454 EESPIRATION. 



posterior part of each nasal chamber, where the nerve of smell 

 ramifies, the epithelium is reduced to a single layer, and is 

 unprovided with cilise. In the interior of the turbinated 

 bones and sinuses, the mucous membrane, and especially the 

 epithelial layer, is thinner than in the nasal chambers. This 

 membrane contains numerous racemose glands for the secre- 

 tion of mucus, and at various points, especially over the 

 posterior portions of the turbinated bones, presents a dense 

 venous network or erectile tissue. The chief object of the 

 sinuses seems to be to assist in preserving the proper contour 

 of the face, without adding to its density. 



The pharynx is that space through which food and air 

 both pass, as already noticed in the article on the digestive 

 organs. In solipedes it communicates on each side, through 

 a narrow opening, with a large cavity (Eustachian pouch), 

 lined, like itself, with ciliated epithelium, and communicating 

 through the Eustachian tube with the middle ear. 



The larynx is a cartilaginous box, compressed laterally, 

 placed at the upper extremity of the windpipe, and conduct- 

 ing the air into that passage. Its framework is composed of 

 five cartilages, the cricoid, thyroid, two arytenoid, and the 

 epiglottis; these are bound together by more or less elastic 

 ligaments, and moved upon one another by special muscles. 

 The cricoid cartilage is a complete ring, placed at the lower 

 part of the larynx, and connecting it with the windpipe. 

 The thyroid is composed of an anterior and two lateral por- 

 tions, which embrace the cricoid on all sides save the poste- 

 rior. The arytenoid are two quadri-lateral cartilages, placed 

 above and behind the cricoid, and bounding laterally the 

 superior opening of the larynx. The epiglottis is an irregu- 

 larly triangular fibro-cartilage, attached by its base to the 

 front of the thyroid by yellow and white fibrous tissue, and 

 to the semicircular portion of the hyoid bone by muscle. 



