i28o A MANUAL OF ANATOMY 



The external border separates the antero-external from the posterior 

 surface, and terminates below in the muscular process. 



The thyroid and cricoid cartilages usually retain their cartilaginous con- 

 dition up to about the twentieth year. In the case of the thyroid cartilage 

 ossification proceeds from the inferior cornu, there being a special osseous 

 nucleus in the region of the pomum Adami. 



The anterior part and lower margin of the cricoid cartilage remain carti- 

 laginous for some time, but the remainder undergoes ossification simultane- 

 ously with the thyroid cartilage. 



Ossification of the arytenoid cartilages takes place at a later date than 

 in the case of the two preceding cartilages. 



Cornicula Laryngis or Cartilages of Santorini.— These are two 



small, somewhat conical nodules of yellow elastic cartilage which 

 cap the apical parts of the arytenoid cartilages, their direction 

 being backwards and inwards. Each lies within the aryteno- 

 epiglottidean fold of mucous membrane, 



Cuneiform Cartilages or Cartilages of Wrisberg. — ^These are two 

 nodules of yellow elastic cartilage, which are situated, one on either 

 side, in the aryteno-epiglottidean fold of mucous membrane at its 

 back part, not far from the cornicula laryngis. 



Development. — The arytenoid cartilages and the aryteno-epiglottidean folds 

 are developed from the lateral parts of the furcula. The cornicula laryngis 

 are offshoots of the arytenoid cartilages. The cuneiform cartilages are derived 

 from the epiglottis. 



Ligaments of the Larynx — Thyro-hyoid Membrane. — This is a 

 broad membranous sheet, which passes between the superior 

 border of the thyroid cartilage and the back of the upper border 

 of the body of the hyoid bone, as well as the deep surface of each 

 great cornu. Its central and lateral portions are strong, and are 

 composed chiefly of elastic tissue. The central portion is known 

 as the middle thyro-hyoid ligament, its lower attachment being to 

 the margins of the thyroid notch. The lateral portions, round 

 and cord-like, are very elastic, and are known as the lateral thyro- 

 hyoid ligaments. Each extends from the superior cornu of the 

 thyroid cartilage to the tip of the great cornu of the hyoid bone, 

 and enclosed within it, towards its upper part, there is a small 

 nodule of cartilage called the cartilago triticea. Between the upper 

 median portion of the thyro-hyoid membrane and the concave 



Eosterior surface of the body of the hyoid bone there is a synovial 

 ursa. It is to be noted that the superior attachment of the thyro- 

 hyoid membrane is such as to enable the upper part of the thyroid 

 cartilage, when raised, to be received within the outline of the 

 hyoid bone. The central portion of the membrane is subcutaneous, 

 but on either side it is covered by the thyro-hyoid muscle. Beneath 

 the posterior border of this muscle the internal laryngeal nerve and 

 superior laryngeal artery pierce this membrane. 



Crico-thyroid Membrane. — ^This membrane is composed of a 

 median and two lateral portions. The median portion is composed 

 chiefly of elastic tissue, and is attached to the adjacent borders of 

 the cricoid and thyroid cartilages. It is subcutaneous in the median 



