106 • Roaring in Horses. 



of stimulating the laryngeal muscles it supplies, apparently 

 the first of these to suffer in function is the dilator muscle. 

 This, failing to contract for want of stimulus, leaves its 

 arytsenoid cartilage and attached vocal cord more or less 

 immovable towards the middle of the glottis, and itself 

 undergoes those histological changes with which we are so 

 familiar, before the constrictor muscles, whose office is not 

 nearly so important in respiration. 



Clinically and experimentally, the evidence is strong 

 that such is the fact. Semon^ has shown that in all cases 

 of acute or chronic organic disease or injury of the nuclei 

 or trunks of the motor laryngeal nerves (spinal accessory, 

 pneumogastric, recurrent laryngeal), the abductor muscle 

 or muscles first feel the effects; whilst, on the other hand, 

 in cases of functional disorder, the adductors usually alone 

 suffer. That authority and Horsley,^ experimenting to- 

 gether, found that, in all classes of animals experimented 

 upon (monkeys, dogs, cats, rabbits), if the larynx was 

 excised immediately after death and its muscles indi- 

 vidually stimulated, the dilators (posterior crico-arytsenoids), 

 which are absolutely the largest of all the laryngeal muscles, 

 lose their electrical excitability long before the adductors. 

 This is, in all probability, due to the circumstance that the 

 two sets of muscles are histologically different, the dilators, 

 according to Griitzner and Simanowsky, belonging to the 

 class of Krause and Kanvier's red muscles, and the con- 

 strictors to the so-called white muscles."' 



Onimus had already demonstrated that, after death, both 

 the extensor muscles and their nerves elsewhere lose their 

 excitability before the flexors ; and Rosenbach and Semon 

 compare the dilators of the glottis to extensor muscles. 

 Jeanselme and Lermoyez have found, on stimulating, within 



1 "Archives of Laryngology," 1881, No. 3 ; Berlin, Klin. Wochen- 

 schrift, 1883, No. 4G. 



- " On an apparently Peripheral and Differential Action of Ether 

 upon the Laryngeal Muscles," London. 1886. 



3 Ihid., p. 5. 



