NORMAL ANATOMY OF THE LARYNX. 



113 



recurrent; and, 7, to the aryteno-epigloltic 

 niucous folds and muscles. 



The inferior laryngeal or recurrent nerve 

 gives filaments, 1, to the pneumo-gastric and 

 cardiac plexus; 2, to the pharynx; 3, to the 

 trachea ; 4, to the oesophagus ; 5, to the crico- 

 arytenoideus posticus ; 6, to the arytenoideus 

 obliquus and trans versu s ; 7, to the crico- 

 arytenoideus lateralis and thyro-arytenoideus ; 

 8, an anastomosing branch to the superior 

 laryngeal. 



Our knowledge of the anatomical distribu- 

 tion of the laryngeal nerves, and of the func- 

 tions of the intrinsic muscles of the larynx, 

 are sufficient, independently of experiment, to 

 demonstrate the inaccuracy of the well known 

 assertion of M. Magendie, supported by Clo- 

 quet, Pinel, Percy, and several others, that the 

 recurrent nerve presides over those actions 

 which open the glottis, whilst the superior la- 

 ryngeal influences those muscles which close 

 the glottis. The principal facts opposed to 

 this theory of M. Magendie may be briefly 

 stated as follows. 1 . It was well known long- 

 before the promulgation of Magendie's views 

 that the inferior laryngeal nerve gave to the 

 arytenoid muscle a filament which had been 

 described by Andersch,* Bichat,f and Mec- 

 kel,|. and subsequently by Schlemm BischofF, 

 Swan, Cruveilhier, Dr. Reid, and others, there- 

 fore it has been sufficiently demonstrated that 

 the recurrent nerve supplies the muscles that 

 close, as well as those which open the glottis. 

 2. M. Magendie has stated that the crico- 

 arytenoideus lateralis and thyro-arytenoideus 

 opened the glottis, whereas in the preceding 

 details it has been proved that these muscles 

 close it. 3. The loss of voice which follows 

 the section of the recurrent nerves results from 

 the paralysis of all the muscles (except the 

 crico-thyroid) which both open and close the 

 glottis, a fact proved by the experiments of 

 Le Gallois and Dr. Reid. The limned space 

 allotted to this article will only permit us to 

 notice the conclusions to which recent expe- 

 rimenters have arrived respecting the functions 

 of the laryngeal nerves. The external branch 

 of the superior laryngeal is composed chiefly 

 of motor fibres, and it controls the action of 

 the crico-thyroid and the other muscles to 

 which it gives filaments. The internal branch 

 of the superior laryngeal is composed of sensi- 

 tive fibres, which confer the most exquisite 

 sensibility on the mucous membrane of the 

 larynx, more especially in its supra-glottideal 

 region. It is therefore the sensitive and the 

 excitor nerve of the larynx. The inferior la- 

 ryngeal supplies the muscles that both open 

 and close the glottis, and is chiefly a nerve of 

 motion when it reaches the larynx, but a few 

 of its fibres go to the mucous membrane. The 

 union of the superior with the inferior laryngeal 

 branch by an anastomosing filament, preserves 

 a reciprocal play in the functions of these 



* Fragmentum descr. nervor. 

 t Traite d'Anat. torn. iii. p. 216. 

 J Man. d'Anat. torn. iii. p. 66. 

 VOL. III. 



nerves : whilst the branches anastomosing with 

 the sympathetic, connect the larynx with the 

 ganglionic system ; the pulmonary and cardiac 

 branches connect it with the respiratory and 

 circulating systems, and thus associate the 

 larynx with those vital functions. The laryn- 

 geal nerves also belonging to the reflex system, 

 impressions made on the sensitive filaments of 

 the larynx are reflected to the medulla ob- 

 longata, and propagated by a circuitous route 

 to the motor filaments of the recurrent, so that 

 a long interval is traversed in circulating an 

 impression from the sensitive to the motor 

 nerves of the larynx; but according to the esti- 

 mate made of the speed with which an impulse 

 is propagated along a nerve, which is assumed 

 to be equal to that of electricity, the time occu- 

 pied to transmit an impression from the fila- 

 ments of sensation to those of motion must be 

 inappreciable to our senses. Other important 

 physiological considerations result from recent 

 experimental researches, those of Le Gallois 

 and Dr. Reid in particular. 1. With respect 

 to the motions of the glottis during respiration, 

 the dilatation during inspiration, and contrac- 

 tion during expiration, are the effects of the 

 play of muscular force in opposition to the 

 direction of the current of air in its passage 

 to and from the lungs, the tendency of which is 

 to produce the reverse action.* There is a 

 constant periodical oscillatory motion of the 

 arytenoid cartilages, revolving upon the axis of 

 articulation, O P, (Jig. 30,) at every expiration 

 and inspiration ; hence the necessity of a syno- 

 vial membrane to lubricate the crico-arytenoid 

 articulation. 2. When the recurrent nerves 

 are diseased, compressed, or cut, so as to para- 

 lyse the crico-arytenoideus posticus, the power 

 of muscular action in opposition to the direction 

 of the inspired air is lost. The valves of the 

 glottis are drawn downwards with the air, the 

 anterior apophysis of the arytenoid cartilages 

 rotated inwards, the chink closes, symptoms of 

 suffocation supervene, and asphyxia results. 



When spasmodic closure of the chink of the 

 glottis occurs, the obstacle to the ingress of air 

 is increased by convulsive attempts to draw in 

 the breath, which causes a rarefaction of the 

 air below the glottis, and augments the atmos- 

 pheric pressure above it ; and the chest thus, 

 says Dr. Ley, " becomes hermetically sealed." 

 If the aperture of the glottis be partially open, 

 the air rushing through it causes a stndulous 

 sound ( ' laryngismus stridulus), whilst in ano- 

 ther position of the glottis the crowing inspi- 

 ration is produced ; this effect arises (accord- 

 ing to Dr. Ley) from the chink of the glottis 

 being partially open for the admission of air, 

 and remaining so until an explosive expiration 

 such as screaming, coughing, or belching, me 

 chanically bursts open the floodgates, and 

 terminates the paroxysm. 



* In the production of these periodical move- 

 ments, the action of the muscles is involuntary, but 

 in their action for the purposes of voice, they be- 

 come subordinate to the will, and therefore belong 

 also to the voluntary system. 



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