vii THE MEDULLA OBLONGATA 395 



In 1840 Volkmann, in collaboration with Bidder, denied, on 

 the strength of a number of experiments, that intracranial 

 stimulation of the roots of the accessory influences the laryngeal 

 muscles; the opposite results obtained by Longet with galvanic 

 excitation of these roots were due to spread of the stimulus to 

 neighbouring roots of the vagus. Van Kempen and Stilling 

 (1863), Navratil (1871), obtained the same negative results. 

 Schech (1873), on the contrary, extirpated both accessories in 

 puppies, and showed by a series of laryngoscopical observations 

 that both vocal cords were paralysed in the cadaveric position, 

 with complete aphonia, as already stated by Bernard. 



Eecent work on the innervation of the larynx has been directed 

 to solving the two questions : (a) what difference is there between 

 the effects of dividing the recurrent nerves and extirpating the 

 accessory ? (b) do the motor nerves to the larynx come from the 

 accessory, the vagus, or from both these nerves ? 



The experiments of Wagner in Halle (1890-91) on cats, rabbits, 

 and dogs demonstrated that the section of a recurrent nerve at 

 once produces marked adduction of the corresponding vocal cord 

 and consequent asymmetry of the glottis, and that section of both 

 the recurrent nerves produces either closure of the glottis by com- 

 plete bilateral adduction of the vocal cords and necessitates 

 tracheotomy to prevent the animal from dying of asphyxia, or a 

 pronounced adduction of the cords which reduces the glottis to a 

 mere fissure. In all cases, after dividing the recurrent nerves 

 there is immobility of the vocal cords. This fact agrees with 

 Bernard's observations. 



The adduction of the cords and narrowing of the glottis does 

 not, however, depend on the action of the muscles innervated by 

 the recurrent nerve, but on that of the crico-thyroid muscles 

 which are innervated by the superior laryngeal; in fact, it dis- 

 appears immediately after section of this nerve and the glottis 

 assumes the cadaveric position. If after section of the recurrent 

 nerves the glottis is observed daily, it is seen that after a few (two 

 to six) days the vocal cords pass from the median position of com- 

 plete adduction to the cadaveric position of moderate abduction, 

 in which they remain. These facts agree with the observations of 

 Longet, Schiff, and others in opposition to Bernard. 



It was more difficult to decide the question of the origin 

 of the motor laryngeal fibres contained in the recurrent nerves. 

 Grabower solved this problem by the research which he carried 

 out under Gad's direction (1889). Using cats, dogs, and rabbits, 

 he demonstrated plainly that the accessory has no part in the 

 motor innervation of the larynx, which is supplied by the 4th 

 to 6th lower rootlets of the vagus. These same lower roots of the 

 vagus also contain the sensory fibres for the larynx. 



In his experiments on the accessory Grabower employed 



