yo6 



VAGUS NERVE. 



It is a noteworthy fact that in some persons coughing can be induced by 

 irritation of even remotely situated sensory nerves, for example of the external 

 auditory canal (auricular branch of the vagus) , the nasal mucous membrane 

 (trigeminal cough of Schadewald), the liver, the spleen, the stomach and intestine, 

 the uterus, the mammary glands, the ovaries, and even some portions of the skin. 

 Whether under such circumstances the perhaps abnormally irritable cough-center 

 is directly stimulated centripetally through the irritated nerve, or whether in 

 consequence of the nerve-irritation the vascularization and the secretion of the 

 respiratory organs are first affected, and in turn cause the cough-reflex, 

 must be submitted to future investigation, although to the writer the latter 

 appeared the more probable. 



The cough induced through irritation of the trachea and the bronchi (dog, 

 cat) occurs immediately and persists as long as the irritation continues. On 

 irritation of the larynx there occurs first inhibition of breathing, with accompany- 

 ing movements of deglutition, cough occurring only on cessation of the irritation. 



The superior laryngeal contains further centripetal fibers, irritation of which 

 causes arrest of breathing, with closure of the glottis; and also fibers that excite 

 movements of swallowing; and, finally, centripetal fibers, irritation of which 

 stimulates the vasomotor center to increased activity, therefore designated pressor 

 fibers. 



(6) The inferior laryngeal or recurrent nerve passes on the left around 

 the arch of the aorta, on the right around the subclavian artery, and, 

 ascending in the interval between the trachea and the esophagus, gives 

 off motor fibers to these structures and the inferior constrictor of the 

 pharynx, and then passes to the larynx, to whose muscles it distributes 

 motor fibers (with the exception of the cricothyroid muscle). In apes 

 these fibers are derived from the most posterior fibers of the internal 

 branch of the accessory nerve. The muscles of the epiglottis (aryepi- 

 glottic and thyroepiglottic) are innervated at times by the superior and 

 at other times by the inferior laryngeal nerve. Irritation of the latter 

 nerve also exerts an inhibitory effect upon the respiratory center. 



The fibers of the nerves that subserve the respiratory functions pass isolated 

 from those that control the phonetic activity of the muscles, from the origin to 

 the muscle. From the superior laryngeal nerve an anastomotic branch passes to 

 the inferior laryngeal (the so-called anastomosis of Galen) , and it gives off sensory 

 branches to the upper half of the trachea, to the larynx, perhaps also to the eso- 

 phagus, and the muscle-sense fibers (?) for the laryngeal muscles supplied by the 

 recurrent nerve. 



Exner describes a middle laryngeal nerve, derived from the pharyngeal nerve 

 of the vagus and its anastomoses in the pharyngeal plexus, which takes part 

 in the innervation of the cricothyroid muscle (present only in rabbits) and the 

 anterior and inferior portions of the laryngeal mucous membrane. According to 

 Onodi fibers from the inferior cervical and the superior thoracic ganglion of the 

 sympathetic take part in the innervation of the laryngeal muscles. On the other 

 hand, the accessory is not believed to participate in this. 



Irritation of the superior laryngeal nerves is painful and causes movement of 

 the cricothyroid muscles, as well as, reflexly, of the remaining laryngeal muscles. 

 Division of these nerves is said to cause slight slowing of the respiration in conse- 

 quence of the paralysis of the cricothyroids. At the same time the voice in the 

 dog becomes deeper and rough in consequence of deficient tension of the vocal 

 bands. Further, the larynx is anesthetic, so that fluid from the mouth and 

 particles of food (without causing reflex closure of the larynx or coughing) gain 

 entrance into the trachea and the lungs, in consequence of which so-called deglu- 

 tition-pneumonia results, with a fatal termination. 



Irritation of the recurrent nerves causes spasm of the glottis. Division 

 paralyzes the laryngeal muscles supplied by these nerves and the voice becomes 

 toneless and rough (in the pig, in man, the dog, the cat, while rabbits retain their 

 clear, shrill voice). The glottis is small. With each inspiration the vocal bands 

 approach each other considerably in their anterior portions. In expiration they 

 are blown apart. Therefore, inspiration (particularly in young individuals having 

 a narrow respiratory glottis) is labored and noisy, while expiration takes place 



