Anatomy and Physiology of the Larynx. 79 



which divides it into two portions, the fibres of each muscle 

 are numerous, and constitute a plump, deep-red, fleshy- 

 mass; they pass obliquely upwards and outwards, and, 

 becoming more or less tendinous, especially the fibres 

 towards the outer border, they all converge towards the 

 processus muscularis of the arytsenoid cartilage (Figs. 1, i; 

 2, g), into which they are inserted, and on which they act. 

 When the two muscles contract (in a healthy condition they 

 always do so together), they act as levers of the first order 

 in drawing the arytsenoids backwards and outwards, causing 

 them to swing on the cricoid cartilage in the manner 

 already described, and in this way widening the glottis. 

 The extent of this action will depend upon the require- 

 ments of inspiration ; but as their special function is to 

 maintain the glottal aperture always more or less open 

 (except during swallowing, coughing, and some other acts 

 of brief duration), these abductor muscles have an un- 

 ceasing, and therefore fatiguing duty, which demands not 

 only that they should be larger and more vigorous than the 

 other muscles of the larynx, but that they be reinforced by 

 tendinous fibres to relieve them from undue strain in the 

 perpetual efforts of elevating the cartilages at rather a 

 mechanical disadvantage. 



The Adductor Muscles. — These may be considered as 

 the antagonistic muscles of those just described, inasmuch as 

 they, in contracting, close the glottis. They consist of four 

 pairs, which are named as follows : thyroid-arytaenoid, lateral 

 crico-arytsenoid, crico-thyroid, and arytsenoideus. Of these, 

 the most active in approximating the vocal cords, and so 

 closing the rima glottidis, are the arytsenoidei and crico- 

 arytsenoidei laterales muscles. The former (Fig. 2, a a) are 

 the smallest of the laryngeal muscles, and situated behind 

 the arytsenoid cartilages; their action is to bring these 

 together, and so to diminish the space between them — the 

 pars respiratoria (Fig. 5, C) — in the larynx. The crico- 

 arytsenoidei laterales . pass, on each side, from the cricoid 



