LARYXGEAL CARTILAGES. 827 



inferior maxillary sinus, is generally isolated from the rest. 

 (See p. 44.) The sinuses are lined with mucous membrane, and 

 contain air. The nasal chambers give passage to the lespired air, 

 and are at the same time concerned in the special sense of smell. 



The pharynx has been described with the digestive organs. 

 (See p. 296.) 



LABYETJL 



This is a complex musculo-cartilaginous valve, situated at the 

 anterior extremity of the windpipe. It gives passage to air, and 

 at the same time is the organ of voice. The anterior extremity 

 opens into the pharynx ; the posterior is continuous with the 

 trachea. It lies at the posterior part of the maxillary space, is 

 directed obliquely from" above downwards and backwards, being 

 suspended below the os hyoides, and united by one of its 

 cartilages to the extremity of the heel process on either side. 

 It is attached to the pharynx by muscles, and partly supported 

 by the trachea. 



LARYXGEAL CARTILAGES. 



The cartilages which form the larynx are seven in number, three 

 single ones, and two pairs. The former are the Cricoid, Thyroid, 

 and Epiglottis ; the latter, the Arytenoid and Cuneiform cartilages. 



The cricoid, or ring-like cartilage, is situated at the base of 

 the larynx, surrounding the air passage. It is narrow and convex 

 infero-anteriorly ; deep and broad postero-superiorly. It presents 

 two surfaces and two borders. The internal surface is smooth, 

 and covered by mucous membrane ; the external one postero- 

 superiorly presents in the median line a longitudinal ridge, to 

 which are attached a few longitudinal fibres of the oesophagus. 

 On either side of the ridge is a broad concavity, in which rests 

 the crico-arytenoideus posticus ; while on each side of the con- 

 cavity is a small protuberance for articulation with the posterior 

 cornu of the thyroid cartilage. The superior border bounding 

 the oval orifice is directed obliquely upwards and backwards, and 

 comprised between the two branches of the thyroid. On either 

 side of this border is a smooth, convex surface for articulating 

 with the arytenoid cartilages. The inferior border is level, and 

 encircles the upper part of the first ring of the trachea, to which 

 it is attached. 



The thyroid, or shield-like cartilage, is the largest in the 



