94 Roaring in Horses. 



arytsenoid). Bischoff afterwards demonstrated that motor 

 filaments in this nerve were derived from the spinal acces- 

 sory nerve. 



With the superior laryngeal nerve we are not now so 

 much concerned, and may therefore merely mention that it 

 is chiefly a sensory nerve, endowing the larynx with sensa- 

 tion ; it also gives fibres to the crico-thjTroid muscle, which, 

 according to some physiologists, are motor, and therefore 

 stimulate that muscle to contraction, but which, according 

 to Moeller, are trophic filaments, and are concerned in the 

 nutrition of all the laryngeal muscles. 



Stimulation of the superior laryngeal nerves is stated to 

 cause paralysis of the crico-thyroid muscles and slowing of 

 the respiration; but Mceller satisfied himself that the muscles 

 remained imaffected under such stimulus. However this 

 may be, it is certain that division of the nerves deprives the 

 larynx of sensibility ; so that saliva and particles of food pass 

 through it into the trachea and lungs without causing reflex 

 contraction of the glottis, or coughing, and this leads to the 

 production of " traumatic pneumonia." 



Experimental stimulation of the recurrent nerves pro- 

 duces spasm of the glottis, while section of them paralyses 

 all the muscles they supply. When stimulation is applied 

 to them, after the larynx has been exposed for observation, 

 the effect is very perceptible. As soon as the electrodes are 

 brought into contact with the central stump of the divided 

 nerve, or with the peripheral end of the vagus, the aryttenoid 

 cartilages begin to move convulsively ; and by inserting the 

 finger into the lateral ventricle, one is soon convinced 

 of the energetic contraction of the lateral crico-arytgenoidei 

 and thyro-arytisenoidei muscles, the crico-thyroid muscles 

 remaining passive. The glottis is narrowed, and at 

 every inspiration the vocal cords approximate con- 

 siderably, as do also the arytenoid cartilages, while 

 during expiration they are separated from each other. 

 Hence the inspiration, especially in young animals whose 

 glottis respiratoria is .narrow, is difficult and noisy, while 



