308 HUMAN PHYSIOLOGY 



attention. The true vocal cords are fibrous ligamentous 

 structures which run from the arytenoids forward to the 

 posterior aspect of the middle of the thyroid. They contain 

 many elastic fibres and are covered by a stratified squamous 

 epithelium and appear white and shining. 



The vocal cords increase in length as the larynx grows, 

 and in adult life they are generally longer in the male than 

 in the female, and the whole larynx is larger. 



3. Muscles. The crico-thyroids take origin from the 

 antero-lateral aspects of the cricoid, and are inserted into 

 the inferior part of the lateral aspect of the thyroid. In 

 contracting they approximate the two cartilages anteriorly, 

 and render tense the vocal cords (Fig. 141). 



The crico-arytenoidei postici arise from the back of the 

 cricoid and pass outwards to be inserted into the external 

 or muscular process of the arytenoids. In contracting 

 they pull these processes inwards, and thus diverge the 

 anterior processes and open the glottis (Fig. 142). 



The crico-arytenoidei laterales take origin from the lateral 

 aspects of the cricoid, and pass backwards to be inserted into 

 the muscular processes of the arytenoids. They pull these 

 forward and so swing inwards their anterior processes, and 

 approximate the vocal cords (Fig. 142). 



A set of muscular fibres run between the arytenoids the 

 arytenoidei while other fibres run from the arytenoids up 

 to the side of the epiglottis. These help to close the upper 

 orifice of the larynx. 



The thyro-arytenoid is a band of muscular fibres lying 

 in the vocal cords and running from the thyroid to the 

 arytenoids. Its mode of action is not fully understood. 



5. Mucous Membrane. The mucous membrane of the 

 larynx is raised on each side into a well-marked fold 

 above each true vocal cord the false vocal cord. Be- 

 tween this and the true cord is a cavity the ventricle 

 of the larynx. The other folds of mucous membrane, 

 although of importance in medicine, have no special physio- 

 logical significance. 



The interior of the larynx may be examined during life by 

 the laryngoscope. (Practical Exercise.) 



5. Nerves. The muscles of the larynx are supplied chiefly 



