394 PHYSIOLOGY CHAP. 



of filaments along the lateral column of the cord and the bulb 

 below the vagus. 



The external or spinal portion of the accessory, after passing 

 out by the jugular foramen, is directed backwards, and perforates 

 the sterno-mastoid and trapezius muscles, where it forms a plexus 

 with branches of the cervical nerves. Division of the external 

 branch therefore produces, not total, but only partial paralysis 

 of these muscles. According to Longet, if the animal, after bi- 

 lateral section of the external branch of the accessory, is made to 

 run, it soon becomes breathless, not being able, on account of the 

 partial paralysis of the steruo-mastoid and trapezius muscles, to 

 elevate the thorax sufficiently and dilate the lungs. 



The internal bulbar branch of the accessory, after joining the 

 trunk of the vagus, sends part of its fibres into its pharnygeal 

 branch, while the rest anastomose with the vagus trunk, so that it 

 is impossible to distinguish them anatomically, and recourse must 

 be had to physiological tests. 



Bischoff (1832) was the first who maintained, on the basis of 

 certain experiments on goats, that intracranial bilateral section of 

 all the root bundles of the spinal accessory paralyses the muscles 

 of the larynx, as after section of the recurrent nerves (see pp. 140 

 et seq.}. Longet (1841), Morgan ti (1843), confirmed the results of 

 Bischoff, and suggested for the bulbar part of the accessory the 

 name of nervus vocalis. 



Cl. Bernard introduced a new method of extirpation of the 

 whole of the accessory nerve by pulling it out with a stout forceps 

 as it emerges from the jugular foramen. The operation is easy 

 in rabbits and cats, but difficult in adult dogs. After bilateral 

 destruction of this nerve the respiratory movements of the glottis 

 cease; according to Bernard, the glottis remains open in the 

 normal position, while after section of the two recurrent nerves 

 the glottis becomes constricted by adduction of the vocal cords, 

 leaving such a narrow fissure that the animal is in danger of 

 suffocation. Bernard concluded that the fibres which adduct the 

 vocal cords are distinct from the respiratory nerves which widen 

 the aperture of the glottis. The former come from the roots of the 

 accessory, the latter from the roots of the vagus, but both are 

 contained in the recurrent nerves. 



Bernard's views were contested by Longet, Schiff, Heidenhain, 

 and others, who maintained that the effects on extirpating the 

 accessory and dividing the recurrent nerves were identical. 



A. Waller (1856) and Burckhard (1867) supported the theory 

 that the motor fibres of the recurrent nerves come from the 

 accessory by the fact that in rabbits, after section of the nerve, 

 many or all the recurrent fibres degenerate. Although these 

 results all agree with Longet's theory, other experimenters bring 

 forward facts that are diametrically opposed to it. 



