92 Roaring in Horses. 



the muscles are healthy and vigorous, the space between 

 the vocal cords at their junction with the arytsenoid car- 

 tilages is two or three times greater than in the passive state 

 of these muscles (Fig. 6, d) ; should a simultaneous con- 

 traction of the ary-epiglottic muscles take place, the upper 

 compartment of the larynx will be also enlarged. 



In expiration, the abductor muscles are relaxed, and the 

 arytsenoid cartilages fall downwards and inwards by a kind 

 of elastic recoil, aided, no doubt, by the lateral crico-thyroid 

 and thyro-arytfenoid muscles, which approximate the 

 arytsenoid cartilages and vocal cords to each other, causing 

 them to move towards the centre of the laryngeal cavity 

 (Fig. 4). But unless under the special circumstances 

 already referred to, the adductor muscles do not bring 

 these parts into contact, a space always existing between 

 them during expiration for the passing out of air from the 

 lungs, and which meets with but little resistance from the 

 relaxed vocal cords, as it easily lifts these aside. This 

 space is somewhat less than in expiration, in what is termed 

 the " cadaveric position " of the vocal cords and arytenoid 

 cartilages — that is, the position in which we find them after 

 death. The function of these adductor muscles of the 

 larynx is, therefore, not very important in respiration, and 

 they only act as antagonists of the dilators on certain 

 occasions. For instance, it has been stated as a clinical 

 fact, that if inspiration be unduly forced the adductors are 

 brought into play, and the glottis may then be narrowed 

 rather than increased. Though they are the vocal muscles 

 in man, yet in the horse they may be looked upon as con- 

 stituting, in conjunction with the muscles which close the 

 supra-glottic portion, a sphincter or ring muscle for the 

 larjmx, such as is found around the mouth, eyes, and other 

 openings ; but here the opening is maintained always patent 

 by the abductors, just as the nostrils are by their dilator 

 muscles, though they are also provided with a sphincter or 

 closing muscle. There is this further resemblance between 



