894 



PAR VAGUM. 



and also some of those distributed upon the 

 pharynx and back parts of the tongue, so that it 

 is chiefly composed of sensiferous and incident 

 filaments. The inferior laryngeal furnishes 

 incident and sensiferous filaments to the greater 

 part of the trachea, to the cervical portion of 

 the oesophagus, a few to the mucous surface of 

 the pharynx, and still fewer to the larynx ; it 

 supplies the motor filaments of the cervical 

 portion of the (Esophagus and of all the muscles 

 which are attached to and move the arytenoid 

 cartilages, and is chiefly composed of motor 

 filaments.* When any excitation is applied to 

 the mucous membrane of the larynx in the 

 healthy state, this does not excite the contraction 

 of the muscles which move the arytenoid carti- 

 lages by acting directly upon these through the 

 mucous membrane, but is the result, as Dr. M. 

 Hallf had maintained, of a reflex or excito- 

 motory action, in the performance of which the 

 superior luryngeal is the incident, and the infe- 

 rior laryr/geal the motor nerve. In each re- 

 current nerve two sets of motor filaments are 

 included, one set transmitting the nervous in- 

 fluence which stimulates the opening muscles 

 of the larynx to act synchronously with the other 

 muscles of inspiration, the other set transmit- 

 ting the nervous influence which calls the 

 closing muscles into synchronous action with 

 the muscles of expiration.]; 



Upon these views we can readily explain how, 

 when the inferior laryngeal nerves are cut, all 

 the movements of the muscles of the arytenoid 

 cartilages are arrested, and the superior aper- 

 ture of the larynx, as was first pointed out by 

 Legallois, can no longer be dilated during in- 

 spiration. In fact, the sides of the larynx are 

 not only no longer separated by an active in- 

 fluence, but are rendered quite passive, and 

 yield readily within the limits of their natural 

 movements to any external force applied to 

 them. When the recurrent nerves are cut in 

 an adult animal, where the cavity of the larynx 

 is large, a quantity of air may still find its way 

 through the diminished aperture, adequate, in 

 many cases, to carry on the respiratory process 

 in a sufficient manner, particularly if the mus- 

 cles of inspiration are not acting violently. If, 

 on the other hand, the capacity of the larynx be 

 proportionally smaller as in young animals, the 

 air rushes through the diminished superior aper- 

 ture of the larynx in a narrower stream and with 

 increased force, more especially when the in- 

 spiratory movements are powerful or in other 

 words, when the capacity of the thorax is sud- 

 denly and greatly enlarged, and an insufficient 

 quantity of air reaches the lungs. This quan- 

 tity is still further reduced by the circumstance 

 that the now passive sides of the superior aper- 

 ture of the larynx are carried inwards by the 



* We also suggested that some of these filaments 

 distributed in the trachea might be motor, though 

 we had not succeeded in obtaining experimental 

 evidence of it. 



t Lectures on the Nervous System and its Dis- 

 eases, Lecture 1, 1836. 



t Each of these two sets may again be subdivided 

 into other two one composed of the excito-motory 

 rilaments of Dr. M. Hall, the other of sensifero- 

 vulidonal filaments. 



current of air, and at each inspiration the ary- 

 tenoid cartilages may be so closely approx- 

 imated as to prevent the ingress of air and suf- 

 focate the animal. It is the inspiration alone 

 of the animal which is difficult, for the expira- 

 tion is easy. The occurrence or non-occurrence 

 of dypsncea, or suffocation, after section of the 

 inferior laryngeals, is to be explained by the 

 greater or less capacity of the larynx in the indi- 

 vidual animal, and the activity and extent of 

 its respiratory movements at the time. The 

 crowing sound which frequently attends this 

 condition of the larynx is a mere physical 

 effect, and depends upon the current of air 

 rushing rapidly through the diminished aper- 

 ture of the larynx, and may be imitated in the 

 dead larynx. Severe dyspnoea amounting to 

 suffocation may arise both from the opposite 

 conditions of irritation and compression of the 

 inferior laryngeal nerves or the trunks of the 

 pneumogastric above the origin of this branch. 

 \Ve have stated above that on irritating one 

 recurrent nerve we observed that the arytenoid 

 cartilages were approximated so as in some 

 cases to shut completely the superior aperture 

 of the larynx, and we have already explained 

 how paralysis of this nerve by compression or 

 any other cause should produce this effect by 

 arresting the movements of all the muscles 

 attached to the arytenoid cartilages.* We also 

 found that after the section of both superior 

 laryngeal nerves in dogs and rabbits they swal- 

 lowed solids and fluids readily, and without 

 exciting cough or difficulty of breathing.f 

 Mr. Hilton has arrived at the conclusion, from 

 the anatomical distribution of the nerves alone, 

 that the superior laryngeal is chiefly sensitive, 

 and that the only motor filaments which it con- 

 tains are distributed in the crico-thyroid muscle, 

 while the inferior laryngeal supplies all the 

 muscles attached to the arytenoid cartilages 

 with motor filaments, a view in exact ac- 

 cordance with that which we have given above. I 

 Volkmann in his experiments found that the 

 movements of the glottis were not affected by 

 dividing thesupenor laryngeal nerves. Longet|| 



* Professor Henderson (Cormack's Journal of 

 Medical Science, p. 10, for 1841) adduces cases to 

 shew that in the human species the narrowing of 

 the superior aperture of the larynx, termed laryn- 

 gismus stridulus, may be induced both by irritation 

 and paralysis of the .recurrents. 



t An account of the above experiments and in- 

 ferences was read at the meeting of the British 

 Scientific Association in 1837 ; a short epitome of 

 them was given in the Athenaeum for Sept. 16, 

 1837, and they were published in full in the Edin- 

 burgh Medical and Surgical Journal for January, 

 1838. 



J Guy's Hospital Reports for October, 1837, 

 forming part of the 2nd volume. 



Opus.cit. Volkmann states that on irritating 

 the external branch of the superior laryngeal in 

 dogs and calves, not only the crico-thyroid muscle 

 was thrown into contraction, but also the constrictor 

 pharyngeus superior and the thyro-hyoid. If this 

 be confirmed, these two last muscles must receive 

 their motor nervous filaments from two sources, as 

 the constrictor receives a supply from the pharyn- 

 geal branch of the vagus, and the thyro-hyoid from 

 the hypoglossal. 



|| Hecherches Experimentales sur les Functions 

 drs Nerfs, des Muscles du Larynx, &c. Paris, 1841. 



