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).

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.Medical literature
/ref> 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'' (), 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.

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 .Triepel, H. (1910). ''Die anatomischen Namen. Ihre Ableitung und Aussprache. Mit einem Anhang: Biographische Notizen.''(Dritte Auflage). Wiesbaden: Verlag J.F. Bergmann. 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. The latter is a translation of Ancient Greek ,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. attested in the writings of the Greek physician Galen. The Latin word , as well as the Ancient Greek word , both mean ''cartilage'',Lewis, C.T. & Short, C. (1879). ''A Latin dictionary. founded on Andrews' edition of Freund's Latin dictionary.''Oxford: Clarendon Press. while the ancient Greek word means ''shield-like'' or ''shield-shaped''. The latter compound is composed of Ancient Greek , ''shield'' and , ''form''/''shape''. The Greeks used in compounds to indicate a resemblance with the first part of the word.Triepel, H. (1927). ''Die anatomischen Namen. Ihre Ableitung und Aussprache. Anhang: Biographische Notizen.''(Elfte Auflage). München: Verlag von J.F. Bergmann.

The ancient Greek word can be found in the ''Odyssey'' of Homer,Hyrtl, J. (1880). ''Onomatologia Anatomica. Geschichte und Kritik der anatomischen Sprache der Gegenwart.'' Wien: Wilhelm Braumüller. K.K. Hof- und Universitätsbuchhändler. and represented a large square stone that was put against the door to keep it shut. Those θυρεοί were eventually used by the Greek army as shields to protect themselves. This shield was adapted by Roman legions and referred to by them as a ''scutum''. The Roman ''scutum'' was an oblong shield with an oval shape. Numerous shields were used by the Roman soldiers, such as the ''pelta'', ''parma'' and ''clypeus''. In contrast to the ''scutum'', these shields were round. Despite these latter shields bearing a clear round shape, coinages like ''petalis cartilago'',Columbo, R. (1559). ''De re anatomica. Libri XV.'' Venice: Nicola Beviliacqua. ''cartilago parmalis'', and ''cartilago clypealis''Schreger, C.H.Th. (1805). ''Synonymia anatomica. Synonymik der anatomischen Nomenclatur.'' Fürth: im Bureau für Literatur. were coined for the thyroid cartilage. In 16th-century Italian anatomist Realdo Colombo's ''De re anatomica'', 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 . The latter Latin expression can be found in its English form in medical dictionaries as ''scutiform cartilage'',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. while the name of the shield itself, i.e. ''scutum'', is still being mentioned as a synonym for the thyroid cartilage.Dorland, W.A.N. & Miller, E.C.L. (1948). ''The American illustrated medical dictionary.’’ (21st edition). Philadelphia/London: W.B. Saunders Company.Anderson, D.M. (2000). ''Dorland’s illustrated medical dictionary'' (29th edition). Philadelphia/London/Toronto/Montreal/Sydney/Tokyo: W.B. Saunders Company.

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''.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. ''cartilago thyroidea''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.International Anatomical Nomenclature Committee (1966). ''Nomina Anatomica'' . Amsterdam: Excerpta Medica Foundation.International Anatomical Nomenclature Committee (1977). ''Nomina Anatomica, together with Nomina Histologica and Nomina Embryologica''. Amsterdam-Oxford: Excerpta Medica.International Anatomical Nomenclature Committee (1983). ''Nomina Anatomica, together with Nomina Histologica and Nomina Embryologica''. Baltimore/London: Williams & WilkinsInternational Anatomical Nomenclature Committee (1989). ''Nomina Anatomica, together with Nomina Histologica and Nomina Embryologica''. Edinburgh: Churchill Livingstone.Federative Committee on Anatomical Terminology (FCAT) (1998). ''Terminologia Anatomica''. Stuttgart: Thieme and the previously mentioned '.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. The variant with the adjective ''thyreoidea'' (with the ending -ea) would be a faulty renderingTriepel, 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. of Ancient Greek in Latin. Greek compounds ending in -, when imported into Latin as a loanword, ended in -ides.Kossmann, R. (1903). ''Allgemeine Gynaecologie.'' Berlin: Verlag von August Hirschwald. In the 17th-century the non-classical Latin form -ideus/-idea/ideum for Greek -/- came into use, mostly by French anatomist Jean Riolan the Younger. No Greek loanwords (originally -/-) ending in -ideus/-idea/-ideum exist in classical Latin, thereby making the -ideus/-idea/-ideum form non-Latinate in character. The first edition of the Jena Nomina Anatomica (''JNA'') contained the incorrect ''cartilago thyreoidea'',Suzuki, S., Katsumata, T., Ura, R. Fujita, T., Niizima, M. & Suzuki, H. (1936). Über die Nomina Anatomica Nova. Folia Anatomica Japonica, 14'', 507-536. but after a list of recommendations/corrections was made this was corrected in subsequent editions of the JNA.

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,Drukker, J, & Walvoort, H.C. (2000). Terminologia anatomica: een nieuw anatomisch referentiewerk. ''Nederlands Tijdschrift voor Geneeskunde, 144'', 890-891. forcing a greater resemblance between Latin and English orthography. Dorland's medical dictionary from 1948 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. The spelling without an ''e'' is commonly accepted in EnglishDirckx, J.H. (Ed.) (1997).''Stedman’s concise medical dictionary for the health professions.'' (3rd edition). Baltimore: Williams & Wilkins. but earlier works preferred the etymologically correct ''thyreoid cartilage''.Barker, L.W. (1907). ''Anatomical terminology with special reference to the NA With vocabularies in Latin and English and illustrations.'' Philadelphia: P. Blakiston’s Son & Co. The official Latin veterinary nomenclature, ''Nomina Anatomica Veterinaria'', has the form ',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. in common with the human Nomina Anatomica/Terminologia Anatomica, but allows (in contrast to the latter) ''cartilago thyreoidea'' as an alternative spelling.

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

See also

*Cricoid
*Laryngeal prominence
*Larynx
*Phonation
* Thyroid cartilage reduction
*Vocal fold

References

External links

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Human head and neck