytenoid cartilages, which changes the length and tension of the vocal folds. The cricothyroid muscle drives this movement. In the bowhead whale, the lateral cricothyroid muscle connects the caudal horn of the thyroid cartilage with the cricoid, and a medial cricothyroid muscle connects the two cartilages as well, showing that the basic joint-and-muscle arrangement is conserved even in extreme laryngeal anatomy [4]. ## The Thyrohyoid Cartilage and Other Species Variations In some species a separate piece of cartilage sits in the thyrohyoid membrane. This is the thyrohyoid cartilage. It is not part of the thyroid cartilage proper. It is a distinct structure that develops in the membrane between the superior cornu and the hyoid, and it varies in size and presence across species. In people it is usually a small nodule within the lateral thyrohyoid ligament. In dogs and cats it is a small, inconsistent element. The practical point is that a thyrohyoid cartilage seen on imaging or at dissection should not be mistaken for a fragment of the thyroid cartilage or for a fracture. Species differences in the thyroid cartilage are substantial and matter for anyone working with animal airways. In dogs and cats the thyroid cartilage is relatively smaller than in people, and the laryngeal prominence is much less pronounced. The feline larynx is short and narrow, and the thyroid cartilage contributes less to the external neck profile. Laryngeal tumors are rare in cats, but when they occur they can involve the thyroid cartilage. A case report describes a cat with an osteochondroma of the thyroid cartilage treated by partial laryngectomy, with survival and progression-free interval both at 574 days [5]. An osteochondroma is a benign cartilage-capped bony outgrowth. The report shows that even a small larynx can tolerate partial cartilage resection when the airway is managed carefully. In horses the larynx is large and the thyroid cartilage is prominent. The equine larynx must handle high airflow during exercise, and the cartilage is correspondingly robust. The recurrent laryngeal nerve runs a long course to the larynx in horses, and its dysfunction causes recurrent laryngeal neuropathy, a common cause of exercise intolerance and abnormal respiratory noise. The size and rigidity of the equine thyroid cartilage is part of why the equine larynx is a favored model for studying laryngeal function under load. In rabbits the thyroid cartilage forms the narrowest part of the airway. A CT study of 66 adult domestic rabbits found that the narrowest laryngotracheal width was at the level of the caudal thyroid cartilage and rostral cricoid cartilage, and the smallest cross-sectional area was at the rostral thyroid cartilage at the level of the arytenoids. All airway dimensions scaled positively with body weight, and the likelihood of a good endotracheal tube fit was strongly associated with weight. To have at least an 80% chance of appropriate fit with a 2.0 mm, 2.5 mm, or 3.0 mm tube, the predicted minimum body weights were 2.99 kg, 5.24 kg, and 5.80 kg respectively [6]. This is directly useful in rabbit anesthesia, because the thyroid cartilage level is where the tube is most likely to meet resistance. In sheep the larynx falls between the male and female human larynx in most dimensions, with the height, anteroposterior diameter, and inferior breadth of the thyroid cartilage all in that range. The arytenoid cartilages are relatively large, and the upper incisure of the thyroid is absent [1]. Sheep are therefore a reasonable size match for human laryngeal research, with the caveat that the upper laryngeal shape differs. In pigs the thyroid cartilage is similar in shape and size to the human counterpart and undergoes mineralization with age. A histological study comparing human, porcine, and bovine laryngeal cartilages found that pig thyroid cartilage shows predominantly cartilage mineralization rather than true ossification, and identified a second pattern of mineralization in which crystals grow along collagen fibrils that act as guide rails [7]. A separate study of minipig and domestic pig thyroid cartilage showed that cartilage canals branch from the perichondrial vascular network and carry an arteriole, a venule, and a capillary network into the cartilage, with mineralization occurring only in the interterritorial matrix [8]. These findings are relevant to any species in which the thyroid cartilage calcifies with age, because calcified cartilage behaves differently under imaging and under the scalpel. ## Function: Protection, Suspension, and Sound The thyroid cartilage performs three broad functions. First, it protects. The laminae form a shield around the vocal folds and the entrance to the trachea. The cartilage is flexible enough to absorb blunt force and stiff enough to keep the airway open. In forensic and trauma settings, the thyroid cartilage is one of the structures examined for fracture, along with the hyoid and cricoid. A prospective anthropological study of 56 suicidal hangings found fractures in 71.4% of cases, with the thyroid cartilage the most commonly fractured structure. Age correlated significantly with fracture frequency, while sex, height, and weight did not show a strong correlation [9]. The takeaway for clinicians is that laryngeal cartilage fracture is common in strangulation and hanging and should be actively looked for. Second, it suspends. Through the thyrohyoid membrane and the cricothyroid joint, the thyroid cartilage links the hyoid apparatus to the trachea. That linkage allows the larynx to be pulled up during swallowing and to recoil back afterward. It also transmits the pull of the extrinsic laryngeal muscles to the airway as a whole. Third, it supports sound production. The vocal folds attach to the inner surface of the thyroid cartilage at the anterior commissure and to the arytenoid cartilages behind. When the cricothyroid muscle contracts, the thyroid cartilage tilts forward, the vocal folds lengthen, and pitch rises. When the thyroarytenoid muscle contracts, the folds shorten and thicken, and pitch falls. The thyroid cartilage is the fixed anterior anchor for this system. Without it, the vocal folds would have nothing to pull against. ## Comparative Anatomy Across Species The table below summarizes the main comparative points for the species most often encountered in veterinary practice and in laryngeal research. | Species | Thyroid cartilage size | Laryngeal prominence | Notable features | |--|--|--|--| | Human | Large, with marked male-female size difference | Prominent, sharper angle in males | Anterior commissure about 6 to 10 mm above inferior border [2] | | Dog | Relatively smaller | Less pronounced | Short larynx, prominent arytenoids | | Cat | Small | Minimal | Rare laryngeal tumors can involve the cartilage [5] | | Horse | Large and robust | Prominent | High airflow demands, recurrent laryngeal neuropathy is common | | Rabbit | Small | Minimal | Narrowest airway at thyroid cartilage level, tube fit scales with weight [6] | | Sheep | Between male and female human in most dimensions | Absent upper incisure | Arytenoids relatively large [1] | | Pig | Similar to human in shape and size | Present | Cartilage mineralization with age, cartilage canals present [7][8] | | Bowhead whale | Very large, with prominent caudal horn | Not applicable | Fibrous articulation to ventrally incomplete cricoid [4] | The bowhead whale is included because it shows how far the basic plan can be stretched. Its larynx extends from the skull base into the thoracic inlet, the thyroid cartilage has a prominent caudal horn with a fibrous articulation to a cricoid cartilage that is incomplete ventrally, and the arytenoid cartilages are rod-shaped and extend through the laryngeal cavity [4]. The same cartilage, the same joint, a completely different mechanical problem. ## Aging and Mineralization Hyaline cartilage is avascular. It has no blood vessels of its own, so nutrients and waste move by diffusion through the extracellular matrix. That is why cartilage heals poorly. Once damaged, it has limited intrinsic regenerative capacity, and laryngeal cartilage defects from tumor surgery, trauma, or congenital deformity are difficult to repair with the original tissue [10]. With age, laryngeal cartilages mineralize and in some species ossify. The process is not uniform. In mice, the shape of the thyroid cartilage changes throughout life, and the changes in shape are not synchronized with changes in cartilage matrix composition. A study of 30 CD-1 mice across five age groups found that Hounsfield units, a measure of tissue density on CT, increased with age, while shape changed independently [11]. In other words, an older larynx is not simply a scaled-up younger larynx. It is denser and differently shaped, and those two changes run on separate clocks. In pigs, mineralization follows two patterns. One is mediated by matrix vesicles, the same mechanism used in growth plate cartilage. The other involves crystal growth along collagen fibrils, which act as guide rails [7]. Cartilage canals supply some regions, but mineralization also occurs in areas without canals [8]. Understanding these patterns matters for tissue engineering, because a scaffold designed to repair thyroid cartilage has to cope with a tissue that mineralizes slowly and unevenly. ## Clinical Relevance, Limitations and Common Mistakes The thyroid cartilage shows up in veterinary and human medicine in several ways. Airway management is the most common. The thyroid cartilage level is a narrow point in several species, and in rabbits it is the narrowest part of the entire laryngotracheal lumen [6]. A tube that passes the arytenoids can still meet resistance at the thyroid cartilage. Pre-measuring the airway on CT or choosing tube size by body weight reduces the risk. Tumor invasion is the next. Laryngeal squamous cell carcinoma can invade the thyroid cartilage, and detecting that invasion changes treatment and prognosis. CT-based deep learning models have been developed for this purpose. One convolutional neural network model trained on 61 cases and tested on 30 achieved an area under the curve of 0.82, with 90% accuracy, 80% sensitivity, and 95% specificity for thyroid cartilage invasion [12]. An ensemble model combining ResNet50 and MobileNet architectures reached an area under the curve of 0.99 and 96.54% accuracy on its test set [13]. A separate radiomics and deep learning study of 418 patients found that a 2D deep learning signature and clinical N stage were independent predictors of disease-free survival [14]. Contrast-enhanced ultrasound has also been used, with a difference in time to peak of 8.9 seconds or less distinguishing invaded from non-invaded non-ossified thyroid cartilage at 100% sensitivity and 76.9% specificity, rising to 96.8% accuracy when combined with peak intensity [15]. These are human oncology figures and are included because the thyroid cartilage is the same anatomical structure, but the models are not validated for animals. Vascular relationships matter during neck surgery. The superior laryngeal artery normally runs near the superior cornu, but it can take an aberrant course. A cadaveric report described a case in which the superior laryngeal artery penetrated the thyroid cartilage before entering the larynx, alongside a unilateral absence of the artery on the other side [16]. A surgeon who expects the usual course can be surprised. Rare tumors of the cartilage itself occur. Thyroid cartilage hemangioma is exceedingly rare, and one case in a 46-year-old man was initially suspected to be a chondrosarcoma before pathology showed a hemangioma with reactive cartilage changes [17]. Thyroid cartilage metastasis is also rare, with fewer than 63 cases reported, and isolated thyroid cartilage resection has been described for clear cell renal cell carcinoma metastasis with a nine-year follow-up [18]. Three mistakes are common. The first is confusing the thyroid cartilage with the thyroid gland. They are different structures with different functions, and a problem in one does not imply a problem in the other. The second is assuming that the human sex difference in laryngeal prominence applies to animals. It does not. Sheep show almost no size difference between sexes [1], and the prominence in dogs and cats is subtle at best. The third is treating the thyrohyoid cartilage as part of the thyroid cartilage. It is a separate structure in the thyrohyoid membrane, and its presence varies by species. What remains uncertain is how much of the human data on cartilage mineralization, anterior commissure position, and tumor invasion can be transferred to animals. The basic anatomy is conserved. The numbers are not. Individual cases need a veterinarian, and species-specific imaging or surgical planning should be based on species-specific data whenever it exists. ## Frequently Asked Questions ### What is the thyroid cartilage? The thyroid cartilage is the largest cartilage of the larynx, made of two hyaline laminae that meet at the laryngeal prominence and carry superior and inferior cornua on each side. ### Is the thyroid cartilage the same as the thyroid gland? No. The thyroid cartilage is structural cartilage in the airway. The thyroid gland is an endocrine organ that sits nearby and produces thyroid hormones. ### What is the thyrohyoid cartilage? The thyrohyoid cartilage is a separate small cartilage that sits in the thyrohyoid membrane between the superior cornu and the hyoid bone. It is not part of the thyroid cartilage. ### Why is the laryngeal prominence bigger in men? The angle between the two laminae is sharper in men, so the midline ridge projects further forward. This sex difference is pronounced in humans but not in sheep, where male and female laryngeal skeletons are similar in size. ### Do dogs and cats have an Adam's apple? They have a laryngeal prominence, but it is much less pronounced than in humans. The thyroid cartilage in dogs and cats is relatively smaller and does not create a visible neck bump. ### What does the thyroid cartilage do? It protects the vocal folds, suspends the larynx from the hyoid bone, and provides the rigid anterior anchor that the vocal folds pull against during sound production. ### What is the cricothyroid joint? The cricothyroid joint is a synovial joint between the inferior cornu of the thyroid cartilage and the cricoid cartilage. It lets the thyroid cartilage tilt and change vocal fold tension. ### Does the thyroid cartilage heal well after injury? No. Hyaline cartilage is avascular and has limited regenerative capacity, so laryngeal cartilage defects heal poorly and often need surgical reconstruction or tissue-engineered repair. ## Related Articles - [Bovine Heart Anatomy and Auscultation Landmarks](/knowledge/veterinary-medicine/veterinary-anatomy-physiology/bovine-heart-anatomy-auscultation-landmarks) - [Thyroid Function Testing in Veterinary Medicine](/knowledge/veterinary-medicine/diagnostics/thyroid-function-testing-in-veterinary-medicine-comparing-total-t4-free-t4-and-tsh-stimulation-tests) - [Equine Larynx Anatomy and Function in Respiration](/knowledge/veterinary-medicine/veterinary-anatomy-physiology/equine-larynx-anatomy-function-respiration) - [Canine Lymphatic System: Anatomy and Function](/knowledge/veterinary-medicine/veterinary-anatomy-physiology/canine-lymphatic-system-anatomy-function) - [Equine Hoof Anatomy: Structures and Function](/knowledge/veterinary-medicine/veterinary-anatomy-physiology/equine-hoof-anatomy-structures-function) - [Fish Gills: Anatomy, Function, and Common Health Issues](/knowledge/animal-farming/aquaculture/fish-gills-anatomy-function-and-common-health-issues) ## Sources 1. 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