CRICOID CARTILAGE. THYROID CARTILAGE. 477 



ponding facet of the inferior cornua of the thyroid cartilage. 

 Posteriorly are two slight vertical depressions, to which are 

 attached the crico-arytenoidei postici muscles. Its internal fcrce 

 is covered by mucous membrane. Its superior border gives 

 attachment in front to the crico-thyroid membrane, on the sides 

 to the lateral crico-arytenoid muscles, and posteriorly presents 

 a little notch, limited by two convex facets upon which are 

 articulated the arytenoid cartilages. 



The Thyroid cartilage is a single plate, bent in such manner 

 that it forms an acute angle with two similar broad surfaces 

 on each side of it. It is so applied to the cricoid cartilage, that 

 the lower edge of the angular part is at a small distance above 

 the front part of that cartilage, and connected to it by ligamen- 

 tous membrane ; while its broad sides are applied to it later- 

 ally, and thus partially enclose it. 



The upper edge of the angular part of the thyroid cartilage 

 forms a notch ; and the natural position of the cartilage is such, 

 that this part is very prominent in the neck ; it is called the 

 Pomum Adami. 



Both the upper and lower edges of the thyroid cartilage 

 terminate posteriorly in processes, which are called Cornua. 

 The two uppermost are longest : they are joined by ligaments 

 to the extremities of the os hyoides. The lower and shorter 

 processes are fixed to the cricoid cartilage. The thyroid car- 

 tilage, therefore, partly rests upon the cricoid cartilage below, 

 and is attached to the os hyoides above. It is influenced by the 

 muscles which act upon the os hyoides, and also by some mus- 

 cles which are inserted into itself. It is moved obliquely 

 downwards and forwards in a slight degree upon the cricoid 

 cartilage, by a small muscle, the crico-thyroideus, which 

 arises from that cartilage and is inserted into it. 



The external lateral surface of the thyroid cartilage is 

 slightly concave, and across it, passes a small ridge obliquely 

 from above downwards, and from behind forwards, which 

 gives attachment above to the thyro-hyoid and below to the 

 sterno-hyoid muscles. The posterior or inside face of the 

 Pomum Adami presents an entering angle, where the two 



