Thyroid cartilage

The thyroid cartilage is the largest of the nine cartilages that make up the laryngeal skeleton, the cartilage structure in and around the trachea that contains the larynx. It does not completely encircle the larynx (only the cricoid cartilage encircles it).

Thyroid cartilage
The cartilages of the larynx.
Details
Precursor4th and 6th branchial arch
Identifiers
LatinCartilago thyroidea
MeSHD013957
TA98A06.2.02.002
TA2967
FMA55099
Anatomical terminology

Structure

The thyroid cartilage is a hyaline cartilage structure that sits in front of the larynx and above the thyroid gland. The cartilage is composed of two halves, which meet in the middle at a peak called the laryngeal prominence, also called the Adam's apple.[1] In the midline above the prominence is the superior thyroid notch. A counterpart notch at the bottom of the cartilage is called the inferior thyroid notch.

The two halves of the cartilage that make out the outer surfaces extend obliquely to cover the sides of the trachea. The posterior edge of each half articulates with the cricoid cartilage inferiorly at a joint called the cricothyroid joint. The most posterior part of the cartilage also has two projections upwards and downwards. The upper projection is called the superior horn (cornu), and the lower is called the inferior horn. The superior horn is long and narrow, backward, and medialward, and ends in a conical extremity, which gives attachment to the lateral thyrohyoid ligament. The inferior horn is short and thick; it is directed downward, with a slight inclination forward and medialward, and presents, on the medial side of its tip, a small oval articular facet for articulation with the side of the cricoid cartilage.

The entire superior edge of the thyroid cartilage is attached to the hyoid bone by the thyrohyoid membrane. The thyroid cartilage is found between the levels of the C4 to C5 vertebrae.

The oblique line is a line on the thyroid cartilage. It marks the upper lateral borders of the thyroid gland. Two muscles originate along the line, the thyrohyoid muscle and inferior pharyngeal constrictor. The sternothyroid inserts along the line.

Thyroid cartilage

Movement of the cartilage at this joint produces a change in tension at the vocal folds, which in turn produces variation in voice.

Function

The thyroid cartilage forms the bulk of the front wall of the larynx. It protects the vocal folds ("vocal cords"), which are located directly behind it.

When the angle of the thyroid cartilage changes relative to the cricoid cartilage, this changes the pitch of voice.

The cartilage also serves as an attachment for several muscles.

Etymology

Shield-like

The English term thyroid cartilage is derived from the Latin expression cartilago thyreoides.[2][3] The latter is a translation of Ancient Greek χόνδρος θυρεοειδής,[4] attested in the writings of the Greek physician Galen.[4] The Latin word cartilago, as well as the Ancient Greek word χόνδρος, both mean cartilage,[4][5] while the ancient Greek word θυρεοειδής means shield-like or shield-shaped.[2][4] The latter compound is composed of Ancient Greek θυρεός, shield[2][4] and εἶδος, form/shape.[4] The Greeks used εἶδος in compounds to indicate a resemblance with the first part of the word.[6]

The ancient Greek word θυρεός can be found in the Odyssey of Homer,[4][7] and represented a large square stone that was put against the door to keep it shut.[4][7] Those θυρεοί were eventually used by the Greek army as shields to protect themselves.[7] This shield was adapted by Roman legions and referred to by them as a scutum.[7] The Roman scutum was an oblong shield with an oval shape.[4][7] Numerous shields were used by the Roman soldiers, such as the pelta, parma and clypeus.[7] In contrast to the scutum, these shields were round.[7] Despite these latter shields bearing a clear round shape, coinages like petalis cartilago,[8] cartilago parmalis,[7] and cartilago clypealis[9] were coined for the thyroid cartilage. In 16th-century Italian anatomist Realdo Colombo's De re anatomica,[8] besides the aforementioned incorrect petalis cartilago, correct forms like scutalis cartilago and scutiformis cartilago can be found, as the scutum is the real Roman pendant of the Greek θυρεός. The latter Latin expression can be found in its English form in medical dictionaries as scutiform cartilage,[10] while the name of the shield itself, i.e. scutum, is still being mentioned as a synonym for the thyroid cartilage.[11][12]

Spelling

In the various editions of the official Latin nomenclature (Nomina Anatomica, in 1998 rebaptized as Terminologia Anatomica), three different spellings can be found, i.e. cartilago thyreoidea.[13] cartilago thyroidea[14][15][16][17][18][19] and the previously mentioned cartilago thyreoides.[3][20] The variant with the adjective thyreoidea (with the ending -ea) would be a faulty rendering[6][21] of Ancient Greek θυρεοειδής in Latin. Greek compounds ending in -ειδής, when imported into Latin as a loanword, ended in -ides.[6][22] In the 17th-century the non-classical Latin form -ideus/-idea/ideum for Greek -ειδής/-ειδές came into use, mostly by French anatomist Jean Riolan the Younger.[7] No Greek loanwords (originally -ειδής/-ειδές) ending in -ideus/-idea/-ideum exist in classical Latin,[5][22] thereby making the -ideus/-idea/-ideum form non-Latinate in character.[22] The first edition of the Jena Nomina Anatomica (JNA) contained the incorrect cartilago thyreoidea,[23] but after a list of recommendations/corrections was made[23] this was corrected in subsequent editions of the JNA.[3][20]

The variant with thyroidea (omitting e after thyr) is a compromise for English-speaking anatomists, as they have difficulties pronouncing that specific combination of letters,[24] forcing a greater resemblance between Latin and English orthography. Dorland's medical dictionary from 1948[11] already adopted this incorrect spelling with an erroneous reference to the official Basle Nomina Anatomica even before the nomenclature committee of the Nomina Anatomica officially approved this orthographic revision in its edition of 1961.[14] The spelling without an e is commonly accepted in English[12][25] but earlier works preferred the etymologically correct thyreoid cartilage.[10][26] The official Latin veterinary nomenclature, Nomina Anatomica Veterinaria has the form cartilago thyroidea,[27] in common with the human Nomina Anatomica/Terminologia Anatomica, but allows (in contrast to the latter) cartilago thyreoidea[27] as an alternative spelling.

Shield versus door

An unfortunate mishap is the resemblance between Latin thyroidea and English thyroid on the one side and Ancient Greek θυροειδής on the other side, as the latter does not mean shield-like, but actually means like a door,[4] derived from θύρα, door.[4] Θυροειδής is however used in anatomic nomenclature in the expression θυροειδές τρῆμα (τρῆμα = hole, perforation, aperture[4]), coined by the Greek physician Galen.[7] Ancient Greek θύρα can be translated, besides the aforementioned door, as gate,[4][7] entrance[4][7] and opening.[7] The Greek name θυροειδές τρῆμα for this opening between the os pubis and the os ischii, currently called obturator foramen,[12] clearly originates from its being an opening (θύρα), while bearing no resemblance to a shield (θυρεός).[7] The Latin translation foramen thyreoideum for θυροειδές τρῆμα by the 18th–19th-century German physician and anatomist Samuel Thomas von Sömmerring is clearly mistaken.[7] The current foramen thyroideum of the Terminologia Anatomica is not a Latin translation of Galen's θυροειδές τρῆμα, but an orthographic revision of what was previously known in the Nomina Anatomica as foramen thyreoideum,[3][13] an inconstantly present opening in the lamina of the thyroid cartilage.[12]

See also
This article uses anatomical terminology.

References

This article incorporates text in the public domain from page 1073 of the 20th edition of Gray's Anatomy (1918)

  1. Medical literature
  2. Triepel, H. (1910). Die anatomischen Namen. Ihre Ableitung und Aussprache. Mit einem Anhang: Biographische Notizen.(Dritte Auflage). Wiesbaden: Verlag J.F. Bergmann. (in German)
  3. Kopsch, F. (1941). Die Nomina anatomica des Jahres 1895 (B.N.A.) nach der Buchstabenreihe geordnet und gegenübergestellt den Nomina anatomica des Jahres 1935 (I.N.A.) (3. Auflage). Leipzig: Georg Thieme Verlag. (in German)
  4. Liddell, H.G. & Scott, R. (1940). A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with the assistance of. Roderick McKenzie. Oxford: Clarendon Press.
  5. Lewis, C.T. & Short, C. (1879). A Latin dictionary. founded on Andrews' edition of Freund's Latin dictionary.Oxford: Clarendon Press.
  6. Triepel, H. (1927). Die anatomischen Namen. Ihre Ableitung und Aussprache. Anhang: Biographische Notizen.(Elfte Auflage). München: Verlag von J.F. Bergmann.
  7. Hyrtl, J. (1880). Onomatologia Anatomica. Geschichte und Kritik der anatomischen Sprache der Gegenwart. Wien: Wilhelm Braumüller. K.K. Hof- und Universitätsbuchhändler.
  8. Columbo, R. (1559). De re anatomica. Libri XV. Venice: Nicola Beviliacqua.
  9. Schreger, C.H.Th. (1805). Synonymia anatomica. Synonymik der anatomischen Nomenclatur. Fürth: im Bureau für Literatur.
  10. Foster, F.D. (1891–1893). An illustrated medical dictionary. Being a dictionary of the technical terms used by writers on medicine and the collateral sciences, in the Latin, English, French, and German languages. New York: D. Appleton and Company.
  11. Dorland, W.A.N. & Miller, E.C.L. (1948). The American illustrated medical dictionary.’’ (21st edition). Philadelphia/London: W.B. Saunders Company.
  12. Anderson, D.M. (2000). Dorland’s illustrated medical dictionary (29th edition). Philadelphia/London/Toronto/Montreal/Sydney/Tokyo: W.B. Saunders Company.
  13. His, W. (1895). Die anatomische Nomenclatur. Nomina Anatomica. Der von der Anatomischen Gesellschaft auf ihrer IX. Versammlung in Basel angenommenen Namen. Leipzig: Verlag Veit & Comp.
  14. Donáth, T. & Crawford, G.C.N. (1969). Anatomical dictionary with nomenclature and explanatory notes. Oxford/London/Edinburgh/New York/Toronto/Syney/Paris/Braunschweig: Pergamon Press.
  15. International Anatomical Nomenclature Committee (1966). Nomina Anatomica . Amsterdam: Excerpta Medica Foundation.
  16. International Anatomical Nomenclature Committee (1977). Nomina Anatomica, together with Nomina Histologica and Nomina Embryologica. Amsterdam-Oxford: Excerpta Medica.
  17. International Anatomical Nomenclature Committee (1983). Nomina Anatomica, together with Nomina Histologica and Nomina Embryologica. Baltimore/London: Williams & Wilkins
  18. International Anatomical Nomenclature Committee (1989). Nomina Anatomica, together with Nomina Histologica and Nomina Embryologica. Edinburgh: Churchill Livingstone.
  19. Federative Committee on Anatomical Terminology (FCAT) (1998). Terminologia Anatomica. Stuttgart: Thieme
  20. Stieve, H. (1949). Nomina Anatomica. Zusammengestellt von der im Jahre 1923 gewählten Nomenklatur-Kommission, unter Berücksichtigung der Vorschläge der Mitglieder der Anatomischen Gesellschaft, der Anatomical Society of Great Britain and Ireland, sowie der American Association of Anatomists, überprüft und durch Beschluß der Anatomischen Gesellschaft auf der Tagung in Jena 1935 endgúltig angenommen. (4th edition). Jena: Verlag Gustav Fischer.
  21. Triepel, H. (1908). Memorial on the anatomical nomenclature of the anatomical society. In A. Rose (Ed.), Medical Greek. Collection of papers on medical onomatology and a grammatical guide to learn modern Greek (pp. 176-193). New York: Peri Hellados publication office.
  22. Kossmann, R. (1903). Allgemeine Gynaecologie. Berlin: Verlag von August Hirschwald.
  23. Suzuki, S., Katsumata, T., Ura, R. Fujita, T., Niizima, M. & Suzuki, H. (1936). Über die Nomina Anatomica Nova. 'Folia Anatomica Japonica, 14, 507-536.
  24. Drukker, J, & Walvoort, H.C. (2000). Terminologia anatomica: een nieuw anatomisch referentiewerk. Nederlands Tijdschrift voor Geneeskunde, 144, 890-891.
  25. Dirckx, J.H. (Ed.) (1997).Stedman’s concise medical dictionary for the health professions. (3rd edition). Baltimore: Williams & Wilkins.
  26. Barker, L.W. (1907). Anatomical terminology with special reference to the [BNA]. With vocabularies in Latin and English and illustrations. Philadelphia: P. Blakiston’s Son & Co.
  27. International Committees on Veterinary Gross Anatomical Nomenclature, Veterinary Histological Nomenclature, & Veterinary Embryological Nomenclature (1994). Nomina Anatomica Veterinaria together with Nomina Histologica and Nomina Embryologica Veterinaria. Zürich/Ithaca/New York.
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