I 



Anatomy and Physiology of the Larynx. 93 



the nostrils and the larj^nx, that the widening and con- 

 traction of both occur synchronously in inspiration and 

 expiration. 



From what has just been stated, it will be understood 

 that, in order to have respiration performed in a perfect 

 manner under all conditions of active exertion, the dilator 

 or abductor muscles must be in the healthiest condition 

 possible. Various causes may impair the vigour of the 

 laryngeal muscles, but the chief is diminished supply or 

 total loss of nerve-stimulus to them ; and how this is effected 

 can best be made clear by briefly describing what is known 

 with regard to the innervation of the larynx. With respect 

 to this subject, however, it must be stated that notwith- 

 standing the most careful investigations of physiologists 

 and pathologists for many years, there are several important 

 points yet to be settled. 



When treating of the construction of the horse's larj^nx, 

 the distribution of the nerves was described, these being the 

 superior and inferior laryngeal, and a portion of the first 

 cervical nerve. In elucidating the functions of the larj^n- 

 geal nerves, the way was led by Vesalius, Haller, Majendie, 

 and Legallois. But it may be remarked that the Greek 

 physician, Galen, who lived about the middle of the second 

 century of our era, observed the difficulty pigs experienced 

 in breathing, and their inability to scream, after division of 

 the recurrent nerves; and Eiolan, in 1618, was also aware 

 of these phenomena as a result of such an operation. But 

 it was reserved for Legallois, in 1812, to determine the full 

 significance of section of this nerve on the larynx, and 

 consequently on respiration, by experiments on young 

 dogs, cats, and rabbits. He found that all the muscles, 

 with the exception of the crico- thyroid, received their 

 motor filaments from the recurrent nerve on each side. 

 Majendie likewise described the chief points in the inner- 

 vation of the larynx, though he erred in stating that the 

 recurrent only supplied the dilator muscle (posterior crico- 



