126 ORGANS OF RESPIRATION. 



the os hyoides, which is common to it and to the root of the 

 tongue, also contributes to its- superior part, in a manner which 

 will be presently mentioned. The cartilages are one Thyroid, 

 one Cricoid, one Epiglottis, and two Arytenoid. 



The Thyroid Cartilage (Cartilago Thyroidea) is the largest of 

 the five, and being placed about one inch below the os hyoides, 

 produces in the upper part of the neck the prominence called 

 Pomum Adami. It consists in two lateral halves, which in 

 most individuals are perfectly symmetrical, and are continuous 

 \vith each other on the middle line of the body. These two 

 sides form at their line of junction an angle projecting forwards, 

 and resembling that of the canal or hydraulic gate: the superior 

 part of the angle is more prominent than the inferior; particu- 

 larly in the male subject. The sides of this body lean outwards, 

 by which its transverse diameter above is increased. 



The angle is terminated above by a deep notch, from which 

 the superior margin begins to form a curvature, on either side, 

 like the letter S; the inferior margin is also somewhat curved, 

 but to a smaller degree. The posterior margin of each half is 

 nearly straight, but is elongated above, with the aid of the upper 

 margin into a long process, the Cornu Majus; and below with 

 the aid of the inferior margin, into another process not so long, 

 Cornu Minus. By the latter, the thyroid cartilage is articulated 

 by ligamentous fibres called the Lateral Crico-thyroid ligament, 

 to the side of the cricoid cartilage, which thereby becomes tho 

 fulcrum of many of its motions. 



The internal surface of each half of the thyroid cartilage is 

 flat; but the exterior surface is slightly marked by the sterno- 

 ;hyroid and the thyreo-hyoid muscles, 



The Cricoid Cartilage (Cartilago Cricoidea) is placed below 

 the thyroid, and is the base of the larynx. It is an oval ring, of 

 an unequal thickness and breadth. 



Its inferior margin is nearly straight and horizontal, and is 

 connected to the first ring of the trachea ; it is also thinner than 

 the superior: the latter is very oblique, and rises from before 

 backwards and upwards so abruptly, that the breadth of the cri- 

 coid cartilage behind-becomes three times as great as it is in 

 front, under the inferior margin of the thyroid cartilage. 



