DISSECTION OF THE LARYNX. 225 



The Cricoid Cabxilage has the forai of a finger ring, from which 

 it receives its name. The depth of the ring is greatest behind, 

 ■where it presents a portion comparable to the bezel, or part of a ring 

 in which the stone is set. The inner surface of the ring is smooth, 

 and lined by the laryngeal mucous membrane. The outer sm-face of 

 the bezel is divided by a vertical median ridge which increases the 

 surface of origin of the posterior crico-arytenoid muscle. Towards the 

 outer limit of this surface there will be seen on each side a little cavity 

 which is smooth for articulation with the thyroid cartilage. The inferior 

 border is notched in the middle line of the bezel, and is connected by 

 ligament to the first ring of the trachea. The upper border has a wide 

 notch in front ; and posteriorly, over the bezel, it shows a pair of 

 smooth convex facets for articulation with the arytenoid cartilages. In 

 texture the cricoid is composed of hyaline cartilage. 



The Thyroid Cartilage receives its name from covering the front and 

 sides of the larynx like a shield. It consists of a median thickened 

 portion, or body ; and two lateral plates — the alse, or wings. The body 

 is known in human anatomy as "Adam's apple" — the pomiim Adami. 

 The epiglottis is superposed to it, the two cartilages being united by 

 elastic fibres. On each side it is continuous with the wings. Each ala 

 is a rhomboidal plate of cartilage. The outer surface is slightly convex, 

 and the inner is correspondingly concave. The upper edge of the cartilage 

 is attached to the thyroid cornu of the hyoid bone by the thyro-hyoid 

 membrane. The lower edge slightly overhangs the cricoid, and receives 

 the insertion of the crico-thyroid muscle. The other two edges are 

 directed obliquely, one backwards and upwards, the other forwards and 

 downwards. The first of these receives the insertion of the palato- 

 pharyngeus muscle ; the other, in receding from the corresponding edge 

 of the opposite wing, leaves beneath the body a triangular gap which is 

 occupied by the crico-thyroid membrane. Of the four angles of each, 

 plate, three demand mention. The supero-anterior angle is acute, and 

 joins the ala to the body of the thyroid. The supero-posterior angle is 

 obtuse, and carries a small bar of cartilage — the superior cornu of man — 

 which is articulated to the extremity of the thyroid cornu of the hyoid 

 bone. Close to the base of this process the plate is perforated by a 

 foramen for the passage of the superior laryngeal nerve. The postero- 

 inferior angle is acute like the first, to which it is diagonally opposite. 

 It is drawn out a little, forming a projection— the inferior cornu of 

 man— which is terminated by a convex facet for articulation with the 

 cricoid. The thyroid is composed of hyaline cartilage. 



The Arytenoid Cartilages. These stand at the upper aperture of 

 the larynx like the mouth of a pitcher, and from this resemblance they 

 are named. They are irregular in shape, but each bears some resemblance 

 to a three-sided pyramid. The inner surface of the pyramid is covered 



