Vocal Cords 127 



The superior aperture of the larynx is triangular, the base being 

 formed by the epiglottis, and the sides by the arytaeno-epiglottidean 

 folds and the arytaenoid cartilages. In the folds the cuneiform carti- 

 lages may be recognised. 



The glottis (-yXcoo-o-a, -yXcorra, tongue, throat] or rima glottidis 

 (rima, chink) is the narrow triangular opening between the true vocal 

 cords and the bases of the arytaenoid cartilages. The apex of this 

 space is forwards, corresponding to the thyroid attachment of the cords. 



In ordinary respiration the glottis is wide open, the arytaenoid car- 

 tilages being far apart, but in vocalisation, and when respiration is 

 forced, the space is narrowed. 



The rima is the narrowest part of the larynx. In the adult male it 

 measures about an inch from before backwards. 



The false vocal cords are folds of mucous membrane lying parallel 

 with and above the true cords ; they are attached in front to the retir- 

 ing angle of the thyroid, below the epiglottis, and behind to the front 

 of the arytasnoid cartilages. The interval between them is wider than 

 that between the true cords. 



The true vocal cords are delicate elastic bands between the re- 

 tiring angle of the thyroid and the anterior angle of the arytasnoid 

 cartilage. They are covered with mucous membrane, continuous 

 below with the upper border of the crico-thyroid membranes. The 

 epithelium upon the true cords is squamous. 



Between the true and false cords there is on each side a space, the 

 ventricle of the larynx, which is continued upwards for nearly half an 

 inch between the false vocal cord and the ala of the thyroid. It con- 

 tains a large number of mucous glands for lubricating the vocal cords, 

 for the membrane of the cords themselves is too delicate to contain 

 glandular tissue. 



Muscles. The crico-thyroid, triangular, arises from the side of the 

 cricoid cartilage and is inserted into the lower border of the thyroid. 

 Its action is to tilt the thyroid down to the cricoid (or the front of the 

 cricoid up to the thyroid), and so to tighten and elongate the cords. 

 It is supplied by the external branch of the superior laryngeal 

 nerve. 



The posterior crico-aryteenoid arises from the back of the cri- 

 coid, and, passing upwards and outwards, is inserted into the outer 

 angle of the arytaenoid cartilage. Drawing this angle backwards, the 

 two muscles rotate the anterior angles outwards (abduction of cord) 

 and widen the glottis. ' They come into action during deep inspira- 

 tion. If paralysed, the lips of the glottis approach the middle line 

 and come in contact with each inspiration, so that severe dyspnoea 

 may be produced. Expiratory efforts, however, are not impeded, and 

 vocalisation is unaffected.' (Quain.) 



The lateral crico-arytsenoid arises from the upper border of the 

 side of the cricoid, and, passing back, is inserted into the outer angle 



