162 DISSECTION OF THE LAKYNX. 



The ligament is partly concealed by the cri co-thyroid muscle, and some 

 small apertures exist in it for the passage of fine arteries into the larynx. 



The strong forepart of the ligament serves the purpose of uniting the 

 two large laryngeal cartilages ; and the lateral piece, closing the larynx, 

 ends above in the vocal cord. 



A capsular ligament surrounds the articular surfaces between the side 

 of the cricoid and the lower corhu of the thyroid cartilage. Its fibres are 

 strongest behind. A synovial membrane lines the capsule. 



This joint admits forward and backward movements of the thyroid car- 

 tilage, by which the condition of the vocal cords is altered. If that carti- 

 lage is moved forwards the cords are stretched, and if backwards the cords 

 are relaxed. 



Articulation of the cricoid and arytcenoid cartilages. The articular 

 .surfaces of the cartilages are retained by a loose capsule, and possess a 

 synovial sac. 



The capsular ligament is fixed to each cartilage around its articular 

 surface; and one part posterior ligament, is strongest on the inner and 

 posterior aspects. A loose synovial membrane is present in the articu- 

 lation. 



The arytienoid cartilage glides freely forwards and backwards, inwards 

 and outwards; but if its horizontal movements are controlled by muscular 

 action, it can be rotated around a vertical axis, the anterior spur being 

 moved inwards and outwards. Obviously the state of the vocal cords will 

 be changed by the movements of the cartilages. When the arytsenoids 

 glide in and out the cords will be approximated and separated; when 

 backwards and forwards, the cords will be tightened and relaxed; and in 

 rotation the cords will be moved away from, and brought towards each 

 other. 



A kind of capsule, formed of thin scattered fibres, with a synovial sac, 

 unites the apex of the arytaenoid cartilage with the hollowed base of the 

 capitulum of Santorini. Sometimes these cartilages are blended together. 



Fibrous bands (thyro-arytsenoid) join the thyroid with the arytcenoid 

 cartilages, and have been examined as the vocal cords (p. 156). 



Ligaments oj the epiglottis. A band, thyro-epiglottidean, connects the 

 lower part of the epiglottis to the thyroid cartilage, close to the excavation 

 in the upper border of the latter (fig. 42). Some fibrous and elastic tis- 

 sues hyo-epiglottid ligament, connect likewise the front of the epiglottis 

 to the hyoid bone. 



STRUCTURE OF THE TRACHEA. The air tube consists of a series of 

 pieces of cartilage (segments of rings) (fig. 40), which are connected, 

 together by fibrous tissue. The interval between the cartilages at the back 

 of the tube is closed by fibrous membrane, and by muscular fibres and 

 mucous glands. The trachea is lined by mucous membrane with subja- 

 cent elastic tissue. 



Cartilages. The pieces of cartilage vary in number from sixteen to 

 twenty. Each forms an incomplete ring, which extends about three- 

 fourths of a circle ; and each is convex forwards, forming the front and 

 sides of the air tube. Both above and below, the cartilaginous pieces are 

 less constant in size and form : for towards the larynx they increase in 

 depth, whilst in the opposite direction they may be slit at their ends or 

 blended together ; and the lowest piece of cartilage is shaped like the 

 letter V. 



A fibrous tissue is continued from one to another on both aspects, though 



