THE HEAD AND NECK, POSTERIOR. 145 



of the soft palate downward and forward, or the tongue 

 upward and backward. 



The Eustachian Tube. 



The cartilaginous portion of this tube will be exposed 

 from its anterior part, lying between the levator and tensor 

 palati muscles and giving origin to some fibres of these 

 muscles. The palatopharyngeus also has a small bundle 

 arising from the tube, the salpingopharyngeus. 



The opening of the Eustachian tube is in the shape of a 

 vertical slit, and the canal leads into the cavity of the middle 



ear. 



DISSECTION. 



Separate the tongue and larynx from the skull. Remove any remains of the 

 oesophagus. Identify the epiglottis, hyoid bone, thyroid, cricoid, and (upon 

 the top of the cricoid behind) the small arytenoid cartilages. Forward and 

 upward from the arytenoid cartilages pass the aryteno-epiglottic folds to the 

 side of the epiglottis. Between these folds is the upper opening of the 

 larynx. 



Looking into this opening the canal of the larynx will be seen to be con- 

 stricted at two places by two anteroposterior bands. The upper pair are the 

 false vocal cords and the lower pair the true vocal cords. 



The slit between the vocal cords is the rima glottidis and varies in width 

 according to the approximation of the vocal cords. 



The true vocal cords may be made to approach or diverge from each other 

 by depressing or elevating the thyroid upon the cricoid cartilage, or by rotat- 

 ing the arytenoid cartilages upon the cricoid cartilages. 



The description of the cartilages of the larynx is omitted 

 from this manual as being to the larynx what the bones are 

 to the other parts of the body. 



External Structures. 



Muscles. 



Cricothyroid. 



Origin. From the anterior part of the cricoid cartilage. 



Insertion. Into the inferior border of the thyroid carti- 

 lage. 



10 



