THE PHYSIOLOGY OF THE MOUTH. 201 



longer pieces of bone ; there being a synovial joint between 

 each of the different parts, which always describe angles 

 one upon another. 



The laryngeal cartilages are, the thyroid, cricoid, the two 

 arytenoid, and the epiglottis. The cricoid cartilage is the 

 lowest in position, and in form resembles a thick ring. 

 Part of it is inserted within the thyroid cartilage, and the 

 two arytenoids rest upon its uppermost and most backward 

 portion. The thyroid cartilage, the most considerable of 

 the five, being thought to resemble a shield, has a promi- 

 nence running downward over its front. The epiglottis is 

 connected with its highest and most forward point. The 

 arytenoid are two small tibro-cartilages, uniting together at 

 the back of the opening to the larynx : their inferior sur- 

 face rests upon the superior surface of the cricoid cartilage, 

 and their superior extremities form a kind of point, which is 

 curved backwards. The epiglottis is a very elastic body, 

 composed principally of yellow fibrous tissue, attached to 

 the anterior portion of the thyroid cartilage by a strong 

 ligament. In shape it somewhat resembles a leaf which 

 has been bent downward, and its termination thus forms a 

 point which is curved, in the direction we have stated. 



The larynx gives insertion to a great number of muscles, 

 being covered by them both within and without ; its 

 motions are consequently much more varied than man can 

 satisfactorily account for. The epiglottideus is a single 

 muscle connected wuth the hyoides ; and is inserted into 

 the inferior portion of the epiglottis, which it pulls back or 

 stretches open. The other laryngeal muscles act in pairs : 

 the crico-thyroid(Bi draw the larynx downwards, after it has 

 been raised in deglutition, by the action of the hyo-thyroidcci. 

 The crico-arytenoidcei lateralis and posticus arytenoidceus 

 are muscles appropriated to their specified cartilages ; by 

 means of which the cavity of the larynx is altered in its 

 figure and dimensions. In consequence of the effect pro- 

 duced upon its internal ligaments, the sounds of the voice 

 thereby become variously modulated. The thyroid bodies 

 are situated one on each side of the cricoid cartilage, and 

 are larger in the young than the old subject ; but their 

 functional purpose is unknown. The membrane lining the 



