THE HEAD AND NECK 



1281 



line, but laterally it is overlapped by fibres of the crico-thyroid 

 muscles. Its centre is crossed by the crico-thyroid arterial arch, 

 formed by the crico-thyroid branches of the superior thyroid 

 arteries, and it presents a few openings for the passage of blood- 

 vessels. Through this portion laiyngotomy may be performed. 

 The lateral portion of the crico-thyroid membrane is connected 

 below with the inner margin of the upper border of the lateral 

 part of the cricoid cartilage. Superiorly it is not connected with 

 the thyroid cartilage, but passes within its ala into the larynx, 

 where it expands in an inward direction, and extends from the back 

 of the ala of the thyroid cartilage in its lower part, close to the 

 receding angle, to the under aspect of the vocal process of the 

 arytenoid cartilage. Between these points it becomes continuous 

 with the inferior thyro-arytenoid Ugament or true vocal cord. 

 The lateral portion of the crico-thyroid membrane (within the ala 

 of the thyroid cartilage) is covered by the lateral crico-arytenoid 

 and thyro-arytenoid muscles. 



Superior Thyro-arytenoid Ligaments. — ^These form two small 

 fibrous bands, one at either side, which lie within the folds of 

 mucous membrane, called the false vocal cords. Each is attached 



. Superior Cornn of Thyroid 

 Cartilage 



.Superior Tubercle of Ala 

 • Oblique Line of .-Ua 



Isthmus (Pomum Adami) 



Cricoid Cartilage 



— Inferior Cornn 



»^ Crico-thyroid Ligament 



Inferior Tubercle of Ala 



Fig. 529. — The Thyroid and Cricoid Cartilages of the Larynx 

 (Lateral View). 



in front to the receding angle of the th5n-oid cartilage immediately 

 below the attachment of the thyro-epiglottidean ligament, and 

 behind to the antero -external surface of the arytenoid cartilage a 

 little alxDve the vocal process. 



Inferior Thyro-arytenoid Ligaments. — ^These important ligaments, 

 covered by mucous membrane, constitute the true vocal cords, and 

 each is continuous with the upper part of the expanded lateral 

 portion of the crico-thyroid membrane. Each is composed of 



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