128 ORGANS OF RESPIRATION. 



Its surfaces, though nearly flat, are not fully so; for, ante- 

 riorly, it forms a cylindrical convexity, and posteriorly, a cy- 

 lindrical concavity, from side to side. When nicely stripped 

 of its covering, a number of very small foramina are seen to 

 exist in it, which are considered to give passage principally 

 to the ducts of muciparous glands. Its connexions, aided by 

 its natural elasticity, keep it in a vertical attitude behind the 

 base of the tongue; its rounded margin is elevated above the 

 latter, and overlooks it. 



In addition to the preceding cartilages, there are always two, 

 and sometimes four others. On the top of each arytenoid is to 

 be found one, (Corniculum Laryngis:) it is somewhat triangu- 

 lar and elongated: its inferior face is attached by a few liga- 

 mentous fibres to the end of the arytenoid; it is included in the 

 soft parts, and is very moveable. The others, when they exist, 

 which is rare, are found on the margin of the glottis, in the 

 duplicature of the membrane which is extended from the side 

 of the epiglottis to the tip of the arytenoid cartilage. 



From the whole superior margin of the thyroid cartilage in- 

 cluded between its greater cornua, there proceeds upwards a 

 thin lamina of somewhat condensed cellular substance, which 

 is attached to the inner margin of the base and of the cornua 

 of the os hyoides their whole length. It fills completely the 

 space between the os hyoides and the thyroid cartilage. This 

 membrane is called the middle Thyreo-hyoid Ligament, (Li- 

 gament. Thyreo-Hyoid. Medium,) though its ligamentous cha- 

 racter is by no means well developed. It completes the pe- 

 riphery of the larynx in the space alluded to, and, from its thin 

 yielding nature, presents no obstacle to the motions of the os 

 hyoides and of the thyroid cartilage upon each other. 



The posterior margin of this membrane, on each side, is 

 bounded by a long, rounded, fibrous chord, the Lateral Thy- 

 reo-Hyoid Ligament, (Ligamentnm Thyreo-Plyoideum Laterale.) 

 The latter is extended from the cornu major of the thyroid car- 

 tilage to the tuberculated extremity of the os hyoides, and fre- 

 quently contains, about its centre, a small, oval cartilage or 

 bone, (CartilagO'Triticea,} riot quite so large as a grain of 

 wheat. 



