23 



PHYSIOLOGY FOR BEGINNERS 



"th. 



closes the opening into the larynx, and leaves a straight 

 smooth passage from the pharynx on into the oesophagus. 



Remove the loose muscles and fat from the trachea and from 

 one side of the larynx. Tear away the oesophagus, beginning 

 from the lower end, and proceed upwards as far as the glottis, 

 cutting as you go the connective tissue attaching the oesophagus 

 to the trachea and larynx. Stretch the trachea and examine 

 its rings of cartilage more closely. Notice that the top one 

 is broader than the others, but like them 

 is also incomplete behind. Just above 

 this is the cricoid cartilage of the 

 larynx, a complete ring, shaped like a 

 signet ring, narrow in front, but very 

 broad behind, forming in fact a cartila- 

 ginous wall for the greater part of the 

 back of the larynx. Above this is a 

 broad V-shaped cartilage, the thyroid 

 cartilage, forming a prominent ridge in 

 front and flat sheets at the sides. Notice 

 that the thyroid does not extend quite to 

 the back, but ends at the sides, its edge 

 being produced above and below into 

 horn-like processes. The thyroid carti- 

 FIG. 109. Diagram to show i a g e is attached to the cricoid cartilage 

 the structure of the larynx. b elow by membrane and muscles only, 



The thyroid cartilage (TA) g ,. where he t ; Q( ^ j ower horn Qn 



supposed to be transparent r . r . . 



so that the right arytenoid each side forms a joint with the cricoid. 



cartilage (Ar), thyro- The thyroid cartilage can be tilted up 



arytenoid muscle (TAA), anc j down, these joints acting as hinges. 



\ and th " At the back of the larynx, seated on the 



upper part of the cricoid . 



cartilage are represented. *P of the broad part of the cricoid, are 

 c.th, the crico - thyroid two small cartilages called the aryte- 

 muscle ; Tr, trachea ; Hy, no i d cartilages. These, with the 



hyoid bone ; Ep, epiglottis. , , f , 



mucous membrane on them, form the 



two cushions mentioned above, which help to guard the glottis. 

 There is a muscle arising from each side of the cricoid car- 

 tilage which, passing upwards and backwards, is inserted into 

 the thyroid cartilage ; this is called the crico- thyroid muscle. 

 When this muscle contracts, the front of the thyroid cartilage 

 is drawn down, or when the thyroid is fixed, as it may be by 



