THE HEAD AND NECK 1277 



Thyroid CariUage. — ^This cartilage is composed of two flat quadri- 

 lateral ala, which meet in front by their anterior borders, but diverge 

 widely behind. The angular projection formed by their imion is 

 called the isthmus or pomum Adami. The xmion is confined to 

 about the lower half of each anterior border, and there is left 

 superiorly a deep triangular cleft called the thyroid notch. The 

 posterior border, of greater length than the anterior, is round, and 

 gives attachment to fibres of the palato-pharyngeus and stylo-pharj^n- 

 geus muscles. At either extremity it is prolonged into a projection, 

 the superior comu and inferior comu respectively. The superior cornu 

 gives attachment to the lateral thyro-hyoid ligament, and the inferior 

 cornu, which is slightly incurved, is facetted on its inner aspect 

 to articulate with fiie cricoid cartilage. The superior border is for 



Thyrwd Notch 



Superior Conia of Thyroid 

 Cartilage 



Saperior Tabercle of Ala 



Obliqae Line of Ala 



~-~-. Isthmns (Pomum Adami) 

 ^- Inferior Tuberde of Ala 



.Inferior Comu 

 Cricoid Cartilage Crico-thyroiJ Menhrane 



Fig. 525. — The Thyroid and Cricoid Cartilages of the Larynx 

 (Anterior View). 



the most part convex, and near its back part it presents a slight 

 eminence, called the superior tubercle. The inferior border is almost 

 horizontal, and presents an eminence about the jimction of the 

 posterior third with the anterior two-thirds, called the inferior 

 tubercle. Tt gives attachment to the median portion of the crico- 

 thjToid membrane and the crico-thjToid muscle. The outer surface 

 of the ala is marked by an oblique line, or, it may be, ridge, which 

 extends downwards and forwards from the superior to the inferior 

 tubercle. This line gives insertion to the stemo-th}Toid, and 

 origin to the thjro-hyoid, muscles. It divides the outer surface 

 into two imequal parts, an anterior three-fourths and a posterior 

 fourth, the latter giving origin to fibres of the inferior constrictor 

 muscle. The inner surface of the ala is smooth, slightly concave, 

 and covered by mucous membrane. In the median line, behind the 

 pomum Adami, there is a vertical depression known as the receding 

 angle. Commencing just below the thyroid notch on the upper 

 border and passing downwards, this region gives attachment to the 



