8 2 8 SPLANOHNOLOGY. 



larynx. It consists of two lateral expansions or alae, which meet 

 and unite antero-superiorly at a rather acute angle, forming a 

 projection called 'the body of the thyroid, equivalent to the 

 pomum Adami in man. Its inferior surface is smooth, giving 

 attachment to a tendon of the sterno-thyro-hyoideus. On the 

 superior surface is a blunt, irregular protuberance, with which 

 the epiglottis articulates. The ala3 are quadrilateral, slightly 

 convex externally, and clothed by the attachments of the 

 hyo-thyroid and thyro-pharyngeal muscles. They are slightly 

 concave internally, and covered postero-superiorly by mucous 

 membrane. From the angle of the wings anteriorly and internally 

 spring the thyro-arytenoideus muscles, the thyro-arytenoidean 

 ligaments or vocal cords, and the thyro-epigiottidean ligament ; 

 to the inferior border the crico-thyroid ligament is attached, to 

 the superior the hyo-thyroid ligaments. Posteriorly, each 

 wing terminates in two cornua. The superior inclines upwards, 

 and is attached by fibre-cartilage to the extremity of the heel 

 process of the os hyoides ; the inferior, the larger and more 

 prominent, articulates with the small protuberance on the 

 posterior surface of the cricoid cartilage. 



The arytenoid, or ewer-shaped cartilages, a pair, lie upon the 

 cricoid, and bound supero-posteriorly the entrance of the larynx. 

 They are irregularly pyramidal, each presenting two surfaces, four 

 borders, and an apex. The internal surface is smooth; and covered 

 by mucous membrane ; the external is divided by a ridge into 

 two portions ; a superior, Avhich is covered by the arytenoid muscle, 

 and an inferior, which receives the attachment of the crico- 

 arytenoideus lateralis and thyro-arytenoideus. The inner border 

 unites with its fellow; the posterior one, forming the base, is turned 

 backwards, and receives the attachment of the crico-arytenoideus 

 posticus, the outer angles articulating with convexities on the side 

 of the superior border of the cricoid cartilage. The anterior 

 border is thick, and covered by mucous membrane, while the 

 inferior border receives the insertion of the vocal cords. The 

 apex formed in front by the junction of the two arytenoids is 

 prolonged by two pieces of fibro- cartilage, .the cornicula laryngis, 

 which pass outwards and backwards, forming a spout or lip, in 

 which rests the epiglottis when the larynx is closed. 



The epiglottis is a soft, leaf-like cartilage, flexible, and situated 

 in front of the opening of the larynx, which it completely closes 

 during the passage of food through the pharynx into the ceso- 



